MICROVASCULAR RESPONSE IN THE RABBIT EAR TO TOTAL-BODY COOLING - A MODEL FOR STUDY OF HUMAN DIGITS

Conditions such as Raynaud's disease, cold intolerance following digit replantation, and reflex sympathetic dystrophy are all exacerbated by diminished blood flow in the digits. The rabbit ear, being similar to the human digit, is an excellent model for studying microvascular res ponses during thermoregulation and was used in this study of microcirc ulatory changes during total-body cold stress. In eight rabbits a win dow was placed in one ear each, and the underlying vascular beds were photographed with the unanesthetized animal at room temperature (23-de grees-C) and in a cold room (6-degrees-C). Luminal arterial diameters constricted more than venular diameters during cold stress (39.6% vs. 16.5%, respectively, of the control diameters; P = 0.014). All respons es were linear; the slopes of the regression lines were significantly different between arterioles and venules (P < 0.0001). This study sugg ests that decreased circulation in response to cold is due to decrease s in the diameter and number of vessels available for perfusion, as pr edicted by the Poiseuille equation.