Absolute lung size explains the sex difference in breathlessness in the general population

Abstract

Rationale: Breathlessness is twice as common in women as men in the general population for unknown reasons. We tested the hypothesis that the higher prevalence of breathlessness in women is due to their lower absolute lung volumes. Methods: Cross-sectional analysis of the population-based Swedish CardioPulmonarybioImage Study (SCAPIS) Pilot, with data from questionnaire and on dynamic and static spirometry and diffusing capacity (n=1,013). Sex difference in breathlessness, measured using the modified Medical Research Council (mMRC) scale, was analyzed using ordinal logistic regression adjusting for age, pack-years of smoking, body mass index, chronic airway limitation, asthma, chronic bronchitis, depression and anxiety in all models. Results: Breathlessness (mMRC ≥ 1) was twice as common in women (12.0%) as in men (6.4%); adjusted odds ratio (OR) 2.20 (95% confidence interval 1.32 to 3.66). Lower absolute lung function was associated with higher rates of breathlessness overall and in men and women separately. The sex difference was unchanged when adjusting for lung function in %predicted in multivariable analysis, but became non-significant when controlling for absolute values of total lung capacity (OR 1.12; 0.59 to 2.15), inspiratory capacity (OR 1.26; 0.68 to 2.35), forced vital capacity (OR 0.84; 0.42 to 1.66), forced expiratory volume in one second (OR 0.70; 0.36 to 1.35) or lung diffusing capacity (OR 1.07; 0.58 to 1.97). Conclusions: In the general population, the markedly higher prevalence of breathlessness in women is explained by their smaller absolute lung volumes. People with smaller lungs may be at increased risk of developing more severe breathlessness.