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 (VO2) in the clinical exercise laboratory. An incremental, exhaustive, upright exercise test can be safely used to determine the plateau in oxygen uptake during exercise, or maximal VO2 (VO2max), in patients with chronic cardiac or circulatory failure. We define VO2max in these patients as an increase in VO2 of less than 1 ml/min/kg despite an increment in work load. The value for VO2max 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 VO2 during exercise, termed maximum oxygen uptake but more appropriately peak VO2, bears no relationship to VO2max. The two terms should not be used interchangeably.