Statement on Spirometry

_ _ accp scientific section recommendations Statement on Splrometry A Report of the Section on Respiratory Pathophyslology*

tests of pulmonary function have become Spirometric an integral part of epidemiologic studies of lung diseases, and standards have been set by various government agencies fur the determination of impairment and disability, due to pneumoconioses and chronic obstructive lung diseases. The most common use of spirometry, however, should be by the practicing physician in the diagnosis of lung disease, in determining the extent of imj;>airment of lung function, and in evaluating the response of patients with lung diseases to specific treatment, such as the administration of bronchodilators, glucocorticoids, etc. A number of scientific groups and committees, including the American Thoracic Society (ATS); the Epidemiology Standardization Project of the Division of Lung Diseases; National Heart, Lung and Blood Institute; and the National Institute of Occupational Safety and Health have reviewed existing data and routine practices and have published documents outlining minimum requirements and standards for spirometry. 1.a A statement of the American College of Chest Physicians' Committee on Clinic and Office Pulmonary Function Testing was published in 1978. 4 At present, the minimum requirements and standards1 are as fullows: The spirometer should be capable of accurate measurement of expired volumes up to 7 L, BTPS, and of accumulating the volume of expired air fur at least ten seconds. The spirometer should have low inertia and low resistance, less than 1.5 cm H10/ll second at an airflow ofl2 L per second. The instrument should be calibrated regularly with a calibrated syringe of at least 3 L of volume. The calibration should be accurate within 3 percent and should be perfurmed at least once a month fur conventional spirometers and once a week fur the automated computerized type of equipment. The furced vital capacity (FVC) maneuver is the basic spirometric maneuver fur the evaluation of the mechanics of breathing. The maneuver entails a max•Prepared by Noe Zamel, M.D., F.C.C.P., Toronto; Murray D. Altose, M.D., F.C.C.P., Cleveland; and William A. Speir, Jr., M.D., F.C.C.P., Augusta, Georgia. Reprint requests: Dr: Zamel, Mt. Sinai Hoapltal, 60 Unroerlaty Aiienue, Toronto, Ontario, Canada MSG lXS

imum inspiration to total lung capacity fullowed by a maximum furced exhalation to residual volume. Patients must be carefully instructed, by well-trained technicians, in this somewhat artificial maneuver; practice attempts are frequently required befure acceptable spirograms are obtained. The elements of an acceptable FVC maneuver include: (1) full inspiration to total lung capacity befure furced expiration begins; (2) the beginning of furced expiration should be abrupt, without hesitation; (3) maximum effort must be exerted throughout expiration; (4) spirograms during which inteITUptions are observed due to coughing, glottis closure, obstruction by the tongue or false teeth should be discarded (the contour of the volume-time tracing should be smooth and without inteITUption); and (5) in general, an FVC maneuver that takes less than fuur seconds should be discarded; the maximum expiration should continue until an obvious "plateau" appears on the volume/time tracing, and the volume change per 0.5-second interval is 25 ml or less. A permanent record of the spirographic curve is important fur evaluation of its acceptability. It is generally agreed that three furced expiratory tracings that meet the above criteria constitute an acceptable test. Acceptability is contingent on reproducibility of the FVC and furced expiratory volume at 1 second (FEVJ among the curves. The two best of three acceptable spirograms should not vary by more than 5 percent of the largest value or by more than 100 ml, whichever is greater. Adherence to such standards will ensure that the values reported represent maximum effort and reflect actual pulmonary function. If the steepest slope of the spirogram does not occur at the onset of the curve, a back extrapolation technique-in which the steepest slope of the curve is extrapolated to maximum inspired volume (zero point) and the FEV1 measured from that point-should be used. The details of this extrapolation technique have been published by Smith and Gaensler. 11 For purposes of reporting pulmonary function values, the largest observed FVC, and the largest observed FEV1> corrected to BTPS, obtained from any of the three acceptable spirograms (regardless of CHEST I 83 I 3 I Mln:h, 1983

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whether they are obtained from the same curve) should be used. The furced expiratory flow over the midportion from 25 percent to 75 percent of the FVC (FEF25-75%) should, however, be determined from the tracing with the greatest sum of FVC and FEV1• The FEV1 and the FEF25-75% have the dimension of volume/time and represent average ranges of airflow during expiration over different portions of the FVC. The FEV1 is the volume of air expelled during the first second of maximal expiration and usually is an index of the average airflow over the initial two thirds or more of the FVC. The index of the average flow over the middle half of the FVC is the FEF25-75%, the variability of which is much greater than that ofFEV1• This must be taken into consideration when interpreting spirometric test results. Pulmonary abnormalities that produce airflow limitation will result in reductions in both the FEV1 and FEF25-75%. In general, a mild impairment in patients with chronic obstructive pulmonary disease tends to reduce airflow rates at lower lung volumes befure there is significant reduction in flow at larger lung volumes. It has been suggested that the FEF25-75% is a relatively sensitive test of small airways obstruction;8 this is, however, controversial. 1 Considerable compression of thoracic gas may occur during a furced expiratory maneuver, such that the values of FVC, FEV1 and FEF25-75% determined from the expired volume at the mouth may be lower during a maximum effurt and somewhat greater during a submaximum effurt. The recent data of Suratt et al8 suggest that although increases in one or all of these spirometric values may occur in approximately 30 percent of subjects who exert submaximum effurt during the FVC maneuver, the effect is much more pronounced in patients with airway obstruction. Expiratory flow during a maximum expiratory maneuver is also critically dependent on lung volume. Restrictive ventilatory disorders that lower t
were included in their study, so that the reference values they report fur the elderly may not be conclusive. Their standards were determined from measurements in healthy nonsmokers residing in an environment relatively free of air pollution. This contrasts with the commonly used reference standards compiled by the Veterans Administration-Army Cooperative Study1" in large urban centers, in which many of the subjects were cigarette smokers. Morris et al9 did not use the back extrapolation technique recommended by the ATS. Crapo et al11 have recently developed reference values using techniques and equipment that met ATS recommendations. They recalculated the data of Morris et al, 9 using the back extrapolation technique, and fuund that by adding 179 ml to the FEVh the values were adjusted to those that would have been obtained by the back extrapolation technique, and that the data of the two studies were then very similar. Several other standard reference values for time/ volume spirometry have been published. None is widely used as standards fur general pulmonary function laboratories; however, the reference standards of Knudson et al12 have been designated by federal agencies fur use in the evaluation of certain categories of disease in patients exposed to occupational hazards (eg, cotton dust exposure). The predicted reference values fur FVC, FEVh and FEF25-75% vary with the height, sex, and age of the subject. The values increase with increasing height; they are lower in females than in males of similar height and age; and decline progressively in the adult with advancing age. Determination of whether the observed values fur FVC, FEVh and FEF25-75% in a given patient are normal or abnormal requires the establishment of limits of normality. The widely used convention of setting the lower limits of normal at 80 percent of the predicted normal value should be avoided. The use of a fixed percentage may give rise to error either by setting the limits too widely at high values, or within too narrow a range at low values. If either the SEE or the coefficient of variation is large, setting the lower limit of normal at 80 percent of the mean may result in a large fraction of the normal population being included in the abnormal range. Normal limits are set by the regression equations derived from studies of large groups of normal subjects. An acceptable statistical method to establish normal limits fur general use is to define the lower limit of normal as a point located 1. 64 SEE (the SD from the regression line) below the mean value fur normal subjects of the same height, sex, and age on the regression line. Using this method, 95 percent of the normal population will generally fall within the normal range. An alternative statistical option is to use percentile limits. A number of studies have demonstrated that for any Sllllment on Spkomelry (Sltcllon d Respif8foly Palhophyslology ACCP}

given age and height, the FVC and FEV1 are approximately 12 to 14 percent lower in normal black males than in normal white males. The FEF25-75%, however, when corrected for differences in lung volume, is no different. Schoenberg et al13 reported predicted values for North American blacks and whites. Unfortunately, the number of black males included in their study was small, and some were former cigarette smokers. A reasonable approximation for normal values in black subjects is to reduce the predicted values of Monis et al8 for FVC and FEV1 by12 percent. It should be noted, however, that the appropriateness of adjusting predicted values depends on a precise definition of race. In many laboratories, routine pulmonary function testing also includes the measurement of maximum voluntary ventilation (MVV). This test involves maximal voluntary ventilation at a breathing frequency of at least 60 breaths per minute and a volume of about 60 percent of the vital capacity for a period of 12 to 15 seconds. The volume of air that is breathed is expressed in liters per minute, BTPS. This test requires considerable motivation, cooperation, and eflOrt, and it may be fatiguing. Although the MVV reftects the function of the entire ventilatory apparatus, there is a very close correlation between the MVV and the FEV1• The MVV is approximated by multiplying the FEV1 by a factor of 35. This relationship is found not only in normal subjects but also in patients with chronic airHow limitation and in patients with pulmonary restrictive disorders. Discrepancies between the observed MVV and that expressed based on the FEV1 generally indicate inconsistent eflOrts. A disproportionate reduction in the MVV is also found in patients with extrathoracic upper airway obstruction and in some patients with respiratory muscle weakness. The MVV is required by some agencies for disability evaluation, but from a clinical standpoint the test is of limited value. Spirometry is often repeated following the administration of inhaled sympathomimetic bronchodilators in patients with chronic obstructive pulmonary disease in order to ascertain the degree of reversibility of airHow limitation. The response to bronchodilators can be considered significant only if the increases in FVC, FEVb and FEF25-75% exceed normal within-day variations. A statistically significant difference, for practical purposes, in a normal (Gaussian) distribution of patients, would entail an increase of more than 1. 64 times the coefficient of variation above the mean. According to the data of Pennock et al, 1' the within-day coefficients of variation of FVC, FEV1> and FEF25-75% in patients with reversible airways obstruction are approximately 7, 8, and 14 percent, respectively. Accordingly, a significant response to inhaled bronchodilators would require a minimum

increase in the FVC and FEV1 ofatleast12 percent and an increase in the FEF25-75% ofat least 25 percent. In patients with marked airway obstruction, an increase of 12 percent in FEV1 and 25 percent in FEF25-75% may have statistical significance, but larger increases may be required to be considered clinically important. Usually the changes in FEV1 are sufficient to evaluate the acute effect of the bronchodilator. However, the assessment of bronchodilator response based on the FEF25-75% is more complex. H the vital capacity increases after bronchodilator therapy, comparison of FEF25-75% before and after bronchodilation measured by the conventional methods may result in underestimation of the improvement. The total lung capacity does not usually change after bronchodilator administration, and the i.Jicrease in vital capacity that frequently occurs is consequent to a fall in residual volume. Therefore, the FEF25-75% before and after bronchodilator administration should be compared over a similar absolute lung volume interval. This can be done using the prebronchodilator vital capacity 25 and 75 percent points and the same distance from the onset of the maneuver applied to the postbronchodilator vital capacity. u.111 Care must be exercised in interpreting the response of the patient in terms of expiratory How to acute administration of inhaled bronchodilators. Generalb:ations based on a single pre- and post-bronchodilator spirometric test are to be discouraged. Responsiveness to bronchodilators may vary in a given patient from time to time. Many patients demonstrate considerable spirometric and/or clinical improvement following long-term bronchodilator therapy, despite small and inconsistent spirometric changes following acute administration of bronchodilators. In summary, spirometry is a useful tool in the diagnosis and management of patients with lung diseases, as well as in epidemiologic studies, and assisting in determining degrees of pulmonary impairment or disability. The physician should ensure that the spirometer utilized in the office or hospital meets minimum standards and is calibrated regularly. In addition, it is the physician's responsibility to ensure that pulmonary function technicians in the office or hospital are properly trained and supervised in the performance of spirometric tests and in the accurate calculation Of values obtained from the FVC maneuver and that the observed values for a given patient are compared with appropriate standard reference values. Interpretation of spirometric test results is the responsibility of the physician and should be carefully correlated with both objective and subjective clinical findings in each individual patient. Periodic exaniinations of spirometric pulmonary function variables are often an invaluable guide to therapy and prognosis in patients with chronic obstructive and restrictive pulmoCHEST I 83 I 3 I Mln:h. 1983

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nary diseases and, as such, are to be strongly encouraged as a routine practice. REFERENCES

1 Gardner RM, et al. ATS Statement-Snowbird workshop on standardization of spirometry. Am Rev Respir Dis 1979;

119:831-38 2 Ferris BG (principal investigator). Epidemiology standardization project. Am Rev Respir Dis 1978; 118(part 2):55-88 3 Federal Register. 1980; 45,(42):13695-96 4 Permutt S, Chester E, Anderson W, Cugell D, Petty TL, Sharp JT. Office spirometry in clinical practice: Statement of the American College of Chest Physicians Committee on Clinic and Office Pulmonary Function Testing. Chest 1978; 74:298 5 Smith AA, Gaensler EA. Tuning of farced expiratory volume in one second. Am Rev Respir Dis 1975; 112:882-85 6 McFadden ER Jr, Linden JA. Reduction in maximum midexpiratory flow rate: a spirographic manJfestation of small airway disease. Am J Med 1972; 52:725-37 7 Permutt S, Menkes HA. Spirometry: analysis oftorced expiration within the time domain. In: Macklem FI; Permut S, eds. The lung in the transition between health and disease. New York: Marcel Dekker, 1979:124

8 Suratt PM, Hooe DM, Owens DA, Anne A. Effect of maximal versus submaximal effort on spirometric values. Respiration 1981; 42:233-36 9 Morris JF, Koski A, Johnson LC. Spirometric standards tor healthy nonsmoking adults. Am Rev Respir Dis 1971; 103:57-67 10 Kory RC, Callahan R, Boren HG, Syner JC. The Veterans Administration-Army cooperative study of pulmonary function: I. Clinical spirometry in normal men. Am J Med 1961; 30:243-58 11 Crapo RP, Morris AH, Gardner RM. Reference spirometric values using techniques and equipment that met ATS recommendations. Am Rev Respir Dis 1981; 123:659-64 12 Knudson RJ, Slatin RC, Lebowitz MD, Burrows B. The maximal expiratory flow-volume curve. Am Rev Respir Dis 1976;

113:587-600 13 Schoenberg JB, Beck GJ, Bouhuys A. Growth and decay of pulmonary function in healthy blacks and whites. Respir Physiol 1978; 33:367-93 14 Pennock BE, Rogers RM, McCaffree. Changes in measured spirometric indices-what is significant? Chest 1981; 80:97-99 15 Olsen CR, Hale FC. A method tor interpreting acute response to bronchodilators from the spirogram. Am Rev Respir Dis 1968; 98:301-2 16 Cockcroft DW, Bersheid BA. Volume adjustment of maximal midexpiratory flow-importance of change in total lung capacity. Chest 1980; 78:595-600

Statement on Spkomatry (Section d Reaplndoty P9thoplryllolog ACCP)