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

Abstract

At low stimulation rates (mean 47/min) the highest attainable leg blood flow during bicycle exercise was calculated to be 20–25 per cent of the normal maximal level. Muscular pain in the legs, an almost complete desaturation of the femoral venous blood, and a rapid accumulation of lactate early during graded exercise were considered to reflect the functional insufficiency of the peripheral arterial circulation. The interruption of exercise seemed to be determined by the ultimate failure of the cardiac output to maintain the arterial perfusion pressure when the metabolic vasodilatation in the active muscles had 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 oxygen 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 were de creased. This could be ascribed to a 10 per cent mean increase in the leg blood flow evidently brought about by a corresponding increase of the arterial perfusion pressure.

The arterial lactate concentration levels during standardized exercise and the arterial blood pressure reaction are suggested as simple guides in the functional assessment of the appropriate stimulation rate in patients with artificial pacemakers.

Key Words:

• Artificial pacemaker
• blood flow
• blood pressure
• cardiac output
• exercise test
• heart block
• ischemia
• lactates
• oxygen consumption