spirometry spirometry spirometry (meaning the measuring of breath) is the most common of the pulmonary function tests (pfts). it measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. spirometry is helpful in assessing breathing patterns that identify conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and copd. it is also helpful as part of a system of health surveillance, in which breathing patterns are measured over time. spirometryflow-volume loop showing successful fvc maneuver. positive values represent expiration, negative values represent inspiration. at the start of the test both flow and volume are equal to zero (representing the volume in the spirometer rather than the lung). the trace moves clockwise for expiration followed by inspiration. after the starting point the curve rapidly mounts to a peak (the peak expiratory flow). (note the fev1 value is arbitrary in this graph and just shown for illustrative purposes; these values must be calculated as part of the procedure).meshd013147ops-301 code1-712 tlctotal lung capacity: the volume in the lungs at maximal inflation, the sum of vc and rv.tvtidal volume: that volume of air moved into or out of the lungs during quiet breathing (tv indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol tv or vt is used.)rvresidual volume: the volume of air remaining in the lungs after a maximal exhalationervexpiratory reserve volume: the maximal volume of air that can be exhaled from the end-expiratory positionirvinspiratory reserve volume: the maximal volume that can be inhaled from the end-inspiratory levelicinspiratory capacity: the sum of irv and tvivcinspiratory vital capacity: the maximum volume of air inhaled from the point of maximum expirationvcvital capacity: the volume of air breathed out after the deepest inhalation.vttidal volume: that volume of air moved into or out of the lungs during quiet breathing (vt indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation, the symbol tv or vt is used.)frcfunctional residual capacity: the volume in the lungs at the end-expiratory positionrv/tlc%residual volume expressed as percent of tlcvaalveolar gas volumevlactual volume of the lung including the volume of the conducting airway.fvcforced vital capacity: the determination of the vital capacity from a maximally forced expiratory effortfevtforced expiratory volume (time): a generic term indicating the volume of air exhaled under forced conditions in the first t secondsfev1volume that has been exhaled at the end of the first second of forced expirationfefxforced expiratory flow related to some portion of the fvc curve; modifiers refer to amount of fvc already exhaledfefmaxthe maximum instantaneous flow achieved during a fvc maneuverfifforced inspiratory flow: (specific measurement of the forced inspiratory curve is denoted by nomenclature analogous to that for the forced expiratory curve. for example, maximum inspiratory flow is denoted fifmax. unless otherwise specified, volume qualifiers indicate the volume inspired from rv at the point of measurement.)pefpeak expiratory flow: the highest forced expiratory flow measured with a peak flow metermvvmaximal voluntary ventilation: volume of air expired in a specified period during repetitive maximal effort doing spirometry spirometry generates pneumotachographs, which are charts that plot the volume and flow of air coming in and out of the lungs from one inhalation and one exhalation. indications spirometry is indicated for the following reasons: to diagnose or manage asthma to detect respiratory disease in patients presenting with symptoms of breathlessness, and to distinguish respiratory from cardiac disease as the cause to measure bronchial responsiveness in patients suspected of having asthma to diagnose and differentiate between obstructive lung disease and restrictive lung disease to follow the natural history of disease in respiratory conditions to assess of impairment from occupational asthma to identify those at risk from pulmonary barotrauma while scuba diving to conduct pre-operative risk assessment before anaesthesia or cardiothoracic surgery to measure response to treatment of conditions which spirometry detects to diagnose the vocal cord dysfunction. contraindications forced expiratory maneuvers may aggravate some medical conditions. spirometry should not be performed when the individual presents with: hemoptysis of unknown origin pneumothorax unstable cardiovascular status (angina, recent myocardial infarction, etc.) thoracic, abdominal, or cerebral aneurysms cataracts or recent eye surgery recent thoracic or abdominal surgery nausea, vomiting, or acute illness recent or current viral infection undiagnosed hypertension spirometry testing a modern usb pc-based spirometer. device for spirometry. the patient places his or her lips around the blue mouthpiece. the teeth go between the nubs and the shield, and the lips go over the shield. a noseclip guarantees that breath will flow only through the mouth. screen for spirometry readouts at right. the chamber can also be used for body plethysmography. spirometer the spirometry test is performed using a device called a spirometer, which comes in several different varieties. most spirometers display the following graphs, called spirograms: a volume-time curve, showing volume (litres) along the y-axis and time (seconds) along the x-axis a flow-volume loop, which graphically depicts the rate of airflow on the y-axis and the total volume inspired or expired on the x-axis procedure the basic forced volume vital capacity (fvc) test varies slightly depending on the equipment used, either closed circuit or open circuit, but should follow the ats/ers standardisation of spirometry. generally, the patient is asked to take the deepest breath they can, and then exhale into the sensor as hard as possible, for as long as possible, preferably at least 6 seconds. it is sometimes directly followed by a rapid inspiration, (inhalation) in particular when assessing possible upper airway obstruction. sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor (tidal volume), or the rapid breath in (forced inspiratory part) will come before the forced expiration. during the test, soft nose clips may be used to prevent air escaping through the nose. filter mouthpieces may be used to prevent the spread of microorganisms. limitations of test the maneuver is highly dependent on patient cooperation and effort, and is normally repeated at least three times to ensure reproducibility. since results are dependent on patient cooperation, fvc can only be underestimated, never overestimated. due to the patient cooperation required, spirometry can only be used on children old enough to comprehend and follow the instructions given (6 years old or more), and only on patients who are able to understand and follow instructions — thus, this test is not suitable for patients who are unconscious, heavily sedated, or have limitations that would interfere with vigorous respiratory efforts. other types of lung function tests are available for infants and unconscious persons. another major limitation is the fact that many intermittent or mild asthmatics have normal spirometry between acute exacerbation, limiting spirometry's usefulness as a diagnostic. it is more useful as a monitoring tool: a sudden decrease in fev1 or other spirometric measure in the same patient can signal worsening control, even if the raw value is still normal. patients are encouraged to record their personal best measures. example of a modern pc-based spirometer printout. related tests spirometry can also be part of a bronchial challenge test, used to determine bronchial hyperresponsiveness to either rigorous exercise, inhalation of cold/dry air, or with a pharmaceutical agent such as methacholine or histamine. sometimes, to assess the reversibility of a particular condition, a bronchodilator is administered before performing another round of tests for comparison. this is commonly referred to as a reversibility test, or a post bronchodilator test (post bd), and is an important part in diagnosing asthma versus copd. other complementary lung functions tests include plethysmography and nitrogen washout. parameters the most common parameters measured in spirometry are vital capacity (vc), forced vital capacity (fvc), forced expiratory volume (fev) at timed intervals of 0.5, 1.0 (fev1), 2.0, and 3.0 seconds, forced expiratory flow 25–75% (fef 25–75) and maximal voluntary ventilation (mvv), also known as maximum breathing capacity. other tests may be performed in certain situations. results are usually given in both raw data (litres, litres per second) and percent predicted—the test result as a percent of the "predicted values" for the patients of similar characteristics (height, age, sex, and sometimes race and weight). the interpretation of the results can vary depending on the physician and the source of the predicted values. generally speaking, results nearest to 100% predicted are the most normal, and results over 80% are often considered normal. multiple publications of predicted values have been published and may be calculated based on age, sex, weight and ethnicity. however, review by a doctor is necessary for accurate diagnosis of any individual situation. a bronchodilator is also given in certain circumstances and a pre/post graph comparison is done to assess the effectiveness of the bronchodilator. see the example printout. functional residual capacity (frc) cannot be measured via spirometry, but it can be measured with a plethysmograph or dilution tests (for example, helium dilution test). average values for forced vital capacity (fvc), forced expiratory volume in 1 second (fev1) and forced expiratory flow 25–75% (fef25–75%), according to a study in the united states 2007 of 3,600 subjects aged 4–80 years. y-axis is expressed in litres for fvc and fev1, and in litres/second for fef25–75%. forced vital capacity (fvc) forced vital capacity (fvc) is the volume of air that can forcibly be blown out after full inspiration, measured in liters. fvc is the most basic maneuver in spirometry tests. forced expiratory volume in 1 second (fev1) fev1 is the volume of air that can forcibly be blown out in first 1-second, after full inspiration. average values for fev1 in healthy people depend mainly on sex and age, according to the diagram. values of between 80% and 120% of the average value are considered normal. predicted normal values for fev1 can be calculated and depend on age, sex, height, mass and ethnicity as well as the research study that they are based on. fev1/fvc ratio fev1/fvc is the ratio of fev1 to fvc. in healthy adults this should be approximately 70–80% (declining with age). in obstructive diseases (asthma, copd, chronic bronchitis, emphysema) fev1 is diminished because of increased airway resistance to expiratory flow; the fvc may be decreased as well, due to the premature closure of airway in expiration, just not in the same proportion as fev1 (for instance, both fev1 and fvc are reduced, but the former is more affected because of the increased airway resistance). this generates a reduced value (<70%, often ~45%). in restrictive diseases (such as pulmonary fibrosis) the fev1 and fvc are both reduced proportionally and the value may be normal or even increased as a result of decreased lung compliance. a derived value of fev1 is fev1% predicted (fev1%), which is defined as fev1 of the patient divided by the average fev1 in the population for any person of the same age, height, gender, and race. forced expiratory flow (fef) forced expiratory flow (fef) is the flow (or speed) of air coming out of the lung during the middle portion of a forced expiration. it can be given at discrete times, generally defined by what fraction of the forced vital capacity (fvc) has been exhaled. the usual discrete intervals are 25%, 50% and 75% (fef25, fef50 and fef75), or 25% and 50% of fvc that has been exhaled. it can also be given as a mean of the flow during an interval, also generally delimited by when specific fractions remain of fvc, usually 25–75% (fef25–75%). average ranges in the healthy population depend mainly on sex and age, with fef25–75% shown in diagram at left. values ranging from 50 to 60% and up to 130% of the average are considered normal. predicted normal values for fef can be calculated and depend on age, sex, height, mass and ethnicity as well as the research study that they are based on. mmef or mef stands for maximal (mid-)expiratory flow and is the peak of expiratory flow as taken from the flow-volume curve and measured in liters per second. it should theoretically be identical to peak expiratory flow (pef), which is, however, generally measured by a peak flow meter and given in liters per minute. recent research suggests that fef25-75% or fef25-50% may be a more sensitive parameter than fev1 in the detection of obstructive small airway disease. however, in the absence of concomitant changes in the standard markers, discrepancies in mid-range expiratory