Cardiovascular Drift

Cardiovascular drift is the gradual change in cardiovascular responses that occurs during prolonged, steady-intensity exercise. It is characterized mainly by a progressive rise in heart rate together with a decline in stroke volume, even though the external exercise workload remains unchanged. The pattern commonly develops after the initial period of exercise, although its timing and magnitude vary with conditions .^1,2

Because heart rate rises as stroke volume falls, the increase in heart rate can partly compensate for the decline in stroke volume, helping maintain cardiac output during moderate exercise. Under greater heat stress or dehydration, however, the decline in stroke volume can become larger and cardiac output may also decrease. Cardiovascular drift is generally more pronounced when body temperature rises substantially or when fluid loss produces hypohydration .^1,2

Several interacting mechanisms can contribute. Prolonged exercise increases heat production and skin blood flow as the body attempts to dissipate heat. Fluid loss through sweating can reduce circulating blood volume, while the accompanying rise in heart rate can reduce ventricular filling time. These changes can reduce ventricular filling and the amount of blood ejected with each heartbeat, contributing to the progressive fall in stroke volume .^1,2

Cardiovascular drift should not be confused with an increase in heart rate caused by increasing the exercise workload. During cardiovascular drift, heart rate rises despite a relatively constant external workload. Heart rate can therefore represent progressively greater cardiovascular strain as prolonged exercise continues, particularly under heat stress .^2,3