Sekere aspekte van veranderinge in die intraventrikulêre druk en afgeleides daarvan by skape tydens hipo- en hiperdinamiese toestande

Abstract

Very little is known regarding the haemodynamics of the sheep heart. In order to obtain more information, a left ventricular pressure curve was registered for the intact heart. As this still yields only limited information regarding heart function, the first time derivative of the pressure {dP/dt) was also registered, so that information regarding constractility and isovolumetric relaxation could be obtained during systolic and diastolic phases. Left ventricular pressure was registered by means of a pressure transducer inplanted directly at the apical dimple of the left ventricle of the sheep heart. The first derivative of the pressure {dP/dt) was obtained with the help of an electronic differentiator, and the parameters of peak positive dP/dt, t-dP/dt (positi ve), dP/dt/IP, peak negative dP/dt and t-dP/dt (negative) were ·determined through it. By means of the left ventricular pressure curve left ventricular systolic pressure and left ventricular end diastolic pressure were determined. Together with the left ventricular pressure curve and the first time derivative of it, the EKG was also registered. The heart frequency and the PQ interval were calculated from the EKG. In order to discern changes in the function of the sheep heart as observed from left ventricular pressure and its derivative, it was necessary to induce hypodynamic and hyperdynamic conditions. Hyperdynamic conditions were induced through the application of adrenaline, noradrenaline, digoxin as well as adrenaline in the course of a-receptor blockage. Hypodynamic conditions were induced by means of the application of acetylcholine,propranolol and the induction of gousiekte. From results it has emerged that hyperdynamic conditions caused an increase in peak positive dP/dt and other parameters which point to increased contractility. Peak negative dP/dt also increased, and this points to the fact that increased strength of contraction is associated with a more rapid isovolumetric relaxation. The LVSP and the LVEDP also increased as a result of these conditions. Hypodynamic conditions caused a decrease in contractility and in the tempo of isovolumetric relaxation. In the course of gousiekte this decrease in isovolumetric relaxation was very noticeable. Heart frequency did not change very significantly during the application of pharmaceutical' preparations, except in the course of gousiekte where it showed an increase a few days before death. During hypodynamic conditions the LVEDP and the LVSP decreased, except in the case of gousiekte where the LVEDP showed an increase shortly before the day on which death occurred. From the results it has become clear that the sheep heart undergoes significant change during hyperdynamic and hypodynamic changes, as emerges from the left ventricular pressure curve and its time derivative. These parameters are useful in the study of the higher dynamic functions of the sheep heart, such as contractility.