Ventilatory efficiency in athletes, asthma and obesity

Abstract

During submaximal exercise, minute ventilation (V' _E) increases in proportion to metabolic rate (i.e. carbon dioxide production (V' _CO2 )) to maintain arterial blood gas homeostasis. The ratio V' _E/V' _CO2 , commonly termed ventilatory efficiency, is a useful tool to evaluate exercise responses in healthy individuals and patients with chronic disease. Emerging research has shown abnormal ventilatory responses to exercise (either elevated or blunted V' _E/V' _CO2 ) in some chronic respiratory and cardiovascular conditions. This review will briefly provide an overview of the physiology of ventilatory efficiency, before describing the ventilatory responses to exercise in healthy trained endurance athletes, patients with asthma, and patients with obesity. During submaximal exercise, the V' _E/V' _CO2 response is generally normal in endurance-trained individuals, patients with asthma and patients with obesity. However, in endurance-trained individuals, asthmatics who demonstrate exercise induced-bronchoconstriction, and morbidly obese individuals, the V' _E/V' _CO2 can be blunted at maximal exercise, likely because of mechanical ventilatory constraint.

FIGURE 1

Representative ventilatory and gas exchange responses to incremental exercise in a–c) an endurance trained athlete, d–f) an asthmatic with exercise induced bronchoconstriction and g–i) an individual with morbid obesity, when compared to a healthy individual of average aerobic fitness. EIB: exercise-induced bronchoconstriction; V′_E: minute ventilation; V′_CO2: carbon dioxide production; V′_E/V′_CO2: ventilatory equivalent for carbon dioxide production; P_aCO2: arterial partial pressure of carbon dioxide.