Breathing at Extremes: The Restrictive Consequences of Super- and Super-Super Obesity in Men and Women

Background: Massively obese subjects frequently undergo pulmonary function tests nowadays. Obesity-associated decreases in key operating lung volumes (reduced inspiratory capacity and reduced vital capacity) are particularly concerning because they may shorten the "room" for tidal volume expansion with negative physiologic and sensory consequences.

Research question: Is massive obesity associated with reduced operating lung volumes? If so, is this effect more pronounced in men than women?

Study design and methods: We performed an observational, retrospective study in a tertiary, hospital-based laboratory. Pulmonary function test results from 248 super-obese (SO; BMI, 50 to 59.9 kg/m²) and 83 super-super obese (SSO; BMI, ≥60 kg/m²) men and women were analyzed. Electronic medical records were screened to ensure that subjects were free of any disease that potentially could interfere with lung volumes.

Results: The prevalence of a low total lung capacity (restriction) was 26.9%, which increased to 38.6% in SSO. Despite the absence of between-sex differences in BMI and spirometric variables derived from the forced maneuver in both SO and SSO, men presented with higher prevalence of restriction (46.7%) than women (19.4%) (P < .05). Between-sex differences in residual volume differed according to the BMI group; SO men presented with higher values than SO women; the opposite was found in the SSO group. The prevalence of restriction with low operating lung volumes was approximately twice (SSO) and approximately thrice (SSO) as high in men compared with women (P < .01). Linear prediction equations as a function of sex, demographic, and anthropometric attributes markedly reduced the prevalence of these abnormalities across the population.

Interpretation: Obesity-related restriction leading to low operating lung volumes is highly prevalent in the massively obese subject, particularly in men. These alterations that are associated with massive obesity should be taken into consideration for an accurate interpretation of pulmonary function tests in this growing population.