Assessing cardiac function by gas exchange.

Exercise stresses the primary function of the cardiovascular system, which is the supply of O2 and removal of CO2 from the cells of the body. Even ordinary walking requires an increase in O2 consumption and CO2 production by the exercising muscles of 20 times the resting level. While pulmonary dysfunction may affect arterial blood gas tensions, the dynamics of O2 uptake and CO2 output by the lungs depend on the circulatory responses to exercise. Thus, measurement of the dynamics of O2 uptake in response to exercise has been shown to reflect cardiovascular function. Inability of the circulatory responses to meet an increased O2 requirement may be reflected in abnormalities in O2 uptake dynamics, and an early increase in CO2 output relative to O2 uptake consequent to bicarbonate buffering of lactic acid. Application of currently available technology for the continuous measurement and analysis of pulmonary gas exchange can afford the practicing or investigative cardiologist with a noninvasive and inexpensive means for assessing cardiovascular function.