Pneumatically Powered Blood Pumps Used as a Bridge to Cardiac Transplantation: Characteristics and Development

Measurement of Oxygen Consumption and Arterial-Venous Oxygen Saturation following Total Artificial Heart Implantation

Current algorithms for control of the total artificial heart are directed at maintaining hemodynamic homeostasis. Future control systems will also need to modify cardiac output in response to metabolic needs. This study was undertaken to evaluate oxygen metabolism monitoring as an indicator of the adequacy of organ and tissue perfusion. Following recovery from implantation of the Utah-100 pneumatic total artificial hearts, five calves (85 to 95 kg) underwent placement of fiberoptic oxymetry catheters to determine mixed venous and arterial oxygen saturations. By continuously measuring oxygen consumption with a gas analyzer, oxygen utilization and delivery were determined. In the awake calves, at-rest cardiac output was varied to produce hyperperfused and hypoperfused conditions while the adequacy of tissue perfusion was assessed with continuous mixed venous oxymetry and confirmed with serum lactate (Lact) levels. Inadequate tissue perfusion (Lact > 1.0 mmol/L) was evidenced by a mixed venous oxygen saturation <40%, oxygen delivery of < 200.0 milliliters/minute/m2), and oxygen delivery to utilization ratio of < 1.8 during the hypoperfusion conditions of the experiment. By accounting for oxygen consumption, the ratio of oxygen delivery to oxygen utilization was predictive of the adequacy of tissue perfusion. These results suggest that continuous oxygen metabolism monitoring may be useful as a physiologic control modifier to maintain total artificial heart output sufficient to meet physiologic needs, while avoiding hyperperfusion, unnecessary wear and deterioration of the implanted device due to excessive heart rates.

Calves Chronically Implanted with a Total Artificial Heart as a Pharmacological Model

Pharmacological therapy for congestive heart failure includes drugs that have both inotropic and vasoactive effects, although it is sometimes difficult to differentiate between the two effects. An animal with an implanted total artificial heart (TAH) allows the investigation of the vascular effect of these drugs in the absence of the effect on the myocardium. An advantage of the TAH model is its sensitivity to changes in right and left ventricular preload and afterload. Four instrumented TAH calves were given vasoactive drugs and the response was compared to control. Epinephrine, dopamine, isoproterenol, and nitroprusside were selected because of the predictability of their responses. Epinephrine caused a significant increase in systemic vascular resistance (SVR), and dopamine caused a significant increase in Pulmonary vascular resistance (PVR) and Isoproterenol caused a significant decrease in PVR. TAH implanted calves can thus serve as a pharmacological model to study the vascular response, which may be useful in investigation of new agents with inotropic and vascular effects.