Measurement and interpretation of maximal oxygen uptake in patients with chronic cardiac or circulatory failure

Rapidly responding gas.analyzers have simplified the monitoring of oxygen uptake\(\left( {\dot V_{O_2 } } \right)\) in the clinical exercise laboratory. An incremental, exhaustive, upright exercise test can be safely used to determine the, plateau in oxygen uptake during exercise, ormaximal \(\dot V_{O_2 } \left( {\dot V_{O_2 } \max } \right)\), in patients with chronic cardiac or circulatory failure. We define\(\dot V_{O_2 } \max \) in these patients as an increase in\(\dot V_{O_2 } \) of less than 1 ml/min/kg despite an increment in work load. The value for\(\dot V_{O_2 } \max \) indicates the patient's aerobic capacity; it also predicts the maximal cardiac output during exercise and therefore serves as an estimate of cardiac reserve and of the severity of cardiac or circulatory failure. Symptom-limited\(\dot V_{O_2 } \) during exercise, termedmaximum oxygen uptake but more appropriatelypeak \(\dot V_{O_2 } \), bears no relationship to\(\dot V_{O_2 } \max \). The two terms should not be used interchangeably.