the impact of heat on nerve conduction was initially described by hodgkin and katz in 
 19491 .
changes in sodium and potassium 
 channel activation are primarily responsible for heat - related nerve conduction changes1 , 2 . 
 with increasing temperature , voltage - gated sodium channel activation and deactivation 
 becomes increasingly rapid , and channels remain open for a shorter duration . depending on 
 the decreasing ion passage , the action potential amplitude diminishes and conduction 
 velocity ( cv ) accelerates2 .
these 
 differences that were defined at a single - fiber level were found to be similar in an in vivo 
 environment3 . in healthy nerve fibers , 

heating has been reported to increase both the sensory and motor nerve cv4 , 5 . in 
 demyelinating diseases ,
nerve conduction blocks are observed with increasing body 
 temperature6 , 7 . with respect to focal demyelinating conditions , superficial
superficial heating modalities primarily increase the temperature of the skin and 
 superficial subcutaneous tissues .
in contrast , deep heating modalities change the 
 temperature of deeper tissues to a depth of approximately 5  cm11 .
therapeutic ultrasound ( us ) is a deep - heating agent used 
 to treat various musculoskeletal disorders12,13,14 . 

the biophysical effects of us on tissues occur through 2 mechanisms : ( 1 ) thermal effects 
 acquired with continuous application , and ( 2 ) non - thermal effects acquired from pulse 
 application15 .
studies have reported contradicting results concerning the effects of deep heating produced 
 by us on healthy nerve conduction parameters . with respect to motor nerve cvs , continuous
zankel and farmer reported decreased ulnar motor nerve cvs 
 with sonation intensities of 1 to 2  w / cm , but increased velocities at other 
 intensities16 , 17 .
madsen reported decreased cvs after sonation at 0.88 and 
 1.28  w / cm , but increased cvs with sonation at 1.92  w/  cm18 . on the other hand , kramer19 observed increased motor cvs with all 5 
 tested sonation intensities in a range of 0.52.5  w/ cm . regarding sensory 
 conduction velocities , us application is generally associated with decreased sensory 
 latencies and increased cvs in healthy nerves20 , 
 21 .
recently , burnham et al . reported no significant change in healthy nerve 
 conduction parameters after us application5 .
carpal tunnel syndrome ( cts ) , the most common neuropathy , is caused by entrapment of the 
 median nerve under the flexor retinaculum .
patients usually present with paresthesias , pain , and numbness or a tingling 
 sensation in the fingers innervated by the median nerve .
initial treatment of this condition 
 is conservative , and includes splinting , exercises , medication , and physical therapy 
 modalities . in a previous study , continuous us therapy at different intensities
the researchers observed a decreased 
 motor nerve conduction velocity and increased motor distal latency in median nerve 
 conduction .
the authors therefore suggested that continuous us should not be recommended for 
 the treatment of carpal tunnel syndrome because of possible adverse effects on nerve 
 conduction parameters due to overheating22 .
this negative effect of us on demyelinating nerve conduction must 
 be considered , and therefore the biophysical effects of us should be assessed to confirm 
 this result .
previous reports do not appear to have described the instantaneous effects of deep heating 
 on demyelinating nerves .
however , such information would be important to the clarification 
 of the effects of deep - heating modalities such as us on diseased nerves . therefore , the 
 authors aimed to analyze and compare instantaneous changes after deep heating in 
 demyelinating and healthy nerves in the present study .
the effects of deep heating on motor and sensory nerve conduction studies were 
 analyzed immediately before , at the midpoint , and immediately after the application of 
 therapeutic us .
the study was conducted in compliance with the principles of the declaration 
 of helsinki .
the study protocol was approved by the local ethical committee ( dated 
 20.06.2012 , no .
69 ) , and patients provided written informed consent to participate . before all applications , the room temperature was recorded .
patients were left to rest to 
 allow their skin temperature to adapt to room temperature . the skin surface temperature on 
 the palm
was measured before , at the midpoint , and at the end of the us application using an 
 infrared skin thermometer ( medisana ag , neuss , germany ) .
the infrared skin thermometer was 
 reported to be highly reliable and valid for the purposes of an electrodiagnostic 
 laboratory23 .
the probe head of the 
 thermometer was placed on the skin surface of the palm , and the temperature was recorded 
 in  c .
a total of 32 hands of 25 subjects ( mean age : 51.6  9.5  years ) were recruited for the 
 study .
eligible subjects were identified among patients referred to our electrodiagnostic 
 laboratory with symptoms and diagnoses of cts24 .
a sample size of 19 would achieve 92% power for the detection of a 
 mean difference in pre - treatment and post - treatment sensory velocities of 1.9 m / s with an 
 estimated standard deviation of 2.4 m / s , and a significance level ( alpha ) of 0.05 using a 
 2-sided paired t - test25 .
patients were 
 excluded if they had diseases that would affect nerve conduction , such as polyneuropathy , 
 cervical radiculopathy , rheumatic diseases , or traumatic nerve injury .
patients were also 
 excluded if they had contraindications to us application and/or were administered a 
 corticosteroid injection in the last 6 months .
nerve conduction studies were conducted using a nihon kohden neuropack - s1 electromyogram 
 device ( tokyo , japan ) .
motor conduction studies were conducted using low- and high - frequency 
 amplifier settings at 5 and 10 khz , respectively .
the amplifier settings for sensory 
 conduction studies were 2 khz for the low and 20 khz for the high frequency .
the sensitivity 
 and sweep velocity were respectively set at 20 microvolts ( v)/division and 2  msec / division 
 for sensory studies and 5 millivolts / division and 2  msec / division for motor conduction 
 studies .
median motor nerve conduction parameters were recorded from the abductor pollicis 
 brevis muscle , and ulnar motor nerve conduction parameters were recorded from the adductor 
 digiti minimi muscle using superficial electrodes ( orthodromic ) .
the nerve was first 
 stimulated from 7  cm proximal to the recorded muscle .
a second stimulation was applied from 
 the antecubital fossa for the median nerve , and from the cubital tunnel for the ulnar nerve . 

median sensory nerve conduction studies were 
 recorded from the 2nd finger , and ulnar sensory nerve conduction studies were recorded from 
 the 5th finger using a ring electrode ( antidromic ) .
median versus ulnar sensory conduction comparison studies 
 were recorded from the 4th finger , and the peak latency of the sensory response was 
 recorded .
electrodiagnostic 
 studies were repeated from the same marked points at the midpoint ( 4th min ) and end ( 8th 
 min ) of us application .
us applications were performed using an intellect mobile combo us unit ( chattanooga , tn , 
 usa ) .
each subject was exposed to continuous - wave us treatment with a sonation intensity of 
 1.0  w / cm and frequency of 3.3  mhz .
a 0.5-cm us head was used . a 
 circular application technique with a soundhead movement speed of approximately 3  cm / second 
 was used .
the treatment area was 4  cm  2.5  cm , expanding from 1-cm distal to 2.5-cm 
 proximal of the wrist crease , including the median and ulnar nerve traces .
the size of the 
 radiated area with respect to the diameter of the us head was within the recommended 
 limits18 .
the kolmogorov - smirnov test was used to assess the normality of numeric variables . for 
 numeric variables that were normally distributed ,
comparisons between 2 groups were made 
 using the independent sample t - test , and results are expressed as means  standard 
 deviations . for
the scores and numeric variables that were non - normally distributed , 
 comparisons between 2 groups were made using the wilcoxon t - test or friedman test , and 
 results are expressed as medians ( 25th75th percentiles ) .
there were no 
 statistically significant differences between skin surface temperature measurements before 
 us application and at the 4th and 8th minutes ( p > 0.05 ; table 1table 1.changes in skin surface temperaturebefore application4th minute8th minutetemperature ( c)36.8 ( 36.537.0)36.8 ( 36.537.1)36.7 ( 36.537.2)absolute change values are presented as medians ( 2575 percentiles ) ) .
absolute change values are presented as medians ( 2575 percentiles ) table 2table 2.summary of changes in nerve conduction parameters with deep heatinginitial4th minute8th minutemedian nervemotorlatency ( msec)4.61 ( 4.264.95)4.58 ( 4.325.19)4.66 ( 4.095.14)cv ( m / s)53.95 ( 50.6056.55)52.15 ( 50.1554.75)52.60 ( 50.8554.75)sensorylatency ( msec)4.03 ( 3.334.61)4.03 ( 3.394.5)4.05 ( 3.424.64)cv ( m / s)37.0 ( 33.545.0)36.0 ( 33.543.1)36.9 ( 33.341.3)ulnar nervemotorlatency ( msec)2.60 ( 2.462.88)2.64 ( 2.542.95)2.77 ( 2.543.03)cv ( m / s)62.65 ( 59.555.60)60.60 ( 58.1563.85)61.40 ( 57.6564.10)sensorylatency ( msec)2.40 ( 2.342.67)2.43 ( 2.312.58)2.48 ( 2.312.59)cv ( m / s)56.35 ( 51.5559.20)56.50 ( 52.0059.10)56.45 ( 51.9059.55)med - uln 4papld ( msec)1.20 ( 0.922.30)1.18 ( 1.002.34)1.13 ( 0.982.26)absolute change values are median ( 25th75th percentiles ) .
cv : conduction velocity ; 
 med - uln 4p : median and ulnar nerve sensory conduction study to the fourth digit ; apld : 
 absolute peak latency difference . *
the first measurement differs significantly from the 4th and 8th minute measurements 
 ( p < 0.05 ) . *
* the first measurement differs significantly from the 8th minute measurement ( p 
 < 0.05 ) summarizes the median values of changes in motor and sensory latencies and 
 nerve cvs recorded from median and ulnar nerves before and at the 4th and 8th minutes of us 
 application .
regarding motor studies , the cvs of demyelinating median nerves exhibited 
 significant decreases at the 4th and 8th minutes .
in addition , a significant prolongation in 
 the healthy ulnar nerve onset latency was identified at the 8th minute when compared to the 
 initial value .
there were no significant differences in the before- and after - us values for 
 median motor latency , median sensory latency and cv , ulnar motor cv , ulnar sensory latency 
 and cv , and median - ulnar 4th finger peak latency .
cv : conduction velocity ; 
 med - uln 4p : median and ulnar nerve sensory conduction study to the fourth digit ; apld : 
 absolute peak latency difference . *
the first measurement differs significantly from the 4th and 8th minute measurements 
 ( p < 0.05 ) . *
* the first measurement differs significantly from the 8th minute measurement ( p 
 < 0.05 ) relative changes in electrophysiological parameters obtained from demyelinating and normal 
 nerves at the 4th and 8th minutes of us application are compared in table 3table 3.comparison of changes in demyelinated and normal nerves with deep heatingmedian nerveulnar nerveml1-ml20.05 ( 0.28)0.06 ( 0.21)ml1-ml30.01 ( 0.230.21)0.08 ( 0.310.02)mcv1-mcv21.25 ( 0.004.77)1.30 ( 1.222.60)mcv1-mcv30.91 ( 3.77)1.57 ( 3.55)sl1-sl20.03 ( 0.100.08)0.01 ( 0.070.07)sl1-sl30.00 ( 0.100.10)0.01 ( 0.050.11)scv1-scv20.14 ( 1.99)0.30 ( 4.67)scv1-scv30.55 ( 0.601.72)0.25 ( 4.373.20)absolute change values are shown as means ( standard deviations ) or medians ( 25th75th 
 percentiles ) as indicated .
1 : initial value ; 2 : value at 4th minute ; 3 : value at 8th 
 minute ; ml : motor latency ; mcv : motor conduction velocity ; sl : sensory peak latency ; 
 scv : sensory conduction velocity . there were no significant differences between demyelinating and normal nerves 
 in terms of velocity and latency changes due to deep - heat application .
absolute change values are shown as means ( standard deviations ) or medians ( 25th75th 
 percentiles ) as indicated .
1 : initial value ; 2 : value at 4th minute ; 3 : value at 8th 
 minute ; ml : motor latency ; mcv : motor conduction velocity ; sl : sensory peak latency ; 
 scv : sensory conduction velocity
the main question addressed in this study was whether the application of deep heating would 
 differently affect demyelinating and normal nerves .
some of these reports16,17,18 suggested that the cvs of healthy motor nerves decreased at 
 sonation intensities of approximately 1  w / cm , except for 1 study25 that observed an increased cv . in 
 addition , previous research indicated an association between sonation and increased sensory 
 nerve cvs in healthy nerves19 , 21 , 25 . in the present 
 study ,
a statistically significant deceleration was observed with deep heating in both in 
 demyelinating and healthy nerve motor cvs , but not in sensory cvs .
previously , reduced healthy nerve motor conduction speed following us radiation has been 
 attributed to micromassage action16 or a 
 mechanical effect17 of us .
this non - linear relationship between body 
 temperature and nerve cvs might also explain the results of the present study .
the authors 
 of that earlier study also surmised that a decreased motor cv might be related to the 
 cooling effect of the transmission gel . according to a report by kramer et al .
, intensities 
 above 1.5  w / cm were necessary to exceed the cooling effect of the transmission 
 gel25 . in the present study ,
the 
 sonation intensity was 1.0  w / cm , or below the lower limit determined by kramer 
 et al25 .
however , previous work has demonstrated temperature elevation in 
 deeper tissue layers at a continuous us application of 1  mhz27 .
additionally , the effective radiating area and output power of us 
 devices from different manufactures may differ , resulting in different degrees of tissue 
 heating28 , 29 .
consequently , these variables differed between studies and 
 increased the difficulty of drawing a precise conclusion .
the median and ulnar nerves , which have similar structures and anatomical locations , 
 respond similarly to temperature changes30 , 31 . in the present study , healthy ulnar 
 nerves in the arms affected by cts comprised the control group and were compared with 
 demyelinating median nerves .
use of the ipsilateral ulnar nerves as the control group 
 enabled the elimination of potential biases such as deep tissue temperature differences or 
 the amount of us radiation . as nerve conduction studies can be affected by many other 
 parameters , such as height , age , sex , tissue temperature , and room temperature , the 
 simultaneous comparison of healthy control and demyelinated nerves in the same arm is a 
 strength of this study .
several studies have evaluated the cumulative effect of us treatment 
 in patients with cts18 , 32 , 33 . in the first 
 study ,
us pulsed mode 1:4 us was applied at 1  mhz and 1.0  w / cm for 15 minutes 
 and 20 sessions , and significant improvements were observed in motor distal latency and 
 sensory nerve conduction32 . in another 
 study , improvements in motor latencies and amplitudes of were observed in patients with cts 
 after 15 sessions of us33 .
in contrast , 
 another study found no significant difference in nerve conduction after 10 sessions of us 
 with changing dosages , but identified a mild increase in motor latencies and deceleration of 
 motor cvs with us applications at 1.5  w / cm and 0.8  w / cm22 .
in contrast , the present study focused on 
 the immediate biophysiological results of deep heating from us .
subcutaneous temperature measurement was not performed in this study , and this omission 
 could be perceived as a limitation . however , previous reports described a significant 
 correlation between intramuscular and skin surface temperatures , and skin surface 
 temperature measurement is more reliable and reflective of the subcutaneous tissue 
 temperature close to the nerve23 , 30 .
therefore , in the present study used skin 
 surface temperatures measured with an infrared thermometer , rather than subcutaneous tissue 
 temperatures .
the present study revealed a significant reduction in the demyelinating motor nerve cv , but 
 not the sensory nerve cv , after deep heating .
this finding could raise questions about the 
 effectiveness of deep heating for diseased peripheral nerves .
however , the present study 
 only obtained results using continuous us at 3.3  mhz and 1w / cm , with application 
 times of 4 and 8 minutes . in the future , similar studies involving different us parameters 
 will enable researchers to obtain a wider variety of results .
 [ purpose ] physiotherapeutic heating agents are classified into two groups : 
 superficial - heating agents and deep - heating agents . therapeutic ultrasound is a 
 deep - heating agent used to treat various musculosketal disorders . 
 numerous studies have 
 attempted to determine the impact of ultrasound on healthy nerve conduction parameters . 
 
 however , the instantaneous effects of deep heating via ultrasound on demyelinating nerves 
 do not appear to have been described previously . 
 the present study aimed to assess and 
 compare the impact of ultrasound on demyelinating nerve and healthy nerve conduction 
 parameters . 
 [ subjects and methods ] carpal tunnel syndrome was used as a focal 
 demyelination model . 
 thirty - two hands of 25 participants with carpal tunnel syndrome were 
 enrolled in the study . 
 ultrasound parameters were 3.3  mhz , 1.0  w / cm2 , 8 
 minutes , and continuous wave . 
 electrodiagnostic studies were performed initially , at the 
 midpoint ( 4th min ) , and immediately after ( 8th min ) ultrasound application . [ results ] 
 
 reduced motor conduction velocity was found in demyelinating nerves at the 4th and 8th 
 minutes . 
 ulnar nerve onset latency was significantly prolonged in the 8th minute 
 recording , compared to the initial value . 
 there were no significant differences in 
 relative velocity and latency changes between demyelinating and normal nerves . 
 
 [ conclusion ] deep heating via ultrasound may inversely affect conduction velocity in 
 demyelinating nerves . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION