Study on the mechanical effects of cardiac assist by implantable sono-micrometer

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1. Ultrasonic displacement meter An eight-channel sono-micrometer with implantable miniature sensors (2 mm in diameter) was designed for the measurements of ventricular diameter and myocardial segment length.2. Acute animal experiments An left ventricular assist device (LVAD) was implanted between the left atria and the descending aortas or between the left ventricles and the descending aortas in dogs, whose left anterior descending coronary arteries were ligated to locally induce ischemic areas. The ultrasonic sensors were used to measure the left ventricular diameter and myocardial segment length during pumping and non-pumping, from which left ventricular work and local work done by the normal and ischemic myocardium were calculated. The results indicated that the LVAD unloads the normal myocardium and exerts no excessive load to the ischemic region, and that the normal myocardial work is reduced to near zero in the case of the implantation of LVAD between the ventricle and aorta.3. Chronic animal experiments Goats with normal hearts were implanted with the LVADs and the ultrasonic sensors by using the same way as used in the acute experiments. It was found that the long term unloading develops the myocardial atrophy. The results obtained from experiments on goats with induced heart failure showed that the recovery of the left ventricular function is brought about by the compensatory function done by the normal myocardium. The hypertorophy of the myocardium was observed in the normal area.