Biomedical subjects

K Fukamachi

Publications and source records attributed to K Fukamachi.

At least 73 records · Page 4Linked to original sources

PubMedDate not supplied

Initial in vivo tests of an electrohydraulic actuated total artificial heart.

The authors are involved in developing a total artificial heart (TAH) for permanent human use. This device was designed to fit human anatomy, and it has housings made of carbon fiber-epoxy composite and titanium. Tissue valves and protein coating of blood contacting surfaces minimize the need for anticoagulants. A continuously reciprocating electrohydraulic actuator is packaged between two alternately ejecting and passively filling ventricles. The control system varies the pump rate to maintain average left ventricular filling at 90%. This TAH in vivo successively progressed through 1, 5, 9, and 45 day implants in calves of 84, 94, 82, and 82 kg preoperative body weights. The operating modes include automatic and fixed rate. The chronic and acute effects of varying the right pump displaced stroke volume indicated the need for it to be limited to 85% of that of the left for stable hemodynamics at maximum flow. The pump exhibited afterload insensitive and preload sensitive performance. Pump output ranged from 4.0-9.5 L/min at left atrial pressures of 7-16 mmHg at pump rates of 80-160 beats/min in these four experiments. These data suggest that this device will meet clinical hemodynamic requirements; it has the potential for total implantable cardiac replacement.

Animals↗

PubMedDate not supplied

Hemodynamic changes with posture in calves with total artificial heart.

Hemodynamic changes with posture, sitting versus standing, were analyzed in five Holstein calves with the Cleveland Clinic-Nimbus TAH. This total artificial heart (TAH) has a left master alternate control mode that adjusts the pump rate and consequently pump flow proportional to the pulmonary venous return to the left pump (AUTO period). However, in this series of experiments, the pump reached its maximum beat rate within 1-5 days post operatively, after which pump flow could not increase (MAX period). Hemodynamic parameters (RAP, LAP, PAP, AoP, and pump flow) were obtained every 15-20 min throughout the experiments for as long as 120 days and averaged for each posture for each period. During the AUTO period, the flow while standing was significantly higher than that while sitting (standing: 8.7 +/- 0.2 L/min; sitting: 7.5 +/- 0.4 L/min; p < 0.05), and the systemic vascular resistance (SVR) was significantly lower (standing: 895 +/- 93 dyne.sec.m-5; sitting: 1,041 +/- 124 dyne.sec.m-5; p < 0.05). During the MAX period, the AoP and SVR standing were significantly lower than those sitting (AoP standing: 91 +/- 7 mmHg; AoP sitting: 98 +/- 7 mmHg; p < 0.05; SVR standing: 652 +/- 75 mmHg; SVR sitting: 730 +/- 96 mmHg; p < 0.05). The Cleveland Clinic-Nimbus TAH responded well to these changes in position, increasing pump flow and maintaining the AoP during the AUTO period.

Animals↗

PubMedDate not supplied

The effects of radiation therapy on the tissue capsule of soft tissue implants.

A prosthesis has been developed for cosmesis after lumpectomy surgery for breast carcinoma. The device is saline filled and percutaneously adjustable in volume to permit an optimal cosmetic result after surgical wound healing. A series of 24 studies of 18 weeks' duration using the adult rabbit animal model were first used to study tissue capsule formation around textured versus smooth surface control implants and to evaluate the effects of volume adjustments on the tissue capsule. Single or multiple adjustments of implant volume had no effect on tissue capsule thickness or morphology. Because lumpectomy surgery is invariably followed by radiation therapy, a series of six studies was then conducted to determine the effects of a typical course of radiation therapy on tissue capsule formation. One week after device implantation, a 4 x 4 cm field including the implant was irradiated with 5,000 rad (200 rad/day x 5 days/week x 5 weeks). The animals were maintained for a 6 week period after radiation treatment. After sacrifice, the implants were removed, and the tissue capsules studied using conventional histologic techniques, including scanning and transmission electron microscopy. There was no statistically significant difference in tissue capsule thickness compared to nonirradiated controls. Tissue capsule morphology, however, differed markedly. Radiation therapy decreased angiogenesis, cellularity, and the inflammatory cell response to the implants. Qualitatively, radiation treatment seemingly improved rather than compromised the connective tissue response to the implants.

Animals↗

PubMedDate not supplied

Adaptation of tissue to a chronic heat load.

Determination of the chronic effect of heat on tissue is one of the important issues facing mechanically actuated total artificial heart (TAH) development. In an effort to characterize this effect, implantations of heating devices producing constant heat fluxes of 0.04 watts/cm2, 0.06 W/cm2, and 0.08 W/cm2 were performed in 11 calves (H-series). Heated disks were implanted adjacent to lung and muscle tissue for a period of 7 weeks. Temperature sensors were placed at the surface as part of the heater assemblies. The results showed that initially, temperature elevations above body temperature (delta T) were 6.4 +/- 0.6 degrees C, 4.5 +/- 0.2 degrees C, and 1.8 +/- 0.5 degrees C at the muscle heater surface for 0.08, 0.06, and 0.04 W/cm2, respectively. At 2 weeks after implant delta T values changed to 5.5 +/- 0.6 degrees C, 3.4 +/- 0.2 degrees C, and 1.8 +/- 0.2 degrees C, respectively. Seven weeks after implant, delta T values decreased to 3.7 +/- 1.2 degrees C, 2.8 +/- 0.1 degrees C, and 0.8 degrees C for 0.08, 0.06, and 0.04 W/cm2, respectively. The authors think this change is attributable to an adaptive response of the tissue to increase heat dissipation through angiogenesis. Results from three TAH cases indicated that at two measured tissue interfaces, delta T decreased by 1 degrees C during a 15 day period. At the same time, the waste heat (volts x current in-flow x afterload to the blood) remained constant at 11.1 +/- 0.5 W during this period. This decrease in delta T corresponded to that observed for the H-series experiments at the higher heat fluxes. Thus, it appears that adaptation observed in the H-series experiments also is seen for tissues surrounding heat sources such as the TAH.

Adaptation, Physiological↗

PubMedDate not supplied

Assessment of circulating blood volume in calves with a total artificial heart.

Measurement of the circulating blood volume (CBV) is essential to a proper understanding of the hemodynamic performance of total artificial hearts (TAHs). Recently, the authors employed CBV measurements using indocyanine green dye in calves with a TAH. The advantages of this method over previous methods using radionuclides include simplicity, low cost, and the capability of repeated and frequent measurements. Reproducibility of the measurements was demonstrated in three normal calves with a relative standard deviation of 3.9 +/- 2.4%. CBV was measured in eight calves with the Cleveland Clinic-Nimbus TAH and compared with that of seven calves that underwent mitral valve replacement. Small standard deviations in pre operative values in both TAH and mitral valve replacement groups demonstrated the precision of CBV measurements. Although there was no change in CBV in the mitral valve replacement group, CBV in the TAH group increased to more than twice the pre operative value after 2 weeks. Although the right atrial pressure increased similarly after TAH implantation, there was no correlation (r = 0.08) between the right atrial pressure and CBV, which suggested a possible inaccuracy in estimating CBV from the right atrial pressure. A negative correlation between the hematocrit value and CBV suggested that hemodilution might be one of the causes of anemia observed in our TAH animals.

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PubMedDate not supplied

A comprehensive hematologic study in calves with total artificial hearts.

Thromboembolism and infection remain potential threats for long-term circulatory assist and replacement devices. The alteration of the hemostatic system and of blood cell functions caused by device implantation may predispose the recipient to these complications. Many sensitive coagulation assays and the technology of flow cytometry would be powerful tools for this investigation. The availability of such immunologic technologies for animal species other than humans has yet to be established. In a series of in vitro tests we found that the following assays, among others, are usable in calves: TAT, TxB2, platelet surface glycoprotein IIbIIIa, and membrane aminophospholipid. F1.2, D-dimer, beta TG, PF-4, and platelet surface expression of GMP-140 and receptors for fibronectin, thrombospondin, and vWF were not measurable. A sustained mild decrease in hematocrit levels in six calves with the Cleveland Clinic-Nimbus total artificial heart for 11-120 days was attributed to an increase in circulating blood volume, but not to red blood cell damage. Whole blood platelet aggregation was suppressed only for the first 3 post operative days, with decreased GPIIbIIIa expression. Polymorphonuclear phagocytosis, chemotaxis, and superoxide anion production were not altered. Device infection and thromboembolism occurred in one of 13 cases overall.

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PubMedDate not supplied

Anatomic fitting studies of a total artificial heart in heart transplant recipients. Critical dimensions and prediction of fit.

Anatomic fitting studies of the Cleveland Clinic-Nimbus total artificial heart were performed in 33 patients undergoing heart transplantation. The pump fit in the pericardial space in 20 men (80%) and 4 women (50%). There was no significant difference between the Fit and Non-Fit groups in external chest dimensions. Among 42 intrathoracic dimensions, the distance from the center of the mitral valve to the diaphragm (Fit: 5.6 +/- 2.2 cm, Non-Fit: 3.6 +/- 0.4 cm, p < 0.00001) and the distance from the caudal end of the pulmonary valve to the diaphragm (Fit: 9.4 +/- 1.6 cm, Non-Fit: 6.3 +/- 0.8 cm, p < 0.0001) were the most critical. To predict anatomic fit, an index (A x B x C) was obtained from chest X-ray measurements (A, the craniocaudal distance from the dorsal region of the 8th left rib to the left diaphragm; B, the maximum left chest width; and C, the maximum anteroposterior sternum-vertebrae dimension). The pump fit in 88.5% of the patients with an index above 1200 cm3, whereas it fit in only 14.3% of the patients with an index below 1200 cm3 (p < 0.001). This index was an easily obtainable, good predictor of anatomic fit.

Diaphragm↗

PubMedDate not supplied

In vitro evaluation of automatic control performance of a total artificial heart with changes in pump orientation.

Unlike in animal experiments, the pump orientation of a total artificial heart (TAH) can change remarkably in humans with the recipient's posture (upright, supine, or prone), thus affecting its filling characteristics. The left master alternate control mode of the Cleveland Clinic-Nimbus (CC-N) TAH adjusts beat rate by maintaining the left pump at 90% filling, producing a Frank-Starling like preload sensitivity. In order to verify that the CC-N TAH functions properly regardless of the gravity effects on pump filling, the preload sensitivity curves of the CC-N TAH were evaluated on a mock circulatory loop with the simulated supine (right pump up) and prone (left pump up) positions in humans. The right preload sensitivity was slightly higher when the right pump was up versus down, and likewise the left preload sensitivity was higher when the left pump was up versus down. Despite these gravity effects on pump filling, right and left preload sensitivity remained within physiologic range and the automatic control of the CC-N TAH functioned properly without significant postural effects.

Animals↗

PubMedDate not supplied

Platelets are deposited early post-operatively on the leaflet of a mechanical heart valve in sheep without post-operative anticoagulants or antiplatelet agents. A scanning electron microscopic observation of the pyrolytic carbon surface in a mechanical heart valve.

Pyrolytic carbon has been used for mechanical heart valves as a thromboresistant, wear resistant, and fatigue resistant material. Thrombosis and thromboembolism, however, remain major mechanical heart valve associated complications and may frequently occur during the early post-operative period. In depth morphologic studies on blood-pyrolytic carbon surface interactions are limited. The purpose of this study was to evaluate the blood compatibility of the pyrolytic carbon surface of St. Jude Medical mechanical heart valves that were implanted in the mitral position of sheep without the administration of post-operative anticoagulants or antiplatelet agents for 2, 4, and 6 weeks. Almost the entire leaflet and orifice ring surfaces were observed by scanning electron microscopy. Although the surfaces appeared clean macroscopically, when observed by electron microscopy, the surface were mottled, mainly by solitary platelets and aggregations. There were only a few leukocytes or red blood cells observed. No fibrin clots were observed on the leaflets. The density of platelet deposition was higher in the vicinity of the pivots and near the edges of the leaflets. The sizes of the platelet aggregations decreased with longer duration. The outer surfaces of the pivot guards were covered by various amounts of deposition composed of platelet aggregations and thrombi. Thus, the administration of antiplatelet agents is recommended during the early post-operative period after mechanical heart valve implantation.

Animals↗

PubMedDate not supplied

Novel device to change left ventricular shape for heart failure treatment: device design and implantation procedure.

The Myocor Myosplint is designed to decrease left ventricular (LV) wall stress by changing LV shape, thus improving contractile function in dilated hearts. This shape change is accomplished by surgically placing three Myosplints perpendicular to the LV long axis, drawing the LV walls inward, and creating a symmetric, bilobular LV. Specially designed instruments aid in the precise delivery of these devices. The purpose of this study was to test the safety and feasibility of the procedure in dogs. Dilated cardiomyopathy was induced in 40 healthy dogs (26.3+/-1.7 kg) by ventricular pacing at 230 beats per minute for an average of 25+/-4 days. Using epicardial echocardiography, we placed the Myosplints across the LV chamber, avoiding the major coronary arteries, papillary muscles, and mitral valve. Once placed, the Myosplints were used to draw the LV walls inward to a prescribed distance. In all cases, we successfully implanted three Myosplints without using cardiopulmonary bypass. There were no complications related to the device or procedure. Myosplint implantation to change LV shape is safe and repeatable on a beating cardiomyopathic canine heart. Further study of the procedure will be needed in humans.

Animals↗

PubMedDate not supplied

A novel miniature ventricular assist device for hemodynamic support.

The HemoDynamics Systems enabler is a new cardiac assist pump that can expel blood from the left ventricle and provide pulsatile flow in the aorta. We evaluated the efficacy of the 18 Fr enabler. The enabler was inserted from the left ventricular apex into the ascending aorta in eight sheep. Heart failure (mild, moderate, and severe) was induced by microsphere injection into the coronary arteries to reduce cardiac output by 10-30%, 31-50%, and more than 50% from baseline, respectively. The enabler was activated, and its flow was increased to approximately 2.0 L/min. Hemodynamic variables were recorded before and after activation. In moderate heart failure, cardiac output and mean aortic pressure increased from 2.3 +/- 0.6 L/min and 59 +/- 12 mm Hg before assist to 2.8 +/- 0.6 L/min and 70 +/- 8 mm Hg at 30 minutes after activation, respectively (p < 0.01). Left atrial pressure decreased from 17 +/- 3 to 13 +/- 4 mm Hg (p < 0.05). Similar findings were observed in mild and severe heart failure. Despite its small diameter, the enabler significantly improved the hemodynamics of failing hearts and may potentially serve as a means of peripheral left ventricular support. Further study is warranted.

Animals↗

PubMedDate not supplied

Anatomic study for in vivo evaluation of a total artificial heart in calves.

A poor fit will negate any physiologic evaluation of an implantable total artificial heart (TAH). Fifteen Holstein calves (weight, 65-111 kg) were used to measure intrathoracic dimensions for TAH design, to find correlations between intrathoracic and external parameters for preoperative animal selection, and to suggest minor modifications for fitting a TAH in calf chests. The following dimensions were found to be critical to avoid compromising venous return: 1) mitral annulus center (MVC)-sternum, 10.4 +/- 1.0 cm; 2) tricuspid annulus center (TVC)-sternum, 9.8 +/- 1.6 cm; 3) MVC-TVC, 5.5 +/- 0.4 cm; 4) MVC-diaphragm, 3.4 +/- 0.8 cm; 5) MVC-left chest wall, 4.5 +/- 0.9 cm; and 6) TVC-right chest wall, 4.5 +/- 1.0 cm. These dimensions had no statistically significant correlation with body weight, but three of them did with the following external parameters: 1) bronchial carina-sternum on chest radiograph, p less than 0.05; 2) dorsoventral dimension at xiphoid, p less than 0.05; and 3) circumference at the caudal end of the scapula, p less than 0.05. Based on these results, the port orientation of the left housing of this electrohydraulic TAH designed for humans was modified for in vivo evaluation in calves. No other pump features required change. These data should prove useful to others involved in TAH development.

Animals↗

PubMedDate not supplied

Optimal timing for application of ventricular assist devices in patients who cannot be weaned from cardiopulmonary bypass. An experimental study.

Missing the moment for application of ventricular assist devices (VAD) may be one of the major causes of multiple organ failure in patients who are to be weaned from cardiopulmonary bypass (CPB) with the aid of VAD. To determine the optimal timing for application of VAD in such patients, we examined the effect of a CPB assist on cardiac functional recovery from severe global ischemia using an experimental canine system. In the present study we created myocardial ischemia by clamping the aorta for 20 minutes (Group I; N = 7) or 45 minutes (Group II; N = 11) under normothermic CPB. The reliability of the method in creating severe cardiac failure was confirmed by testing the levels of adenosine triphosphate (ATP), creatine phosphate (CP), and lactate. After reperfusion of the myocardium, the heart was assisted by a totally vented CPB. The left ventricular end-systolic pressure-volume relationship (Emax), which is a load-independent index of contractility, was obtained every 15 minutes for up to 120 minutes of reperfusion. The Emax revealed that the function of the damaged heart recovers exponentially with time after reperfusion. From curves of the functional recovery of the heart, CPB support appeared to be beneficial for the first 60 minutes after reperfusion, and aided in the recovery of cardiac function in hearts damaged by global myocardial ischemia. However, CPB assist thereafter may not be effective in further improving cardiac function. We therefore concluded that the decision to use VAD should be determined by cardiac function by 60 minutes of reperfusion to avoid prolonging CPB time.

Adenosine Triphosphate↗

PubMedDate not supplied

Effect of respiration on the arterial pressure wave in calves with nonpulsatile biventricular bypass.

The possibility of idioperipheral pulsation in calves with chronic nonpulsatile biventricular bypass has been previously reported. To test the hypothesis that both spontaneous respiration and mechanical ventilation are the cause of pulsation in the arterial pressure recording in calves with nonpulsatile biventricular bypass, two protocols were used to generate data. Both right and left ventricles were bypassed using two centrifugal pumps followed by electrical fibrillation in seven calves. In protocol 1, the spontaneous respiratory rate was increased in awake calves by carbon dioxide gas inhalation. In protocol 2, the animals were anesthetized and intubated to control ventilation, and data were collected as the ventilation rate or tidal volume was changed in a stepwise fashion, as well as when the ventilation was stopped for several seconds. The results of protocol 1 showed good correlation between the arterial pulse rate and spontaneous respiratory rate (Y = 1.03 X, r = 0.822, p < 0.001). The results of protocol 2 showed that the relationship between the ventilation rate and the arterial pulse cycle was identical (Y = X, r = 1.000, p < 0.001), and no pulsation was seen when the ventilator was stopped. The authors conclude that the arterial pulsation observed in calves with nonpulsatile biventricular bypass is caused by respiration.

Animals↗

PubMedDate not supplied

Continuing development of the Cleveland Clinic-Nimbus total artificial heart.

A completely implanted total artificial heart (TAH) is under development by Nimbus, Inc., and the Cleveland Clinic Foundation (CCF). Key features of the system include an electrohydraulic energy converter, an automatic control system that produces a Frank-Starling response, and dual ventricles composed of graphite-epoxy and titanium with gelatin blood contacting surfaces. The system is controlled by a single substrate, hybridized microcircuit (the hybrid). Fabrication of the TAH control hybrid has recently been completed and testing begun. Its design emphasizes simplicity, reliability, and efficiency. Particular attention was given to optimizing thermal management. Externally controlled TAH systems have been used in eight in vivo experiments of up to 120 days' duration. In the last two of these experiments, a variable volume device was also implanted with excellent results. In vivo use of the system has demonstrated the Frank-Starling pump response, but the systems quickly reach maximum output with the bovine animal models. Human fitting studies, including adult patients undergoing heart transplantation, demonstrated satisfactory fit of the pump within the pericardium without compression of the vascular structures or chest wall. Measurements of chest circumference, plain chest films, and transesophageal echocardiograms should provide reliable predictions of pump fit in the majority of patients.

Animals↗

PubMedDate not supplied

Development of a magnetically operated artificial urethral sphincter. Chronic effects of compression on the skin structure and blood flow.

The artificial urethral sphincter (AUS) has been in clinical use for more than 20 years. Currently available AUS devices, however, are difficult to use and not entirely reliable. A magnetically operated AUS is currently under the development. Although the skin between the magnets will be compressed all day long, little information exists on the effects of chronic pressure on the skin structure and blood flow. In five miniature pigs, two internal magnets and one control metal disk were implanted subcutaneously at three different positions, and external magnets with differing magnetic forces were applied to the skin overlying the internal magnets for six weeks. In four pigs, the skin blood flow was measured by a laser Doppler flow meter applying different pressures. Compression of 10 mmHg preserved normal skin morphology in all but one animal where blood flow had not recovered 2 weeks after surgery. Compression of 20 mmHg for 6 weeks, however, produced pressure ulcers in all five cases (p < 0.05 vs. 10 mmHg group). The skin blood flow declined for pressures exceeding 20 mmHg (0 mmHg: 4.3 +/- 1.2, 10 mmHg: 4.3 +/- 3.3, 20 mmHg: 2.6 +/- 2.7 ml/min/100 g). We concluded that the magnetically operated AUS should use a magnetic coupling with a pressure less than 10 mmHg exerted on the interposing skin.

Animals↗

PubMedDate not supplied

Effects of a total artificial heart right stroke volume limiter on left-right hemodynamic balance.

In a completely implantable total artificial heart (TAH), the left-right flow difference attributable to higher volumetric efficiency of the right pump and bronchial artery shunting has always been a significant problem. The automatic control of the Cleveland Clinic-Nimbus TAH accommodates for the left-right flow difference when the beat rate is below maximum (AUTO range). However, at its maximum beat rate (MAX), high left atrial pressure (LAP) (greater than 25 mmHg) with relatively low right atrial pressure (RAP) (less than 8 mmHg) were observed both in vitro and in vivo, suggesting the need for a stroke volume limiter (SVL) of the right pump. In vitro volume loading tests showed 10%, 15%, and 20% SVLs prevented a disproportionate increase of LAP. In vivo studies in five Holstein calves also showed a balanced LAP-RAP relationship with 10% and 15% SVLs at MAX. The left pump flow was not affected by this range of SVLs either in vitro or in vivo. Pulmonary function was maintained with either size SVL, with autopsies revealing absence of pulmonary congestion and minimal pleural effusions in two calves surviving for more than 1 month. Although additional studies are needed to determine the appropriate size of the SVL, both 10% and 15% SVLs were effective in maintaining left-right hemodynamic balance in this TAH.

Animals↗

PubMedDate not supplied

Progress in Cleveland Clinic-Nimbus total artificial heart development.

A totally implantable, Cleveland Clinic-Nimbus total artificial heart (TAH) uses electrohydraulic energy conversion and an automatic left master-alternate mode control scheme, with a filling sensitivity of 1.0 l/min/mmHg and a maximum output of 9.5 l/min. The TAHs were tested in 12 calves for 1-120 days with normal major organ and blood cell function. Post-operative suppression of platelet aggregation recovered by the second post-operative week. The gelatin-coated pump surface generally was clean without any anticoagulants and free from infection. Embolism, which occurred in two cases, was caused by complications attributable to fungal infection in a Dacron graft and by thrombus formed around a jugular vein catheter. A system with a hybridized microcircuit controller in the interventricular space has been tested successfully in the three most recent cases, with a peak device surface temperature elevation of 6.5 degrees C. Heat effects were confined to the tissues immediately adjacent to the hottest spots. The carbon fiber-reinforced epoxy housing and 60 ml butyl rubber compliance chamber showed good tissue compatibility with a thin, fibrous tissue capsule. The transcutaneous energy transmission system and the internal battery functioned well as designed in the most recent animal implant.

Animals↗