Maximal expiratory flow at FRC, adjusted for absolute lung volume: specific Vmax FRC

Maximal expiratory flow-volume curves were recorded in 85 healthy subjects, aged from 18 to 78 years. The maximal expiratory flow was measured at 75, 50 and 25% of the vital capacity (VmaxVC), at 60 and 40% of the total lung capacity (VmaxTLC), and at the functional residual capacity level (VmaxFRC). The latter was adjusted for the lung volume at which it was measured. The new parameter was named specific VmaxFRC (SVmaxFRC) and expressed in s-1. Normal values and prediction formulas based on height, weight, age and sex were established. It was found that: (1) adjustment for lung volume narrowed the interindividual variability of SVmaxFRC from 47 to 37%; (2) did not diminish the influence of age (p less than 0.001); (3) erased the influence of height and VC; (4) reduced the correlation with FEV1 (p less than 0.05), and (5) unveiled a borderline correlation with specific conductance (p less than 0.05).