Central venous pressure during exercise: role of muscle pump.

Central venous pressure (CVP) gives the integral result of changes in cardiac and peripheral factors. Thus, the sudden increase in CVP observed at the onset of dynamic exercise has been attributed to the action of the muscle pump but is also affected by reflex changes in cardiac response. To determine which predominates at the onset of exercise, we compared the change in CVP from rest to onset of upright exercise and after 3 min of exercise in four healthy normal subjects (N) and six patients following heart transplantation (HT), who thus had a delayed cardiac response. CVP immediately increased to a similar extent in both groups at exercise onset (by 4.6 +/- 0.6 mmHg (1 mmHg = 133.3 Pa) in HT and 4.0 +/- 0.4 mmHg in N) (mean +/- SE). After 3 min of exercise, CVP remained constant in N (2.0 +/- 1.1 vs. 2.6 +/- 1.8 at onset) but increased further in HT (7.0 +/- 0.8 vs. 3.5 +/- 1.1 at onset, p < 0.05). The immediate increase in CVP with leg movement in both groups supports an initial central shift in blood volume because of muscle contractions. During the first minute of exercise, muscle blood flow most likely continues to increase and CVP increased further in HT but not in N, which had adequate reflex cardiac adjustment. We conclude that the muscle pump increases CVP at exercise onset, but the interaction between cardiac response and circuit function determines CVP as exercise continues.