Relationship between peak cardiac pumping capability and indices of cardio-respiratory fitness in healthy individuals.

Cardiac power output (CPO) is a unique and direct measure of overall cardiac function (i.e. cardiac pumping capability) that integrates both flow- and pressure-generating capacities of the heart. The present study assessed the relationship between peak exercise CPO and selected indices of cardio-respiratory fitness. Thirty-seven healthy adults (23 men and 14 women) performed an incremental exercise test to volitional fatigue using the Bruce protocol with gas exchange and ventilatory measurements. Following a 40-min recovery, the subjects performed a constant maximum workload exercise test at or above 95% of maximal oxygen consumption. Cardiac output was measured using the exponential CO(2) rebreathing method. The CPO, expressed in W, was calculated as the product of the mean arterial blood pressure and cardiac output. At peak exercise, CPO was well correlated with cardiac output (r = 0·92, P<0·01), stroke volume (r = 0·90, P<0·01) and peak oxygen consumption (r = 0·77, P<0·01). The coefficient of correlation was moderate between CPO and anaerobic threshold (r = 0·47, P<0·01), oxygen pulse (r = 0·57, P<0·01), minute ventilation (r = 0·53, P<0·01) and carbon dioxide production (r = 0·56, P<0·01). Small but significant relationship was found between peak CPO and peak heart rate (r = 0·23, P<0·05). These findings suggest that only peak cardiac output and stroke volume truly reflect CPO. Other indices of cardio-respiratory fitness such as oxygen consumption, anaerobic threshold, oxygen pulse, minute ventilation, carbon dioxide production and heart rate should not be used as surrogates for overall cardiac function and pumping capability of the heart.