| Many end-stage congestive heart failure patients could benefit from a totally implantable pulsatile artificial heart that responds to physiological needs. Such a device, the Electro-Hydraulic Total Artificial Heart (EHTAH) was developed.;The EHTAH's left and right ventricles operate at the same beat rate and have the same gross stroke volume. However, the net stroke volume of the artificial right ventricle, if unchanged, is 5--10% higher than that of the left. If unresolved, the EHTAH's recipient will quickly develop pulmonary edema, a life-threatening condition. As a result, a critical long-term requirement for the EHTAH is to balance blood volumes between the systemic and pulmonary circulations.;Another requirement is to insure that the EHTAH automatically responds to the recipient's physiological needs, i.e., the cardiac output responds to preload changes and is relatively independent of afterload changes.;It was hypothesized that the EHTAH could: (a) Maintain balance without adverse clinical consequences using an Inter-Atrial Shunt (IAS). This solution mimics a common and naturally occurring, yet survivable, abnormality called an atrial septal defect. (b) Provide physiological demand responsiveness by microprocessor-based auto-control of the EHTAH's pump using only hydraulic fluid pressure information.;Based on the results of in vitro, b ex vivo and 13 chronic in vivo calf studies totaling 227 implanted days, including one 159-day chronic animal study, the first hypothesis was confirmed, but the second was not.;The IAS remained patent and thrombus-free. It caused low hemolysis (net gain < 5 mg/dl pfHb). It balanced blood volumes: the mean difference between left and right atrial pressures (RAP) stayed <10 mmHg. The effect of minute mixing of arterial and venous blood as measured by arterio-venous blood gases was shown to be clinically acceptable.;The EHTAH's cardiac output at 0 mmHg (RAP) was 4 L/min, and at 15 mmHg RAP was 9.5 L/min. It was relatively independent of large changes in afterload: varied ex vivo from 40--200 mmHg. The EHTAH responded appropriately to a calf subjected to treadmill exercise by increasing its heart rate and output with increasing exercise. However, recurring hydraulic fluid pressure transducer failures prevented confirmation of the physiological demand responsiveness hypothesis. |
