The effect of brain death on cardiovascular function in rats. Part I. Is the heart damaged?

Abstract

Brain death induces important haemodynamic changes in rats, with a drop in arterial blood pressure, left ventricular developed pressure and dP/dtmax to less than 50% of its control value. Myocardial damage was reported to contribute to this paradigm. The role of potential underlying pathogenetic mechanisms, such as a circulating cardiodepressant factor, NO, endogenous opioid peptides, vagal or beta-adrenergic activation, or hypophyseal dysfunction, were explored, but none of them could be demonstrated as the culprit. This study investigated whether functionally important intrinsic myocardial damage was induced by brain death in the rat, and whether coronary endothelial cell dysfunction, possibly causing multifocal ischaemia, contributed to this. Brain death was induced in rats by sudden inflation of an intracranial balloon. Extensive haemodynamic measurements, including heart rate, arterial blood pressure central venous pressure, left ventricular pressure, and cardiac output, were performed. Hearts excised 1 and 4 h after brain death were examined histologically. The contractile reserve of these hearts was tested by administration of increasing doses of adrenaline (10(-9) to 10(-6) mol/l) in a Langendorff system. The coronary endothelium was tested with regard to its barrier function for macromolecules by determining the extravasation of injected Evans blue, and with regard to its vasoactive function by testing the effects of serotonin and nitroglycerin in a Langendorff system. The haemodynamic measurements suggested that the cardiovascular collapse consisted mainly in alterations in afterload. Contractile reserve, as tested with increasing adrenaline doses, revealed a normal dose-response curve. No histological myocardial damage was found after brain death in rats. No abnormal extravasation of Evans blue was seen. Coronary vasoreactivity towards nitroglycerin and serotonin was normal. Myocardial damage, if present at all, contributes only minimally to the changes in haemodynamic profile seen after brain death in the rat, and the coronary endothelium appears to preserve its barrier and vasoactive function.