'n Ondersoek van die hoërdinamiese funksies van die konynhart
Green, Susara Cecilia Jacoba Elizabeth
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The higher dynamic _functions of the heart are related to the work power and force of contraction of the myocardium. The rate of volume-, pressure- and flow changes is closely related to the higher dynamic functions. Indirect techniques for early diagnosis of heart disease in man are needed which give information about the higher dynamic functions of the heart. In the recent study various direct and indirect haemodynamic techniques were studied simultaneously in rabbits. Direct techniques included direct arterial blood pressure and its time derivatives as well as aortic blood flow and its time derivatives. Indirect techniques included precordial accelerography (Peg a) and ultra-low frequency acceleration ballistocardiography (ULF Beg a). The electrocardiogram (ECG) and phonocardiogram (Phono) were also registered. The normal values of the heart rate, ECG, bloodpressure and Phono were in the same order as the values obtained by other investigators. The normal values of the amplitudes of the ULF Beg a and Peg a displayed much individual variation. The influence of a few anaesthetics on the results obtained by means of the above techniques was investigated. Sodium pentobarbital seemed to be the best anaesthetic for the recent study. When the more or less predictable changes in the different parameters were studied, after the administration of various drugs, an evaluation could be made of the value as well as the genesis of the ULF Beg a of the rabbit. A systolic and diastolic complex could be distinguished in the rabbit ULF Beg a. The HI-segment of the ULF Beg a is related to .the isovolumetric contraction and the IJ-segment is related to aortic blood flow velocity and acceleration. The influence on the cardiovascular system of a negative inotropic drug as well as a positive inotropic drug was investigated by means of the above mentioned techniques. It is concluded that the ULF Beg a can be used to study the influence of various drugs on the cardiovascular system in vivo. The ULF Beg a may also be of value as an indirect technique to detect certain heart diseases at an early stage. For example, in experimental atherosclerosis the ULF Beg a may be used during an anoxia test to distinguish between the cardiovascular reactions of normal animals and atherosclerotic animals.