Impact of ageing and pregnancy on the minute ventilation/carbon dioxide production response to exercise

Ventilatory efficiency can be evaluated using the relationship between minute ventilation (V'_E) and the rate of CO₂ production (V'_CO ). In accordance with the modified alveolar ventilation equation, this relationship is determined by changes in dead space volume (V _D) and/or the arterial CO₂ tension (P _aCO ) equilibrium point. In this review, we summarise the physiological factors that may account for normative ageing and pregnancy induced increases in V'_E/V'_CO during exercise. Evidence suggests that age-related increases in V _D and pregnancy-related decreases in the P _aCO equilibrium point are mechanistically linked to the increased V'_E/V'_CO during exercise. Importantly, the resultant increase in V'_E/V'_CO (ratio or slope), with normal ageing or pregnancy, remains below the critical threshold for prognostic indication in cardiopulmonary disease, is not associated with increased risk of adverse health outcomes, and does not affect the respiratory system's ability to fulfil its primary role of eliminating CO₂ and maintaining arterial oxygen saturation during exercise.