Energy expenditure of autoperfusing heart-lung preparation

The autoperfused heart-lung preparation was developed as a method for extending the acceptable donor-to-recipient interval in clinical heart-lung transplantation. Metabolic substrate enhancement has been shown to be necessary for the survival and homeostasis of the functioning preparation. To define basic metabolic requirements and to determine the resting energy expenditure of the working canine heart-lung preparation, two groups were studied. Ten canine heart-lung blocks were placed in a normothermic autoperfusion circuit. In Group 1 (n = 5), a hyperalimentation solution of balanced substrate was infused (15% dextrose, 4.25% amino acids, 8 meq magnesium sulfate, 30 IU/dl insulin, and 10% lipids). In Group 2 (n = 5), no substrate was given. The preparations were ventilated with a mixture of room air and 5% CO2 at a rate of 4 breaths/min to maintain physiological pH. Myocardial function was assessed by cardiac output determinations and mixed venous gases. Pulmonary function was assessed with arterial blood gases. The oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured with a Metabolic Cart, and the resting energy expenditure was calculated. The mean survival time for Group 1 was 360 minutes, and all preparations were terminated electively. The mean survival time for Group 2 was 219 +/- 43 minutes (p less than 0.01) with congestive heart failure as the common terminal event. All parameters of cardiac function and blood gases remained within physiological limits without significant differences between groups. The resting energy expenditure, a measure of metabolic rate, was 2.5 +/- 0.3 kcal/hr in Group 1 and 1.0 +/- 0.2 in Group 2 at termination (mean +/- SD) (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)