THE INFLUENCE OF RESPIRATORY AND RENAL FACTORS ON CARDIAC ACTIVITY DURING DEEP HYPOTHERMIA

Abstract

In this study evidence is presented which supports the thesis that the maintenance of blood pressure, and a physiological heart capable of maintaining this blood pressure, is dependent upon the maintenance of a renal cortical circulation. In this context a physiological heart is capable of a forceful contraction, and the S.A. node is the dominant pacemaker. By inference it is concluded that the kidneys are the source of some substance which on release into the systemic circulation is responsible for cardiac activity. This evidence is as follows: The fall in blood pressure associated with a fall in body temperature can be altered and maintained by selectively warming the kidneys during general hypothermia. The final drop in blood pressure during deep hypothermia can be associated with complete renal shut-down. The gradual fall in blood pressure preceding the final debility of the heart is associated with partial renal circulatory shut-down which culminates in complete cessation of renal cortical blood flow. In these experiments the renal circulatory impairment precedes any serious fall in blood pressure. Deep hypothermia is ultimately equivalent to the isolation of the kidneys by tying off the renal vessels. This latter procedure has been carried out and it duplicates the results obtained by hypothermia. Any possible adrenal contribution to the results obtained is dismissed on the evidence that the results obtained with a warmed kidney preparation, adrenalectomized before the hypothermic procedure, are equivalent to the results obtained during similar treatment with adrenals intact. The infusion of renin or angiotensin II is effective in maintaining the blood pressure of animals in which the kidneys were isolated from the circulation at 33 °C by tying off the renal vessels. The results obtained with both renin and angiotensin II approach those obtained with the artificially warmed kidneys – ventilated preparation, and both these agents appear to substitute for the deficiency which is associated with renal circulatory impairment during deep hypothermia. Epinephrine and norepinephrine infused under the same conditions were much less effective than renin or angiotensin in maintaining the systemic circulation.