Effect of maximal versus submaximal expiratory effort on spirometric values.

Data from flow volume curves suggest that flow measured at the mouth may be lower with maximal effort than with submaximal effort. We consequently studied the effect of maximal vs. submaximal expiratory effort on spirometric values. Significant increases in FVC, FEV1 or FEF25-75% with submaximal effort occurred in 12 of 38 subjects. All subjects who improved spirometric values had peak flows with submaximal efforts that varied from 91 to 65% of peak flow with maximal efforts. We conclude that spirometric values in some subjects are larger with submaximal rather than maximal effort.