Pulmonary function in obese subjects with a normal FEV1/FVC ratio.

Study Objective: To determine pulmonary function test (PFT) profile and respiratory muscle strength (RMS) of a group of obese individuals who did not have evidence of obstructive airway disease or other underlying diseases affecting their respiratory system.
Design: Prospective, open.
Setting: PFT laboratory, VA Medical Center.
Participants: Sixty-three consecutive obese (body mass index greater than 27.8 kg/m2) male subjects without overt obstructive airway disease (FEV1/FVC ratio greater than 80%).
Measurements and Results: Standard PFTs and maximum static inspiratory (PImax) and expiratory (PEmax) mouth pressures were determined. RMS was calculated from the following formula: (PImax+PEmax):2. Two distinct groups were identified, those with normal maximum voluntary ventilation (MVV) (> 80% predicted) and those with low MVV. Both inspiratory and expiratory flow rates (FVC, FEV1, forced expiratory flow at 50% vital capacity [V50], maximum inspiratory flow rate [MIFR]), lung volumes (vital capacity [VC], inspiratory capacity [IC], expiratory reserve volume), PImax, and RMS were significantly lower, and residual volume/total lung capacity (RV/TLC) ratio was significantly higher in obese subjects with low MVV compared with those in whom MVV was normal. MVV correlated significantly with FVC, FEV1, V50, MIFR, TLC, VC, IC, RV/TLC, and RMS; the strongest correlation was with MIFR (r = 0.76, p < 0.0001).
Conclusions: Standard PFTs allow recognition of a subgroup of obese subjects without overt obstructive airway disease who have more severe lung dysfunction, the marker of which is a low MVV. Peripheral airway abnormalities may be responsible for these observations.