THE REGULATION OF CIRCULATION

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Abstract
Mild anoxemia was produced in trained unnarcotized dogs by 2 methods, by re-breathing in a closed circuit, the CO2 being absorbed, and by breathing a constant mixture low in O from a Douglas bag or a Tissot spirometer. The minute cardiac output was determined according to the Fick principle. In the "rebreathing" experiments the O consumption was measured with the Roth-Benedict spirometer, while in the "constant mixture" experiments it was determined by analyzing the inspired and expired air. Arterial and mixed venous blood was obtained by simultaneous puncture of the left and right sides of the heart. The 2 methods gave similar results. When the arterial blood was less than 70% saturated with O the minute cardiac output was increased. At arterial saturations greater than 80% the minute output was usually not changed. The "anoxemic threshold" seemed to be about 70% O saturation. Anoxemia caused a slight increase in the pulse rate and a great increase in the minute ventilation and respiratory quotient. The O consumption was not changed until the anoxemia became extreme.

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