[Surgical treatment for acute type A aortic dissection].

The purpose of this study was to assess the factors for clinical outcome of the surgical treatment of acute type A aortic dissection. From April 1996 to March 2006, 44 patients underwent emergency operation for acute type A dissection within 2 weeks from the onset. Resection of the intimal tear was performad with open distal anastomosis. The mean age was 63.4 (range 29-83) years, and 28 were female. As for their preoperative condition, 5 patients were in severe hemodynamic instability including cardiac arrest in 2, apnea in 1, and rupture in 4. Distal resection extended to ascending aorta in 24 patients (54.5%), hemiarch in 7 (15.9%), and total arch in 13 (29.5%). 30-day mortality was 4.5% and the incidence of stroke was 13.6%. Several methods were used including axillary artery cannulation and central repair with adventitial inversion technique. Patients with malperfusions caused by acute type A dissection should undergo immediate aortic reconstruction by adequate circulatory assisting methods.

[Atrial fibrillation after isolated coronary bypass surgery].

Postoperative atrial fibrillation (Af) remains a significant source of morbidity after coronary artery bypass grafting (CABG). Prophylactic therapy with beta-adrenergic blockers or amiodarone hydrochloride is reported to reduce the incidence of Af. We studied the incidence of Af retrospectively and considered the risk factors for it. Ninety-three patients who underwent isolated CABG from April 2003 to March 2004 are included in this study. Postoperative Af was observed in 22 (25%) patients. Ten of them were operated on off-pump procedure, and 14 had any type of beta-adrenergic blockers preoperatively. The mean age of the group of postoperative Af is 69.7 +/- 9.2 years old (older than the non-Af group: 65.5 +/- 10 years old, p = 0.087). And the preoperative left atrial size was larger in the Af group than in the non-Af group (43.4 +/- 6.1 versus 40.6 +/- 5.4mm, p = 0.064) Major embolic complication occurred in only 1 (1.1%) patient of non-Af group. We observed postoperative Af in 25% of patients after CABG. Older age and larger left atrial size may relate to the incidence of Af, and appropriate anticoagulant therapy and medication of beta-blockers are important for the patients who have such risk factors.

[Operative decision for acute type A aortic dissection; ascending aorta or arch replacement].

Operative technique of acute type A aortic dissection remains controversial. We adopted the strategy to replace the aortic arch only when the entry of the dissection was found in the aortic arch, or atherosclerotic arch aneurysm existed. The purpose of the current study was to elucidate the feasibility of the ascending aorta and hemiarch replacement and to follow the fate of the patent false lumen distal to the anastomosis after surgery. Nineteen patients operated from 2000 to 2004 were included in this study. Ascending or hemiarch replacement were performed in 15/19 (78.9%) patients. The early mortality rate was 10.5% (2/19). The causes of death included major brain infarction and rupture of the descending aortic aneurysm 25 +/- 23 days after surgery. Thrombosed distal false lumen of the thoracic aorta was observed in 60% (9/15) of patients of De Bakey type I dissection. Thus our strategy for acute type A aortic dissection including entry closure and the ascending or hemiarch replacement is a reasonable option especially for the elderly patients in acute phase. Our results also indicated that the thrombosis of the false lumen distal to the anastomosis can be expected and the enlargement of the distal aorta is minimal.

Aortic valve implantation in the calf: a successful approach using Heartport cannulation and minimally invasive techniques.

BACKGROUND AND AIM OF THE STUDY: Aortic valve replacement (AVR) for mechanical prosthetic valvular testing has not been performed in calves because of anatomic difficulties, and sheep have traditionally been used in this situation. Hemodynamically, however, the calf constitutes an excellent model due to vigorous myocardial contractility, high stroke volumes and high cardiac output, and so has been used for preclinical evaluation of mechanical assist devices and mechanical valves in the mitral and tricuspid positions, which can be approached with relative surgical ease. Recently, a juvenile bovine model has been used to test a newly developed mechanical valve in the aortic position. METHODS: Ten calves (body weight 91+/-11 kg) underwent AVR with a 21-mm mechanical prosthesis via a small left intercostal thoracotomy with the aid of a Heartport cannulation device. A standard cardiopulmonary bypass (CPB) circuit was used. To circumvent the short bovine ascending aorta and to gain additional space to perform the aortotomy, two aortic cannulas were inserted for arterial-systemic perfusion. Nine calves each received a 21-mm experimental trileaflet aortic central flow valve prosthesis, and one calf received a 21-mm St. Jude Medical prosthesis. RESULTS: Mean CPB duration was 154.2+/-44.4 min, and mean ischemic time 80.1+/-15.9 min. Mean study duration was 42.6+/-53.7 days. Three calves were killed prematurely: two on days 2 and 7 due to complications arising from inadvertent entrapment of the right coronary artery ostium by a suture, and one on day 0 due to an accidental overdose of magnesium. Three calves, all of which had a first-version test valve, were killed electively due to valve malfunction secondary to early valvular thrombosis. Four animals (three with the final version valve and one with a standard valve as a control) survived until killed electively (range: 33-172 days). CONCLUSION: Results indicate that replacement of the native bovine aortic valve with a mechanical prosthesis can be performed safely in calves. Complication-free survival of up to six months can be achieved in the growing calf, provided that the test valve design satisfies minimum hemodynamic and coagulation criteria.

[Development of a novel artificial heart-lung system for long-term cardiopulmonary support--experimental evaluation in goats with total cardiopulmonary bypass].

A novel cardiopulmonary support (CPS) system for long-term use was designed and evaluated. The CPS system consists of an air-driven ventricular assist device (VAD) and a newly developed compact membrane oxygenator (MO). The VAD had proven durable and antithrombogenic in over 200 clinical uses. The membrane oxygenator, with a membrane area of 1.2 m2 and priming volume of 140 ml, is compact and designed to be interposed in the VAD conduit. It is made with a special hollow fiber membrane, in which micropores are blind-ended so that serum leakage can be prevented during prolonged use. The blood contacting surface of the MO is heparinized with a newly developed covalent bonding technique that ensures good thrombus resistance. Chronic animal experiments of total CPS were carried out for up to 336 hr in seven goats weighing from 28 to 36 kg. Venoarterial bypass was instituted with the CPS system in which all venous blood was drawn from both the right atrium and ventricle and returned to the aorta. No systemic anticoagulant therapy was used, except for a heparin-added fluid infusion to keep the monitoring lines open. Blood flow rate ranged between 107 to 130 ml/kg/min, oxygen transfer between 142 to 174 ml/min, and carbon dioxide removal between 78 to 148 ml/min. No plasma leakage was observed at the hollow fiber membrane. Substantial changes were not found in platelet count or other coagulation factors. And no perceptible thromboembolism was found at necropsy in any case. These results indicate that the system is competent enough to be used for long-term CPS, such as a bridge to lung or heart-lung transplantation.

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 concentration increased from 1.5 +/- 0.6 to 8.8 +/- 0.6 pg/ml following the decrease in PAF from 100 to 0%. The renin-angiotensin system increased in proportion to the decrease in PAF. In contrast, the epinephrine and norepinephrine concentrations (60 +/- 10 and 227 +/- 80 pg/ml, respectively, at 100% PAF) did not change appreciably even at 10% PAF, but were markedly elevated to 335 +/- 117 and 2,088 +/- 1,503 pg/ml at 0% PAF. The antidiuretic hormone level similarly changed. In conclusion, decrease in PAF during VAB exerts significant effects on hemodynamics in a proportional manner and on vasoactive humoral factors in a diverse manner.

Effects of self washout structure on the antithrombogenicity and the hemolytic properties of a centrifugal pump.

Antithrombogenicity in an initial type (N1) of a centrifugal pump (CP) developed in our institute is provided by the central balancing hole of an impeller. A new CP (N2) was modified to obtain better antithrombogenicity, in which the balancing hole was widened to improve self washout flow velocity (Vsf), and an edge of the thrust bearing was rounded off to minimize flow separation. Effects of the modifications were assessed in vitro and in vivo studies. The Vsf of the N1 and the N2 evaluated by a Doppler velocimeter were 12.8 and 22.1 cm/s, respectively. Flow around the thrust bearing, which was visualized by a light cutting method, confirmed less flow stagnation in the N2. The hemolytic indices of the N1 and the N2 were 0.023 and 0.008 mg/dl, respectively. In vivo antithrombogenicity and the hemolytic properties of the N2 and the N1 were investigated without anticoagulation therapy in 3 goats. In each goat the N2 was driven for 1 week and exchanged for the N1, which was driven for the same period. Red thrombi at the thrust bearing were found in 2 N1s, and 2 small thrombi were on the impeller of another N1, whereas a thrombus of less than 1 mm3 at the TB was noted in 1 N2. Plasma free hemoglobin was not increased in either CP. These results indicate that the N2 has better antithrombogenicity and hemolytic properties than the N1.

A volume-controlled liquid ventilator with pressure-limit mode: imperative expiratory control.

Liquid ventilation with perfluorocarbon (PFC) has been considered to offer advantages over gas ventilation to respiratory distress syndrome patients. We developed a volume-controlled liquid ventilator with pressure-limit mode; inspiration is performed mechanically with an actuator under the preset limit of the intratracheal pressure (Paw); expiration is performed by gravity assistance. Oxygenation and CO2 removal of PFC are done with a membrane oxygenator. An endotracheal tube with a Paw monitor line was placed in 5 rabbits weighing 2.7 +/- 0.6 kg, and liquid ventilation was conducted with the condition that the upper and lower limits of Paw were 20 and -20 mm Hg, respectively. The best arterial pH and gas tension were examined. The averaged arterial pH and gas tension were examined. The averaged arterial pH. Pao2, Paco2, and Sao2 were 7.45 mm Hg, 369 mm Hg, 46.2 mm Hg, and 100% at the best values, respectively. Ventilatory conditions at the best values were as follows: ventilation rates, tidal volume peak Paw, average Paw, and trough Paw were 5-15 (11 +/- 4) times/min, 13.3-17.3 (15.6 +/- 1.4) ml/kg, 5-18 (12 +/- 5) mm Hg, -7-4 (-1 +/- 4) mm Hg, and -20(-)-6 (-13 +/- 5) mm Hg, respectively. Pressure-limit control of the system worked well, but in the initial 3 animals, fluorothrax, that is the leakage of PFC into thoracic cavity, was recognized at the Paw from 20 to 25 mm Hg after the upper pressure limit was raised to 25 mm Hg to improve Paco2. The fluorothrax seemed to be caused by excess end-expiratory residual volume. An expiratory control mechanism appears to be imperative for further improvement of our liquid ventilator.

Set-up, improvement, and evaluation of an electrohydraulic total artificial heart with a separately placed energy converter.

The authors have been developing an electrohydraulic total artificial heart (TAH) system with a separately placed electrohydraulic energy converter to minimize anatomic constraints in the pericardial space. Improvements to the system and current status of the development are reported. The energy converter was miniaturized to improve implantability, and its thickness was reduced to 54 mm. System efficiency was increased by suppressing rush current at the time of motor reversal. Maximum cardiac output of the TAH system was 9 L/min, and maximum system efficiency increased to 10%. The blood pump system was implanted easily in the body of a 57 kg calf, and no significant temperature rise on the energy converter surface was observed. As the next step, main components were integrated into a total system. The transcutaneous energy transfer system could supply power to the TAH without a decline in pump performance, and the internal battery could support the system at 6.5 L/min of cardiac output for 1 hour without a decrease in cardiac output. The authors consider the TAH system with a separately placed energy converter the most promising approach to development of a TAH for smaller sized patients.

Influence of non pulsatile systemic circulation on tissue blood flow and oxygen metabolism.

Influence of non pulsatile systemic circulation on oxygen metabolism was examined regarding tissue perfusion in 12 adult goats weighing from 46 to 55 kg. Under general anesthesia, a flow character, changeable total left heart bypass circuit consisting of pulsatile and non pulsatile pumps was installed through a left thoracotomy. Systemic flow was converted from pulsatile to non pulsatile in 7 of 12 animals, and in the reverse order in the other 5, by changing the driving pump. Esophageal mucosal blood flow was determined by a colored microsphere method that estimated tissue blood flow at the pre capillary level. Esophageal intramucosal pH was evaluated with a silicone balloon tonometer catheter surgically placed in the submucosal space. Hemodynamic and arterial blood gas parameters were unchanged at flow mode conversion. Although oxygen delivery was comparable between pulsatile and non pulsatile circulation, oxygen extraction ratio was lower and venous oxygen saturation was higher in non pulsatile than pulsatile circulation. Although statistically not significant, serum lactate level tended to be higher with non pulsatile circulation. No difference was observed in esophageal mucosal blood flow between pulsatile and non pulsatile circulation, whereas intramucosal pH, which strongly correlated with arterial pH regardless of the flow mode, was significantly lower under non pulsatile than pulsatile conditions. In conclusion, systemic oxygen uptake is less efficient in non pulsatile than pulsatile circulation in the setting of an acute experiment using animals, which may be accounted for by the disparity between the pre capillary blood flow and actual tissue oxygen metabolism.

Importance of metabolic function of the natural lung evaluated by prolonged exclusion of the pulmonary circulation.

It is generally considered that the natural lung metabolizes various vasoactive substances through the pulmonary circulation. However, the influences of bypassing or eliminating the pulmonary circulation have not been fully elucidated, especially for prolonged periods. In this study, we performed total cardiopulmonary bypass and exclusion of the pulmonary circulation for up to 336 hr in awake goats to clarify the importance of the metabolic function of the lung. In seven adult goats, biventricular bypass with a pulsatile ventricular assist system was first established. After 2 weeks, the biventricular bypass was converted to total cardiopulmonary bypass without anesthesia. Adequate gas exchange and perfusion support were achieved in all animals. However, the institution of total cardiopulmonary bypass led to marked decreases in the mean aortic pressure and systemic vascular resistance, and they remained low thereafter. The arterial levels of prostaglandin E2 and norepinephrine, which are inactivated naturally through the pulmonary circulation, increased remarkably. These results indicate that the natural lung plays an important role in controlling systemic circulation by metabolizing various vasoactive substances. Understanding the non respiratory function of the natural lung is of prime importance for advancement of lung and heart-lung support.

Development of an integrated artificial heart-lung device for long-term cardiopulmonary support.

An integrated artificial heart-lung device has been developed as a long-term cardiopulmonary support system. The device is composed of gas exchange and pumping units. The gas exchange unit consists of a special hollow fiber membrane that can prevent serum leakage. The entire blood contacting surface of the gas exchange unit is treated with covalent heparin bonding. The pumping unit consists of two pusher-plate artificial hearts joined to each end of the artificial lung unit. The core size and priming volume of the device are 11 x 14 x 17 cm and 400 ml, respectively. In in vitro evaluation, the device exhibited a maximum output of 7.0 L/ min, with a pressure gradient of 10 mmHg per 1 L/min flow rate. In acute in vivo evaluation with adult goats, the device satisfactorily replaced the animals' circulation and respiration for 6 hr. Pumping output ranged from 5.5 to 6.0 L/min, whereas PaO2 and PaCO2 were kept above 500 mmHg and below 30 mmHg, respectively. The device demonstrated prominent thrombus resistant properties in nonheparin animal use trials. These results indicate that the integrated artificial heart-lung device has a potential to be a long-term cardiopulmonary support system that can be used with minimal anticoagulant therapy.

Development of a membrane oxygenator for long-term respiratory support and its experimental evaluation in prolonged ECMO.

The authors developed a new membrane oxygenator (MO) for long-term respiratory support and evaluated its performance in animal experiments for as long as 336 hr. The MO, with a membrane area of 1.2 m2 and priming volume of 140 ml, is compact and designed to be interposed in a ventricular assist system (VAS) conduit. It is made with a novel hollow fiber membrane, in which micropores are blind-ended so that serum leakage can be prevented during prolonged use. The blood contacting surface of the MO is heparinized with a newly developed covalent bonding technique that ensures good thrombus resistance. In vivo evaluation with five adult goats was performed by installing the MO into a venoarterial or venovenous bypass circuit. No systemic anticoagulant therapy was used, except for a heparin-added fluid infusion to keep the pressure monitoring lines open (2-3 U/kg/hr). Throughout the experiments, no plasma leakage was observed, and gas transfer rates were maintained in a satisfactory range. Platelet counts did not decrease to less than 60% of levels before bypass, and hemolysis was negligible. The levels of coagulation parameters including fibrinogen, fibrin degradation products (FDP), antithrombin III (AT III), antiplasmin, prothrombin time (PT) and activated partial thromboplastic time (APTT) remained within physiologic ranges and relatively constant. At the end of the evaluation, no thrombus formation was noted in three of five MOs. These results suggest that this MO is a promising device for long-term respiratory support.

Altered oxygen metabolic conditions associated with increased norepinephrine levels in a nonpulsatile systemic circulation.

Change in oxygen metabolic conditions accompanying the conversion of systemic flow from pulsatile to nonpulsatile (from P-mode to N-mode) was investigated in association with blood norepinephrine levels. Total left heart bypass was instituted through a left thoracotomy under general anesthesia in 10 adult goats. Pulsatile and nonpulsatile pumps were incorporated in the circuit in parallel, and the flow character was rapidly converted from the P-mode to the N-mode. Norepinephrine levels increased significantly after the conversion, from 222 +/- 54 pg/ml to 285 +/- 65 pg/ml. While oxygen delivery (DO2) was kept constant, the oxygen extraction ratio significantly decreased, from 21 +/- 3% to 16 +/- 3%, and venous oxygen saturation (SvO2) significantly increased, from 77 +/- 6% to 84 +/- 6% after depulsation. The serum lactate level was significantly higher in the N-mode than the P-mode (P-mode: 35 +/- 2 mg/dl, N-mode: 45 +/- 5 mg/dl). Strong positive and negative correlations of norepinephrine levels were observed with oxygen extraction ratio and SvO2, respectively, whereas norepinephrine levels did not correlated with DO2. Regression lines in these correlations unveiled higher oxygen uptake in the P-mode than the N-mode at the same norepinephrine level. These results indicate that, in the setting of an acute animal experiment, oxygen uptake is less efficient with the absence of pulsatility, and the higher norepinephrine concentration functioned to tune the oxygen metabolism in the initial stage of nonpulsatile systemic circulation.

Development of a centrifugal pump with improved antithrombogenicity and hemolytic property for chronic circulatory support.

A centrifugal pump with a unique structure has been developed for chronic support. The pump is driven by a magnetic coupling and has no rotating shaft, no seal around the rotating part, and a balancing hole at the center of the impeller and the thrust bearing. The pump was improved in stepwise fashion to realize good antithrombogenicity and low hemolysis. The first pump, the National Cardiovascular Center (NCVC)-0, had an impeller with 4 rectangular and curved vanes; 6 triangularly shaped curved vanes were employed in the second model, the NCVC-1, to reduce trauma to the blood. In the third design, the NCVC-2, the central hole was enlarged, and the thrust bearing shoulder was rounded so that blood washing was enhanced around the impeller; stream lines also were smoothed for improved antithrombogenicity. The hemolytic property of the device was evaluated in vitro with heparinized fresh goat blood; hemolysis indexes of the NCVC-0, -1, and -2 were 0.05, 0.01, and 0.006 g per 100 L, respectively. Antithrombogenicity of the pumps was examined in animal experiments as a left heart bypass device in goals weighing 52-75 kg. Six NCVC-0 pumps were driven for 14 to 33 (22.0 +/- 7.6) days in goats receiving the antiplatelet drug cilostazol orally. Four NCVC-1 pumps ran for 1 to 80 (28.5 +/- 30.6) days with the same drug regimen in 2 cases and with no anticoagulation therapy in 2 cases. After 3 preliminary 1-week tests of NCVC-2 pumps in animals, the pump was installed in 3 goats; 2 pumps were still running on the 182nd and 58th pumping day. Intracorporeal implantation also was attempted successfully. The results indicate that this pump has promising features for chronic support although longer term and additional evaluations are necessary.

Tandem operation of a turbo blood pump (BP-80--type centrifugal pump) to reduce hemolysis.

When 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, 35, 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.

Influence of ventricular fibrillation on sympathetic nerve activity under biventricular bypass circulation.

Autonomic nerves play an important role in circulatory control. The characteristics of sympathetic nerve activity (SNA) during artificial circulation, however, are not well understood. In this study, we examined the influence of natural heart beating on the renal SNA (RSNA) using pulsatile 100% biventricular assistance and electrically induced ventricular fibrillation in anesthetized goats, whose heart rate and size are similar to the human heart's. Following induction of the ventricular fibrillation, the pulse-synchronous discharges in the RSNA did not change their periodicity and quantity significantly. It was concluded that the beating of the heart had little influence on the RSNA and was presumably not essential for maintaining nervous control of circulation as long as the circulation was maintained by an artificial heart.

Tandem Operation of a Turbo Blood Pump (BP-80-Type Centrifugal Pump) to Reduce Hemolysis.

When 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.

Heat generation and hemolysis at the shaft seal in centrifugal blood pumps.

The heat and hemolysis around a shaft seal were investigated. Materials were original pumps (Nikkiso HMS-15:N-original, and 3M Delphin:D-original), vane-removed pumps (Nvane(-), Dvane(-)), and a small chamber with a shaft coiled by nichrome wire (mock pump). The original pumps were driven at 500 mmHg and 5 L/min, and vane-removed pumps were driven at the same rotation number. An electrical powers of 0, 0.5, 2, and 10 W was supplied to the mock pumps. In vitro hemolytic testing showed that hemolytic indices were 0.027 g/100 L in N-original, 0.013 in Nvane(-), 0.061 in D-original, and 0.012 in Dvane(-). Measurement of heat with a thermally insulated water chamber showed total heat within the pump of 8.62 and 10.85 W, and heat at the shaft seal of 0.87 and 0.62 W in the Nikkiso and Delphin pumps, respectively. Hemolysis and heat generation of mock pumps remained low. The results indicate that the heat generated around the shaft seal was minimal. Hemolysis at the shaft-seal was considerable but not major. Local heat did not affect hemolysis. It was concluded that the shaft-seal affected hemolysis, not by local heat but friction itself.

Development and in vivo evaluation of an implantable left ventricular assist system with an impedance based monitoring and control system.

We have developed an implantable pneumatically driven diaphragm left ventricular assist system (LVAS) for small adults, and an electric impedance based monitoring and control system (Z system). In this Z system, measurement of electric impedance of the blood chamber is performed by charging an alternating current with a constant amplitude between two metal connectors without compromising anti-thrombogenicity. Automatic calibration was performed periodically by measuring trough values of impedance in the blood chamber for several beats while the blood pump was in a full-fill state under preset driving conditions. For precise control of the fill-to-empty (F/E) drive, an automatic trigger level adjustment method was developed. This method is an automatic searching algorithm that identifies the volume change of the last ejection or filling by the Z system and settles the next trigger level to maintain a definite stroke volume. In chronic in vivo evaluation, this LVAS was used in 13 adult goats. The pump was installed between the LV apex and the descending aorta and was placed in the abdominal wall. Pump output ranged from 2.5 to 5.8 L/min, and the Z system provided good monitoring. The F/E drive was achieved satisfactorily by this Z system. The physical condition of the goats was excellent for as long as 19 weeks. Hematologic, hepatic, and renal functions were within the normal range, and no prominent thromboembolic symptoms were observed. A new mobile control drive unit with this Z system is being developed. We conclude that this LVAS with the Z system is promising for long-term use in a clinical setting.