Revisiting dysanapsis: sex-based differences in airways and the mechanics of breathing during exercise

What is the topic of this review? This review focuses on sex-based differences in the anatomy of the respiratory system, which manifest in mechanical ventilatory constraints and potentially alter the integrative response to exercise. What advances does it highlight? Recent evidence indicates that women have smaller conducting airways than men, even when matched for lung size. Consequently, women are more likely to experience mechanical ventilatory constraints to exercise hyperpnoea. Furthermore, at a given ventilation, women have a higher work and oxygen cost of breathing, both of which may lead to differences in the whole-body integrative response to dynamic exercise. Our understanding of the human ventilatory response to exercise is largely based on a historical body of literature focused primarily on male rather than female research subjects. In recent years, important sex-based differences in the anatomy of the human respiratory system have been identified; for a given lung size, women appear to have smaller-diameter conducting airways than men. The presence of such inherent differences in the tracheobronchial tree greatly affects the mechanics of airflow generation, especially during conditions of high ventilation rates, such as exercise. Data from a growing number of studies suggest that women may be more susceptible to respiratory system limitations during exercise than their male counterparts. Specifically, women are more likely to experience expiratory flow limitation and exercise-induced arterial hypoxaemia and have a higher metabolic cost of breathing for a given ventilation. Collectively, the available evidence suggests that sex differences in the ventilatory response to exercise are present and may have important ramifications for the integrated response to exercise; however, several fundamental questions remain unanswered.