Epidural anaesthesia and cardiovascular responses to static exercise in man

1. In human subjects, sustained static contractions of the knee extensors were performed in one leg with the same absolute (10% of the initial maximal voluntary contraction) and relative (30% of the maximal voluntary contraction immediately prior to the static exercise) intensities before and during epidural anaesthesia. Epidural anaesthesia reduced strength to 62 +/- 8% of the control value and partially blocked sensory input from the working muscles. During contractions performed with the same relative force, the increases in mean arterial pressure and heart rate were greater during control contractions than during epidural anaesthesia. During contractions at the same absolute force, there was no significant difference in magnitude of cardiovascular responses between control contractions and contractions performed during epidural anaesthesia. 2. The metabolic role in the exercise pressor reflex was assessed by applying an arterial leg cuff 10 s before cessation of exercise and through the following 3 min of recovery. Although mean arterial pressure and heart rate decreased immediately after cessation of exercise, application of the arterial occlusion cuff resulted in higher post-exercise mean arterial pressure and heart rate values. Control and epidural mean arterial pressures during arterial occlusion were not significantly different. 3. The results of this study suggest that the reflex neural mechanism rather than the intended effort (central command) is important in determining the blood pressure and heart rate responses to static exercise in man. That is, when epidural anaesthesia diminishes sensory feedback and produces muscular weakness, central command does not determine the cardiovascular response. This conclusion, however, is opposite to that derived from experiments with partial neuromuscular blockade which demonstrated the importance of central command in determining the cardiovascular response to static exercise (Leonard, Mitchell, Mizuno, Rube, Saltin & Secher, 1985). Taken together, these two studies are complementary and support the concept that both central and reflex neural mechanisms play roles in regulating arterial blood pressure and heart rate during static exercise in man.