Experiments on Nervous Factors Controlling Respiration and Circulation During Exercise Employing Blocking of the Blood Flow

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Abstract
During uninterrupted work on the bicycle ergometer the blood flow to the legs was suddenly interrupted by means of blood pressure cuffs. In the period with blocked circulation CO2 was added to the inspired air in such amounts that the alveolar PCO2 was maintained constant. The excess work O2‐uptake decreased up to 50%. The pulmonary ventilation, the pulse rate and the systolic blood pressure showed a steady and considerable increase. The cardiac output remained nearly constant with a tendency to decrease during the blocking period. The (a—v̄)O2‐difference and the mixed venous PCO2 consequently decreased considerably. These changes in respiratory and circulatory functions were well reproducible and the scattering of the values only small. It was concluded that the observed changes are neurogenic and caused by the increasing anaerobiosis in the blocked muscles. The nervous impulses involved may be elicited from muscle chemoreceptors, or they may stem from mechanoreceptors being activated through an observed recruitment of new motor units necessitated by the anaerobiosis.