Experimental investigations of the higher dynamic functions of the heart in the albino rat

Abstract

The recent progress made in ballistocardiography emphasized the urgent need for a clinical and experimental method that may furnish information about the higher dynamic functions of the heart. Very little experimental work on small animals has been done to establish the genesis of the UF Beg (a) or to investigate the applicability of the method to experimentation with small animals. In the present study a UF Beg (a) system suitable for experiments with small animals is described. The physical properties of the system compare favourably with the ideal recommended values. A parallel suspended pendulum type of ballistocardiograph with a natural platform frequency of O.J8 Hz was used. The platform with accelerometer attached weighed 4.1 grams and a mean body to platform weight ratio of 65: 1 was obtained. When the body to platform ratio was reduced to J:1, the atrial and isometric wave complexes were seriously attenuated. It is concluded that the system is able to record with high fidelity the UF Beg (a) of rats. To investigate the normaJ UF Beg (a) pattern of rats, the ECG, phonocardiogram, carotid pressure pulse and its first time derivative were simultaneously recorded in most rats. Q time interval and over-all amplitude measurements of the different waves were carried out. Rats were divided into three different age groups -according to weight, viz. a young group . {'me?.n weight l98 :, grams), a young fully outgrown (normal) group (mean weight about 275 grams) and an old group (mean weight about 400 grams). The UF Beg (a) of old rats showed a decrease in HI and IJ wave amplitude and slope. The Q-H"' and Q-J times were increased in the recordings of old rats. The decreased HI and IJ wave amplitudes indicate a reduced force of ejection in old rats. The increased Q-H"' time indicates a longer period of isovolumetric conctraction and an increase in the latent or energizing period. It is concluded that cardiac incoordination also developed with age and that the UF Beg (a) demonstrates these changes in the higher dynamic functioning of the myocardium. When the 'myocardial efficiency index' of rats was calculated by the use of a crude formula based mainly on the IJ segment of the UF Beg (a), the recordings for old rats revealed an efficiency index of about 75%. Young adult rats showed an ' index' of about 99,J%, The administration of arterenol to young rats resulted in a 'cardiac efficiency index' of about 350%. The lowered 'myocardial efficiency' of old rats might be due to the development of myocardial fibrosis and possibly coronary sclerosis. The UF Beg (a ) could therefore be utilized to demonstrate the development of myocardial disease. Various experiments e.g. vena caval occlusion, reduction of blood volume, changes in the course of the aorta, administration of arterenol and levarterenol, to evaluate wave identification and to obtain information about the genesis of the different waves in the UF Beg (a) of rats have been described. From the results of these experiments it is evident that the general UF Beg (a) pattern of rats shows some aspects of similarity to that of man and rabbits. Anatomical and age differences should be considered in the recording and interpretation of animal Begs. The UF Beg (a) of rats showed a clearly defined atrial wave complex in the normal recordings not seen in the recordings obtained from other species. When atrial activity was completely isolated during A-V block or ectopic beats, a systolic and diastolic atrial wave complex could be identified . Only the systolic part of the atrial wave complex was visible in normal recordings. Calculations showed that the atrial wave might contribute about 25% towards the H (isometric) wave complex. The isometric wave complex (H', H" and H"') in the UF Beg (a) of rats is more complex than in other species. The H wave complex persisted in some ectopic beats where no e jection of blood could be measured. A close time relationship between the H wave complex and the first heart sound was demonstrated. This indicated that the H wave complex in the UF Beg (a) of rats is mainly due to myocardial and blood vibrations before aortic and pulmonic valve opening during isovolumetric ventri cular contraction. The H' wave, however, exhibits some contribution of atrial systolic origin. Arterenol administration increased the IJ amplitude to a greater extent than the HI amplitude. The IJ wave amplitude was more markedly decreased during vena caval occlusion and reduction of the blood volume than the HI amplitude. A close time relationship between the HI wave and the initial segment of the pressure pulse and its time derivative was demonstrated. The HI and IJ segments in the UF Beg (a) of rats are therefore caused by different haemodynamic events. It is suggested that the HI wave is mainly caused by event s during initial ventricular ejection but that it might reflect some late isometric components and possibly a component of right ventricular ejection. The J wave in the UF Beg ( a) of rats might be caused by the interaction of :