DEPENDENCE OF MAXIMAL FLOW-VOLUME CURVES ON TIME-COURSE OF PRECEDING INSPIRATION

Thirteen normal subjects, sitting in a body plethysmograph and breathi ng through a pneumotachograph, performed forced vital capacity maneuve rs after a rapid inspiration without or with an end-inspiratory pause (maneuvers 1 and 2) and after a slow inspiration without or with an en d-inspiratory pause (maneuvers 3 and 4), the pause lasting 4-6 s. Insp irations were initiated close to functional residual capacity. At all lung volumes, expiratory flow was larger with maneuver 1 than with any other maneuver and, over the upper volume range, larger with maneuver 3 than with maneuver 4, whereas it was similar for maneuvers 2 and 4. Relative to corresponding values with maneuver 4, peak expiratory flo w was approximately 16 and approximately 4% larger with maneuvers 1 an d 3, respectively, whereas forced expiratory volume in 1 s increased b y approximately 5% only with maneuver 1. The time dependence of maxima l flow-volume curves is consistent with the presence of viscoelastic e lements within the respiratory system (D'Angelo et al. J. Appl. Physio l. 70: 2602-2610, 1991).