Transient Ventilatory Responses to Carbon Dioxide Inhalation and to Exercise in Man

Abstract

The ventilatory response to dynamic exercise is divided into three phases. Initially, there is a fast rise in expiratory ventilation ($\mathop \text{V}\limits^\text{.}$)at the onset of exercise. This phase I occurs within the first breath (Asmussen, 1983) and is mainly due to a rise in frequency (Cunningham et al., 1986). Then follows an exponential increase in ventilation, with a time constant (Tc) of 1 min, to steady state. Cardiac output ($\mathop \text{Q}\limits^\text{.}$) changes similarly, due to a rapid increase in heart rate, followed by an exponential rise. During the latter two phases, metabolic CO₂diffuses from the venous blood into the alveoli at a rate or flux, whicfh is dependent on the venous CO₂concentration (C_v) and the blood flow rate ($\mathop \text{Q}\limits^\text{.}$), but independent$\mathop \text{V}\limits^\text{.}$