No abstract

To obtain a physiological response by a total artificial heart (TAH), while eliminating the hemodynamic abnormalities commonly observed with its use, we proposed the use of a conductance- and arterial pressure-based method (1/R control) to determine TAH cardiac output. In this study, we endeavored to make use of a variable more closely tied to central nervous system (CNS) efferents, systemic conductance, to provide the CNS with more direct control over the output of the TAH. The control equation that calculates the target cardiac output of the TAH was constructed on the basis of measurement of blood pressures and TAH flow. The 1/R control method was tested in TAH-recipient goats with an automatic method by using a microcomputer. In 1/R control animals, the typical TAH pathologies, such as mild arterial hypertension and substantial systemic venous hypertension, did not occur. Cardiac output varied according to daily activity level and exercise in a manner similar to that observed in natural heart goats. These results indicate that we have determined a control method for the TAH that avoids hemodynamic abnormalities exhibited by other TAH control systems and that exhibits physiological responses to exercise and daily activities under the conditions tested. The stability of the control and the complete lack of inappropriate excursions in cardiac output is suggestive of CNS involvement in stabilizing the system.

No abstract

This study has three purposes, as follows. The first is to develop a microscopic system to observe the microcirculation of animals implanted with an artificial heart. The second is to investigate the influence of flow pattern change from pulsatile to nonpulsatile on the microcirculation. The third is to study the effects of pulsatility in blood flow on endothelium-derived nitric oxide release in the microvasculature. When the flow pattern was changed from pulsatile to nonpulsatile, the velocity of erythrocytes in many capillaries dropped and remained at a low level, and the number of perfused capillaries decreased. After the flow pattern was returned to pulsatile, the velocity of erythrocytes recovered to the initial level. In many cases, the flow of nonperfused capillaries recovered to the initial level as well. Also, the pulsatile flow enhances the basal and flow-stimulated endothelium-derived nitric oxide release in microvessels.

A new system toI observe the microcirculation on the bulbar conjunctiva was developed using a digital high definition microscope to investigate the influence of the flow patterns on the microcirculation in a goat with a total artificial heart (TAH). The undulation pump TAH was implanted into the goat. When the whole body condition became stable, the flow pattern was modulated between the pulsatile and the nonpulsatile mode, and the changes in the microcirculation were observed. When the flow pattern was changed from pulsatile to nonpulsatile mode, the erythrocyte velocity in capillaries dropped from 526 Ϯ 83 to 132 Ϯ 41 m/s and remained at a low level. The number of perfused capillaries decreased as well. Then the nonpulsatile flow mode was maintained for 20 minutes. After the flow pattern was returned to the pulsatile mode again, the erythrocyte velocity recovered to the initial level (433 Ϯ 71 m/s). In many cases, the flow of the nonperfused capillaries in the nonpulsatile mode recovered to the initial level after the flow pattern was changed to the pulsatile mode again. The perfused capillary density in the nonpulsatile mode (19.7 Ϯ 4.1 number of capillaries/mm) was significantly lower than that in the pulsatile mode (34.7 Ϯ 6.3 number of capillaries/mm).It is thought that the basal and flow stimulated endothelium derived nitric oxide release in the microvessels decreased because of the disappearance of pulsatility and that the nitric oxide induced the constriction of arterioles after the flow pattern was changed to the nonpulsatile mode. At the same time, the baroceptors might sense the decrease in the arterial peak pressure or dp/dt, and the sympathetic nerve increases activities and induce the constriction of arterioles. Then, the erythrocyte velocity in capillaries would decrease. Because of the flow pattern further in the chronic phase, it is important to follow the change in the microcirculation. ASAIO Journal 2004; 50:321-327. mplantation of the total artificial heart (TAH) triggers complex responses in the recipient's organism. Therefore, an important question is whether the microcirculation (MC) of the animal with a TAH is kept normal . The physiologic relations of the cardiovascular system can be changed and can lead to significant alterations because of a TAH. 1-2 Artificial perfusion is a complex process, and, at this point, the interactions taking place on the level of central and peripheral regulations are not fully understood. There is also another long standing question of whether arterial pulsation is essential to maintain adequate blood flow and aerobic metabolism in key organs. Nonpulsatile circulation has been widely used in the clinical setting of cardiopulmonary bypass or circulation support. 3-5 Many studies have been performed in cardiopulmonary bypass or in left ventricular support. 6 -13 In some studies, the organ to which attention was directed was the brain. 14 -20 The undulation pump total artificial heart (UPTAH) is an implantable TAH that has been in development at the Univers...