Static Respiratory Mechanics are Unaltered in Mild-to-Moderate Obese Men and Women

Abstract

Morbid obesity can affect spirometric function and lung volume subdivisions. Additionally, compliance of the lung and chest wall are unfavorably altered. However, in mild-to-moderate obesity, rarely are expiratory flows and lung volumes influenced to an extent that they become less than normal. It is unclear if mild-to-moderate obesity alters the flow-pressure-volume relationship of the respiratory system. PURPOSE: To examine whether the interrelationships of maximal flow-pressure-volume are altered due to mild-to-moderate obesity in men and women METHODS: Obese (30 ≤ BMI ≤ 45) and lean (BMI < 25) men (n = 20) and women (n = 17) completed pulmonary function testing. Maximal expiratory flow, static lung elastic recoil pressure (Pst), and the minimal pressure for maximal flow (Pcrit) were determined in a pressure-compensated, volume-displacement body plethysmograph. Parameters were compared at 25, 50, and 75% of forced vital capacity (FVC). Additionally, dysanapsis, the association between airway size and lung size, was estimated using measured values of maximal expiratory flow at 50% FVC, FVC, and Pst at 50% FVC. Dysanapsis also was estimated using a regression equation for the calculation of Pst at 50% FVC. RESULTS: Obese and lean men had similar maximal expiratory flow, Pst and Pcrit at each lung volume examined. Additionally, obese and lean women displayed similar flow-pressure-volume characteristics. However, men had greater maximal expiratory flows, Pst, and Pcrit at all lung volumes, with the exception of Pcrit at 25% FVC, compared with women (p < 0.05). Dysanapsis was unaffected due to mild-to-moderate obesity in men and in women. Dysanapsis estimated using the predicted value for Pst at 50% FVC was significantly different from that obtained using measured parameters. CONCLUSIONS: Unlike in morbid obesity, mild-to-moderate obesity does not affect flow-pressure-volume relationships in men or in women. Furthermore, due to the inability to accurately predict static lung elastic recoil pressure, the use of prediction equations in the estimation of dysanapsis is cautioned.