Fall in cardiac output after a scald burn to the anaesthetised rat

Speakman, Elisabeth Anne (1989) Fall in cardiac output after a scald burn to the anaesthetised rat. University of Southampton, Doctoral Thesis.

Abstract

Cardiovascular function was studied in deeply anaesthetised rats subjected to a scald burn injury. All animals were sacrificed without recovery from anaesthesia. Measurements obtained from such animals were compared with those from appropriate, anaesthetised control animals. The scald burn injury led to significant fatalities after four to six hours. It was also observed that the cardiac output, i.e. the volume pumped by the heart, was approximately halved after the burn injury, although the arterial and venous pressures and the heart rate remained almost unchanged. It was therefore inferred that muscular properties of the heart, i.e. the cardiac contractility, were reduced after the burn injury. Direct measurement of the cardiac contractility in vivo by the construction of ventricular function curves, and in vitro by the construction of length-tension diagrams for papillary muscle strips removed from the heart of burn injured rats, indicated that the cardiac contractility is indeed reduced within minutes after a burn injury. It is known that the blood volume falls after burn injury, but there is some confusion in the literature concerning the timing and the significance of this fall. Methods were developed for the continuous monitoring of the blood volume of the rats using a radioactive label dilution technique. These direct measurements showed that the blood volume does fall very soon after a burn injury (within minutes), but that the fall in blood volume is too small to account for the fall in cardiac output. The maintenance of the arterial blood pressure appeared to be due to the measured increase in peripheral vascular resistance to blood flow. The constancy of the venous pressure was shown to result from a combination of: unaltered venous smooth muscle tone; a reduction in the blood volume; and a reduction in the activity of the heart. In addition, studies were performed to validate the methods used for measuring the cardiac output in these animals. Further studies did not provide evidence to support the concept that oxygen free radicals, or indeed any other chemical, travels from the site of the burn to cause the fall in cardiac function.(DX88334)

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