Effect of O2 and CO2 Tensions Upon the Resistance of Pulmonary Blood Vessels

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Abstract
Pulmonary arterial and venous pressures were obtained from anesthetized dogs by cardiac catheterization. Blood flow was measured by the Fick method. The calculated resistance to the flow through the pulmonary circuit was detd. while the animals were breathing 8, 15, 21 and 30% O2 in N2, or a mixture containing 5% CO2, 25% O2 and 70% N2. The resistance increased 25 and 48% as the inspired O2 tension decreased from 21 to 15 and 8%, respectively, but did not change when the CO2 tension of the inspired air was raised. An attempt was made to relate these changes to actual alterations in the relative caliber of the pulmonary vessels. It appears that these changes in resistance are produced by actual vasomotion. Three dogs subjected to a 2-stage transthoracic sympathectomy failed to show an increased resistance postoperatively when breathing 8% O2-N2 mixture. The possible significance of these results is discussed.

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