In vivo testing of a magnetically suspended centrifugal pump designed for long-term use

The life of currently-available centrifugal pumps is limited to no more than three days. As a magnetically suspended centrifugal pump (MSCP) contains no shaft or seal, it could be expected to have a longer life expectancy. The MSCP was evaluated in a chronic animal model using eight adult sheep. Left ventricular assist with the MSCP was instituted between the left atrium and the descending aorta. The flow rates ranged from 2.5 to 6.0 L/min. The duration of the experiments ranged from 14 to 60 days. No mechanical failure occurred. The plasma free hemoglobin levels remained within an acceptable range (3-19 mg/dL). No reduction in the counts of red blood cells or platelets was observed. Thrombus formation within the MSCP was recognized in one pump. The main reason for termination was thromboembolism derived from the circuits. Three types of regulation methods (constant rotational speed, constant motor current, and controlled motor current) were also investigated. Regulation by a constant motor current mode altered the pressure-flow (P-Q) characteristics, and thereby, a steadier pump flow was obtained compared with regulation in the constant rotational speed mode. Moreover, the controlled motor current mode can change the P-Q relationship. These results demonstrate that the MSCP is a promising device for long-term use.

Control of the pressure flow relationship with a magnetically suspended centrifugal pump in a chronic animal experiment

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.

In vivo and in vitro evaluation of the pulsatile mode of a magnetically suspended centrifugal pump

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.

More than 1 year continuous operation of a centrifugal pump with a magnetically suspended impeller

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 computer simulation study of isometric contraction of latissimus dorsi muscle used for cardiac assistance

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.

Pulmonary hypertension caused by medial hypertrophy associated with aortic stenosis and preductal coarctation

A 7-month-old female infant with aortic stenosis, preductal coarctation, and pulmonary hypertension underwent operation. Intraoperative lung biopsy revealed marked medial hypertrophy of the pulmonary arterioles. This histopathology is compatible with persistent pulmonary hypertension in the newborn. She is alive about 5 years after the operation, but pulmonary hypertension remains. The pathogenesis is discussed.

Chronic animal experiment with magnetically suspended centrifugal pump

We have been developing a new type of centrifugal pump for long-term use. The magnetically suspended centrifugal pump (MSCP) contains no shaft and seal so that long life expectancy is predicted. Paracorporeal left ventricular (LV) assist circulation between the left atrium and the descending aorta was instituted using sheep. The flow rates ranged from 2.5-5.5 L/min. The sheep that lived the longest (46 days) died of an embolism as a result of the thrombus in the pump. No thrombus formation was observed in other pumps. Plasma free hemoglobin levels ranged from 9 to 18 mg/dl, which led to the conclusion that the hemolysis level remained within an acceptable range. Two driving modes were compared. The slope of the pressure-flow relationship plot under a constant motor current mode was steeper than that under a constant rotational speed mode, and thus, the flow fluctuation decreased. In conclusion, the MSCP is durable for more than a month at the current stage of development and is a promising device for long-term ventricular assist.

Evolution of phosphagen kinase V. cDNA-derived amino acid sequences of two molluscan arginine kinases from the chiton Liolophura japonica and the turbanshell Battilus cornutus

The cDNAs of arginine kinases from the chiton Liolophura japonica (Polyplacophora) and the turbanshell Battilus cornutus (Gastropoda) were amplified by polymerase chain reaction (PCR), and the complete nucleotide sequences of 1669 and 1624 bp, respectively, were determined. The open reading frame for Liolophura arginine kinase is 1050 nucleotides in length and encodes a protein with 349 amino acid residues, and that for Battilus is 1077 nucleotides and 358 residues. The validity of the cDNA-derived amino acid sequence was supported by chemical sequencing of internal tryptic peptides. The molecular masses were calculated to be 39,057 and 39,795 Da, respectively. The amino acid sequence of Liolophura arginine kinase showed 65-68% identity with those of Battilus and Nordotis (abalone) arginine kinases, and the homology between Battilus and Nordotis was 79%. Molluscan arginine kinases also show lower, but significant homology (38-43%) with rabbit creatine kinase. The sequences of arginine kinases could be used as a molecular clock to elucidate the phylogeny of Mollusca, one of the most diverse animal phyla.

[A successful surgical repair of total anomalous pulmonary venous connection associated with Williams syndrome]

The surgical correction was performed successfully in a 14-year-old boy with total anomalous pulmonary venous connection (type Ia) associated with Williams syndrome. The diagnosis was made at the age of 3 and he had been well until the age of 13 when sudden chordal rupture caused severe mitral regurgitation and supraventricular tachyarrhythmia. The operational procedure includes common pulmonary vein and left atrium anastomosis through Gersony-Malm approach, chordal reconstruction of mitral valve with 4-0 Core Tex sutures. His postoperative course has been well without the sign of venous obstruction. As far as we know, this is the first documentation of a case of Williams syndrome associated with total anomalous pulmonary venous connection.

Plasma levels of brain and atrial natriuretic peptides elevate in proportion to left ventricular end-systolic wall stress in patients with aortic stenosis

Brain natriuretic peptide (BNP) is a novel cardiac hormone secreted predominantly from the ventricle. We examined the plasma levels of BNP and atrial natriuretic peptide (ANP) in 13 patients with aortic stenosis undergoing corrective surgery. Preoperative plasma BNP and ANP levels correlated highly with preoperative left ventricular end-systolic wall stress (ESS) (r = 0.96, p < 0.0001 and r = 0.95, p < 0.0001, respectively). Moreover, between preoperative and late postoperative states, the difference of the plasma levels of BNP and ANP correlated with the difference of ESS. In two patients with elevated ESS and quite high preoperative plasma BNP (> 1000 pg/ml), rapid decrease of the plasma level after operation was observed. These results suggest that synthesis and secretion of BNP and ANP are stimulated by the increase of left ventricular end-systolic wall stress in patients with aortic stenosis.

Reperfusion causes significant activation of heat shock transcription factor 1 in ischemic rat heart

BACKGROUND

The myocardial protective role of heat shock protein (HSP) has been demonstrated, and there has been increasing interest in stress response in the heart. We examined the DNA-binding activity of heat shock transcription factor (HSF), by which the transcription of heat shock genes is mainly regulated, during heat shock or ischemia/reperfusion in isolated rat heart.

METHODS AND RESULTS

Rat hearts were isolated and perfused with Krebs-Henseleit buffer by the Langendorff method. Whole-cell extracts were prepared for gel mobility shift assay using oligonucleotides containing the heat shock element, which is present upstream of all heat shock genes. Induction of mRNAs for HSP70, HSP90, and GRP78 (glucose-regulated protein) was examined by Northern blot analysis. Although the activation of HSF during global ischemia was weak and rapidly attenuated, postischemic reperfusion induced a significant activation of HSF. In addition, although HSP70 mRNA was hardly induced during ischemia, its burst induction was detected during postischemic reperfusion. Supershift assays using specific antisera for HSF1 and HSF2 revealed that ischemia/reperfusion as well as heat shock induced the activation of HSF1 in hearts. Although the expression of HSP70 mRNA during heat shock was more vigorous than the expression during ischemia/reperfusion, the induction of HSP90 mRNA in postischemic reperfusion was significantly greater than that in heat shock.

CONCLUSIONS

Our findings demonstrated that reperfusion causes a significant activation of HSF1 in ischemia-reperfused heart. The striking contrast between the induction of HSP70 mRNA and that of HSP90 mRNA suggests the presence of regulatory mechanisms other than HSF.

A compressive type skeletal muscle pump as a biomechanical energy source

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.

Kinetic mechanism of Na+ channel depression by taurine in guinea pig ventricular myocytes

To examine effects of taurine on the kinetics of the Na+ channel current (I(Na)), action potentials and whole-cell Na+ currents were recorded from single ventricular myocytes of guinea pigs. Kinetic parameters for the activation and inactivation of I(Na) were determined in accordance with the first-order kinetic model. Changes in the kinetic parameters were assessed before and after taurine exposure (5-50 mM). While taurine at concentrations higher than 10 mM decreased the peak I(Na) by ca. 15%, the agent did not alter the reversal potential and the maximum Na+ conductance (GNa). Taurine shifted the steady-state inactivation (h(infinity)) curve toward the negative potential direction and decreased the slope of h(infinity). Concomitantly, the slope of the steady-state activation (m(infinity)) was also slightly decreased and the rate of inactivation in the large potential region (-40 to -30 mV) slightly increased, whereas the rate of the activation appeared to remain unchanged. It is suggested that taurine alters the surface charge of the membrane and reduces the number of charges moving upon activation and inactivation of channels, thereby reducing I(Na).

Analysis of right ventricular function during bypass of the left side of the heart by afterload alterations in both normal and failing hearts

This study investigated the mechanism of right ventricular failure during bypass of the left side of the heart by precisely assessing right ventricular function with use of a conductance catheter. Bypass of the left side of the heart was established with a centrifugal pump in 10 mongrel dogs weighing 11 to 19 kg. Right ventricular function during left heart bypass was evaluated by two parameters that were both derived from measurement of relative change in right ventricular volume by the conductance catheter technique. One parameter was the right ventricular end-systolic pressure-volume relationship as a load-independent index, and the other was the peak right ventricular pressure-right ventricular stroke volume relationship as a "force-velocity relationship." These parameters were measured in both normal and failing hearts while afterload was increased by bilateral intrapulmonary balloon inflation. Moreover, changes in these relationships were observed by varying assist ratios of left heart bypass from 0% to 100%. Failing heart models were induced by normothermic aortic clamping for 20 minutes. The right ventricular end-systolic pressure-volume relationship in normal hearts did not change, irrespective of the assist ratio of left heart bypass, whereas that in failing hearts decreased from 4.25 +/- 1.41 mm Hg/ml without bypass of the left side of the heart to 3.53 +/- 1.30 mm Hg/ml after 100% assist of left heart bypass (p < 0.05). In the peak right ventricular pressure-right ventricular stroke volume relationship, right ventricular stroke volume was almost constant in normal hearts when afterload was increased regardless of the assist ratio of left heart bypass. Moreover, right ventricular stroke volume was maintained at a higher level during bypass of the left side of the heart compared with that without left heart bypass. However, that slope of the relationship in failing hearts was inversely linear and became significantly steeper after 100% assist of bypass of the left side of the heart compared with that without left heart bypass (-0.131 +/- 0.042 versus -0.051 +/- 0.038, p < 0.005). Therefore ++these two slopes of the relationship intersected at a point that was considered the critical point of afterload during bypass of the left side of the heart. In other words, right ventricular stroke volume was decreased by 100% left heart bypass above the critical point of afterload. In conclusion, this study demonstrates not only that bypass of the left side of the heart results in an increase in right ventricular stroke volume in both normal and failing hearts at the physiologic range of afterload, but also that right ventricular function against higher afterload is impaired by 100% assist of bypass of the left side of the heart in failing hearts.

Thyrotropin induces G1 cyclin expression and accelerates G1 phase after insulin-like growth factor I stimulation in FRTL-5 cells

We have investigated the mechanism by which TSH pretreatment potentiates insulin-like growth factor I (IGF-I)-induced DNA synthesis in FRTL-5 cells. As previously described, pretreatment with TSH increased IGF-I-induced DNA synthesis, suggesting that the effect of TSH is mediated through the cAMP pathway. TSH and A kinase activators required at least 12 h to precondition cells to respond to IGF-I stimulation. The presence of cycloheximide abolished the effect of TSH to increase IGF-I-induced DNA synthesis. When the time course of thymidine uptake after IGF-I addition was studied, TSH pretreatment increased the maximum DNA incorporation and shortened the G1 phase interval. These results indicated that some proteins induced by TSH are required for the effect of TSH on IGF-I activity, and the proteins are important for cell cycle progression. Cyclins are key regulators of the cell cycle; therefore, we investigated the expression of cyclins D1 and E after TSH stimulation. TSH- and A kinase-activating agents increased the expression of cyclins D1 and E after 24 h. The same amounts of cyclins D1 and E induced by IGF-I were increased after TSH pretreatment. TSH pretreatment induced the expression of G1 cyclin in FRTL-5 cells, and IGF-I caused the accumulation of enough G1 cyclins to drive the cell cycle from G1 to S phase in a short time, which accounts for the effect of TSH on IGF-I induced DNA synthesis.

Protection against reperfusion-induced arrhythmias by human thioredoxin

Adult T-cell leukemia-derived factor (ADF), identified in the supernatant of adult T-cell leukemia (ATL) cell culture, is a human homologue of thioredoxin and consists of 104 amino acids; it has two redox-active half-cysteine residues in an exposed active center. Human thioredoxin has many biological activities, including growth promotion, cell activation, and a catalase-like radical scavenging activity. We examined the protective effect of human thioredoxin (h-thioredoxin) against reperfusion-induced arrhythmias in an isolated rat heart model with 10-min regional ischemia followed by 30-min reperfusion. Male Wistar rats were assigned to six groups: a control, a superoxide dismutase (SOD 8 x 10(4) IU/L), and a catalase group (1 x 10(6) IU/L), and three groups treated with h-thioredoxin [approximately .01 microM (TRX-I group), approximately 0.1 microM (TRX-II group), and approximately 1 microM (TRX-III group)]. In the early reperfusion period, h-thioredoxin reduced the incidence of ventricular fibrillation (VF) to 8% in the TRX-II group (p < 0.01) from the control value of 75%. SOD and catalase reduced the incidence of VF to 43 and 33%, respectively (NS). During the entire reperfusion period, the incidence of VF in the SOD group was 79%, as compared to 83% in the control group. In the catalase and TRX-II groups, the incidence of VF was significantly reduced to 42 and 25%, respectively. These findings indicate that SOD failed to protect against the reperfusion-induced arrhythmias. h-Thioredoxin exerted a protective effect against these arrhythmias; a concentration of approximately 0.1 micro was the most effective.

Suppression of channel conductance by diacetyl monoxime in guinea pig and embryonic chick cardiomyocytes

AIM

To examine the effects of diacetyl monoxime (DAM), and putative dephospohrylating agent, on conductance of the cardiac Ca, Na, and K channels.

METHODS

The Ca (ICa), Na (INa), and K (IK) currents were recorded in single ventricular myocytes from guinea pigs and chick embryos before and after addition of DAM using the whole-cell voltage-clamp technique.

RESULTS

DAM 10 mmol.L-1 reduced rapidly the amplitudes of ICa (by about 30%), INa (by about 25%), and IK (by 25%-50%) without alterations of the voltage-dependence.

CONCLUSION

DAM was a channel inhibitor of the unique type having nonselective phosphatase activities.

Action potential duration-stabilizing action of taurine in guinea pig ventricular myocytes

To examine taurine actions on the rate of repolarization of action potentials (AP), L-type Ca2+ (ICa), late outward K+ (Ik) and the inward rectifier currents as affected by the external Ca2+ concentrations ([Ca2+]o), whole-cell voltage-clamp and current-clamp experiments were conducted in guinea pig ventricular myocytes. At a high (3.6 mM) [Ca2+]o, 10 mM taurine suppressed both ICa and IK, shortened AP duration and decelerated the rate (-dV/dt) of terminal repolarization of AP. In contrast, at a low (0.9 mM) [Ca2+]o, taurine intensified both ICa and IK, lengthened AP duration and accelerated -dV/dt. However, at either [Ca2+]o, the resting membrane potential was slightly hyperpolarized, and the inward rectifier, current examined by the ramp-pulse protocol remained unaffected by taurine. Taurine is suggested to maintain a stable AP duration by altering the inward Ca2+ and IK in the opposite directions, depending on [Ca2+]o. The relevance of the stabilizing action of taurine on the AP duration to its reported anti-arrhythmic efficacies is discussed.

Natriuretic peptide receptors in human artery and vein and rabbit vein graft

Natriuretic peptides elicit their biological effects by elevation of cGMP through activation of two biologically active receptors: natriuretic peptide A receptor, which shows high affinity to atrial and brain natriuretic peptides, and natriuretic peptide B receptor, which is specific to C-type natriuretic peptide. To elucidate the implications of the natriuretic peptide system in arteries and veins, we examined the cGMP production in response to atrial and C-type natriuretic peptide and gene expressions of biologically active natriuretic peptide receptors in human gastroepiploic artery, internal mammary artery, and saphenous vein. Atrial natriuretic peptide augmented cGMP production more potently by one order of magnitude in arteries than in veins. C-type natriuretic peptide stimulated cGMP production weakly and equally in these vessels. Analyzed by reverse transcription-polymerase chain reaction, gene expression of natriuretic peptide A receptor was four times more abundant in arteries than in veins. Gene expression of natriuretic peptide B receptor was approximately the same between these vessels. We also studied the responsiveness to atrial and C-type natriuretic peptide in rabbit jugular vein grafted into carotid artery. In arterialized vein grafts 4 weeks after operation, the effects of atrial and C-type natriuretic peptides on cGMP production did not change from those in jugular veins. In conclusion, atrial natriuretic peptide stimulates cGMP production more potently in arteries than in veins due to the preferential expression of natriuretic peptide A receptor in arteries. These observations support the distinct roles of natriuretic peptides in cardiovascular homeostasis.

A new magnetically suspended centrifugal pump: in vitro and preliminary in vivo assessment

To overcome problems derived from the shaft within the conventional centrifugal pump, we have been developing a new centrifugal pump, namely a magnetically suspended centrifugal pump (MSCP), which has no shaft and operates as a noncontacting and bearingless pump. The impeller is suspended magnetically between the magnetic bearing and the driving motor. Hemolysis tests were performed in comparison with the Biopump (BP80, BioMedicus). The index of hemolysis (IH) was significantly lower in the MSCP than in the Biopump. In addition, a smaller gap in the MSCP induced lower hemolysis. In preliminary studies using mongrel dogs, the layer of thrombus adherent to the impeller was observed in a few hours, which impaired the pumping efficiency. However, by using an impeller coated with silicone, no aggregations of platelets or fibrin on the impeller were observed in 24 h of continuous pumping. In conclusion, the MSCP had a gentler influence on blood cells than the Biopump, and the impeller coated with silicone may contribute to the long-term pumping of the MSCP.