Young-Sang Sohn

Morphologic Changes of the Aortic Wall Due to Reduced Systemic Pulse Pressure in Prolonged Non Pulsatile Left Heart Bypass

The morphologic changes of the aortic wall due to reduced systemic pulse pressure in prolonged non pulsatile left heart bypass (LHB) were investigated. Sixteen adult goats were divided into three groups: the non pulsatile group in which non pulsatile LHB was conducted for 137 days on average, the pulsatile group in which pulsatile LHB was conducted for 79 days on average, and the control group used as the normal control. The average aortic pulse pressures were 12, 48, and 37 mmHg, respectively. At the end of the experiments, the descending aorta was excised and subjected to morphologic examination. The wall thickness of the aorta in the non plus.

Hemodynamic and Humoral Conditions in Stepwise Reduction of Pulmonary Blood Flow During Venoarterial Bypass in Awake Goats

The effects of reduced pulmonary arterial blood flow (PAF) during venoarterial bypass (VAB) on hemodynamic and humoral conditions were investigated in a series of experiments in a chronic animal model. A biventricular bypass system was installed in five adult goats weighing 49.8 ± 1.1 kg. Two weeks later, the extracorporeal circuitry was changed to VAB without anesthesia. The PAF was reduced stepwise from 100% to 50,25,10, and 0% of total systemic flow. The mean aortic pressure and systemic vascular resistance decreased from 110 ± 14 to 66 ± 3 mmHg and from 1,288 ± 77 to 740 ± 73 dyne-sec/cm5, respectively, in proportion to the decrease in PAF from 100 to 0%. The prostaglandin E2 con.

in Vitro And in Vivo Heat Dissipation Of An Electrohydraulic Totally Implantable Artificial Heart

The authors evaluated the heat transfer characteristics of an electrohydraulic totally implantable artificial heart (EH-TAH) developed at our institute. In three in vitro experiments, the heat dissipation of the EH-TAH was investigated. First, the EH-TAH was connected to a closed mock circuit filled with 1 L of saline, and driven at an input power of 20 W. The estimated heat conducted to the blood was ∼10.3 W, which was almost half of the input power. Second, we simulated heat transfer with the circulation of a calf by using a heat exchanger. The amount of heat dissipating directly from the EH-TAH surface was calculated to be 10 W. Third, the temperature of the actuator examined with thermography was found to be almost uniform, and no prominent high temperature area was observed. In an in vivo study, the EH-TAH was implanted for 10 days in a calf weighing 62 kg. The input power was 18 ± 2 W, the temperature of the actuator-tissue contacting surface was 39.4 ± 0.8°C, and that of the pump blood chamber was 39.8 ± 0.4°C. This slight temperature elevation was thought to be attributable to heat dissipation to the blood. On histologic study of the chest wall and the lung in contact with the actuator, vascularized connective tissue envelopes were observed, but unfavorable side effects, such as tissue necrosis, were not observed. These results suggest that the thermal effect of this system is acceptable at the input power used. ASAIO Journal 1997; 43:M592-M597.

In vitro and in vivo evaluation of a left-right balancing capacity of an interatrial shunt in an electrohydraulic total artificial heart system

The authors evaluated the basic performance of an interatrial shunt (IAS) made by punching a hole in the atrial septum, in accommodating the left-right imbalance in our electrohy-draulic total artificial heart (EHTAH) system. In an in vitro study conducted in a closed mock circuit connected with the EHTAH, the interatrial pressure gradient changed in compliance with the amount of bronchial flow and the size of the IAS. The IAS of 4.4 mm diameter or larger maintained the interatrial pressure gradient within physiologically permissible limits when the amount of bronchial flow was 5% of cardiac output or less. A left-to-right one-way valve made of a piece of pericardium, a possible option in this IAS method, successfully prevented right-to-left reverse shunt flow through the IAS. In a chronic in vivo study using a calf implanted with the EHTAH for 10 days, a 4.5 mm IAS without the one-way valve demonstrated satisfactory dynamic left-right balancing capacity with a stable interatrial pressure gradient of 4 ± 1 mmHg over a wide range of atrial pressures. No thrombus was found in or around the IAS at autopsy. The authors conciude that the IAS is a simple and promising means

Early changes in circulating blood volume and volume regulating humoral factors after implantation of an electrohydraulic total artificial heart.

The early changes in circulating blood volume (CBV) and volume regulating humoral factors after implantation of an electrohydraulic total artificial heart (EH-TAH) were investigated in a calf and compared with results in a sham operated control calf. CBV was measured by the dye dilution method using indocyanine green. CBV and humoral factors were periodically investigated. In the EH-TAH implanted calf, the cardiac output was estimated at 6–7 L/min (94–109 ml/kg/min), and the aortic pressure and aerobic metabolic condition were favorable. Nevertheless, the CBV was increased to 132 and 168% of the pre-operative value (range in the control calf, 83–103%) on post operative days 4 and 8, respectively. The atrial natriuretic peptide level on days 2, 5, and 7 was 23, 170, and 240 (in the control calf, 19–61) pg/ml, respectively, and the anti-diuretic hormone level was 7.3, 2.0, and 1.3 (0.5–1.3) pg/ml, respectively. The plasma renin activity was 3.2, 3.7, and 3.1 (0.5–0.3) ng/ml/hr, respectively. The angiotensin-I and angiotensin-II levels were also increased in the EH-TAH implanted calf. It is concluded that significant water retention occurs even at sufficient cardiac output early after EH-TAH implantation. The changes in humoral factors are suggested to arise secondary to the increased CBV or other unknown factors.

Evaluation of a Newly Developed, Heparin-Bonded Artificial Lung in Chronic Animal Experiments

Our artificial lung (AL) for long-term extracorporeal membrane oxygenation (ECMO) consists of a special membrane in which micropores on the outer surface of the hollow fibers are blind-ended to eliminate direct blood-gas contact, and the entire blood-contacting surface is treated with covalent heparin binding to promote antithrombogenicity. Chronic performance of the AL was evaluated for gas-exchange function and thromboresistant properties in four goats weighing 28–36 kg, using a venoarterial bypass circuit perfused by means of a pneumatic ventricular assist device for up to 14 days. Serum leakage was completely prevented in all the devices throughout the experimental period. With 3.3–4.21/min of blood flow and 10–151/min of oxygen flow, the AL transferred 166 ± 25ml/min of oxygen and 116 ± 41ml/min of carbon dioxide. Platelet counts and antithrombin III levels significantly decreased during the initial 3 days but rebounded thereafter. Only in one AL was macroscopic thrombus formation observed, presumably related to severe infection. Scanning electron microscopy showed the surface of hollow fibers to be free of thrombus, while fibrin deposits were observed in all devices, mainly on the polyester threads used for weaving the hollow fibers. These results indicate that our new AL can be used for prolonged ECMO, although further improvement in thromboresistant properties should be achieved.

Altered Hemodynamic, Humoral, and Metabolic Conditions in Nonpulsatile Systemic Circulation

Acute-phase changes in hemodynamic, hormonal, and metabolic conditions after deputation of systemic circulation were investigated in 25 anesthetized goats. A total left heart bypass was instituted between the left atrium and ventricle and the descending aorta with an extracorporeal circuit consisting of pulsatile and nonpulsatile blood pumps. The blood flow rate was finely controlled to maintain the minimum level that allowed total left heart bypass. In this experimental setting, the character of systemic flow was rapidly converted from pulsatile to nonpulsatile mode, and the hieasurements were made 5 min before and 5 min after the deputation. Blood flow rates stayed at the rather low levels of 62.2 ± 15.3 and 62.5 ± 15.4 ml · min-1 · kg-1 in the pulsatile and nonpulsatile modes, respectively. The mean aortic pressure increased from 99 ± 3 to 107 ± 3 mmHg and norepinephrine concentration rose from 300 ± 39 to 373 ± 53 pg/ml, strongly indicating that the sympathetic tone was comparatively high in the initial stage of nonpulsatile circulation. Despite keeping oxygen delivery constant at depulsation, the total oxygen consumption dropped from 1.5 ± 0.2 to 1.0 ± 0.1 ml/min, the venous oxygen saturation increased from 78% ± 6% to 85% ±5%, and the serum lactate level increased from 34 ± 3 to 40 ± 4mg/dl. Thus, the oxygen uptake became less efficient after the depulsation. We conclude that changes in hemodynamic, hormonal, and metabolic conditions occur immediately after the depulsation of systemic circulation in anesthetized goats at relatively low blood flow rates.