DEPENDENCE OF MAXIMAL FLOW-VOLUME CURVES ON TIME-COURSE OF PRECEDING INSPIRATION IN PATIENTS WITH CHRONIC OBSTRUCTION PULMONARY-DISEASE

Thirteen patients with chronic obstructive pulmonary disease (COPD) pe rformed forced vital capacity (FVC) maneuvers either immediately after a rapid inspiration (maneuver 1) or after a slow inspiration with a 4 - to 6-s end-inspiratory pause (maneuver 2). Seated in a body plethysm ograph, they breathed through a pneumotachograph. Inspirations were in itiated from resting end-expiratory lung volume. Abdominal muscle acti vity was recorded by means of surface electrodes. With maneuver 1: (1) expiratory flows were 20 to 40% larger in the volume range 10 to 95% FVC; (2) peak expiratory flow was on average 30% higher; and (3) FEV(1 ), expressed as percent of FVC, increased by about 8%. No substantial differences in the pattern of abdominal muscle activity occurred betwe en maneuvers. The dependence of maximal flow-volume curves on the time course of the preceding inspiration is probably related in part to th e viscoelastic elements present within the respiratory system, which, stretched during rapid inspirations, increase the effective elastic re coil during the FVC maneuver 1. This cannot occur with maneuver 2, bec ause of stress relaxation of the viscoelastic elements during the 4- t o 6-s breathhold preceding the FVC maneuver. Other factors (e.g., time constant inequality) might also be involved. In any case, the results imply that the inspiratory maneuver prior to FVC must be standardized .