The Hemodynamic Effects of Drugs on Myocardial Oxygen Use

The circulatory responses to high equinalgesic doses of morphine are compared with those of pethidin. The decrease in mean arterial blood pressure in case of morphine was 28p.c., with a paralleled and identical de­crease in total peripheral resistance and no negative inotropic effects.  Pethidine decreased blood pressure 54p.c., as a result of peripheral vasodilation of 46p.c. and a sharp drop in dp/dt Max of 59p.c., indi­cating myocardial depression (dp/dt max/Ip is 14p.c. and the fall in cardiac output is 33p.c.). This drop in both cases is offset by the increase in heart rate. (morphine 27p.c.; pethidin IOlp.c.). The coronary blood flow sufficiently met the myocardial energy de­mand, which did not change with the altered haernodynamics.  Both morphine and pethidin produce coro­nary vasodilation, indicated by increased coronary blood flow and coronary venous ox­ygen saturation.  The mechanism for the change in vasodilation is still under discussion. It seems that in case of morphine this is due to Histamin release.