Biventricular Bypass Research Articles

дилатационной кардиомиопатией Клинический случай медицинской реабилитации пациента с дилатационной кардиомиопатией

The paper provides a clinical case of physical and medical rehabilitation of patient D born in 1963. Principal diagnosis established in 2018 according to ICD-10: I42.0 dilated cardiomyopathy. Laboratory testing revealed DNA of herpes virus 6 (HHV6), positive test for cytomegalovirus (CMV) DNA, 6.0×102 copies/mL, positive test for the Epstein–Barr virus (EBV) DNA, 7.2×103 copies/mL. In April 2018, the patient underwent successful surgery, implantation of the biventricular bypass system supplemented by membrane oxygenation. Physical rehabilitation was performed that yielded positive results.

IN-HOSPITAL AND LONG TERM RESULTS OF PERCUTANEOUS CORONARY INTERVENTION WITH BIVENTRICULAR SUPPORT AND EXTRACORPOREAL MEMBRANE OXYGENATION

Patients, due to various reasons not indicated for coronary bypass (CABG), usually have extremely high risk of complications in percutaneous intervention (PCI) as well. Recently it was shown that extracorporeal membrane oxygenation (ECMO) might provide a necessary support in the case of high risk PCI. ECMO can be effective in PCI in patients with refractory cardiogenic shock too, however evidence base for the technological approach in high risk PCI remains underdeveloped. Aim. To evaluate in-hospital and long-term results of high risk PCI with biventricular bypass and ECMO in patients not fitted for CABG. Material and methods. We conducted a retrospective analysis of the treatment of 12 patients having extremely high risk of complications in CABG. In all cases PCI was done in conditions of biventricular bypass and ECMO. Stable angina and non-STelevation acute coronary syndrome occurred in 42 and 58% cases, respectively. Clinical picture of cardiogenic shock was the criteria of exclusion. All patients had severe comorbidity with high score by “EuroScore” — 6,3±4,9%. In all cases there was multivessel disease with high level of coronary lesion involvement by “Syntax Score” (30,1±10,1). Mean level of left ventricle ejection fraction was satisfactory — 51±12,6%. Ten patients (83%) had significant (≥50 %) lesion of unprotected stem of the left coronary artery (SLCA). Results. All procedures were successful. As a success of PCI we meant the opened artery with the flow rate not worse than TIMI 3 and absent of significant cardiovascular complications. Mean quantity of the implanted drug-eluting stents was 2,4±1. Full revascularization was reached in 42% cases. Residual value of “Syntax Score” was at the level about 6,33±6,88. Significant adverse cardiovascular complications (death, myocardial infarction, repeated non-planned revascularization) during inhospital phase were not registered. In one case there was an iliac artery dissection, that did not lead to necessity of surgery. Hemorrhagic complications were found just in one patients (8%, 2nd type by “BARC”). All patients were discharged. There were no any fatal cases or myocardial infarction (MI) in 6 months after observation. Two patients required another revascularization (17%). In long-term period there were no and signs of “definite” or “probable” stent thrombosis. Conclusion. PCI in the conditions of biventricular bypass and ECMO might be effective alternative strategy of revascularization in a cohort of patients not indicated for CABG due to high complications risk.

ARTIFICIAL BAROREFLEX SYSTEM AS THE SIMULATION OF THE MEDICAL TREATMENT OF HYPERTENSION

Several investigators suggested that ACE inhibitor and ARB are the important antihypertensive drugs when we consider the sensitivity of the baroreflex system. Effect of antihypertensive drugs had been evaluated by the various investigators, however, there is no report studied the open loop analysis of the baroreflex system. In this study, open loop analysis of the baroreflex system was performed by the use of an artificial baroreflex system with artificial heart by the use of electrical circuit simulation, animal experiments with artificial heart, and these findings were compared with clinical data of the hypertensive patients. Windkessel model of the circulatory system was used in this study and nonlinear feedback model simulated the baroreflex system was added to the simulation. And animal experiments were performed by the use of biventricular bypass total artificial heart model with an automatic control system simulated the baroreflex system using the six adult goats. The results suggested that the baroreflex system carried out the important role in the fluctuations. HRVs were recorded in the patients with essential hypertension before and after the drug administration. And we found that in several cases complexity in the nonlinear behavior was significantly increased after the successful treatment of the hypertension, suggesting the recovery of the baroreflex system. These results in this study suggested the importance of the baroreflex sensitivity in the complex chaotic behavior in the hemodynamics.

Endogenous NO does not regulate baseline pulmonary pressure, but reduces acute pulmonary hypertension in dogs.

It has remained unclear whether endogenous production of nitric oxide (NO) plays an important role in the regulation of physiologically normal pulmonary pressures. Severe alveolar hypoxia is accompanied by decreased pulmonary NO production, which could contribute to the development of hypoxic pulmonary hypertension. On the other hand, pharmacological NO inhibition further augments this hypertensive response. The aims of the present study were to test: (a) whether NO contributes importantly in the maintenance of baseline pulmonary pressure; and (b) to which degree NO is involved in the pulmonary haemodynamic adjustments to alveolar hypoxia. In anaesthetized dogs (n=37), the systemic and pulmonary haemodynamic effects of the NO synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME, 20 mg kg(-1)) and substrate, L-arginine (200-500 mg kg(-1)), were determined at baseline and during alveolar hypoxia. Constant blood flows were accomplished by biventricular bypass, and systemic normoxaemia was maintained by extracorporeal oxygenation. The primary findings were: (a) L-NAME failed to increase baseline mean pulmonary arterial pressure (10.1 +/- 0.7 vs. 10.5 +/- 0.5 mmHg, P=ns), despite effective NO synthase inhibition as evidenced by robust increases in systemic arterial pressures; (b) L-NAME augmented the pulmonary hypertensive response to alveolar hypoxia (10.2 +/- 0.7 to 19.5 +/- 1.7 with L-NAME vs. 9.9 +/- 1.1 to 15.5 +/- 1.0 mmHg without L-NAME, P<0.05); and (c) L-arginine failed to decrease baseline or elevated pulmonary pressures. Instead, prolonged L-arginine caused increases in pulmonary pressure. These findings suggest that NO plays no significant role in the tonic physiological control of pulmonary pressure, but endogenous NO becomes an important vasodilatory modulator during elevated pulmonary pressure.

Correlation dimension analysis of the artificial circulation

Artificial circulation has been analyzed by decomposing it into parts. However, the sum of the decomposed parts is not equal to the whole system, especially in nonlinear dynamic systems such as biological systems. To evaluate prosthetic circulation as an entity, not as decomposed parts, nonlinear mathematical analytic techniques, including fractal dimension analyzing theory, were used. Two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses (BVB) in chronic animal experiments using four healthy adult goats. For comparison between natural and prosthetic circulation in the same experimental animals, the BVB-type complete prosthetic circulation model with ventricular fibrillation was adopted. All hemodynamic parameters with natural and prosthetic circulation were recorded under awake conditions and calculated by a personal computer system. By the use of nonlinear mathematical techniques, time-series data of the hemodynamics were embedded into the phase space, and correlation dimension analysis was performed to evaluate the reconstructed attractor. Our results suggest that the correlation dimension of the arterial blood pressure does not linearly increase according to the increase of the embedding dimension, even during artificial circulation, suggesting those are the fractal time series data. Dimensional analysis of the hemodynamics revealed that lower dimensional fractal dynamics were observed during prosthetic circulation. Fractal time series data are suggested to have robustness and error resistance. Thus, our results suggest that the circulatory regulatory system with the artificial heart may have these desirable characteristics.

CONTINUOUS EVALUATION OF MYOCARDIAL RECOVERY WITH VAD SUPPORT

Purpose: Evaluation of myocardial contractility during ventricular assist device (VAD) support is important to recognize the mechanism of myocardial recovery, hut that is difficult because VAD support changes preload and afterload conditions. The left ventricular (LV) end-systolic pressure-dimension relationship (ESPDR) is one of useful load independent indexes of cardiac function. We investigated whether the ESPDR could evaluate regional wall motion during VAD support in goats with severe heart failure after myocardial infarction (MI). Materials and Methods: Six adult goats weighing 65.3 ± 4.2 kg were conducted biventricular bypass with pulsatile VADs paracorporealy. Acute MI was created by ligation of the left anterior descending coronary artery. The ESPDR was measured before MI and after MI using LV pressure and simultaneous short axis dimension of the LV by means of ultrasonic crystals inserted into both sides of the endocardium. The VADs were driven asynchronously with the native heart, and the pumping rate was altered from 60 to 30 bpm at 10 bpm intervals in each sampling period. Results: The slope of ESPDR (Ees) was not altered either by pumping rate or bypass flow rate. The Ees significantly decreased after MI (from 26.0 ± 17.1 mm Hg/mm to 16.2 ± 11.8 mm Hg/mm), and reached to a minimum about two weeks later. Conclusion: We can continuously measure the ESPDR during VAD support and accurately evaluate the regional wall motion of myocardium.

Hemodynamic exercise response in calves with an implantable biventricular centrifugal blood pump.

An implantable biventricular assist device (BVAD) has been developed at Baylor College of Medicine using 2 centrifugal blood pumps. The aim of this study was to investigate the exercise-reflex response during nonpulsatile biventricular assistance and to evaluate to which degree the autoregulation of the system would accommodate the changed hemodynamic situation during physical exercise. The Baylor Gyro PI 710 BVAD has been implanted into 2 calves (strain half-Dexter) in a biventricular bypass fashion with native heart remaining. Allowing a 10 day convalescence, 2 animals were subjected to incremental exercise tests. The speed of the treadmill was increased at zero slope from 0.7 mph to 1.5 mph with increments of 0.2 mph every 3 min. During the exercise the pump flows were maintained at a fixed rate (6.93 +/- 0.01 L/min for the left ventricular assist device and 5.36 +/- 1.44 L/min for the right ventricular assist device). Hemodynamic parameters and pump performance were recorded continuously. The cardiac output (CO) and heart rate (HR) increased significantly during the exercise. CO increased from 11.1 +/- 0.3 to 13.1 +/- 0.4 L/min, and HR increased from 99 +/- 7.1 to 114 +/- 2.8 bpm, respectively. Mean aortic pressure, central venous pressure, and left arterial pressure did not change significantly. Also, no change was observed for the left and right pump flows. This totally implantable BVAD showed excellent long-term performance without any mechanical problems. It is feasible to operate without impairment under physical activity. However, the natural heart dominated the hemodynamic response during exercise under BVAD support. The left and the right pump flows did not increase spontaneously with exercise. We therefore conclude that a servo CO control system is necessary to regulate pump flows even during moderate exercise.

Analysis of hemodynamic response with 1/R control on biventricular bypass goat.

A conductance and arterial pressure based method (1/R control) to determine the cardiac output (CO) of a total artificial heart (TAH) was developed to provide a central nervous system with control over the output of TAH. In order to clarify the deference in hemodynamic response between natural heart and 1/R control, biventricular bypass was introduced in the goat. After 2 pneumatically driven sac-type blood pumps were connected to the natural heart, the pulmonary artery was totally clamped to acquire 100% right heart bypass, and the ascending aorta was stenosed to acquire about 60 to 90% left heart bypass; 1/R control was performed substituting the output of the right artificial heart for the CO. The results demonstrated that stable control could be achieved. A discrepancy was often seen between the pulse rate (PR) of the artificial heart and the heart rate (HR) in absolute value. However, the relative changes of PR were quite similar to that of HR for the most part, indicating that the responses of 1/R control were the duplication of natural cardiac responses in normal daily activity.

Pulmonary function after biventricular bypass for autologous lung oxygenation.

Biventricular bypass (BVB) with autologous lung perfusion is an attractive concept to ameliorate systemic inflammatory response by eliminating the oxygenator from the extracorporeal circulation. The effect of biventricular bypass as compared to heart-lung bypass (HLB) on pulmonary function parameters was therefore studied in an experimental model. Heart-lung bypass using a membrane oxygenator or biventricular bypass using the autologous lung for gas exchange was performed for 120 min in an alternating series of 12 mongrel dogs with the heart arrested for 90 min by crystalloid cardioplegia and 30 min reperfusion, followed by a 120 min observation period. Systemic (CO, SVR) and pulmonary hemodynamics (PVR), extravascular lung water (EVLW, double indicator), gas exchange (FiO(2), PaO(2), PaCO(2)), lung compliance (PC), and ventilation (RMV) at FiO(2)=0.5 required to maintain PaCO(2) at 40 mmHg, were measured. Blood cell counts (Leuco, Thrombo) were performed. All animals were weaned from extracorporeal circulation without inotropes, no differences were observed in cardiac output and blood pressures. The following data were obtained in % change from pre-bypass values 60 min after extracorporeal circulation (*:P<0.05, HLB vs. BVB): PVR, +108 vs. +45*; EVLW, +21 vs. -2*; PC, -12 vs. +4*; PaO(2), -8 vs. +21; RMV, +21 vs. +2*; Leuco, -65 vs. -12*; Thrombo, -62 vs. -35*. During and after heart-lung bypass the lung is subject to severe ischemia-reperfusion injury as indicated by edema, cell trapping, and impaired gas exchange. The data demonstrate superior preservation of pulmonary mechanics and function after biventricular bypass as compared to heart-lung bypass and support the clinical strategy of using biventricular bypass in patients with impaired lung function.

Current strategy of temporary circulatory support for severe cardiac failure after operation

Background. After open heart operations about 1% of patients still need temporary circulatory support for severe cardiac failure, and over half of those patients die during or after the support. This study assessed the efficacy of the current strategy of circulatory support. Methods. We assessed clinical outcome of 64 consecutive patients (1.5% of pump cases) who had temporary circulatory support associated with perioperative variables. The results were analyzed by logistic regression analysis. Results. The weaning and discharge rates were 50.0% and 26.7% with venoarterial bypass, 76.2% and 57.1% with biventricular bypass, 87.5% and 37.5% with isolated left ventricular bypass, and 60.0% and 40.0% with pulsatile left ventricular assistance, respectively. Logistic regression analysis identified presupport cardiogenic shock (odds ratio, 9.922) and support type (14.684) as factors significantly associated with nonweaning from the temporary support, and cardiogenic shock (28.268), support duration (2.948), and support type (14.184) as factors significantly associated with mortality during or after the circulatory support. Conclusions. The current strategy of temporary circulatory support improved clinical outcome of patients with severe cardiac failure. Early application of circulatory support before profound cardiogenic shock and proper selection of the support type might be key factors for successful circulatory support postoperatively after operation.

Development of a totally implantable biventricular bypass centrifugal blood pump system

Background. During the past 2 years, the development of a totally implantable biventricular bypass rotary blood pump system has been made. Methods. An extracorporeal gyro centrifugal pump, the CIE3, was miniaturized and developed into the PI601, a totally implantable plastic pump. Two-day anatomic and hemodynamic feasibility studies demonstrated that these two pump systems were easily implantable inside a calf’s abdominal wall, directly under the diaphragm. The priming volume of the pump was 20 mL, with sufficient cardiac outputs at approximately 2,000 rpm and requiring less than 10 W of power. Two-week antithrombogenic screening tests also revealed these pump systems to be quite antithrombogenic. In addition, 1-month system reliability studies demonstrated fail-safe reliable performances. Results and Conclusions. Encouraged by these preliminary studies, the PI601 model was converted to the permanently implantable titanium gyro pump PI702 model. The long-term implantations were initiated approximately 3 months ago, and two such long-term LVAD studies are currently underway with no sign of difficulty (October 10, 1997). They were followed 283 days and 72 days, respectively. Both terminated due to functional inflow obstruction. There were no blood clots or emboli at autopsy.

Mechanical circulatory support for severe heart failure after operation.

To evaluate the clinical results of circulatory support for severe heart failure after operation, we examined 62 patients (39 males and 23 females) who underwent circulatory support for postoperative heart failure from 1984 to 1996. Their ages ranged from 22 to 78 (mean 52) years. In 62 patients, 35 had valvular, 25 had ischemic, and 2 had congenital heart disease. Postoperation, 29 patients underwent venoarterial bypass (VAB), 20 had biventricular bypass (BVB), and 8 had left ventricular bypass (LVB). The remaining 5 patients received a pulsatile left ventricular assist device (LVAD). The weaning and discharge rates of the patients by type of support were 51.7% and 31.0% with VAB, 75.0% and 55.0% with BVB, 87.5% and 37.5% with LVB, and 60.0% and 40.0% with LVAD, respectively. The complete results of this series (64.5% weaning rate and 40.3% discharge rate) were acceptable.

Effect of alveolar hypoxia on segmental pulmonary vascular resistance and lung fluid balance in dogs

In a biventricular bypass preparation with constant-flow perfusion, pulmonary arterial pressure (Ppa), average pulmonary capillary pressure (Ppc), venous pressure (Pv), extravascular lung water volume (EVWd) and capillary permeability-surface area product for urea (PS) were determined in control animals and in animals subjected to alveolar hypoxia. During hypoxia, Ppa increased in a biphasic manner, the site of hypoxic pulmonary vasoconstriction being located in the arterial upstream segment. At baseline, Ppc values were identical in control and experimental animals (3.4 +/- 0.4 vs. 3.6 +/- 0.2 mmHg). During 150 min of airway hypoxia, the rise in Ppc (5.1 +/- 0.3 mmHg) did not exceed the rise in Ppc (4.9 +/- 0.5 mmHg) recorded in control animals at same time interval during normoxic ventilation. EVWd increased during hypoxia to values significantly higher than those obtained in control animals (0.559 +/- 0.036 vs. 0.466 +/- 0.027 mL water g-1 lung). PS remained unchanged at baseline level throughout experiments in both groups of animals. Present data suggest that lung oedema formation during alveolar hypoxia may be caused by increased transcapillary fluid loss preferentially through transcellular hydraulic pathways in capillary endothelial cells.

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.

Development and initial testing of a permanently implantable centrifugal pump.

To be able to salvage heart failure patients, the need for an economical permanent ventricular assist device is increasing. To meet this increasing demand, a miniaturized centrifugal blood pump has been developed as a permanently implantable device. The Gyro permanently implantable model (PI-601) incorporates a sealless design with a blood stagnation free structure. The pump impeller is magnetically coupled to the driver magnet in a sealless manner. This pump is atraumatic and antithrombogenic and incorporates a double pivot bearing system. A miniaturized actuator was utilized in this system in collaboration with the University of Vienna. The priming volume of this pump is 20 ml. The overall size of the pump actuator package is 53 mm in height and 65 mm in diameter, 145 ml of displacement volume, and 305 g in weight. Testing to date has included in vitro hydraulic performance and hemolysis. This pump can provide 5 L/min against a 110 mm Hg total pressure head at 2,000 rpm and 8 L/min against 150 mm Hg at 2,500 rpm. The normalized index of hemolysis (NIH) value of this pump was 0.0028 g/100 L at 5 L/min against 100 mm Hg. A preliminary anatomical study revealed the possibility of the implantability of 2 such systems in biventricular bypass at a preperitoneal location. This system is feasible for use as a permanently implantable biventricular assist device.

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.

Extracting 1/f fluctuation from the arterial blood pressure of an artificial heart.

We have studied the fluctuations of an artificial circulation for the analysis of the physiological aspects; however, the conventionally used fast Fourier transform (FFT) method cannot separate harmonic oscillations, such as respiratory and Mayer waves, from the 1/f fluctuation, which has been though to represent underlying fractal dynamics. Fractal structure was shown in the strange attractor with chaotic dynamics, which is thought to be a flexible and intelligent system. In this study, the coarse-graining spectral analyzing (CGSA) method was utilized to quantitatively evaluate the proportion of the 1/f fluctuation in the total power in the frequency domain and to analyze artificial circulation in the whole system. We implanted two pneumatically actuated ventricular assist devices as biventricular bypasses (BVBs) in chronic animal experiments using 4 healthy adult goats. To compare the natural and prosthetic circulation of each experimental animal, the BVB-type complete prosthetic circulation model with electrically induced ventricular fibrillation was adopted. All hemodynamic parameters of natural and prosthetic circulation were recorded under awake conditions and calculated with the use of a personal computer. With the use of the CGSA method, time-series data of the hemodynamics were analyzed and fractal percentages, extracting the 1/f fluctuation from a given time series, were calculated. Fractal percentages of the arterial blood pressure were 85.8 +/- 10.7% and 82.0 +/- 7.3% with natural and artificial circulation, respectively (not significant [NS]). 1/f fluctuation showed the characteristics of being fractal in a time series. The fractal structure showed robustness and error resistance in nonlinear dynamics. Therefore, our results suggest that the circulatory regulatory system of the artificial heart may have desirable characteristics such as error resistance.

Biventricular Bypass with Oxygenation for Postcardiotomy Ventricular Failure.

Between January 1984 and March 1995, biventricular bypass (BVB) with oxygenation was used in 17 patients for postcardiotomy ventricular failure at the Heart Institute of Japan, Tokyo Women's Medical College. Of the 17 patients, 12 (70.6%) were weaned from the circulatory support, and 8 (47.1%) were discharged from the hospital. The time interval from the end of cardiopulmonary bypass to the start of BVB was significantly shorter in weaned patients than in unweaned patients. The duration on support also has been shortened significantly in the last 6 years, compared with the earlier 6 years. Causes of death were severe heart failure or ventricular arrhythmia in 6 patients and multiple organ failure in 3 patients. These results suggest that early application and timely weaning from biventricular bypass with oxygenation might be the effective circulatory support of choice for treatment of postcardiotomy ventricular failure.

Strange Hemodynamic Attractor Parameter with 1/R Total Artificial Heart Automatic Control Algorithm

To evaluate the automatic control algorithm of the total artificial heart (TAH) as an entity, and not just as parts, a non-linear mathematical analyzing technique including chaos theory was utilized. Chronic experiments on the biventricular bypass type artificial heart implantation were performed in healthy adult goats after the natural ventricles were removed. Hemodynamic time series data were recorded under the awake standing condition with TAH 1/R and fixed driving. Time series data were recorded on a magnetic tape and analyzed on a personal computer system with an A-D converter. Using the nonlinear mathematical technique, the time series data were embedded into the phase space and the Lyapunov numerical method was carried out for the quantitative evaluation of the sensitive dependence on the initial condition of the reconstructed attractor. Calculation of the largest Lyapunov exponents suggested that the reconstructed attractor of the left pump output during TAH 1/R control was a larger dimensional strange attractor, a characteristic pattern of deterministic chaos. A total system indicating chaotic dynamics was thought to be a flexible and intelligent control system. Thus, our results suggest that 1/R TAH control may be suitable for the biventricular assist type total artificial heart.

Chronic nonpulsatile blood flow. III. Effects of pump flow rate on oxygen transport and utilization in chronic nonpulsatile biventricular bypass

The relationship between blood flow and oxygen transport was studied in five calves with chronic nonpulsatile biventricular bypass. Seven days was allowed for recovery from the effects of anesthesia and operation; the natural heart was then fibrillated. Pump flows were maintained at nominal rates of 90, 100, or 120 ml ·kg -1 · min for 1 week each, with the sequence varied from experiment to experiment. Venous and arterial blood samples were taken at rest for blood gas analysis. Serum lactate analysis was done twice a week, on the third and seventh days after each pump flow change. Serum catecholamine levels were assayed on the seventh day of each flow rate. Progressive exercise tests were also conducted during each test segment. Basal oxygen consumption of a 4-month-old calf was 6.3 ± 0.3 ml · kg -1 · min -1. The mixed venous oxygen tension decreased when pump flow rate was reduced (29.6 ± 1.0, 28.3 ± 1.2, and 23.8 ± 0.9 mm Hg at 120, 100, and 90 ml · kg -1 · min -1 of pump flow, respectively), and oxygen extraction increased linearly when pump flow rate was reduced. Hemoglobin concentration significantly affected oxygen extraction rate. Serum lactate concentration increased significantly at a 90 ml · kg -1 · min -1 perfusion compared with concentrations at other pump flow rates (7.81 ± 2.42 mEq/L at 90 ml · kg -1 · min -1 vs 0.71 ± 0.19 and 0.73 ± 0.81 mEq/L at 100 and 120 ml · kg -1 · min -1, respectively; p < 0.01, analysis of variance, Scheffe F test). Maximum oxygen extraction during exercise was 78%. These results suggest that a critical flow level between 90 and 100 ml · kg -1 · min -1 maintains oxidative metabolism in the calf with chronic nonpulsatile flow. The resulting oxygen delivery was slightly higher than that indicated in the literature. Maximal oxygen extraction was normal. (J T HORAC C ARDIOVASC S URG 1996;111:863-72)