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Characteristics of a dual chambered, single layered skeletal muscle powered pump (DCSLP) and a single chamber, multilayered pump (SCMLP) made from similar masses of untrained latissimus dorsi muscle (LD) were compared. For the DCSLP, 16 canine LDs (51.5 +/- 1.6 g) were wrapped in a "figure eight" around two parallel mandrels, whereas for the SCMLP, LDs were made in 10 by wrapping the LD (54 +/- 8.5 g) twice around one mandrel. Chamber compliance and pump isovolumic peak developed pressure (PDP), stroke volume (SV), stroke work (SW), and ejection fraction (EF) of single contractions were measured. In six of the DCSLP dogs (LV), heart left ventricular stroke volume (LVSV) and left ventricular stroke work (LVSW) were determined. Stimulation parameters were the same for all. Student's t-test (* = p < 0.05) was used for statistical analysis. Dual chambered, single layered skeletal muscle powered pumps with a diastolic volume/mass ratio of 0.63 were more compliant than SCMLPs with a ratio of 0.37. Single chamber, multilayered pumps generated slightly higher PDP, but this was significant only at 60 mmHg preload. At a preload of 15 and an afterload of 120 mmHg, DCSLPs had higher SV (10.7 +/- 1.1 ml) and SW (0.98 +/- 0.14 x 10(6) ergs) than SCMLPs (6.8 +/- 0.7 ml* and 0.58 +/- 0.08 x 10(6) ergs*), or their LV counterparts (5.3 +/- 0.9 ml and 0.84 +/- 0.22 x 10(6) ergs).(ABSTRACT TRUNCATED AT 250 WORDS)
The purpose of this study was to assess right ventricular (RV) performance during left heart bypass (LHB) and to determine the optimum LHB driving conditions to preserve RV performance. LHB was established with a centrifugal pump in eight mongrel dogs weighing 11-19 kg. Failing heart models were induced by normothermic aortic clamping for 20 min. RV volume was measured by a conductance catheter, and RV performance was evaluated by two parameters. One was the slope of the RV end-systolic pressure-volume relationship (ESPVR) as a load independent index, and the other was the peak RV pressure (PRVP)-RV stroke volume (RVSV) relationship as a "force-velocity relationship." These parameters were measured during varying assist ratios of LHB at 0% to 100% of pulmonary artery flow, and varying afterload as induced by bilateral intrapulmonary balloon inflation. In failing hearts, RV ESPVR showed an inverse correlation, with the assist ratio of LHB significantly decreasing from 4.23 +/- 1.35 (mmHg/ml) to 3.52 +/- 1.30 (mmHg/ml; P < 0.05) after 100% LHB assist. The correlation between PRVP and RVSV also was inversely linear, the slope of this correlation becoming significantly steeper after 100% LHB assist compared to that without LHB (-0.131 +/- 0.042 vs. -0.051 +/- 0.038, P < 0.005). These two slopes intersected, and this intersection was considered the critical point of afterload above which RVSV was decreased by LHB compared to that without LHB. In addition, reducing the assist ratio made the slope of the PRVP-RVSV correlation significantly more gentle (70%: -0.072 +/- 0.037 vs. 100%: -0.131 +/- 0.042, P < 0.05), with the intersection of the two slopes shifting rightward (i.e., higher afterload). Consequently, the critical level of afterload at 70% LHB assist was significantly higher than that at 100% LHB assist (70%: 38.1 +/- 6.9 vs. 100%: 29.2 +/- 6.8, P < 0.05). Therefore, RV performance against afterload was improved by reducing the assist ratio of LHB. This study demonstrates that RV performance is impaired by full LHB assist if the RV afterload is above the critical level, and that reducing the assist ratio may improve RV performance against afterload.
The arterial ketone body ratio, which reflects the hepatic mitochondrial redox potential (NAD+/NADH), decreases markedly during cardiopulmonary bypass (CPB). One of the reasons for arterial ketone body ratio reduction may be hepatic hypoperfusion during CPB. To evaluate the hepatic circulation under nonpulsatile CPB, the authors used color Doppler ultrasonography to measure the portal venous flow (PVF) in 24 adult patients before, during (aortic clamping and rewarming period), and after CPB. Nonpulsatile hypothermic CPB was performed at a flow rate of 2.4 L/min/m2. PVF was calculated from the product of mean flow velocity and cross-sectional area of the portal vein. PVF was maintained during CPB at 0.44 +/- 0.13 and at 0.54 +/- 0.18 L/min/m2. PVF (%) in relation to systemic blood flow was obtained by calculating PVF/CI or PVF/PI, where CI is the cardiac index and PI is the perfusion index. PVF (%) before, during, and after CPB was 18.3 +/- 9.3, 18.5 +/- 5.5, and 17.4 +/- 6.7%, respectively. In conclusion, PVF was maintained during nonpulsatile CPB at a flow rate of 2.4 L/min/m2 and depended upon systemic blood flow.
The purpose of this study was to assess the applicability of the latissimus dorsi muscle in situ as an energy source for a circulatory assist device. A pneumatic chamber, devised by the authors, was inserted beneath the muscle and compressed by contractions of the muscle so that muscle contractile power was converted into pneumatic pressure. The optimal insertion position of the chamber beneath the latissimus dorsi muscle, and the influence of chamber size on generated pneumatic pressure, were investigated. The pneumatic chamber functioned better when it was placed in a proximal position (third intercostal space) than in a middle or distal position. Using a mock circuit, the performance of the pneumatic chamber as an energy source for a circulatory assist device was evaluated. The pneumatic chamber was able to generate power sufficient to drive a right ventricular assist device as far as stroke work was involved. When the pneumatic chamber was operated with a high afterload, it could even be an energy source for aortic counterpulsation.
The purpose of this study was to assess the applicability of the conditioned latissimus dorsi muscle as an energy source for circulatory assist devices. The authors developed a pneumatic chamber as a muscle actuator. The pneumatic chamber placed between latissimus dorsi muscle and chest wall was compressed by the burst stimulated muscle and, thereby, converted muscle contractile power into pneumatic pressure. The authors report the performance of the implanted pneumatic chamber at a chronic phase, and the capability of the conditioned muscle in situ as an energy source for circulatory assist devices. Six adult mongrel dogs were used. At the first operation, a pacemaker for muscle conditioning and the pneumatic chamber were implanted. After 12 weeks of muscle conditioning, the performance of the pneumatic chamber with conditioned muscle was evaluated. The pressure generating capability of a chamber buried in fibrous adhesions was reduced to approximately 65% of that of a chamber without adhesions. The stroke volume and stroke work of the assist device driven by the developed pneumatic pressure were measured. The maximum stroke work of the circulatory assist was greater than the stroke work of the right ventricle, but less than that of the left ventricle. In respect to stroke volume, the pneumatic chamber could drive the circulatory assist device against not only a pulmonary range of afterload, but also a systemic range of afterload, when high pre load was available. These results indicate that the compressive skeletal muscle pump with conditioned latissimus dorsi muscle generates acceptable hemodynamic work for right ventricular bypass or aortic counterpulsation. In the long-term, the interface between tissue and actuator is the major obstacle to developing a muscle powered assist device.
We studied the effects of 4.8 muM prenylamine on transmembrane potentials in isolated guinea pig papillary muscles using a conventional microelectrode technique and compared them with those of 36.9 microM lidocaine. Prenylamine reduced Vmax at 1 Hz increasingly as the external potassium, [K]o, was increased from 2.7 to 10 mM. The reduction was also increased as the driving rate was increased from 0.25 to 5 Hz. The rate-dependent depression was less in 2.7 and 8.1 mM with 7.2 mM [Ca]o and more in 5.4 and 8.1 mM [K]o with 1.8 mM [Ca]o. Prenylamine produced a marked delay in the recovery of Vmax in premature responses inserted between constant driving stimuli at 0.25 Hz. The delay was also less in the former two, and more in the latter two media. Thus the effects of prenylamine on Vmax were more rate dependent and less [K]o-dependent than those of 36.9 microM lidocaine. At the diastolic interval of 100 ms, prenylamine depressed the overshoot, action potential duration at 0 mV level (APDo) and Vmax in premature responses more markedly than did 36.9 microM lidocaine, the differences of the effects being more significant for the first two. The results are interpreted as representing the calcium-antagonistic property of prenylamine of which lidocaine appears to be devoid.
BACKGROUND AND AIM OF THE STUDY: Supravalvular aortic stenosis (SAS) has been surgically treated by either single-sinus or bisinus patch repair. This article reviews intermediate to long-term results of repair in patients with SAS at our institute. METHODS: Between 1974 and 1995, eight patients underwent surgical repair for SAS. The age range was 1.3 to 14 years (mean 7.3 years). The morphology was the discrete type in seven patients and the diffuse type in one patient. The pressure gradient across the obstruction was 20 to 105 mmHg (mean 68 mmHg). Two patients in the early period of the series underwent single-sinus patch repair, and six underwent bisinus patch repair (pantaloon-shaped patch, extended aortoplasty). RESULTS: There were no operative deaths, and the mean pressure gradient was reduced to 23 mmHg (p < 0.001) in the early postoperative period. The median follow-up period was 8.0 years (1.8-17.3 years). One patient with diffuse type SAS required reoperation 12.8 years later due to progression of the stenosis, and died after the operation. The remaining seven patients were alive and well at the last follow-up, when the pressure gradient ranged from 6 to 31 mmHg (reoperation excluded). CONCLUSION: Surgical repair for discrete type SAS provides satisfactory results in the intermediate to long-term follow-up.
With scanning electron microscopy, we examined the behavior of platelets and leukocytes on the luminal surface of small caliber polyurethane grafts implanted into small arteries of dogs. Thirty-five grafts were implanted to the carotid and/or femoral arteries. The animals were treated with aspirin and/or DN9693, an inhibitor of phosphodiesterase. In the group treated with aspirin (40 mg/kg i.v.), the deposition of platelets on the luminal surface of the implanted polyurethane grafts was suppressed and the luminal surface was covered with adherent leukocytes. Fibrin nets were formed on the adherent leukocytes. In addition, the adhesion of leukocytes on the grafts was considerably suppressed in the group treated with DN9693 (50 micrograms/kg/min i.v.), and the formation of fibrin nets was markedly reduced. In contrast, in the control group the luminal surface was covered with numerous platelets and some leukocytes, which formed thrombi. These findings suggest that leukocytes adhere primarily to the prosthetic graft and play an important role in the initiation of fibrin formation.
We report a case of a 4-year-old girl with interruption of the aortic arch without a patent ductus arteriosus or intracardiac shunts. The anomaly was successfully corrected with the use of a 14 mm Dacron prosthetic graft to bypass the interrupted segment. The postoperative course was uneventful.
To overcome problems derived from the shaft within conventional centrifugal pumps, we have developed a new centrifugal pump, the magnetically suspended centrifugal pump (MSCP), which has no shaft and operates as a bearingless centrifugal pump. The impeller is suspended freely and centrally by magnetic force within the pump. Hemolysis tests were performed in comparison with the Biopump. Index of hemolysis and destruction of platelets were significantly lower in the MSCP than in the Biopump. Animal studies were designed to evaluate the durability and antithrombogenicity of the MSCP. Short-term animal studies were performed using two mongrel dogs. Left heart bypass was established with the MSCP. After 3 hr, the layer of thrombus adherent to the surface of the polycarbonate impeller impaired pumping efficiency. However, using the impeller coated with silicone, no thrombus was observed on the impeller after continuous pumping for 24 hr. In addition, long-term animal studies were performed using two sheep. Left heart bypass was established with the MSCP containing an impeller coated with silicone. In one sheep, the MSCP ran for 14 days without problems in pumping performance and showed no thrombus within the pump. In the other sheep, the MSCP ran for 15 days, and showed no thrombus on the impeller. During each experiment, plasma free hemoglobin levels were less than 15 mg/dl. The MSCP induced less hemolysis than did the Biopump, and the MSCP containing an impeller coated with silicone demonstrated the potential to run for 14 days without thrombus formation within the pump.
To overcome problems with the shaft seal in conventional centrifugal pumps, the authors have been developing a magnetically suspended centrifugal pump (MSCP) that operates as a valveless, sealless, and bearingless pump. The prototype of the MSCP was modified with respect to size of the volute diffuser and impeller blade profiles. A hemolysis test in vitro using a new version of the MSCP was performed in comparison with a commercially available centrifugal pump. The test circuit for the hemolysis test comprised a blood reservoir, a pump, and polyvinyl tubes, and was filled with fresh heparinized bovine blood. The pumping conditions were a flow rate of 5 L/min and a pump head afterload of 100 mmHg. The index of hemolysis in the MSCP was significantly lower than that in the Biomedicus pump (0.0035 +/- 0.0025 versus 0.0097 +/- 0.0056 g/100 L, p < 0.05). Reduction in the platelet count during pumping also was lower in the MSCP compared with the Biomedicus pump at both 6 hrs and 12 hrs of pumping (p < 0.01). This MSCP may be advantageous for extended use of assist devices, not only from the theoretical point of view, but in a practical sense after the results of the current hemolysis test.
Effects of diacetyl monoxime on the fast Na+ current were examined by the whole-cell voltage-clamp method in embryonic chick ventricular myocytes. Diacetyl monoxime (10-20 mM) decreased the duration and amplitude of the action potential and depressed the amplitude of the peak fast inward Na+ current by about 25 (10 mM)-45% (20 mM), without affecting other I-V parameters. Neither the activation and inactivation kinetics of the Na+ channels, such as the time to peak current and the time constant of inactivation, nor the steady state characteristics of the inactivation and activation were affected by diacetyl monoxime. It also did not alter the window conductance and the recovery kinetics from inactivation (reactivation). Hence, diacetyl monoxime suppresses the fast Na+ current, without affecting the time-dependent and voltage-dependent kinetics.
The authors have been developing a centrifugal pump with a magnetically suspended impeller (MSCP) designed for total artificial heart and long-term ventricular support. The MSCP consists of a magnetic bearing, an impeller and housing, and a driving motor. The impeller is suspended by a magnetic bearing, therefore providing contact free rotation of the impeller inside the pump. This study was designed to evaluate long-term durability and nonthrombogenicity of the MSCP in a chronic sheep model. The blood contacting surfaces of the pump and conduits were completely modified by a heparin immobilization technique (Hepaface). The MSCP was placed paracorporeally as a left heart bypass between left ventricle and descending aorta in three adult sheep. Coumadin was given orally to maintain prothrombin time at 15-20 sec. The coagulation and hematologic parameters, including plasma free hemoglobin, were periodically monitored throughout the experiment. Under daily movement in the cage, the pump could produce average flow rates of 3-6 L/min (50-100 ml/kg) at 1,700-2,000 rpm. Although the arterial pulse contour decreased, there was no physiologic deterioration. The axial impeller excursion monitored by a position sensor was < 25 microns. Plasma free hemoglobin level remained at < 5 mg/dl throughout the experiment. There was no increase in the motor current, which indicates no massive thrombus formation around the impeller. One experiment was terminated at 70 days due to Hall sensor dysfunction of the motor. The retrieved pump was entirely free from thrombus formation. There was no detectable thrombus formation inside the pump or the inflow and outflow conduits. Hematologic, renal, and hepatic parameters remained within the normal range throughout the experiment. The other two sheep have survived for more than 395 and 41 days without major complication. These studies demonstrated that the MSCP has significant potential for long-term use.
A magnetically suspended centrifugal pump (MSCP) has been developed for long-term ventricular support. Effective torque to blood of the MSCP is exactly proportional to a motor current because of no friction inside the MSCP. The authors have devised new driving modes using these characteristics and applied it to a chronic animal experiment. Three driving modes were compared: 1) a constant rotational speed (N), 2) a constant motor current (I), and 3) a controlled motor current (CI). In two of nine sheep, the MSCPs were operated by the N and in seven by the I mode. The motor current and the rotational speed were always monitored. The CI mode was studied by altering the resistance of the vessels. In the I mode, the rotational speed varied depending upon the pressure head, and the slope of the pressure-flow (P-Q) relationship was steeper than that of the N mode, so that the pump flow was stabilized. In the CI mode, in which the motor current increased to compensate for the decrease in pump flow as the rotational speed increased, the P-Q slope was effectively controlled when the resistance was changed. The MSCP was able to control the P-Q slope without monitor of the pump flow. Various driving modes could be selected according to changes in resistance.
The authors have been developing a magnetically suspended centrifugal pump (MSCP). They have devised a pulsatile mode for the MSCP, which was generated by altering rotational speed. This article describes in vitro and in vivo studies with the pulsatile mode of the MSCP. Hemolysis tests were performed in two identical circuits to compare the nonpulsatile (NP) mode and the pulsatile (P) mode. In vivo studies were performed in sheep. First, biventricular assisted circulation was instituted in the left heart with the MSCP and in the right heart with the Biopump. The native heart was induced to ventricular fibrillation. Second, a left ventricular assisted circulation was instituted as the native heart was beating. An inflow cannula was inserted into the left atrium in one sheep and into the left ventricle in the other. The normalized indices of hemolysis of the NP and P groups were 0.0025 +/- 0.0018 g/100 L, and 0.0032 +/- 0.0024 g/100 L (N = 4, not significant). During ventricular fibrillation in the P mode, the pulse pressure was 14 mmHg (the rotational speed: 1,500 to 2,600 rpm). In a beating heart, at atrial withdrawal, the pulse pressure increased from 10 to 24 mmHg (2,100 +/- 500 rpm), while at ventricular withdrawal, it decreased from 17 to 40 mmHg (2,000 +/- 500 rpm) on P mode. The MSCP in pulsatile mode did not increase hemolysis. At ventricular withdrawal, it was easier to produce a pulsation than at atrial withdrawal. The pulsatile mode of the MSCP is applicable to a left ventricular assist system.
This study was designed to investigate the feasibility of a skeletal muscle pump employing latissimus dorsi muscle (LDM) for cardiac assistance. We developed and used a 2-dimensional mathematical model for LDM to investigate how the size of pneumatic balloons (30, 38, and 45 ml) and the three different locations (proximal, center, and distal) affect the pressure applied to the balloon by LDM. The computer simulation was performed by coding a visco-elastic and nonlinear 2-dimensional program that employed the finite element method (FEM). The muscle specific parameters of LDM were obtained from animal experiment results. The model is based on Hill's characteristic equation and composed of a contractile component and a passive element. The simulation results indicated that the intermediate and largest sized balloon lead to the highest and the lowest power (volume reduction per unit time interval), respectively. On the other hand, when the balloon is inserted in the distal LDM, the power is lower than in the other two positions, regardless of the balloon size. The above results suggest that the optimal size of the balloon should be selected depending on the muscle specific parameters of the actuator, and that the balloon should be inserted either in the proximal portion or center of the actuator.