NEURAL CONTROL OF CARDIOVASCULAR-RESPONSES AND OF VENTILATION DURING DYNAMIC EXERCISE IN MAN

1. Nine subjects performed dynamic knee extension by voluntary muscle contractions and by evoked contractions with and without epidural anae sthesia. Four exercise bouts of 10 min each were performed: three of o ne-legged knee extension (10, 20 and 30 W) and one of two-legged knee extension at 2x20 W. Epidural anaesthesia was induced with 0.5 % bupiv acaine or 2 % lidocaine. Presence of neural blockade was verified by c utaneous sensory anaesthesia below T8-T10 and complete paralysis of bo th legs. 2. Compared to voluntary exercise, control electrically induc ed exercise resulted in normal or enhanced cardiovascular, metabolic a nd ventilatory responses. However, during epidural anaesthesia the inc rease in blood pressure with exercise was abolished. Furthermore, the increases in heart rate, cardiac output and leg blood flow were reduce d. In contrast, plasma catecholamines, leg glucose uptake and leg lact ate release, arterial carbon dioxide tension and pulmonary ventilation were not affected. Arterial and venous plasma potassium concentration s became elevated but leg potassium release was not increased. 3. The results conform to the idea that a reflex originating in contracting m uscle is essential for the normal blood pressure response to dynamic e xercise, and that other neural, humoral and hemodynamic mechanisms can not govern this response. However, control mechanisms other than centr al command and the exercise pressor reflex can influence heart rate, c ardiac output, muscle blood flow and ventilation during dynamic exerci se in man.