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In previous studies, we investigated the cavitation phenomenon in a mechanical heart valve using an electro-hydraulic total artificial heart. With this system, a 50% glycerin solution kept at 37°C was used as the working fluid. We reported that most of the cavitation bubbles were observed near the valve stop and were caused by the squeeze flow. However, in these studies, the effect of the partial pressure of CO2on the mechanical heart valve cavitation was neglected. In this study, in order to investigate the effect of the partial pressure of CO2on mechanical heart valve cavitation using an electro-hydraulic total artificial heart, we controlled the partial pressure of the CO2in vitro. A 25-mm Medtronic Hall valve was installed in the mitral position of an electro-hydraulic total artificial heart. In order to quantify the mechanical heart valve cavitation, we used a high-speed camera. Even though cavitation intensity slightly increased with increases in the PCO2at heart rates of 60, 70 and 100 bpm, throughout the experiment, there was no significant difference between the PCO2and cavitation intensity.

Recently, cavitation on the surface of mechanical heart valves has been studied as a cause of fractures occurring in implanted mechanical heart valves. In this study, to investigate the mechanism of cavitation bubbles associated with monoleaflet mitral valves in an electrohydraulic total artificial heart (EHTAH), and to select the best valves for our EHTAH system, we measured three parameters. First, an image was created of the cavitation bubbles using a high-speed camera. Second, pressure drop in the vicinity of the valve surface was measured using mini pressure sensor. Then, the closing of the valve was observed using a Laser displacement sensor. Most of the cavitation bubbles in the Medtronic Hall valve were observed at the edge of the valve stop. With the Omnicarbon valve, the cavitation bubbles were observed at the edge of the valve and on the inner side of the leaflet. On the other hand, cavitation bubbles were observed only on the inner side of the leaflet in Björk-Shiley valve. Cavitation bubbles concentrated on the edge of the valve stop; the major cause of these cavitation bubbles was determined to be the squeeze flow. The formation of cavitation bubbles depended on the valve closing velocity and the valve leaflet geometry. From a viewpoint of squeeze flow, a low closing velocity and a small size of the valve stop could minimize cavitation.

Despite its wide clinical application, patient recovery from cardiopulmonary support (CPS) is not necessarily satisfactory. To clarify what influence CPS has on organ perfusion, we investigated the oxygen metabolism under various bypass flow (BF) conditions in a series of chronic animal CPS experiments.The CPS system, which consists of a pulsatile ventricular assist device and a compact artificial lung was installed without anesthesia in 6 adult goats weighing 49–51 kg. BF was adjusted stepwise from 0% to 50%, 75%, 90%, and 100% of total systemic blood flow (TSF) by balancing the pulmonary arterial flow. The animals’ TSF and oxygen delivery (DO2) were sufficiently maintained throughout the experiments.The oxygen consumption (VO2) and the oxygen extraction rate (ExO2) increased from 178 ± 14 to 342 ± 19 ml/min, and from 28 ± 2% to 64 ± 1%, respectively, in proportion to the increase of CPBF dependency from 0% to 100%. The blood lactate level did not change appreciably even at 90% BF from 5.7 ± 0.3 to 11.2 ± 1.2 mg/dl, but drastically elevated to 23.5 ± 4.6 mg/dl at the total bypass. This indicates that CPS leads to a relative lack of oxygen and can induce organ dysfunction due to increasing VO2and ExO2in proportion to the increase of BF dependence even if TSF and DO2are sufficiently maintained.

We investigated possible functional changes in the vascular system accompanying the morphological change in prolonged nonpulsatile left heart bypass (LHB). Three adult goats underwent pulsatile LHB. Two weeks postoperatively, the pulsatile ventricular assist device was replaced with a centrifugal pump and nonpulsatile LHB was subsequently conducted for 4 weeks. The mean aortic pulse pressure was 39 and 16 mmHg during the pulsatile and nonpulsatile LHB, respectively. Systemic vascular resistance (SVR) and plasma norepinephrine levels were measured at the end of pulsatile LHB (PUL), and at the end of 1st, 2nd, 3rd, and 4th week of nonpulsatile LHB (NP1w, NP2w, NP3w, NP4w, respectively). At each point, 50 μg/kg nitroglycerin and 1μg/kg norepinephrine were injected and the minimal and maximal values of SVR after injection were calculated as parameters reflecting the vascular tonus and contractility. The SVR and plasma nor epinephrine level did not significantly change during the entire course (SVR: 1106, 895, 982, 920, and 938 dyne·sec·cm−5; norepinephrine level: 0.3, 0.2, 0.1, 0.2, and 0.1 ng/ml; at PUL, NP1w, NP2w, NP3w, and NP4w, respectively). The minimal value of SVR after nitroglycerin injection remained unchanged, indicating that vascular tonus was stable during the entire course (618, 687, 623, 560, 653 dyne·sec·cm−5, respectively). In contrast, the maximal value of SVR after norepinephrine injection at NP3w and NP4w (1695 and 1759 yne·sec·cm−5) became significantly reduced compared to that at PUL (2346 dyne·sec·cm−5). These results indicated that prolonged nonpulsatile left heart bypass did not affect the vascular tonus, but significantly diminished the vascular contractility.

We have treated ten cardiogenic shock patients after acute myocardial infarction (AMI) with a left ventricular assist device (LVAD). These patients were later divided into three groups: the first group with ventricular septal perforation, the second with aorto-coronary bypass grafting (ACBG) before LVAD implantation and the third group without ACBG. LVAD maintained the systemic circulation in each group, and cardiac function recovered enough to remove LVAD in 70% of the total patients. Two of three patients in the first group were discharged from hospital. Two weaned cases in the second group died of multiple organ failure and one was discharged, and hemorrhagic necrosis was seen in the bypassed area of the myocardium. One patient of the third group could not be weaned from LVAD because of respiratory failure though his heart function began to recover. Another case in the third group underwent bypass grafting after removal of LVAD. However ACBG surgery should be done very carefully because a patient in shock is occasionally intolerant to major surgery. In all groups, the major cause of death was multiple organ failure which was probably caused by the prolonged low output condition prior to LVAD application. In the light of this experience, it appears that LVAD should be applied before irreversible damage occurs to major organs, including the heart itself. To ensure the timely application of LVAD, some way must be found to introduce systematic application of LVAD into the normal course of AMI treatment.

We conducted chronic experiments to determine how to treat profound biventricular failure systematically with ventricular assist devices (VADs) and to analyze the factors that affect prognoses for this condition. Anoxic arrest was induced in ten goats by aortic cross-clamping under normothermic conditions (38.5° C) for 30 (n= 3), 45 (n= 1), and 60 (n= 6) minutes. A left ventricular assist device (LVAD) was implanted in eight animals, and a biventricular assist device (BVAD) was used in two. Three goats — two of which had undergone anoxic arrest for 30 minutes and one for 60 minutes — whose right atrial pressure (RAP) was approximately 18 mm Hg during the acute stage, recovered in two to three weeks, and the pumps were successfully removed. Pathological findings in these animals showed scattered areas of surviving myocardium, with connective tissue replacing the degenerated myocardium. The remaining five LVAD goats required higher RAPs to maintain circulation and died from various causes. Maintaining circulation without volume loading, even in the presence of arrhythmias, was easier with the BVAD. One BVAD animal that underwent 45 minutes of anoxic arrest recovered from right ventricular failure, and the right pump was removed. The second goat (anoxic arrest, 60 min) on the BVAD failed to recover. Autopsy of the myocardium revealed a thin ventricular wall. Our studies show that the use of VADs allows time for a failing heart to recover, but the potential for healing is affected by the severity of myocardial damage prior to VAD application. We believe that although LVADs can maintain circulation with high RAPs, the use of BVADs might be more beneficial for maintaining systemic organ function in cases of persistent biventricular failure.

Abstract: An ultrasonic flowmeter incorporated with implantable miniature sensors was developed. Two sets of miniature ultrasonic sensors are attached to the surface of a blood vessel. The outer diameter of the vessel and the blood velocity are measured simultaneously by means of the ultrasonic transit-time technique and the ultrasonic Doppler method, respectively. Instantaneous blood flow is calculated by multiplying the flow velocity by the cross-sectional area calculated from the diameter Stroke volume and cardiac output can also be obtained, when the system is applied to the ascending aorta. After preliminary benchtop tests, acutein vivo studies were carried out to evaluate the accuracy and performance of the system. The blood flow in the descending aortas of dogs and a goat were measured simultaneously by the ultrasonic system and an electromagnetic flowmeter. The correlation coefficient between the data obtained by the two methods was 0·968. The system was applied to measure the blood flow in the ascending aortas of goats which had had heart failures induced and were implanted with left ventricular assist devices.

AbstractWhen operating turbo blood pumps in tandem, the strength of shear stress is reduced, but the exposure duration of the stress is increased. The purpose of this experiment was to compare the degree of contribution of these two factors on hemolysis as well as to evaluate the effectiveness of the tandem operation of turbo blood pumps. Tandem operation of two Bio‐pumps (BP‐80; Medtronics Bio‐medicus, Inc., Eden Prairie, Minnesota, U.S.A.) were compared with single operation of a BP‐80 in in vitro hemolysis tests in three different driving conditions, that is, pumping heads of 200, 350, and 500 mm Hg under a pump flow rate of 5 L/min. The Allen's hemolytic indexes of the tandem operation at pumping heads of 200, 350, and 500 mm Hg were 0.014, 0.020, and 0.080 mg/dl, respectively. The hemolytic indexes of the single operation at pumping heads of 200, 350, and 500 mm Hg were 0.014, 0.056, and 0.12 mg/dl, respectively. These results indicate that tandem operation is a useful method of reducing hemolysis with the BP‐80 under high pumping heads and that the effect on hemolysis of exposure to higher shear stresses may be more serious than that of longer durations of exposure to shear stress in turbo blood pumps.