Evolution of compensatory cardiovascular control mechanisms in heart transplant subjects

Heart transplantation is a life saving procedure, in which the original heart replaced by a new one. The new heart is fully denervated and is not controlled by the autonomic nervous system. Despite the denervation, heart transplant subjects are not restricted in daily activities, indicating the development of efficient compensatory control mechanisms. The goal of this work is to characterize these compensatory control mechanisms and their evolution following the surgery, using noninvasive tools. The authors recorded ECG, blood pressure and respiration from 13 male heart transplant subjects at various times after transplantation. Subjects lay for 45 min in supine position, changed posture to standing for 5 min, followed by 10 min of sitting. Both time and frequency analyses were performed. The authors' results indicate that a simple control mechanism already developed a few weeks after surgery, and a second, faster and more complicated mechanism, developed about 19 months following heart transplant.