Peripheral Circulatory Adaptation to Exercise in Restricted Cardiac Output a hemodynamic and metabolic study in patients with complete heart block and artificial pacemaker

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Abstract
At low stimulation rates (mean 47/min.) the highest attainable leg blood flow during bicycle exercise was calculated at 20-25% of the normal maximal level. Muscular pain in the legs, an almost complete desaturation of the femoral venous blood and rapid accumulation of lactate early during graded exercise reflected the functional insufficiency of peripheral arterial circulation. The interruption of exercise was determined by the ultimate failure of the cardiac output to maintain the arterial per-fusion pressure when the metabolic vasodilatation in the active muscles reached a high level. Following an increase of the stimulation rate to a mean of 73/min. there was a significant improvement in the ability to sustain bicycle exercise. The degree of O2 utilization in the exercising legs was significantly lower at this higher heart rate than at the lower one, and the lactate concentration levels in blood decreased. This was ascribed to a 10% mean increase in the leg blood flow evidently brought about by a corresponding increase of arterial perfusion pressure. Arterial lactate concentration levels during standardized exercise, and arterial blood pressure reaction are suggested as simple guides in the functional assessment of the appropriate stimulation rate in patients with artificial pacemakers.