pulmonary function testing pulmonary function testing pulmonary function testing (pft) is a complete evaluation of the respiratory system including patient history, physical examinations, and tests of pulmonary function. the primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment. pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease. pfts are normally performed by a pulmonary function technician, respiratory therapist, respiratory physiologist, physiotherapist, pulmonologist, or general practitioner. pulmonary function testingplethysmograph "body box"meshd012129ops-301 code1-71medlineplus003853 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 indications pulmonary function testing is a diagnostic and management tool used for a variety of reasons, such as: diagnose lung disease. monitor the effect of chronic diseases like asthma, chronic obstructive lung disease, or cystic fibrosis. detect early changes in lung function. identify narrowing in the airways. evaluate airway bronchodilator reactivity. show if environmental factors have harmed the lungs preoperative testing neuromuscular disorders pulmonary function testing in patients with neuromuscular disorders helps to evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis. duchenne muscular dystrophy is associated with gradual loss of muscle function over time. involvement of respiratory muscles results in poor ability to cough and decreased ability to breathe well and leads to collapse of part or all of the lung leading to impaired gas exchange and an overall insufficiency in lung strength. tests spirometry main article: spirometry spirometry spirometry includes tests of pulmonary mechanics – measurements of fvc, fev1, fef values, forced inspiratory flow rates (fifs), and mvv. measuring pulmonary mechanics assesses the ability of the lungs to move huge volumes of air quickly through the airways to identify airway obstruction. the measurements taken by the spirometry device are used to generate a pneumotachograph that can help to assess lung conditions such as: asthma, pulmonary fibrosis, cystic fibrosis, and chronic obstructive pulmonary disease. physicians may also use the test results to diagnose bronchial hyperresponsiveness to exercise, cold air, or pharmaceutical agents. helium dilution main article: helium dilution technique the helium dilution technique for measuring lung volumes uses a closed, rebreathing circuit. this technique is based on the assumptions that a known volume and concentration of helium in air begin in the closed spirometer, that the patient has no helium in their lungs, and that an equilibration of helium can occur between the spirometer and the lungs. nitrogen washout main article: nitrogen washout the nitrogen washout technique uses a non-rebreathing open circuit. the technique is based on the assumptions that the nitrogen concentration in the lungs is 78% and in equilibrium with the atmosphere, that the patient inhales 100% oxygen and that the oxygen replaces all of the nitrogen in the lungs. plethysmography main articles: plethysmograph and lung volumes the plethysmography technique applies boyle's law and uses measurements of volume and pressure changes to determine total lung volume, assuming temperature is constant. there are four lung volumes and four lung capacities. a lung's capacity consists of two or more lung volumes. the lung volumes are tidal volume (vt), inspiratory reserve volume (irv), expiratory reserve volume (erv), and residual volume (rv). the four lung capacities are total lung capacity (tlc), inspiratory capacity (ic), functional residual capacity (frc) and vital capacity (vc). maximal respiratory pressures main article: respiratory pressure meter measurement of maximal inspiratory and expiratory pressures is indicated whenever there is an unexplained decrease in vital capacity or respiratory muscle weakness is suspected clinically. maximal inspiratory pressure (mip) is the maximal pressure that can be produced by the patient trying to inhale through a blocked mouthpiece. maximal expiratory pressure (mep) is the maximal pressure measured during forced expiration (with cheeks bulging) through a blocked mouthpiece after a full inhalation. repeated measurements of mip and mep are useful in following the course of patients with neuromuscular disorders. diffusing capacity main article: diffusing capacity measurement of the single-breath diffusing capacity for carbon monoxide (dlco) is a fast and safe tool in the evaluation of both restrictive and obstructive lung disease. bronchodilator responsiveness when a patient has an obstructive defect, a bronchodilator test is given to evaluate if airway constriction is reversible with a short acting beta-agonist. this is defined as an increase of ≥12% and ≥200 ml in the fev1 or fvc. oxygen desaturation during exercise the six-minute walk test is a good index of physical function and therapeutic response in patients with chronic lung disease, such as copd or idiopathic pulmonary fibrosis. arterial blood gases arterial blood gases (abgs) are a helpful measurement in pulmonary function testing in selected patients. the primary role of measuring abgs in individuals that are healthy and stable is to confirm hypoventilation when it is suspected on the basis of medical history, such as respiratory muscle weakness or advanced copd. abgs also provide a more detailed assessment of the severity of hypoxemia in patients who have low normal oxyhemoglobin saturation. risks pulmonary function testing is a safe procedure; however, there is cause for concern regarding untoward reactions and the value of the test data should be weighed against potential hazards. some complications include dizziness, shortness of breath, coughing, pneumothorax, and inducing an asthma attack. contraindications there are some indications against a pulmonary function test being done. these include a recent heart attack, stroke, head injury, an aneurysm, or confusion. technique preparation subjects have measurements of height and weight taken before spirometry to determine what their predicted values should be. additionally, a history of smoking, recent illness, and medications is taken. quality control in order for the forced vital capacity to be considered accurate it has to be conducted three times where the peak is sharp in the flow-volume curve and the exhalation time is longer than 6 seconds. reproducibility of the pft is determined by comparing the values of forced vital capacity (fvc) and forced expiratory volume at 1 second (fev1). the difference between the highest values of two fvcs need to be within 5% or 150 ml. when the fvc is less than 1.0 l, the difference between the highest two values must be within 100 ml. lastly, the difference between the two highest values of fev1 should also be within 150 ml. the highest fvc and fev1 may be used from each different test. until the results of three tests meet the criteria of reproducibility, the test can be repeated up to eight times. if it is still not possible to get accurate results, the best three tests are used. clinical significance changes in lung volumes and capacities from normal are generally consistent with the pattern of lung impairment. spirometry is required for a diagnosis of copd. interpretation of tests classification of copd based on spirometry severity fev1 % predicted mild (gold 1) ≥80 moderate (gold 2) 50–79 severe (gold 3) 30–49 very severe (gold 4) <30