'n Eksperimentele ondersoek na die hoërdinamiese funksies van die skaaphart

Abstract

Studying the higher dynami c f unct i ons of the heart is a relative= ly new approach in evaluating the heart as a pump . The higher dynamic functions are re lated to the tempo of mechani cal events t hat t ake pl ace during the cardiac cycle. It incl udes the tempo of pre ssure rise in the ventricl es , the blood flow velocity and the acceler ation of blood in the aorta. There is evidence t hat a st udy of the higher dynamic funct ions of the heart can supply much i nformation about the pump act ion of the heart. By th is method valuable information can al so be obtained at an ear ly stage during a heart disease . In this study the higher dynamic functions of the sheep heart was studied by means of an invasive and two noninvasive methods. The invasive method was the measuring of the blood flow velocity in the aorta and its first time derivative (acceleration). The two noninvasive methods were the ultra low frequency acceleration ball istocardiogram and systolic time intervals. The time intervals measured, were the left ventricular ejection time, the pre-ejection period, the isovolumetric contraction phase and the total electromechanical systole. The ratio between the pre-ejection period and the left ventricular eject ion time and the ratio between the left ventricular ejection time and the isovolumetric contraction time was also determined . As the systolic time intervals are influenced by the heartrate, these were corrected for heartrate. By the administering of certain pharmacological drugs and hypothermia the heart function was changed in a more or less predictable way . In this way hypo- and hyperdynamic conditions

were obtained. It can be said that the hemodynamics of the sheep heart corresponds in general, to that of other mammals and that of man. However, it appears that the heart of sheep functions at a lower level of efficiency under normal conditions. Gousiekte was evoked in the sheep and the course of the disease was studied until the death ensued. From these experiments it appeared that the ejection phase of the sheep heart consists of two phases, i.e. the tension phase and the maintenance phase. During the course of gousiekte it was found that these two phases separated. This statement needs further investigation. By comparing the sensitivity of the different methods used, it appears that the ratio between the left ventricular ejection time and the isovolumetric contraction time is the more sensitive. The acceleration ballistocardiogram is also very sensitive, even more so than the first derivative of blood velocity in the aorta. However, all three the above mentioned methods seems very useful as indicators of left ventricular performance