Effect of Carbon Dioxide Excess on Contractile Force of Heart, In Situ

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Abstract
The contractile force of a segment of the right ventricle of the dog''s heart was measured in 36 acute expts. by a modified Cushny myocardiograph recording through strain gauge electronic instruments. CO2 : O2 mixtures varying from 5:95 to 50:50 were administered by positive pressure artificial respiration. Contractile force and amplitude of systolic excursion decreased and cardiac dilation increased with increasing concns. of CO2. Depression of contractile force ranged from 13% with 5% CO2 to 50% with 50% CO2. Occasionally with concns. of CO2 25% or less there was recovery of contractile force during administration. In some cases sudden withdrawal of CO2 resulted in a brief period of myocardial stimulation. 50% CO2 produced rapid depression and, if prolonged, permanent injury. Ecg. changes were limited to slurring of the ST segment and increase in the amplitude of T waves.