Pulmonary Function in Obese Subjects With a Normal FEV₁/FVC Ratio

¹ From the Pulmonary Section, Department of Veterans Affairs Medical Center, and University of Cincinnati (Ohio) College of Medicine

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.

Key Words: inspiratory flow rates • maximum voluntary ventilation • pulmonary function tests • respiratory muscles • small airways

Submitted on April 11, 1996
Accepted on June 10, 2007

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