The impact of obesity on lung volumes and diffusion capacity among breathless individuals without evidence of cardiopulmonary disease: a single-center retrospective study

Breathlessness has long been associated with respiratory and cardiovascular diseases. Obesity has also been reported to be independently associated with breathlessness. However, the impact of obesity on lung volumes and diffusion capacity parameters among those with breathlessness who showed no evidence of respiratory or cardiac disease has not been well explored, particularly in Saudi Arabia. Thus, the aims of this study were (1) to assess whether body mass index (BMI) is associated with lung volumes and diffusion capacity parameters, and (2) to explore the impact of overweight and obesity on lung volumes and diffusion capacity parameters among Saudi participants who visited a pulmonary clinic for a follow-up concerning unexplained breathlessness. The medical records of individuals who visited our local respiratory clinic complaining of breathlessness and underwent a full pulmonary function test were reviewed. Participants with known respiratory or cardiovascular diseases and missing lung volumes and diffusion capacity data were excluded. Group comparisons across BMI categories (normal weight, overweight, and obesity) were performed using one-way ANOVA followed by Tukey’s multiple comparisons test. Associations between BMI and lung function parameters were further evaluated using multivariable linear regression analyses adjusted for age, sex, and smoking status. A total of 79 patients met the inclusion criteria and were included in the final analyses, of whom 62% were male. The means ± SD age and BMI were 47 ± 15.5 years and 29.7 ± 7.2 kg/m 2 , respectively. Expiratory reserve volume (ERV), functional residual capacity (FRC), and DLCO (% predicted) were lower in obese participants compared with normal weight and/or overweight groups. In multivariable analysis, BMI remained independently associated with reduced ERV (β = −1.83, 95% CI − 2.74 to − 0.91, p < 0.0001) and DLCO (β = −0.69, 95% CI − 1.15 to − 0.23, p < 0.001), and a modest increase in inspiratory capacity (IC) (β = 0.62, 95% CI 0.05 to 1.20, p < 0.05), with no significant associations observed for other lung volumes. Obesity was associated with lower ERV and DLCO in individuals with unexplained breathlessness. These findings support pulmonary function assessment and weight management in clinical practice. Further studies are needed to explore the underlying mechanisms of obesity and its associations with breathlessness and impairment in lung function.