Determination of aerobic capacity and the severity of chronic cardiac and circulatory failure

The noninvasive determination of maximal oxygen uptake or V̇O₂max, defined as a plateau in V̇O₂ during incremental treadmill exercise, is an objective, reproducible, and negotiable measure of the severity of chronic cardiac or circulatory failure. Moreover, this noninvasive variable predicts the exercise cardiac output response and thereby the cardiac reserve. The lactate or anaerobic threshold has been validated in these patients from the response of mixed venous lactate to incremental exercise and has been shown to be another objective measure of the severity of chronic cardiac or circulatory failure. The anaerobic threshold can be reliably assessed from the response in breath-by-breath respiratory gas exchange by the use of multiple criteria, several of which can be monitored during the exercise test itself and the remainder of which can be measured during the recovery period. We find the breath-by-breath monitoring of respiratory gas exchange and air flow to provide the best means of assessing the anaerobic threshold and for identifying the plateau in V̇O₂, or V̇O₂max, in response to incremental treadmill exercise.