EFFECTS OF ACUTE HEMORRHAGE AND OF SUBSEQUENT INFUSION UPON THE BLOOD VESSELS AND BLOOD FLOW AS SEEN IN THE MESENTERIES OF ANESTHETIZED DOGS

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Abstract
The method used in these expts. wag to bleed the dogs acutely at short intervals until the pressure fell to 30 to 35 mm. Hg, and to maintain the animal in that state for 30-45 mins. Direct microscopic observations of the vessels in the mesentery of the dog showed that the arteries (0.39-1.2 mm. control diams.) constricted 20-60% following removal of 2.5-5.5% of the body wt. of blood. The arterioles (24-65u diams.) usually constricted to a like degree, though sometimes slightly more. In many instances the larger veins (1.0-2.1 mm.) also constricted, the degree being from 12 to 43%. The venules (16-120[mu]) did not constrict; in some instances they dilated to 1.1-1.2 of their control diams. The capillaries were not observed either to constrict or dilate. No measurements were made of arterioles having diams. of less than 24[mu]. At hypotensive levels of 30 mm. Hg, produced in these experiments by the removal of 3.5 to 5.5% of the body wt. of blood, the arterial flow was usually slow and pulsatile. Sometimes it was intermittent. Stasis was frequently present in some of the venules. For the most part the capillary bed was ischemic. Some variation occurred, however, and an occasional dog maintained a moderately good flow even at this low level of pressure, whereas in some instances a sluggish flow was present in the mesenteries of some dogs even when the blood pressure was as high as 60 mm. Hg. Following such large hemorrhages, direct observations showed that the corpuscles in the vessels were separated by more than the normal amt. of plasma. At arterial pressures of 30 to 40 mm. Hg, the intestine became bluish red, in contrast to its normal pink color during control periods. Albumen infusions given into an artery after the pressure had been kept at 30-35 mm. Hg for 1/2 hr. restored the blood flow, caused the constricted arteries and arterioles to relax, the blood pressure to rise, and the intestine and tongue to return approx. to their normal colors, This was similar to the changes observed when the blood previously withdrawn was returned.