Beyond the Threshold: Nonlinear Impact of Body Mass Index on Pulmonary Function in Severe Obesity

The conflicting impact of obesity on pulmonary function has been observed. Our study aimed at exploring the relationship between body mass index (BMI) and pulmonary function parameters in individuals with obesity.

This cross-sectional study included a consecutive cohort of bariatric surgery candidates with pulmonary function tests. BMI, analyzed as both quartile-stratified groups and a continuous variable, was evaluated for associations with pulmonary function parameters and the risk of pulmonary impairment.

A total of 1,834 patients with obesity (BMI range: 27.5-76.4 kg/m2) were included in our study. BMI exhibited a significantly positive correlation with forced vital capacity (FVC), forced expiratory volume in 1 s (FEV₁), total lung capacity, and functional residual capacity (p < 0.001), and a negative correlation with FVC percent predicted (FVC % pred), FEV₁ percent predicted (FEV₁ % pred), FEV₁/FVC%, and residual volume/TLC (p < 0.05). Nonlinear relationships were found between BMI and both FVC % pred and FEV₁ % pred (P for nonlinearity <0.01) after adjusting for covariables. Beyond the threshold BMI of 38.2 kg/m2, FVC % pred and FEV₁ % pred declined significantly (FVC % pred: β = -0.522, 95% CI: -0.756 to -0.289; FEV₁ % pred: β = -0.435, 95% CI: -0.869 to -0.199), and the risk of pulmonary function impairment increased (OR = 1.008, 95% CI: 1.002-1.014).

BMI exhibited a nonlinear relationship with pulmonary function parameters. Beyond the critical threshold of 38.2 kg/m2, increasing BMI led to a significant decline in ventilatory capacity, concomitant with an amplified risk of pulmonary function impairment.