**3. Results**

The number of fatal aviation accidents and relative risks of the likelihood of pilot AAS being due to suicide three years after 11 September 2001, calculated for each year separately, is presented in Table 1. All pilots who died were male. The RR was 3.68 in the first year and decreased close to 1.0 in the third year. Only the observation for the first year was statistically significant.

**Table 1.** The number and the risk ratios of pilot aircraft-assisted suicides five years before and three years after 11 September 2001, in the U.S.

FRQ = frequency.

Altogether 23 fatal aviation accident reports were obtained with the specified search words. All index cases were identified with the search word "suicide", search words "homicide-suicide", or "murder-suicide" did not yield any additional index case incidents. Fourteen of these incidents were caused by a pilot's or co-pilot's suicidal act according to NTSB accident investigations, and these incidents are described in detail in Table 2. All the incidents were operationally related to general aviation, although three pilots had also Class I (commercial pilot) medical certification even though they were not flying commercial aircraft at the time of the suicide crash. It should be noted that three of the deceased pilots were also flight instructors. Altogether fourteen pilots or student pilots died in these incidents. Their ages ranged from 15 to 69 years. Eight of these aircraft-assisted suicides occurred after 11 September 2001; four within the first year, three during the second year, and one in the third year, while six aircraft-assisted suicides took place during the five-year-period before it (see timeline in Figure 1). NTSB causes of death for excluded cases in this search were: four undetermined causes of fatal aviation accidents, two related to psychological problems (drugs or alcohol were mentioned at least as a contributing factor), in two reports weather conditions were mentioned, and in one case death occurred due to a passenger's suicidal act.

**Figure 1.** Timeline of aircraft-assisted pilot suicides five years before and three years after 11 September 2001. Red arrows indicate aircraft assisted suicides.

**Table 2.** *Cont.*

\* Class 1 = Airline Transport Pilot; 2 = Commercial Pilot; 3 = Private or Recreational Pilot; \*\* NTSB = National Transportation Safety Board.


**5.1. Drug delivery**

In DDS, the release of medicine is designed so that the drug efficacy is high. MEMS-based DDS are expected to convey medicine to the vicinity of diseased sites by exploiting the small MEMS size and drug release occurs when appropriate. Santini et al. proposed the controlled release of drugs from cavities that were sealed with a thin gold layer [2]. The thin gold layer is used as an anode and an electrochemical reaction occurs, with subsequent dissolution of the gold film and release of the encapsulated medicine. Drug delivery is thus controlled by electrical control of the reaction.

In this application, the fill and seal approach is employed to maintain the quality of the medicine as a priority. The package chambers are prepared with a thin gold layer as the bottom surface. Drugs are dispensed into the chambers and then sealed with a water-proof membrane using epoxy adhesive. Details of this process can be found in the literature [2].

### **5.2. Hydraulic amplification**

Some MEMS applications require large displacement of several tens of micrometers. Highflow-rate microvalves are one such application. To satisfy the requirements, hydraulic amplification has been reported that utilizes incompressible fluid in a microchamber with an input surface that is larger than the output surface [17-20]. Another example is a tactile display [21,22]; Figure 6 shows an illustration of an array of MEMS actuators that mechanically deform the fingertip and stimulate tactile receptors. These receptors typically require skin deformation of several tens of micrometers, which could be facilitated by hydraulic amplification. Tactile displays are developed to offer a new approach to human-machine interface for virtual reality applications and interactive devices such as pointing devices or game controllers, and also to support visually impaired persons. In the microvalve applications, a working fluid can be used as an incompressible fluid for hydraulic amplification. However, tactile displays cannot afford to have an external fluidic system to drive a working fluid; therefore, complete encapsulation of the liquid is necessary. In addition, the sealing membranes must be flexible. HDAMs have been successfully developed by encapsulating incompressible and non-volatile glycerin in microchambers with flexible and largely deformable PDMS membranes (mixture of DC 3145 CLEAR and RTV thinner, Dow Corning Toray Inc.) via UV curable resin using BiLT. Figure 2 shows a schematic of a HDAM [21,22].

**Figure 6.** Tactile display that employs an array of MEMS actuators.

is achieved. Parylene is more flexible than metals; therefore, by integrating electrodes beneath the liquid lens coated with parylene, the lens can be deformed to vary the focal length according

The direct deposition on liquid approach enables perfect liquid encapsulation with good reproducibility. The useful characteristics of parylene or specific metals can be exploited; however, the disadvantage is that the liquids to be encapsulated must be non-volatile and the type of sealing material is limited. For example, this approach cannot be applied to HDAM,

In DDS, the release of medicine is designed so that the drug efficacy is high. MEMS-based DDS are expected to convey medicine to the vicinity of diseased sites by exploiting the small MEMS size and drug release occurs when appropriate. Santini et al. proposed the controlled release of drugs from cavities that were sealed with a thin gold layer [2]. The thin gold layer is used as an anode and an electrochemical reaction occurs, with subsequent dissolution of the gold film and release of the encapsulated medicine. Drug delivery is thus controlled by electrical

In this application, the fill and seal approach is employed to maintain the quality of the medicine as a priority. The package chambers are prepared with a thin gold layer as the bottom surface. Drugs are dispensed into the chambers and then sealed with a water-proof membrane

Some MEMS applications require large displacement of several tens of micrometers. Highflow-rate microvalves are one such application. To satisfy the requirements, hydraulic amplification has been reported that utilizes incompressible fluid in a microchamber with an input surface that is larger than the output surface [17-20]. Another example is a tactile display [21,22]; Figure 6 shows an illustration of an array of MEMS actuators that mechanically deform the fingertip and stimulate tactile receptors. These receptors typically require skin deformation of several tens of micrometers, which could be facilitated by hydraulic amplification. Tactile displays are developed to offer a new approach to human-machine interface for virtual reality applications and interactive devices such as pointing devices or game controllers, and also to support visually impaired persons. In the microvalve applications, a working fluid can be used as an incompressible fluid for hydraulic amplification. However, tactile displays cannot afford to have an external fluidic system to drive a working fluid; therefore, complete encapsulation of the liquid is necessary. In addition, the sealing membranes must be flexible. HDAMs have been successfully developed by encapsulating incompressible and non-volatile glycerin in microchambers with flexible and largely deformable PDMS membranes (mixture of DC 3145

using epoxy adhesive. Details of this process can be found in the literature [2].

to the voltage applied to the electrodes [34].

**5.1. Drug delivery**

control of the reaction.

**5.2. Hydraulic amplification**

because it is preferable to seal the liquid with flexible membranes.

50 Advances in Micro/Nano Electromechanical Systems and Fabrication Technologies

**5. Applications of liquid encapsulation technology**

**Figure 7.** Large displacement MEMS actuator array that consists of HDAM with glycerin-filled cavities prepared using BiLT, and piezoelectric actuators. (a) Schematic image of HDAM, and (b) micrograph showing the large deformation of a PDMS membrane.

The HDAM shown in Figure 7(b) was combined with piezoelectric actuators and applied to develop large-displacement MEMS-actuators, with a particular aim to application in MEMSbased tactile displays [21,22,40]. When applied to a vibrational Braille code display, it was experimentally verified that the large-displacement HDAM could display Braille codes more efficiently than a static display. This is because both fast and slow adaptive tactile receptors could be used to detect the displayed patterns when individual cells were vibrated at several tens of hertz [40]. When the actuation of the large displacement MEMS actuators was controlled both spatiallyandtemporary,differentsurfacetextures,suchasroughandsmooth,couldbedisplayed.


**2.1.1 Counter-current multiplier mechanism in the loop of Henle**  The countercurrent mechanism in the loop of Henle is illustrated in figure 2: Na+ H2O

Fig. 2. Countercurrent multiplier process in the loop of Henle, in creating osmotic gradient and urine concentration (adapted from [1]). Note Na+ absorption from the ascending limb, and passive diffusion of H2O from the descending limb.

For the loop of Henle shown in figure 2, as a start, it is assumed that the loop of Henle is filled with a fluid with a concentration of 300 mOsm/L. First, the sodium transport from the lumen of the ascending limb to the interstitium, which instantaneously equilibrates with the descending limb. The osmolality in the ascending limb decreases. Because of the higher osmolar interstitium, the fluid in the descending limb increases in osmolality as water is shifted out by passive osmosis. However, the hair-pin structure causes the flow of hyperosmolar fluid in the descending limb to enter the ascending limb. The steps are repeated over and over, with the effect that the process gradually traps sodium in the medulla and multiplies the concentration gradient until the osmolality of the fluid in the loop of Henle and the interstitium reaches 1200 to 1400 mOsm/L.

### **2.1.2 Concentration of urine in the medullary interstitium**

As discussed, tubular fluid entering descending loop of Henle is iso-osmotic to plasma. This tubular fluid becomes progressively concentrated towards the bend. In the ascending loop, it becomes less concentrated as it rises to the cortex (decreasing from over 1000 to 100).

Within the medullary interstitium, other mechanisms co-operate to concentrate the urine. Under the influence of ADH (anti-diuretic hormone) blood flow through the vasa recta is decreased, and osmotic equilibration of blood in the vasa recta with medullary interstitium is enhanced. Solutes such as sodium, chloride and urea enter the descending blood vessels as they pass through the progressively higher osmolality of the interstitium and H2O leaves the vessels. In the ascending limb, the opposite events take place and H2O is reabsorbed into the blood vessels.

In brief, the anatomical configuration of the vasa recta minimises but does not prevent solute loss from the medulla via the blood supply. Because of diffusion of H2O from the tubular lumen into the interstitium, there is equilibrium between fluid in the collecting tubule and that in the interstitium. The withdrawal of H2O from the collecting tubule leads to increase in the concentration of urea in the collecting tubule causing a high gradient across the duct membrane, which favours diffusion of urea from the collecting duct into the interstitium. From there, urea diffuses into the descending limb of the loop of Henle and is recirculated into the ascending limb and back into the collecting duct, contributing to the high urea concentration in the medulla in the concentrating kidney.

Fig. 3. Schematic diagram showing both the countercurrent multiplier process in the loop of Henle and the vasa recta producing the osmotic gradient. Depicted in the figure are: (i) the passive and active exchanges of water and ions, (ii) concentrations of tubular urine and peritubular fluid in millimetres per litre, (iii) percentages of glomerular filtrate within the tubule at various levels.

In summary (please refer to figure 3),

818 Biomedical Science, Engineering and Technology

repeated over and over, with the effect that the process gradually traps sodium in the medulla and multiplies the concentration gradient until the osmolality of the fluid in the

As discussed, tubular fluid entering descending loop of Henle is iso-osmotic to plasma. This tubular fluid becomes progressively concentrated towards the bend. In the ascending loop, it becomes less concentrated as it rises to the cortex (decreasing from over 1000 to 100). Within the medullary interstitium, other mechanisms co-operate to concentrate the urine. Under the influence of ADH (anti-diuretic hormone) blood flow through the vasa recta is decreased, and osmotic equilibration of blood in the vasa recta with medullary interstitium is enhanced. Solutes such as sodium, chloride and urea enter the descending blood vessels as they pass through the progressively higher osmolality of the interstitium and H2O leaves the vessels. In the ascending limb, the opposite events take place and H2O is reabsorbed into

In brief, the anatomical configuration of the vasa recta minimises but does not prevent solute loss from the medulla via the blood supply. Because of diffusion of H2O from the tubular lumen into the interstitium, there is equilibrium between fluid in the collecting tubule and that in the interstitium. The withdrawal of H2O from the collecting tubule leads to increase in the concentration of urea in the collecting tubule causing a high gradient across the duct membrane, which favours diffusion of urea from the collecting duct into the interstitium. From there, urea diffuses into the descending limb of the loop of Henle and is recirculated into the ascending limb and back into the collecting duct, contributing to the

Fig. 3. Schematic diagram showing both the countercurrent multiplier process in the loop of Henle and the vasa recta producing the osmotic gradient. Depicted in the figure are: (i) the passive and active exchanges of water and ions, (ii) concentrations of tubular urine and peritubular fluid in millimetres per litre, (iii) percentages of glomerular filtrate within the

loop of Henle and the interstitium reaches 1200 to 1400 mOsm/L.

high urea concentration in the medulla in the concentrating kidney.

**2.1.2 Concentration of urine in the medullary interstitium**

the blood vessels.

tubule at various levels.


of all anchor nodes is synchronized with the external reference clock, i.e., , = 1∀ ∈ . At time , node has neighbor nodes set as ,, where neighbor anchor node set is , , node set to be located is ,, and all communicable node pairs (, ) constitute communicable node set . according to the real scene of the zone 1, underground parking lot, Beijing University of Posts and Telecommunications. The real scene is shown in Figure 3a and the top view is shown in Figure 3b. According to the actual size of zone 1, the simulation scene is a rectangular area of 20 × 24 m. By the anchor node with known location and synchronized local time, and the node with inaccurate location information and local time out of sync. The position vector of node at time is , = , and the measured value of local clock ̃ , = (). The slope of local clock at time means the system cannot provide reliable vertical positioning results [20], which is usually obtained by other sensors [21]. So, in this paper, a 2D dynamic wireless network is considered, which includes the anchor node with known location and synchronized local time, and the node with inaccurate , Covariance of belief (,) , Weight of the -th Gaussian distribution Cramer-Rao Lower , Covariance of belief (,) , Weight of the -th Gaussian distribution Fisher Information Matrix Cramer-Rao Lower , Covariance of belief (,) , Weight of the -th Gaussian distribution Fisher Information Matrix Cramer-Rao Lower To analyze the performance of the proposed method, we have built a simulation scenarioaccording to the real scene of the zone 1, underground parking lot, Beijing University of Posts and Telecommunications. The real scene is shown in Figure 3a and the top view is shown in Figure 3b.

default, the number of anchor nodes is 4, the number of nodes to be located is 20 and the initial position distribution of nodes in the site conforms to the uniform distribution. In order to limit the communication area of nodes to less than 1/2 of the whole simulation area, the maximum communication distance is set to 10 m. The performance of the proposed method is obtained in the between node and the external standard clock is , = (̃ , − ̃ ,−1)/( − −1). The local clock of all anchor nodes is synchronized with the external reference clock, i.e., , = 1∀ ∈ . At time , node has neighbor nodes set as ,, where neighbor anchor node set is , , node set to be located is ,, and all communicable node pairs (, ) constitute communicable node set . location information and local time out of sync. The position vector of node at time is , = , and the measured value of local clock ̃ , = (). The slope of local clock at time between node and the external standard clock is , = (̃ , − ̃ ,−1)/( − −1). The local clock of all anchor nodes is synchronized with the external reference clock, i.e., , = 1∀ ∈ . At time , CRLB(,) Bound of , The anchor nodes are always deployed at the same height, and high vertical dilution of precision (FIM) of , CRLB(,) Bound of , The anchor nodes are always deployed at the same height, and high vertical dilution of precision (FIM) of , CRLB(,) Bound of , The anchor nodes are always deployed at the same height, and high vertical dilution of precision According to the actual size of zone 1, the simulation scene is a rectangular area of 20 × 24 m. By default, the number of anchor nodes is 4, the number of nodes to be located is 20 and theinitial position distribution of nodes in the site conforms to the uniform distribution. In order to limit the communication area of nodes to less than 1/2 of the whole simulation area, the maximum

, = (). The slope of local clock at time

,−1)/( − −1). The local clock

,−1)/( − −1). The local clock

communication distance is set to 10 m. The performance of the proposed method is obtained in the line of sight (LOS) environment, except the last simulation, which shows localization accuracy with different NLOS probability. All simulation results are the average of 1000 independent runs.

**Figure 3.** (**a**) The real scene of the underground parking lot. (**b**) Simulation scenario. Zone 1 is the simulation area.

The initial position measurement error of the anchor node conforms to the Gaussian distribution with the standard deviation of 0.1 m. The initial position measurement error distribution of the node to be located is composed of Gaussian distributions with the standard deviation of 10 m. According to the performance of the crystal oscillator used in the hardware (TG5032CFN), the clock drift of the node to be located conforms to uniform distribution from [−1 ppm, 1 ppm], that is, the maximum distance measurement error caused by the clock drift between adjacent time (1 s) is 300 m. In the process of simulation, anchor nodes remain stationary, and the velocity of the node to be located is consistent with the uniform distribution of the maximum value of 3 m/s, and the direction is random every time step. The position movement measurement of the node conforms to the Gaussian distribution with the standard deviation of 1 m. The default process is 15 s, 10 iterations per second. Root mean square error (RMSE) and cumulative distribution functions (CDF) are used to measure the performance of algorithms.

In Figure 4a, the relationship between localization RMSE and initial location error is shown. The CLOC method [16] treats the uncertainties of nodes' positions and clock offsets as measurement noise and thus suffers performance degradation. The SPAWN [26] method is implemented by using 4000 particles to represent the messages on FG. The localization accuracy of the VMP method [17] and the proposed M-VMP method are better than the CLOC method, but slightly worse than the SPAWN method.

**Figure 4.** (**a**) Root mean square error (RMSE) of position error with different initial location error. (**b**) Cumulative distribution function (CDF) of position error with different initial location error.

The position error of VMP and the proposed M-VMP method are compared in Figure 4b. The cumulative distribution function of the VMP method and the proposed method under different initial position errors is given in Figure 4b. It is found that the probability of position error less than 1.6 m of the two methods under different initial position errors is basically the same, while the proposed method has a better effect of restraining position error. The result is consistent with the conclusion in Figure 4a.

Figure 5 shows the relationship among the clock drift slope, RMSE of localization accuracy and the number of iterations, respectively. It is seen that three methods converge in the finite iterations, which proves that the algorithms are feasible. Compared with the VMP method [17], the proposed method improves the convergence speed of localization and time synchronization by adding time synchronization parameters into the localization process.

**Figure 5.** (**a**) RMSE of the clock drift slope versus iterations and (**b**) RMSE of position error versus iterations.

In Figure 6, the CDF of the proposed method under different values of the number of Gaussian distribution M are compared. It is seen that the localization accuracy (3σ) of the proposed method is better than that of the VMP method when M is greater than 2. With the increase of M, the localization accuracy is also improved.

**Figure 6.** CDF of position error with different values of the number of Gaussian distribution M in line of sight (LOS) environment.

Figure 7 reflects the influence of communication distance on the localization accuracy of the proposed method under the same node density. Obviously, localization accuracy increases with the increase of communication distance, which increases the connectivity of nodes and the redundancy of information. At the same time, it can be seen that the improvement of localization accuracy is not obvious when the communication distance is 20 and 30 m. The difference of node connectivity between those two conditions is little, so the localization accuracy cannot be greatly improved. Because the communication distance is proportional to the transmission power of the node, it is necessary to determine the appropriate communication distance in practical application by considering the localization accuracy, node power consumption and other indicators.

**Figure 7.** CDF of position error with different communication distance.

In the simulation of Figure 8, in order to amplify the influence of node density on positioning accuracy, we reset some of the simulation parameters, and set the communication distance to 15 m and the variance of the distance observation and the initial position error of the node to be located to 20 m2 . It can be seen from Figure 8 that as the density of nodes increases, the overall positioning accuracy is decreasing. However, when the density of nodes to be located is too large, the positioning error will increase. At the same time, when there are more nodes to be located, the speed at which the positioning error decreases with more anchor nodes also decreases. This is due to the increase in the density of nodes to be located, and the overall weight of the information contained in neighboring nodes to be located in the proposed method becomes larger. When the number of anchor nodes is insufficient, the increase of neighboring nodes to be located helps to improve the positioning accuracy, but the effect is limited.

**Figure 8.** Relationship between position error and nodes' density.

In Figure 9, the relationship between the RMSE of localization accuracy and NLOS occurrence probability of the VMP method and the proposed method is compared. Furthermore, it compares with the method that only deals with LOS. It is seen that both the VMP and the proposed method effectively suppress NLOS error. Because the two-way NLOS parameters between nodes are added in the proposed method, the NLOS error is better suppressed.

**Figure 9.** (**a**) RMSE of position accuracy with different NLOS probability. (**b**) CDF of position error with different NLOS probability.

#### *4.3. Computational Complexity and Communication Overhead Analysis*

Because the proposed method in this paper and the comparison methods are distributed algorithms, the computation and communication are done by the nodes independently, so only one node's time complexity and communication overhead need to be considered in the analysis.

The time complexity is evaluated by the number of operations in local computing, and the communication cost is evaluated by the number of information parameters broadcast by nodes. The time complexity of the CLOC method is related to its neighbor nodes number Ninb, and its communication cost is 3·O(1). The SPAWN method is based on particles. When the number of particles in each message is Np, its time complexity is O Np + N 2 p ·Ninb , and its communication cost is O Np + 2·O(1). Compared with the VMP method, the number of Gaussian messages in the proposed method is M times, and every message from neighbor nodes needs to be processed once. The time complexity of dimension reduction depends on Ninb, so its time complexity is O(M·Ninb) + O(Ninb). In the proposed method, nodes transmit a localization vector including xi,n, yi,n, ai,n and a covariance matrix, so the communication cost is 3O(M) + O(1). The computational complexity, run-time and communication Overhead of the three algorithms is shown in Table 2.

**Table 2.** Comparisons of different methods for each node at each iteration.

#### *4.4. Future Research Directions*

In the next stage of research, we will mainly focus on the following aspects: First, analyze the performance of the positioning and simultaneous joint estimation problem and its influencing factors in principle. Secondly, expand the positioning scene from 2 dimensions to 3 dimensions, and reduce the problem of positioning accuracy degradation in dense scenes with nodes to be located through methods such as signal quality screening. Finally, the proposed algorithm will be implemented based on the hardware platform, and the measured results will be compared with the simulation results to further improve the performance of the proposed method.

### **5. Conclusions**

This paper presented a M-VMP-based TOA localization and time synchronization joint estimation algorithm for mixed LOS and NLOS environments. Firstly, according to the VMP method, a message propagation model based on a factor graph was constructed for localization and time synchronization. Owing to the existence of nonlinear terms, it is difficult to represent the message in a closed form, so Taylor expansion was used for the linearization of nonlinear terms. Moreover, to reduce the communication cost, all messages were expressed in the form of multi-Gaussian distribution, and only the mean value, covariance and weight of each Gaussian distribution need to be transferred in the message transmission. The simulation results showed that the accuracy and convergence speed of the proposed method were close to that of SPAWN method, and the time complexity and communication cost were greatly reduced: the run-time was only 1.5% that of SPAWN.

**Author Contributions:** Conceptualization, S.T.; Data curation, S.T.; Formal analysis, S.T., B.J. and H.W.; Funding acquisition, Z.D. and S.T.; Investigation, S.T., B.J., H.W. and X.D.; Project administration, Z.D., S.T., B.J., H.W. and X.Z.; Resources, Z.D. and S.T.; Software, S.T., B.J., H.W. and X.D.; Supervision, B.J., H.W. and X.Z.; Validation, S.T. and X.D.; Visualization, S.T.; Writing—original draft, S.T.; Writing—review and editing, S.T., B.J., H.W., X.D. and X.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Key Research & Development Program: 2016YFB0502003. **Conflicts of Interest:** The authors declare no conflict of interest.


**4. Experimental part**

Today, while studies on new sound insulating materials continue intensively, the usage of recycled products in this area is also increasing. Recycling technology provides environmental, social, and economic benefits. With environmental awareness and increased sensitivity to sustainability, recycled materials provide significant advantages for sound insulation.

In this study, nonwoven materials produced from conventional polyester (PES), mechanically recycled polyester (rm-PES), recycled polyester (r-PET), polypropylene (PP), and recycled polypropylene (r-PP) were compared with each other in terms of their sound absorption characteristics [47]. In **Figure 5**, photographs of the samples are given.

Supplying the raw materials and producing the nonwoven fabrics were carried out in a Turkish company working especially on recycled products. The processes

**Figure 5.** *Photographs of the samples used in experimental.*

applied for the mechanically recycled polyester and polypropylene fibers were as follows: the collected waste fabrics were cut with guillotine cutting machine and then shredded into pieces with particles of a suitable size. Then, the pieces were weighted on an electronic balance and blended in a vertical mixing blender. Carding process was applied to break down the big fiber bundle to the small size. Two-time carding process was applied to get uniform web formation, and then, the fine opener was used.

r-PET fibers provided by using r-PET flakes gained from PET bottles were used in this study. The common method of fiber production is as follows: at first, PET bottle wastes are separated from the other wastes; then, they are broken into flakes, washed, and dried before the spinning process of the fiber. In this method, r-PET fibers are acquired by transforming PET chips by the melt fiber drawing method [17].

The nonwoven fabric samples were produced by needle-punching technology. The webs were fed to a needling loom to produce nonwoven surfaces. Softness, bulkiness, conformability, fibrousness, and high strength characteristic without binder usage make the needle-punched nonwoven fabrics unique among the other nonwovens.

Before the physical tests, nonwoven samples were conditioned in standard atmospheric conditions (20 ± 2°C temperature, 65 ± 4% relative humidity). The mass per unit area was determined in accordance with the ISO 9073-1 standard, and thickness measurements of the materials were carried out according to the ISO 9073-2 standard using SDL Atlas fabric thickness gauge. Air permeability test was conducted according to the EN ISO 9237 standard by using Textest FX 3300 air permeability meter at 200 Pa pressure difference and 20 cm2 measurement areas.

Two methods were applied to measure sound absorption properties of the samples: alpha cabinet and impedance tube methods. Nonwoven textile products supplied within the scope of the study were tested by using alpha cabinet according to the Renault D49-1977-B standard. The cabinet volume was 6.44 m3 , and the total surface area was 22.2 m2 . The surface area of the test specimens was 1.12 m2 ; the

**97**

**Table 1.**

*Investigation of Sound Absorption Characteristics of Textile Materials Produced from Recycled…*

height of the microphone from the ground was 0.88 m; and the height of the sound source was 0.20 m. The frequency measurement range was set at 400–10,000 Hz.

Impedance tube method was also used to measure the sound absorption coefficients of the samples according to the EN ISO 10534-2 method. The frequency was set from 100 to 1600 Hz. The test was carried out by three test samples randomly

The structural properties and air permeability values of five different nonwoven

The test results obtained from the impedance tube method are given in **Figure 6**.

Compared to conventional polypropylene, r-PP indicates better sound absorption characteristics for all frequencies. It is associated with the micro voids in the

The acoustic absorption test results of the textile surfaces according to the alpha

**100% r-PET**

Mean (**X**¯) 550 596 519 509 500

CV (%) 1.48 2.03 5.25 2.15 0.96

CV (%) 3.93 2.89 9.46 2.67 2.28

Mean (**X**¯) 1136 1270 600 875 1536

CV (%) 5.08 9.17 18.66 17.01 4.50

Mean (**X**¯) 0.136 0.202 0.164 0.141 0.110

**100% rm-PES**

8.14 12.10 27.27 10.92 4.81

0.16 0.09 0.30 0.10 0.10

57.71 116.40 112.13 148.66 69.14

**100% PP**

**100% r-PP**

**PES**

Thickness (mm) Mean (**X**¯) 4.04 2.95 3.17 3.60 4.55

As air permeability results of nonwoven fabrics are examined, the surface produced from r-PP material has the highest air permeability, whereas the lowest air

According to the results, at low frequencies between 100 and 400 Hz, it can be clearly seen that r-PP, rm-PES, and r-PET surfaces have higher sound absorption coefficient values than the conventional PES and PP fabrics. This is an important point that recycled textile surfaces can be suggestible as sound insulation materials in low frequency band gap (100–400 Hz) as an alternative to the conventional fibers. In addition to this, r-PP material has the highest sound absorption coefficient (over 0.50) among the other recycled products since its lower density and porous structure create a higher friction surface. As the performance at the mid frequencies (400–1600 Hz) is analyzed, only PP, r-PP, and rm-PES fabrics have sound absorption coefficient over 0.50. Therefore, these surfaces can be suggested for sound

permeability value belongs to mechanically recycled polyester surface.

*DOI: http://dx.doi.org/10.5772/intechopen.92792*

surfaces used in the study are given in **Table 1**.

insulation materials to be used at mid frequencies.

recycled material caused by the inhomogeneity [48].

cabinet method are given in **Figure 7**.

Mass per unit area (g/m2 )

Air permeability

Fabric density (g/cm3 )

(l/m2 s)

**Measured parameter 100%**

Standard deviation (SD)

Standard deviation (SD)

Standard deviation (SD)

*Properties of nonwoven fabrics used in the study.*

taken from nonwoven fabrics.

Three Brüel and Kjaer 2669 model microphones were used.

## *Investigation of Sound Absorption Characteristics of Textile Materials Produced from Recycled… DOI: http://dx.doi.org/10.5772/intechopen.92792*

height of the microphone from the ground was 0.88 m; and the height of the sound source was 0.20 m. The frequency measurement range was set at 400–10,000 Hz. Three Brüel and Kjaer 2669 model microphones were used.

Impedance tube method was also used to measure the sound absorption coefficients of the samples according to the EN ISO 10534-2 method. The frequency was set from 100 to 1600 Hz. The test was carried out by three test samples randomly taken from nonwoven fabrics.

The structural properties and air permeability values of five different nonwoven surfaces used in the study are given in **Table 1**.

As air permeability results of nonwoven fabrics are examined, the surface produced from r-PP material has the highest air permeability, whereas the lowest air permeability value belongs to mechanically recycled polyester surface.

The test results obtained from the impedance tube method are given in **Figure 6**. According to the results, at low frequencies between 100 and 400 Hz, it can be clearly seen that r-PP, rm-PES, and r-PET surfaces have higher sound absorption coefficient values than the conventional PES and PP fabrics. This is an important point that recycled textile surfaces can be suggestible as sound insulation materials in low frequency band gap (100–400 Hz) as an alternative to the conventional fibers. In addition to this, r-PP material has the highest sound absorption coefficient (over 0.50) among the other recycled products since its lower density and porous structure create a higher friction surface. As the performance at the mid frequencies (400–1600 Hz) is analyzed, only PP, r-PP, and rm-PES fabrics have sound absorption coefficient over 0.50. Therefore, these surfaces can be suggested for sound insulation materials to be used at mid frequencies.

Compared to conventional polypropylene, r-PP indicates better sound absorption characteristics for all frequencies. It is associated with the micro voids in the recycled material caused by the inhomogeneity [48].

The acoustic absorption test results of the textile surfaces according to the alpha cabinet method are given in **Figure 7**.

#### **Table 1.**

*Properties of nonwoven fabrics used in the study.*

*Waste in Textile and Leather Sectors*

applied for the mechanically recycled polyester and polypropylene fibers were as follows: the collected waste fabrics were cut with guillotine cutting machine and then shredded into pieces with particles of a suitable size. Then, the pieces were weighted on an electronic balance and blended in a vertical mixing blender. Carding process was applied to break down the big fiber bundle to the small size. Two-time carding process was applied to get uniform web formation, and then, the fine

r-PET fibers provided by using r-PET flakes gained from PET bottles were used in this study. The common method of fiber production is as follows: at first, PET bottle wastes are separated from the other wastes; then, they are broken into flakes, washed, and dried before the spinning process of the fiber. In this method, r-PET fibers are acquired by transforming PET chips by the melt fiber drawing

The nonwoven fabric samples were produced by needle-punching technology. The webs were fed to a needling loom to produce nonwoven surfaces. Softness, bulkiness, conformability, fibrousness, and high strength characteristic without binder usage make the needle-punched nonwoven fabrics unique among the other

Before the physical tests, nonwoven samples were conditioned in standard atmospheric conditions (20 ± 2°C temperature, 65 ± 4% relative humidity). The mass per unit area was determined in accordance with the ISO 9073-1 standard, and thickness measurements of the materials were carried out according to the ISO 9073-2 standard using SDL Atlas fabric thickness gauge. Air permeability test was conducted according to the EN ISO 9237 standard by using Textest FX 3300 air

Two methods were applied to measure sound absorption properties of the samples: alpha cabinet and impedance tube methods. Nonwoven textile products supplied within the scope of the study were tested by using alpha cabinet according

. The surface area of the test specimens was 1.12 m2

measurement areas.

, and the total

; the

permeability meter at 200 Pa pressure difference and 20 cm2

to the Renault D49-1977-B standard. The cabinet volume was 6.44 m3

**96**

surface area was 22.2 m2

opener was used.

*Photographs of the samples used in experimental.*

**Figure 5.**

method [17].

nonwovens.

**Figure 6.** *Sound absorption coefficients based on the impedance tube method.*

#### **Figure 7.**

*Sound absorption coefficients based on alpha cabinet method.*

Materials can be tested at a wide frequency band in case of their sound absorption properties. In this study, the tested frequency range is 400–10,000 Hz. According to **Figure 7**, between 400 and 1600 Hz, sound absorption coefficients of all nonwoven

**99**

**Acknowledgements**

*Investigation of Sound Absorption Characteristics of Textile Materials Produced from Recycled…*

surfaces are close to each other and are lower than 0.35. Over 2500 Hz frequency, which is a high frequency level, sound absorption coefficients of the nonwovens are over 0.5, which supply a better sound insulation property and can be an alternating

In this study, acoustic absorption coefficients were measured according to two different sound measurement methods. The results obtained from the alpha cabinet and the impedance tube methods complement each other and give the idea for the performance and comparability of the materials at different sound frequencies. For obtaining the required results, the choice of the appropriate method is crucial. The impedance tube method is mostly suitable in order to develop new materials, while a reverberation room test is more relevant to design acoustic adjustments of the space [49]. Moreover, reverberation rooms are often preferred since they give closer results to the actual working conditions of the material by means of the random incidence excitation. However, the tests in impedance tube allow obtaining the additional information about the characteristic acoustic impedance of the sample [50].

Along with the growing population, noise has become one of the major problems of everyday life, affecting our quality of lives and, in some cases, our health. As the studies on reducing the noise generation continue, new solutions are being searched on systems that allow absorbing more quantities of the present disturbing noise. Within this scope, many different technical textile materials are produced, which are closely related to building construction, automotive, and machinery industries. The use of these high-performance products is becoming increasingly widespread in terms of technical specifications. However, in today's competitive conditions, products that can compete in terms of cost are more preferred in the market. Recycled surfaces are one of these preferred products. In addition to the price advantage, waste materials are transformed into usable products by recycling, which is completely an environmentally friendly production that provides sustainability.

In this study, characteristics of conventional polyester and polypropylene nonwoven insulation materials commonly used in the market and the nonwoven fabrics produced from recycled materials were compared. When the test results were examined, it was concluded that the recycled materials used in sound insulation area had very successful competitive performance when compared with the conventional materials. They had the qualifications supplying the expectations in terms of sound

Insulation materials are used, especially in areas where sound insulation is desired (e.g., children's houses, hospitals, entertainment places, and automotive sector) and in civil engineering area. In addition, it is a good application area for recycled materials to supply a sustainable world, to increase the environment friendly approach, and to evaluate the waste materials in a technical field. By the year 2019, price of PP fiber in the market is about 3.2 \$/kg, 1.6 \$/kg for r-PP fiber, about 1.6 \$/kg for 100% PES and r-PET fibers, and 1.2 \$/kg for rm-PES fibers. In the scope of economy, it can be foreseen that recycling materials will provide an

This study was supported by the Ege University Scientific Research Projects Coordination Unit (Project Number: 15-MÜH-078). The authors would also like

insulation when produced in enough thickness value.

important advantage for both producers and consumers.

*DOI: http://dx.doi.org/10.5772/intechopen.92792*

insulation material for the industry.

**5. Conclusion**

*Investigation of Sound Absorption Characteristics of Textile Materials Produced from Recycled… DOI: http://dx.doi.org/10.5772/intechopen.92792*

surfaces are close to each other and are lower than 0.35. Over 2500 Hz frequency, which is a high frequency level, sound absorption coefficients of the nonwovens are over 0.5, which supply a better sound insulation property and can be an alternating insulation material for the industry.

In this study, acoustic absorption coefficients were measured according to two different sound measurement methods. The results obtained from the alpha cabinet and the impedance tube methods complement each other and give the idea for the performance and comparability of the materials at different sound frequencies. For obtaining the required results, the choice of the appropriate method is crucial. The impedance tube method is mostly suitable in order to develop new materials, while a reverberation room test is more relevant to design acoustic adjustments of the space [49]. Moreover, reverberation rooms are often preferred since they give closer results to the actual working conditions of the material by means of the random incidence excitation. However, the tests in impedance tube allow obtaining the additional information about the characteristic acoustic impedance of the sample [50].


*3.3. Dead Trophozoites Do Not Induce NET Release and Contain Scarce ROS*

As shown in Figure 3A, heat-killed or fixed trophozoites did not induce NETosis on human neutrophils, in contrast to viable amoebas that induced NET levels like PMA and A23187. This result suggests that metabolically active trophozoites are required for triggering NETosis. Since most studies suggest that NETosis requires a source of ROS, which is not related to neutrophils in this case, we explored the possibility that ROS from trophozoites was involved. So, we decided to quantify ROS in living and dead amoebas and found, as expected, that formaldehyde-fixed and heat-killed trophozoites exhibited far fewer ROS than live amoebas (Figure 3B).

**Figure 3.** Dead *E. histolytica* trophozoites do not trigger NETosis and possess less ROS. (**A**) Neutrophils (1 × 105) were culture in RPMI-1640 medium supplemented with 5% FBS and added with 500 nM SYTOX® Green. Cells were stimulated with PMA (50 nM), A23187 (10 μM), viable trophozoites (5 × 103), heat-killed trophozoites (5 × 103) or formaldehyde-fixed trophozoites (5 × 103). Fluorescence was read at 4 h. (**B**) Viable, heat-killed and formaldehyde-fixed trophozoites were pretreated with H2DCFDA for 1 h. Posteriorly, amoebas (1 × 105) were placed in a 96 well plate and fluorescence was read. NET and ROS amounts are expressed in fluorescence relative units (FRU). Values are means ± SD of three independent experiments. \* *p* < 0.0001.


**Abstract**

The normal aging process is characterized by a progression of physiological events throughout the life cycle. Age-related changes take place throughout the body and are most prominent in later years. The aims and purposes of this study were to: i) provide a summary of existing and relevant research, ii) assess exercise program variables, and iii) give practical evidence-based recommendations for exercise prescription and resistance training in older adults, according to international guidelines. Using an evidence-based approach, we combined scientific data, experts' statements and end-user concerns to improve references for the aging population's interests, values, requirements, and choices. Thus, the position statement assesses the main studies obtained after a thorough analysis of the literature. In conclusion, we highlight that strength training alone or combined with aerobic training is a fundamental part of the primary prevention of many chronic diseases in older adults, in addition to delaying the progression and reducing the symptoms of related chronic conditions. Multicomponent exercise programs, especially strength exercises that include muscle power training, are the most effective interventions for buffering the impact of physical disability and other adverse health-related outcomes, even in the oldest old.

**Keywords:** aging, physical activity, strength, wellbeing, health-related outcomes


**5. Conclusion**

24 Will-be-set-by-IN-TECH

**Figure 19.** The precision of IFSQ search after 1500 iterations

**Figure 20.** Performance of IFSQ based decoupling module under moderate coupling

the theoretical transmission curve as close as is the SQ approach.

The reduction of permitted number of iterations to 1500 is verified in Figure 20 where the performance of IFSQ decoupling module under moderate coupling conditions is presented. The first curve on the image presents the behavior of system without the decoupling module under coupling of [-10,-12,-10] dB. The lowest curve shows the theoretical system performance with only AWGN. Two curves in the middle present two decoupling module instances based on IFSQ approach stopped after 1500 iterations. Actually, the coefficients used for generating this two curves correspond to the seventh and tenth IFSQ execution depicted in Figure 19. Regardless of the numerical difference of cost functions, the performance of both decoupling modules is very similar. Since the search is abandoned when cost function reaches sufficient *Q* value defined with *Qsuf f* = 0.005 the performance of decoupling module does not follow The effect of coupling are minimized with the software module positioned at the output of analog-to-digital converter and before any further digital signal processing. Inside the module, signal reconstruction based on the approximation of inverse nonlinear coupling is achieved. The generation of inverse coupling function is based on fitting surface approach which can be divided into two steps: calibration process and point-to-point real-time decoupling. Inside calibration process inverse nonlinear coupling surface is build based on function formed with 20 degrees of freedom. Inspired by SA class of approaches, two SQ algorithms are proposed for locating the optimal inverse function parameters.

Even though classical SQ method can not be used under real time conditions it provides the upper limit of the decoupling precision module and is used for tuning the required system parameters like for example calibration data size. It is intended only for proof of concept and precision reference to other two decoupling search approaches. Eventually actually confirms the adequate selection of the surface model and proves the concept of decoupling software module. The performance of decoupling module based on the SQ search method shows stable behavior and excellent decoupling results.

The proposed Improved Fast SQ search method is included in decoupling module as the fast version of the previously developed SQ search. It follows the same search logic as the SQ algorithm with the difference in the annealing schedule which is much steeper, the initial search space is wider and the probability of uphill movement is higher at the beginning. This way the search is carried out more thoroughly in the initial stage, allowing stepper search progress sooner than in the original SQ approach. Furthermore, since the search space is reduced according to the exponential function, the maximum allowed displacement is reduced with temperature, and as consequence the search concentrates more on small space around the global minimum area. The performance of IFSQ decoupling module, based on 1500 iterations, shows good decoupling results, with slightly lower BER level when compared to the standard SQ search. Nevertheless, the required number of iterations is reduced by more than 90% which justifies the precision loss. The approach requires less processing power than SQ, and as such might be used in mobile phones inside the decoupling module.

With the introduction of normalization, the search domain is well defined between �−1, 1�, and the search depth is easily controlled with symbol resolution factor. This proposal allows the adaptation of implemented search methods to general decoupling problem offering at the same time constant precision and efficient optimization of search process with no restrictions on the physical coupling source nor signal constellation.


**Abstract**

Acute pancreatitis has a broad clinical spectrum: from mild, self-limited disease to fulminant illness resulting in multi-organ failure leading to a prolonged clinical course with up to 30% mortality in case of infected necrosis. Management of local complications such as pseudocysts and walled-off necrosis may vary from clinical observation to interventional treatment procedures. Gram negative bacteria infection may develop in up to one-third of patients with pancreatic necrosis leading to a clinical deterioration with the onset of the systemic inflammatory response syndrome and organ failure. When feasible, an interventional treatment is indicated. Percutaneous or endoscopic drainage approach are the first choices. A combination of minimally invasive techniques (step-up approach) is possible in patients with large or multiple collections. Open surgical treatment has been revised both in the timing and in the operating modalities in the last decades. Since 1990s, the surgical treatment of infected necrosis shifted to a more conservative approach. Disruption of the main pancreatic duct is present in up to 50% of patients with pancreatic fluid collections. According to the location along the Wirsung, treatment may vary from percutaneous drainage, endoscopic retrograde pancreatography with sphincterectomy or stenting to traditional surgical procedures. Patients may suffer from vascular complications in up to 23% of cases. Tissue disruption provoked by lipolytic and proteolytic enzymes, iatrogenic complications during operative procedures, splenic vein thrombosis, and pseudoaneurysms are the pathophysiological determinants of bleeding. Interventional radiology is the first line treatment and when it fails or is not possible, an urgent surgical approach should be adopted. Chylous ascites, biliary strictures and duodenal stenosis are complications that, although uncommon and transient, may have different treatment modalities from non-operative, endoscopic to open surgery.

**Keywords:** pancreatic pseudocysts, walled-off necrosis, infected pancreatic necrosis, disconnected pancreatic duct syndrome, vascular complications, chylous ascites

### **1. Introduction**

The majority of patients suffering from acute pancreatitis will have a mild, self-limited and uncomplicated course. Pancreatic necrosis may develop in up to 10%-20% of patients, because of insufficient perfusion of pancreatic parenchyma to support metabolic requirements, leading to a prolonged clinical course with up to 30% mortality in case of infected necrosis [1]. Local and systemic complications, mild or life-threatening, such as pancreatic and/or peripancreatic fluid collections, walled-off necrosis, infected pancreatic necrosis, disconnected pancreatic duct syndrome and vascular complications can occur. The successful management of these patients needs a multidisciplinary team composed by gastroenterologists, surgeons, interventional radiologists, and specialists in critical care medicine, infectious disease, and nutrition. Intervention is generally required for infected pancreatic necrosis and less commonly in patients with sterile necrosis who are symptomatic (gastric or duodenal outlet or biliary obstruction) [2]. The surgical odyssey in managing necrotizing pancreatitis is a notable example of how evidence-based knowledge leads to improvement in patient care. Open surgical necrosectomy has been the traditional surgical treatment for years. However, although it provides a wide access but it is associated with high morbidity (34%-95%) and mortality (11-39%). In the last decades treatment has moved towards minimally invasive techniques: laparoscopy, retroperitoneal and endoscopic or percutaneous approaches. These can allow open surgery to be postponed in a sub-acute setting or even to avoid it [3–6].

## **2. Pancreatic necrosis and pseudocysts**

Local complications such as pancreatic and/or peripancreatic fluid collections can occur after an episode of acute pancreatitis or after recrudescence of chronic pancreatitis or a blunt, penetrating, iatrogenic pancreatic trauma. Peripancreatic fluid collections, with or without a necrotic component, are early manifestations of the pancreatic inflammatory process. They are not delimited by a well-defined inflammatory wall and often remain asymptomatic, ending in spontaneous resolution by a gradual reduction in size. After four weeks from the clinical manifestation, persistent collections usually become wall-defined, encapsulated, with (walled-off necrosis) or without (pancreatic pseudocyst) a necrotic component and a varying degree of pancreatic parenchyma involvement [7].

Management of pseudocysts and walled-off pancreatic necrosis (WOPN) rely on patient's symptoms, location and characteristics of pancreatic and/or peripancreatic collections, local complications (such as pseudoaneurysm), expertise and availability of a multidisciplinary group [8].

In asymptomatic patients, clinical observation and periodic imaging follow up (every three-six months) represent the most successful management, due to the frequent reduction in size and spontaneous resolution of non-complicated homogeneous collections and to the morbidity associated to interventional (endoscopic or radiologic) treatment procedures. In these cases, it is possible to associate nutritional and pharmacological support (nasoenteric feeding reduces pain and improves nutritional status; proton pump inhibitors and somatostatin-analogue such as octreotide reduce pancreatic secretion).

Infection will develop in about one third of patients with pancreatic necrosis. It may arise at any time during the clinical course but peak incidence is between the 2nd and the 4th week after presentation [2]. Gram-negative bacteria are the main infectious species isolated, the most common of which are *Escherichia coli* and *Pseudomonas aeruginosa* [9]. Recently, a trend towards increasing incidence of Gram-positive and multi-resistant bacteria has been demonstrated [10, 11].

Prognosis and management are greatly affected by the recognition between sterile and infected pancreatic necrosis. Clues of suspicion should arise in case of clinical signs of systemic inflammatory response syndrome (SIRS) (new-onset

### *Surgical and Interventional Management of Complications Caused by Pancreatitis DOI: http://dx.doi.org/10.5772/intechopen.96747*

fever, tachycardia, leukocytosis) or organ failure [12]. A blood culture with positive bacterial results and gas in and around the pancreas on a CT scan may give indirect evidence of infection. Prophylactic antibiotic use in patients suffering from acute pancreatitis has not been proven to decrease infection rate and thus, according to the meta-analysis by Wittau et al. [13] it is not recommended a routine prophylaxis. The Cochrane review by Villatoro et al. [14] showed that antibiotic prophylaxis was not associated with a reduced incidence of pancreatic necrosis infection, even though it was associated with significantly decreased mortality. CT- or US-guided fine needle aspiration of pancreatic necrosis for bacteriologic analysis are an accurate, safe and reliable techniques with high accuracy (89.4%-100%) [15, 16].

In symptomatic patients, with rapidly enlarging pseudocysts or systemic manifestations of organ failure sustained by an infectious process, an interventional treatment is indicated. In this case endoscopic drainage approach is the first choice, especially when fluid collection is close to gastroduodenal lumen. A combination of techniques is possible in patients with large collections, extended in pelvis and paracolic gutters, or multiple collections [17].

### **2.1 Endoscopic drainage**

Endoscopic drainage of a walled collection is the preferred method when the drainage criteria are met: mature collections delimited by a well-defined inflammatory capsule and with a mostly liquid content; cystic wall adherent to stomach or duodenum; and collection's size at least 6 cm in size.

This procedure has to be performed by an endoscopist with expertise and when surgical or interventional radiology staffs are available [18]. Contraindications to endoscopic drainage are: presence of pseudoaneurysm due to gastroduodenal or splenic artery erosion, with high risk of bleeding; and collections without a mature wall.

Drainage techniques consist in [19]: *transmural drainage*: creation of a passage through the stomach or duodenum wall into the cyst lumen. This permits cystic drainage after balloon dilatation and placement of one or more stents. This method is preferred to drain WOPN in order to evacuate solid debris. T*ranspapillary drainage*: placement of a ductal pancreatic stent with or without preliminary sphincterotomy to drain cysts in communication with pancreatic duct, especially when endoscopic retrograde pancreatography demonstrates ongoing ductal leak.

Transmural approach is adopted when large and symptomatic walled-off pancreatic fluid collection is close to gastroduodenal structures. Transmural puncture through gastroduodenal wall (where is endoscopically visible a bulge resulting by apposition to the cyst), is nowadays ecoendoscopically guided. This permits to accurately identify puncture site for cystenterostomy, avoiding vessels or other interposed structures and evaluating real distance to pass through [20]. Selfexpanding metal stents or plastic double pig-tail stents can be both used. Lumen Apposing Metal Stent (LAMS) are associated with higher bleeding grade but allow immediate procedures such as endoscopic necrosectomy.

Drainage of turbid necrotic fluid suggests debris presence and can be managed with direct endoscopic debridement and/or with the placement of a naso-cystic catheter for post-procedural lavage. Repeated debridement or association with percutaneous drainage or percutaneous endoscopic gastrostomy can be necessary with unresolved fluid collections [21].

For patients with small pseudocysts derived from main pancreatic duct, transpapillary stent placement is indicated as first drainage approach. This provides continuous drainage of pancreatic fluid, leading to resolution of pancreatic ductal disruption that is responsible of pseudocyst. Follow up with CT or EUS is preferred after four to six weeks if necrotic debridement was not necessary and stents are then removed the fluid cavity is collapsed. More frequent imaging is obtained in patients who underwent necrosectomy, to determine if additional debridement is necessary. When collections are completely evacuated, stents are removed. Long-term stents seem to protect against recurrence allowing ongoing drainage of pancreatic secretions, although cystenterostomy tract matures and persists after eventual stent removal [22].

### **2.2 Percutaneous drainage**

Percutaneous drainage remains an important treatment modality for patients with symptomatic collections. It may be used both as primary therapy or as an adjunct to other techniques. According to the last International [23], American [1] and Japanese [24] guidelines, percutaneous catheter (or endoscopic transmural drainage) should be the first step in the treatment of patients with suspected or confirmed (walled-off) infected necrotizing pancreatitis. This is applied to decompress retroperitoneal fluid collections, to provide a rapid and effective means for source control in patients with infected pancreatic necrosis. It favors clinical stabilization of patients before endoscopic or surgical debridement and is the first choice when endoscopic drainage is unavailable, unsuccessful, or not technically feasible [25].

The positioning can be performed via the transperitoneal or retroperitoneal approaches. It is technically feasible in >95% of patients [26]. Retroperitoneal route is generally preferred because it avoids peritoneal contamination, enteric fistulas and facilitates a possible step-up approach (see "Surgical approach" chapter). Moreover, the catheter tract can act as an entry portal for minimally invasive debridement methods, such as video assisted retroperitoneal or endoscopic debridement [1]. Catheters range from 8 Fr to 30 Fr in diameter; they allow for bedside irrigation and clearance of necrotic material, can be manipulated and replaced according to the evolution of the collections [27].

Percutaneous drainage alone may provide definitive therapy for a subset of patients. The prospective observational multicenter study by Horvath K. et al. in 2010, found that the decrease in the size of the collection of at least 75% after the first 10-14 days predicts successful percutaneous treatment. In 2011, a large prospective multicenter study of treatment outcomes among patients with necrotizing pancreatitis demonstrated that catheter drainage was the first intervention in 63% of cases and did not require additional necrosectomy in 35% of patients [28]. Two prospective randomized trials from the Dutch Pancreatitis Study Group compared various approaches to the management of symptomatic WON. They demonstrated that percutaneous drainage alone was successful in 35%-51% of patients and that a minimally invasive step-up approach was related to a lower rate of pancreatic fistulas, length of hospital stay and death, as compared with open necrosectomy [26, 29].

The risk of pancreatocutaneous fistula formation is the major potential drawback of this technique. The multicentre randomised trial by van Brunschot S. et al. demonstrated that the rate of pancreatic fistula formation was significantly higher in the percutaneous (32%) as compared to the video-assisted retroperitoneal debridement (VARD) group (5%) [29]. The rate is as high as 45% in those with disconnected duct syndrome [30].

### **2.3 Surgical approach**

The surgical odyssey in managing necrotizing pancreatitis is a notable example of how evidence-based knowledge leads to improvement in patient care. In the

### *Surgical and Interventional Management of Complications Caused by Pancreatitis DOI: http://dx.doi.org/10.5772/intechopen.96747*

beginning of the 20th century surgeons such as Mayo Robson, Mickulicz, and Moynihan, in the context of the progression of anesthesia, were induced to deploy laparotomy in an effort to treat complications of severe acute pancreatitis [31]. Over the next decades surgical intervention became the therapy of choice despite a mortality rate greater than 50%. Extensive pancreatic resection became the treatment of choice in the 1960s and 1970s. Innovations and increased accuracy in radiological techniques led to new approaches for management. Surgeons were divided between those who reserved the intervention for cases of infected necrosis by proposing delayed exploration, and those who proposed early debridement for all patients with necrotizing pancreatitis. Since 1990s several studies proved that nonoperative management of patients with sterile pancreatic necrosis was superior to surgical intervention, and that delayed intervention provided improved surgical mortality rates. The treatment of infected necrosis shifted to a more conservative approach also thanks to a comprehensive knowledge of the physio-pathological process of the systemic inflammatory response and the adoption of novel antibiotics in curbing systemic toxicity and protecting against organ failure. Recently, endoscopic debridement and minimally invasive techniques has been introduced [31, 32].

The last guidelines of the Working Group of the International Association of Pancreatology (IAP)/American Pancreatic Association (APA) published in 2013 [23] and of the American Gastroenterological Association (AGA) published in 2020 [1] on the management of acute pancreatitis and pancreatic necrosis list the common indications for intervention. A symptomatic sterile pancreatic necrosis is an indication for intervention (either radiological, endoscopical or surgical). Symptoms can be represented by: gastric, intestinal, or biliary obstruction due to the mass effect of walled-off necrosis, pain, persistent unwellness in patients without signs of infection [1]. In case of infected pancreatic necrosis invasive procedures (e.g. percutaneous catheter drainage, endoscopic transluminal drainage/necrosectomy, minimally invasive or open necrosectomy) should be delayed, where possible, until at least 4 weeks after initial presentation to permit the collection to become "walled-off". A randomized clinical trial [33] that compared early surgery (within 72 h) and delayed surgery (11 days after onset) demonstrated mortality rates of 56% and 27%, respectively.

Percutaneous drainage, alone or in combination with other minimally invasive approaches, can be an effective means for source control in patients with infected pancreatic necrosis. A significant number of patients (23%–47%) will resolve their necrosis with percutaneous drainage alone. In those with persistent disease, a step up to operative intervention may be undertaken. The tract of the drain is utilized to access the retroperitoneal space for an intracavitary videoscopic necrosectomy by which drains are left in the cavity for lavage and fistula control [26, 34, 35]. The PANTER Study in 2010, a prospective randomized multicenter trial, compared the step-up approach to open necrosectomy and found a higher rate of new-onset multiple-organ failure in the open necrosectomy group (40% vs. 12%) and an equivalent mortality between the groups [26]. Surgical transgastric debridement is similar to endoscopic transgastric debridement, can be done laparoscopically or open, and is performed by an anterior gastrotomy to access the posterior wall of the stomach for transmural access to the necrosis cavity. Open surgical debridement is still an important resource in the management of these patients for the debridement of necrotic tissue.

Before surgical approach, abdominal imaging is helpful to determine intraabdominal status. Diagnosis of infected pancreatic necrosis is made by identification of air bubbles in retroperitoneal necrosis (areas with lack of contrast enhancement) on CT scan. Diagnosis can be confirmed by CT-guided fine needle aspiration of necrotic material for culture. CT is also indicated to define extent

and location of necrotic areas, for example into the mesenteric root and down the paracolic gutters; to demonstrate the presence of a disconnected pancreatic segment (a viable pancreatic portion separated by the rest of pancreas by a necrotic segment, that require external drainage to create a controlled external pancreatic fistula); and to evaluate the presence of other local complications, such as gastric outlet obstruction, splenic or portal vein thrombosis and colonic necrosis. Open debridement with external drainage still plays an important, albeit limited, role. After access to retroperitoneum, fluid is evacuated and necrotic dissection and debridement is made. In biliary pancreatitis, cholecystectomy should be practiced but it is associated with increased incidence of postoperative bile leak or biliary injury. Colon resection and colostomy have to be considered if mesocolon is involved in peripancreatic necrosis. A feeding enteral tube and at least two-four drainage tubes should be placed [36].

Video-assisted retroperitoneal debridement approach requires preoperative percutaneous retroperitoneal access. Radiological catheter insertion is a route to guide the subsequent procedure directly down into necrotic cavity and postoperative lavage. The advantage is minimizing the risk of peritoneal contamination, but the access is limited and precludes other procedures over debridement [34]. Postoperative complications are: intra-abdominal residual fluid collections, derived from pancreatic leak not well controlled by drains; bleeding, due to vascular lesion during debridement maneuvers or rupture of pseudoaneurysm, related to vascular erosion caused by mechanical drain damage or infection associated with uncontrolled pancreatic fistula; pancreatic fistulas: amylase-rich (concentration greater than three times the upper limit of normal serum amylase) fluid coming from drains; biliary injury; and pancreatic endocrine and exocrine insufficiency, that may requires supplemental insulin and oral pancreatic enzyme replacement.

Each approach has distinct peculiarities with pros and cons that must be weighted in each case planning: pattern of disease, physiology of the patient, expertise of the multidisciplinary team, and the resources of the center [1].

### **3. Disconnected pancreatic duct syndrome**

The term disconnected pancreatic duct syndrome (DPDS) refers to a subset of patients suffering from a disruption of the main pancreatic duct leading to a normal upstream pancreatic gland having no communication with the gastrointestinal tract [1, 37]. Up to 50% of patients with pancreatic fluid collections might have an underlying disconnected duct. It is best recognized using secretin-stimulated magnetic resonance cholangiopancreatography [38]. DPDS can be the result of acute necrotizing pancreatitis, chronic pancreatitis, and pancreatic trauma. Pancreatic juice is still secreted from the disconnected gland resulting in different resolutions that are a continuum of the same pathophysiologic process: recurrent acute pancreatitis, internal persistent pancreatic fistula (most often presenting as a peripancreatic fluid collection), external fistula, pancreatic pleural effusion, pancreatic ascites, or disconnected pancreatic tail syndrome [39, 40].

Internal fistulae are the result of ductal disruptions that are not contained by the inflammatory response. Anterior ductal disruptions result in pancreatic ascites, posterior ones result in pancreatic pleural effusions. Positive testing for a collection rich in pancreatic enzyme gives the secure diagnosis. A percutaneous drainage is the initial treatment to obtain a controlled fistula that in 70-82% of cases results in a spontaneous closure.

External fistulae may develop after pseudocyst percutaneous drainage. The stricture or the obstruction of the Wirsung result in ductal hypertension thus

*Surgical and Interventional Management of Complications Caused by Pancreatitis DOI: http://dx.doi.org/10.5772/intechopen.96747*

increasing the chance of developing this complication. Endoscopic retrograde pancreatography (ERP) with sphincterotomy or transpapillary stenting should be then performed, both in internal and in external fistulae, to reduce resistance of pancreatic juice flow to the duodenum [41].

If the disruption is in the body or the tail (disconnected pancreatic tail syndrome), open distal pancreatectomy and debridement associated with drainage are the traditional surgical procedures. These are characterized by a high periprocedural morbidity that is counterweighted by the single procedure and a concise overall course. Distal pancreatectomy can be undertaken during the first 30–60 days of illness, in the subacute setting [1].

The high morbidity and mortality associated with open surgical procedures, especially for poor surgical candidates, recommend a minimally invasive endoscopic [42]. Partial duct disruption can be treated with endoscopic transpapillary stent bridging with a fistula resolution rate of 56%, according to Varadarajulu et al. [43]. One possible endoscopic approach in case of complete duct disruption is the use of permanent indwelling transmural stents that allow the creation and maintenance of a fistulous tract into the gastrointestinal lumen [42].

Correct choice of procedure, as well as correct choice of timing of intervention, are mandatory for success.