A number of investigators have studied the normal variability of spirometric indices. In general, airway obstruction increases the variability of measurements made on patients within a single day, between days, and from week to week. The greater the interval between tests, the greater the variability.1-3 The authors of the article entitled "Daily Spirometric Variability," published in the Archives (1982;142:1287-1291), have focused on the variability that exists between consecutive days for the forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) in a more controlled environment than previously studied. The authors concluded that if a patient with previously normal spirometric findings shows a decline in FVC or FEV1 of greater than 5%, or if a patient without asthma with a preexisting obstructive pattern on spirometry shows a decline of 15% or 17% in these tests, respectively, then significant deterioration should be suspected. The findings are of practical
McCaffree DR, Beckett RC. What Is Significant Spirometric Variability? Arch Intern Med. 1982;142(8):1443. doi:10.1001/archinte.1982.00340210035007
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