Abstract
Ventilatory efficiency can be evaluated using the relationship between minute ventilation (V'(E)) and the rate of CO(2) production (V'(CO(2)) ). In accordance with the modified alveolar ventilation equation, this relationship is determined by changes in dead space volume (V (D)) and/or the arterial CO(2) tension (P (aCO(2)) ) 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(2)) during exercise. Evidence suggests that age-related increases in V (D) and pregnancy-related decreases in the P (aCO(2)) equilibrium point are mechanistically linked to the increased V'(E)/V'(CO(2)) during exercise. Importantly, the resultant increase in V'(E)/V'(CO(2)) (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 CO(2) and maintaining arterial oxygen saturation during exercise.