VARIATIONS IN VASCULAR-RESISTANCE OF ISOLATED RAT HEARTS DURING NORMOTHERMIC AND HYPOTHERMIC EXPERIMENTS

The flexibility of an automated, modified Langendorff perfusion column is illustrated by a series of experiments on isolated rat hearts under the following conditions: normothermia, hypothermia, the addition of a cryoprotective agent - ethylene glycol and cooling to minus 13 degree C and minus 22 degree C. Successful normothermic perfusions of up to 14 hr were achieved. Hypothermia prevented a rise in vascular resistance with time and improved the electrocardiograms. Ethylene glycol was administered during the cooling period to minus 22 degree C at temperatures below 23 degree C. It was removed upon warming and before toxic effects were visible, thus leading to good recovery. By controlling the speed of the perfusate's peristaltic pump, the perfusion pressure was not allowed to exceed a pre-set level. A constant and standard vascular resistance at any selected perfusion temperature, normal heart rate and electrocardiograms were the criteria for normality.