Long-term durability test of axial-flow ventricular assist device under pulsatile flow.

A long-term durability test was conducted on a newly developed axial-flow ventricular assist device (VAD) with hydrodynamic bearings. The mock circulatory loop consisted of a diaphragm pump with a mechanical heart valve, a reservoir, a compliance tank, a resistance valve, and flow paths made of polymer or titanium. The VAD was installed behind the diaphragm pump. The blood analog fluid was a saline solution with added glycerin at a temperature of 37 °C. A pulsatile flow was introduced into the VAD over a range of flow rates to realize a positive flow rate and a positive pressure head at a given impeller rotational speed, yielding a flow rate of 5 L/min and a pressure of 100 mmHg. Pulsatile flow conditions were achieved with the diastolic and systolic flow rates of ~0 and 9.5 L/min, respectively, and an average flow rate of ~5 L/min at a pulse rate of 72 bpm. The VAD operation was judged by not only the rotational speed of the impeller, but also the diastolic, systolic, and average flow rates and the average pressure head of the VAD. The conditions of the mock circulatory loop, including the pulse rate of the diaphragm pump, the fluid temperature, and the fluid viscosity were maintained. Eight VADs were tested with testing periods of 2 years, during which they were continuously in operation. The VAD performance factors, including the power consumption and the vibration characteristics, were kept almost constant. The long-term durability of the developed VAD was successfully demonstrated.

Preclinical study of a novel hydrodynamically levitated centrifugal pump for long-term cardiopulmonary support : In vivo performance during percutaneous cardiopulmonary support.

An extracorporeal centrifugal blood pump with a hydrodynamically levitated impeller was developed for use in a durable extracorporeal membrane oxygenation (ECMO) system. The present study examined the biocompatibility of the blood pump during long-term use by conducting a series of 30-day chronic animal experiments. The ECMO system was used to produce a percutaneous venoarterial bypass between the venae cavae and carotid artery in adult goats. No anticoagulation or antiplatelet therapy was administered during the experiments. Three out of four animals survived for the scheduled 30-day period, and the blood pumps and membrane oxygenators both exhibited sufficient hydrodynamic performance and good antithrombogenicity, while one animal died of massive bleeding from the outflow cannulation site. The animals' plasma free hemoglobin had returned to within the normal range by 1 week after the surgical intervention, and their hemodynamic and biochemistry parameters remained within their normal ranges throughout the experiment. The explanted centrifugal blood pumps did not display any trace of thrombus formation. Based on the biocompatibility demonstrated in this study, the examined centrifugal blood pump, which includes a hydrodynamically levitated impeller, is suitable for use in durable ECMO systems.

Development of a flow rate monitoring method for the wearable ventricular assist device driver.

Our research institute has been working on the development of a compact wearable drive unit for an extracorporeal ventricular assist device (VAD) with a pneumatically driven pump. A method for checking the pump blood flow on the side of the drive unit without modifying the existing blood pump and impairing the portability of it will be useful. In this study, to calculate the pump flow rate indirectly from measuring the flow rate of the driving air of the VAD air chamber, we conducted experiments using a mock circuit to investigate the correlation between the air flow rate and the pump flow rate as well as its accuracy and error factors. The pump flow rate was measured using an ultrasonic flow meter at the inflow and outflow tube, and the air flow was measured using a thermal mass flow meter at the driveline. Similarity in the instantaneous waveform was confirmed between the air flow rate in the driveline and the pump flow rate. Some limitations of this technique were indicated by consideration of the error factors. A significant correlation was found between the average pump flow rate in the ejecting direction and the average air flow rate in the ejecting direction (R2 = 0.704-0.856), and the air flow rate in the filling direction (R2 = 0.947-0.971). It was demonstrated that the average pump flow rate was estimated exactly in a wide range of drive conditions using the air flow of the filling phase.

Change of coronary flow by continuous-flow left ventricular assist device with cardiac beat synchronizing system (native heart load control system) in acute ischemic heart failure model.

BACKGROUND: A novel control system for the EVAHEART left ventricular assist device (LVAD), known as the Native Heart Load Control System (NHLCS), can change the device's rotational speed (RS) in synchrony with the heartbeat. The system enhanced coronary flow (CoF) with the counter-pulse mode in normal goats' hearts, so we examined the change in CoF in goats with acute ischemic heart failure (HF). METHODS AND RESULTS: We studied 14 goats (56.1±6.9kg) with acute ischemic HF induced by coronary microsphere embolization. We installed EVAHEART and ran the device in 4 modes [continuous support, circuit-clamp, counter-pulse (raise RS in diastole), and co-pulse (raise RS in systole)] with 50% or 100% bypass in each mode. In comparison with the circuit-clamp mode, CoF was 121.0±14.1% in the counter-pulse mode and 102.9±7.9% in the co-pulse mode, whereas it was 113.5±10.6% in the continuous mode, with 100% bypass (P<0.05). The same difference was confirmed with 50% bypass. The results indicated that a LVAD in an acute ischemic heart enhanced CoF, and that CoF was greater in the counter-pulse mode and smaller in the co-pulse mode relative to the continuous mode. CONCLUSIONS: By using NHLCS to change CoF, recovery of native heart function with a LVAD has a better prognosis.

Hyperoxic condition promotes an inflammatory response during cardiopulmonary bypass in a rat model.

Systemic inflammatory responses in patients receiving cardiac surgery supported by cardiopulmonary bypass (CPB) significantly contribute to CPB-associated morbidity and mortality. We hypothesized that hyperoxia insufflation aggravates the inflammatory responses and organ damage during CPB. To verify this hypothesis, we investigated the inflammatory responses at high and normal levels of arterial pressure of oxygen (PaO2 ) in the rat CPB model. Rats were divided into a SHAM group, a hyperoxia CPB group (PaO2 > 400 mm Hg), and a normoxia CPB group (PaO2 : 100-150 mm Hg). We measured the serum cytokine levels of tumor necrosis factor-α, interleukin (IL)-6, and IL-10, and biochemical markers (lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase) before, 60, and 120 min after the initiation of CPB. We also measured the wet-to-dry weight (W/D) ratio of the left lung and performed dihydroethidium (DHE) stain reflecting superoxide generation in the lung and liver tissues 120 min after the CPB initiation. In the hyperoxia group, the pro-inflammatory cytokines and biochemical markers significantly increased during the CPB compared with the SHAM, but such increases were significantly suppressed in the normoxia group. However, the increase in anti-inflammatory cytokines was more suppressed in the hyperoxia group than in the normoxia group. The W/D ratio increased significantly more in the hyperoxia group than in the normoxia group. In addition, the DHE fluorescence predominantly increased in the hyperoxia group compared with that in the normoxia group. These data suggest that it is better to avoid too much oxygen insufflation for attenuating organ damage associated with the superoxide production and inflammatory responses during CPB.

Insufflation of hydrogen gas restrains the inflammatory response of cardiopulmonary bypass in a rat model.

Systemic inflammatory responses in patients receiving cardiac surgery with the use of the cardiopulmonary bypass (CPB) significantly contribute to CPB-associated morbidity and mortality. We hypothesized that insufflated hydrogen gas (H2) would provide systemic anti-inflammatory and anti-apoptotic effects during CPB, therefore reducing proinflammatory cytokine levels. In this study, we examined the protective effect of H2 on a rat CPB model. Rats were divided into three groups: the sham operation (SHAM) group, received sternotomy only; the CPB group, which was initiated and maintained for 60 min; and the CPB + H2 group in which H2 was given via an oxygenator during CPB for 60 min. We collected blood samples before, 20 min, and 60 min after the initiation of CPB. We measured the serum cytokine levels of (tumor necrosis factor-α, interleukin-6, and interleukin-10) and biochemical markers (lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase). We also measured the wet-to-dry weight (W/D) ratio of the left lung 60 min after the initiation of CPB. In the CPB group, the cytokine and biochemical marker levels significantly increased 20 min after the CPB initiation and further increased 60 min after the CPB initiation as compared with the SHAM group. In the CPB + H2 group, however, such increases were significantly suppressed at 60 min after the CPB initiation. Although the W/D ratio in the CPB group significantly increased as compared with that in the SHAM group, such an increase was also suppressed significantly in the CPB + H2 group. We suggest that H2 insufflation is a possible new potential therapy for counteracting CPB-induced systemic inflammation.

Development and evaluation of endurance test system for ventricular assist devices.

We developed a novel endurance test system that can arbitrarily set various circulatory conditions and has durability and stability for long-term continuous evaluation of ventricular assist devices (VADs), and we evaluated its fundamental performance and prolonged durability and stability. The circulation circuit of the present endurance test system consisted of a pulsatile pump with a small closed chamber (SCC), a closed chamber, a reservoir and an electromagnetic proportional valve. Two duckbill valves were mounted in the inlet and outlet of the pulsatile pump. The features of the circulation circuit are as follows: (1) the components of the circulation circuit consist of optimized industrial devices, giving durability; (2) the pulsatile pump can change the heart rate and stroke length (SL), as well as its compliance using the SCC. Therefore, the endurance test system can quantitatively reproduce various circulatory conditions. The range of reproducible circulatory conditions in the endurance test circuit was examined in terms of fundamental performance. Additionally, continuous operation for 6 months was performed in order to evaluate the durability and stability. The circulation circuit was able to set up a wide range of pressure and total flow conditions using the SCC and adjusting the pulsatile pump SL. The long-term continuous operation test demonstrated that stable, continuous operation for 6 months was possible without leakage or industrial device failure. The newly developed endurance test system demonstrated a wide range of reproducible circulatory conditions, durability and stability, and is a promising approach for evaluating the basic characteristics of VADs.

Change in myocardial oxygen consumption employing continuous-flow LVAD with cardiac beat synchronizing system, in acute ischemic heart failure models.

Aiming the 'Bridge to Recovery' course, we have developed a novel left ventricular assist device (LVAD) controlling system. It can change the rotational speed of the continuous flow LVAD, EVAHEART, synchronized with the cardiac beat. Employing this system, we have already demonstrated that myocardial oxygen consumption (MVO2), which is considered to be equivalent to native heart load, changes in the hearts of normal goats. Herein, we examined changes in goats with acute ischemic heart failure. We studied 14 goats (56.1 ± 6.9 kg) with acute ischemic heart failure due to coronary microsphere embolization. We installed the EVAHEART and drive in four modes: "circuit-clamp", "continuous support", "counter-pulse", and "co-pulse", with 50 and 100 % bypass. In comparison to the circuit-clamp mode, MVO2 was reduced to 70.4 ± 17.9 % in the counter-pulse mode and increased to 90.3 ± 14.5 % in the co-pulse mode, whereas it was 80.0 ± 14.5 % in the continuous mode, with 100 % bypass (p < 0.05). The same difference was confirmed with 50 % bypass. This means that we may have a chance to change the native heart load by controlling the LVAD rotation in synchrony with the cardiac rhythm, so we named our controller as the Native Heart Load Control System (NHLCS). Employing changeable MVO2 with NHLCS according to the patient's condition may provide more opportunity for native heart recovery with LVAD, especially for patients with ischemic heart diseases.

In vivo evaluation of an in-body, tissue-engineered, completely autologous valved conduit (biovalve type VI) as an aortic valve in a goat model.

Using simple, safe, and economical in-body tissue engineering, autologous valved conduits (biovalves) with the sinus of Valsalva and without any artificial support materials were developed in animal recipients' bodies. In this study, the feasibility of the biovalve as an aortic valve was evaluated in a goat model. Biovalves were prepared by 2-month embedding of the molds, assembled using two types of specially designed plastic rods, in the dorsal subcutaneous spaces of goats. One rod had three projections, resembling the protrusions of the sinus of Valsalva. Completely autologous connective tissue biovalves (type VI) with three leaflets in the inner side of the conduit with the sinus of Valsalva were obtained after removing the molds from both terminals of the harvested implants with complete encapsulation. The biovalve leaflets had appropriate strength and elastic characteristics similar to those of native aortic valves; thus, a robust conduit was formed. Tight valvular coaptation and a sufficient open orifice area were observed in vitro. Biovalves (n = 3) were implanted in the specially designed apico-aortic bypass for 2 months as a pilot study. Postoperative echocardiography showed smooth movement of the leaflets with little regurgitation under systemic circulation (2.6 ± 1.1 l/min). α-SMA-positive cells appeared significantly with rich angiogenesis in the conduit and expanded toward the leaflet tip. At the sinus portions, marked elastic fibers were formed. The luminal surface was covered with thin pseudointima without thrombus formation. Completely autologous biovalves with robust and elastic characteristics satisfied the higher requirements of the systemic circulation in goats for 2 months with the potential for valvular tissue regeneration.

Coronary vascular resistance increases under full bypass support of centrifugal pumps--relation between myocardial perfusion and ventricular workload during pump support.

Coronary circulation is closely linked to myocardial oxygen consumption (MVO(2)), and previous reports have suggested decreased coronary flow (CoF) under left ventricular assist device support. Decreased CoF itself under support is not unfavorable because the native heart can be well unloaded and myocardial oxygen demand is also decreased. There should be an autoregulatory system that would maintain optimal CoF according to oxygen demand; however, the detailed mechanism is still unclear. The aim of the current study is to evaluate the effect of centrifugal pumps on CoF under varied bypass rates in relation to left ventricle workload. A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed in an adult goat (n = 10, 61.3 ± 6.5 kg). We set up the following conditions, including Circuit-Clamp (i.e., no pump support), 50% bypass, and 100% bypass. In these settings, CoF, MVO(2), pressure-volume area (PVA), and coronary vascular resistance (CVR) were measured. In 100% bypass, CoF, MVO(2), and PVA were all decreased significantly from clamp. While in 50% bypass, CoF and MVO(2) decreased from clamp, but not PVA. There was a significant 40% increase in CVR in 100% bypass from clamp. This CVR increase in 100% bypass was possibly due to mechanical collapse of coronary vascular bed itself by pump support or increased vascular tone through autoregulatory system. In clinical settings, we should adjust optimal pump speed so as not to cause this vascular collapse. However, to clarify autoregulatory system of the coronary perfusion, further investigation is ongoing in ischemic and heart failure models.

Flow visualization for different port angles of a pulsatile ventricular assist device.

The "washout effect" inside a blood pump may depend in part on the configuration of the blood pump, including its "port angle." The port angle, which is primarily decided based on anatomical considerations, may also be important from the rheological viewpoint. In our department, a next-generation diaphragm-type blood pump is being developed. In this study, we examined the influence of the port angle on flow conditions inside our new blood pump. Acrylic resin mock pumps with three different port angles (0°, 30°, and 45°) were prepared for flow visualization. Mechanical monoleaflet valves were mounted on the inlet and outlet ports of the mock pumps. Flow conditions within the mock pumps were visualized by means of particle image velocimetry during a half stroke. As a result, a high flow velocity region was seen along the main circular flow from the inlet to the outlet port. This circular flow was almost uniform and parallel to the plane of the diaphragm-housing junction (DhJ) when viewed from the inlet and outlet sides. Moreover, the proportion of high flow velocity vectors in the plane in the vicinity of the DhJ decreased as the degree of the port angle increased. In conclusion, we found that the flow behavior in the plane in the vicinity of the DhJ changed with the port angle, and that a port angle of 0° may be suitable for our diaphragm-type blood pump in view of the washout effect.

Effect of the technique for assisting renal blood circulation on ischemic kidney in acute cardiorenal syndrome.

The technique for assisting renal blood circulation may be a useful therapeutic method in acute cardiorenal syndrome (ACRS), because renal ischemic dysfunction due to the reduced renal blood circulation is a powerful negative prognostic factor in ACRS. We constructed a circuit assisting renal arterial pressure and flow, and performed renal-selective blood perfusion (RSP) to the left kidney in a goat model of ACRS induced by right ventricular rapid pacing (n = 8), with the right kidney left intact as an internal control. Upon induction of ACRS, renal arterial flow (RAF), creatinine clearance (CCr), and renal oxygen consumption (RVO(2)) of the left kidney decreased to 49, 48, and 63% of the respective baseline values accompanied by a significant increase in renal vascular resistance (RVR), and similar results were observed in the right kidney. Then, RSP improved RVR and increased left RAF, CCr, and RVO(2) up to 91, 86, and 93% of baseline values, respectively, without a significant change in systemic hemodynamics. The RSP-treated kidney showed significantly higher CCr and urinary excretion of water and sodium compared to the contralateral kidney. Additional infusion of prostaglandin E(1) with RSP decreased RVR further and enabled the left RAF to increase up to 129% of the baseline value, without a significant change in systemic hemodynamic parameters. The CCr and RVO(2) did not change significantly, and urinary excretion of water and sodium showed a tendency to increase. These findings suggest that the technique for assisting renal blood circulation for both kidneys may offer a new treatment strategy for patients with ACRS.

Alteration of LV end-diastolic volume by controlling the power of the continuous-flow LVAD, so it is synchronized with cardiac beat: development of a native heart load control system (NHLCS).

There are many reports comparing pulsatile and continuous-flow left ventricular assist devices (LVAD). But continuous-flow LVAD with the pulsatile driving technique had not been tried or discussed before our group's report. We have previously developed and introduced a power-control unit for a centrifugal LVAD (EVAHEART®; Sun Medical), which can change the speed of rotation so it is synchronized with the heart beat. By use of this unit we analyzed the end-diastolic volume (EDV) to determine whether it is possible to change the native heart load. We studied 5 goats with normal hearts and 5 goats with acute LV dysfunction because of micro-embolization of the coronary artery. We used 4 modes, "circuit-clamp", "continuous", "counter-pulse", and "co-pulse", with the bypass rate (BR) 100%. We raised the speed of rotation of the LVAD in the diastolic phase with the counter-pulse mode, and raised it in the systolic phase with the co-pulse mode. As a result, the EDV decreased in the counter-pulse mode and increased in the co-pulse mode, compared with the continuous mode (p < 0.05), in both the normal and acute-heart-failure models. This result means it may be possible to achieve favorable EDV and native heart load by controlling the rotation of continuous-flow LVAD, so it is synchronized with the cardiac beat. This novel driving system may be of great benefit to patients with end-stage heart failure, especially those with ischemic etiology.

Development and hydrodynamic evaluation of a novel inflow cannula in a mechanical circulatory support system for bridge to decision.

Recent progress in the development of implantable rotary blood pumps realized long-term mechanical circulatory support (MCS) for bridge to transplant, bridge to recovery, or a destination therapy. Meanwhile, a short-term MCS system is becoming necessary for bridge to decision. We developed a novel inflow cannula for the short-term MCS system, which gives sufficient bypass flow with minimal invasion at insertion, and evaluated its hydrodynamic characteristics. The novel inflow cannula, named the Lantern cannula, is made of elastic silicone reinforced with metal wires. The cannula tip has six slits on the side. This cannula tip can be extended to the axial direction by using an introducer and can be reduced in diameter, and the Lantern cannula enables easy insertion into the left ventricle apex with minimal invasion. The sufficient bypass flow rate can be obtained due to low pressure loss. Moreover, this Lantern shape also resists suction complication around the cannula tip. The pressure loss through the Lantern cannula was measured using a mock circulation and compared with two commercially available venous cannulae (Sarns4882, Terumo, Tokyo, Japan and Stockert V122-28, Sorin Group, Tokyo, Japan), which have almost same diameter as the Lantern cannula. Moreover, the flow patterns around the cannula tip were numerically analyzed by computational fluid dynamics (CFD). Acute animal experiment was also performed to confirm the practical effectiveness of the Lantern cannula. The pressure loss of the Lantern cannula was the lowest compared with those of the commercially available venous cannulae in in vitro experiment. CFD analysis results demonstrated that the Lantern cannula has low pressure loss because of wide inflow orifice area and a bell mouth, which were formed via Lantern shape. The highest bypass flow was obtained in the Lantern cannula because of the low pressure loss under pulsatile condition in in vivo experiments. The Lantern cannula demonstrated superior hydrodynamic characteristics as the inflow cannula in terms of pressure loss due to its specially designed Lantern shape.

Electrocardiogram-synchronized rotational speed change mode in rotary pumps could improve pulsatility.

Continuous-flow left ventricular assist devices (LVADs) have greatly improved the prognosis of patients with end-stage heart failure, even if continuous flow is different from physiological flow in that it has less pulsatility. A novel pump controller of continuous-flow LVADs has been developed, which can change its rotational speed (RS) in synchronization with the native cardiac cycle, and we speculated that pulsatile mode, which increases RS just in the systolic phase, can create more pulsatility than the current system with constant RS does. The purpose of the present study is to evaluate the effect of this pulsatile mode of continuous-flow LVADs on pulsatility in in vivo settings. Experiments were performed on eight adult goats (61.7 ± 7.5 kg). A centrifugal pump, EVAHEART (Sun Medical Technology Research Corporation, Nagano, Japan), was installed by the apex drainage and the descending aortic perfusion. A pacing lead for the detection of ventricular electrocardiogram was sutured on the anterior wall of the right ventricle. In the present study, we compared pulse pressure or other parameters in the following three conditions, including Circuit-Clamp (i.e., no pump support), Continuous mode (constant RS), and Pulsatile mode (increase RS in systole). Assist rate was calculated by dividing pump flow (PF) by the sum of PF and ascending aortic flow (AoF). In continuous and pulsatile modes, these assist rates were adjusted around 80-90%. The following three parameters were used to evaluate pulsatility, including pulse pressure, dp/dt of aortic pressure (AoP), and energy equivalent pulse pressure (EEP = (∫PF*AoP dt)/(∫PF dt), mm Hg). The percent difference between EEP and mean AoP is used as an indicator of pulsatility, and normally it is around 10% of mean AoP in physiological pulse. Both pulse pressure and mean dp/dt max were decreased in continuous mode compared with clamp condition, while those were regained by pulsatile mode nearly to clamp condition (pulse pressure, clamp/continuous/pulsatile, 25.0 ± 7.6/11.7 ± 6.4/22.6 ± 9.8 mm Hg, mean dp/dt max, 481.9 ± 207.6/75.6 ± 36.2/351.1 ± 137.8 mm Hg/s, respectively). In clamp condition, %EEP was 10% higher than mean AoP (P = 0.0078), while in continuous mode, %EEP was nearly equivalent to mean AoP (N.S.). In pulsatile mode, %EEP was 9% higher than mean AoP (P = 0.038). Our newly developed pulsatile mode of continuous-flow LVADs can produce pulsatility comparable to physiological pulsatile flow. Further investigation on the effect of this novel drive mode on organ perfusion is currently ongoing.

Computational fluid dynamic analysis of the flow field in the newly developed inflow cannula for a bridge-to-decision mechanical circulatory support.

The flow field of the newly developed inflow cannula designed for a bridge-to-decision circulatory support was numerically analyzed by computational fluid dynamics. This new cannula has elastic struts at the tip that enable minimal invasive insertion into the left ventricle while maintaining a wide inflow area by its lantern-like tip. The cannula's hydrodynamic loss, including change in pressure loss due to deformation, and its thrombus potential were numerically examined. Hydraulic resistance of the cannula with blood analog fluid was 31 mmHg at the flow rate of 5.0 L/min. There were regions on the inner surface of the struts where the shear rate was <100 s(-1), and these regions can be a potential for thrombus formation, especially at low flow rates or under limited anticoagulant therapy.

Development and long-term in vivo testing of a novel skin-button system for preventing driveline infection of an implantable VAD system.

Driveline infection is a serious complication in long-term therapy using a ventricular assist device (VAD). However, measures taken against this complication have not been sufficient. In this study, we evaluated our newly developed infection-resistant skin-button system against driveline infection of an implantable VAD in a chronic animal study. The skin button is made of two flanges using tissue-compatible segmented polyurethane. The exposed upper layer is made of a nonporous sheet with relative flexibility similar in texture to the skin. In addition, this shape was designed to defuse excessive stress at the edge of the skin caused by the external force put on the driveline. The lower layer, which is implanted subcutaneously, is made of a porous material with a three-dimensional reticular structure. The combination of these two flanges with different features enables the driveline to fix to the skin without epithelial downgrowth and peridriveline pocket formation and can prevent bacterial infection over a prolonged period. Results of 90 days of animal tests, the button maintained secure adhesion to the skin and did not exfoliate without special daily treatments, such as dressing or disinfection, and there were no infections or inflammations at the exit site. This study demonstrates that our newly developed skin-button system can be useful for preventing infections at the driveline exit site.

Neointima-inducing inflow cannula with titanium mesh for left ventricular assist device.

The formation of wedge thrombus is a crucial problem in any left ventricular assist device (LVAD) with a left ventricle apical inflow cannula. We therefore developed a new titanium mesh wrapped inflow cannula expecting to induce autologous neointima to avoid such wedge thrombus formation. We performed animal experiments to evaluate the feasibility of this newly developed inflow cannula with titanium mesh for the induction of autologous neointima. Four calves were implanted with the inflow cannula as well as an EVAHEART centrifugal pump LVAD (Sun Medical Technology Research Corp., Nagano, Japan) for a duration of about 2 months. The titanium mesh was enveloped with neointimal tissue grown from the ventricular endocardium. There was no thrombus formation in any of the blood pumps or around the outside of the inflow cannulas. The histological findings showed that the neointimal tissue consisted of a layer of endothelial cells and fibroblasts. The newly developed inflow cannula using a titanium mesh induces autologous neointima formation, avoiding wedge thrombus formation.

A novel counterpulsation mode of rotary left ventricular assist devices can enhance myocardial perfusion.

The effect of rotary left ventricular assist devices (LVADs) on myocardial perfusion has yet to be clearly elucidated, and several studies have shown decreased coronary flow under rotary LVAD support. We have developed a novel pump controller that can change its rotational speed (RS) in synchronization with the native cardiac cycle. The aim of our study was to evaluate the effect of counterpulse mode, which increases the RS in diastole, during coronary perfusion. Experiments were performed on ten adult goats. The EVAHEART LVAD was installed by the left ventricular uptake and the descending aortic return. Ascending aortic flow, pump flow, and coronary flow of the left main trunk were monitored. Coronary flow was compared under four conditions: circuit-clamp, continuous mode (constant pump speed), counterpulse mode (increased pump speed in diastole), and copulse mode (increased pump speed in systole). There were no significant baseline changes between these groups. In counterpulse mode, coronary flow increased significantly compared with that in continuous mode. The waveform analysis clearly revealed that counterpulse mode mainly resulted in increased diastolic coronary flow. In conclusion, counterpulse mode of rotary LVADs can enhance myocardial perfusion. This novel drive mode can provide great benefits to the patients with end-stage heart failure, especially those with ischemic etiology.

A novel counterpulse drive mode of continuous-flow left ventricular assist devices can minimize intracircuit backward flow during pump weaning.

Recent developments in adjunct therapeutic options for end-stage heart failure have enabled us to remove implanted left ventricular assist devices (LVADs) from more patients than before. However, a safe and proper protocol for pump-off trials is yet to be established, because diastolic backward flow in a pump circuit turns up when it is driven at low-flow conditions. We have developed a novel drive mode of centrifugal pumps that can change its rotational speed in synchronization with the cardiac cycle of the native heart. The purpose of this study was to test-drive this novel system of a centrifugal pump in a mock circulation and to evaluate the effect of the counterpulse mode, which increases pump speed just in diastole, on the amount of this nonphysiological intracircuit retrograde flow. A rotary pump (EVAHEART, Sun Medical Technology Research Corporation) was connected to the mock circulation by left ventricular uptake and ascending aortic return. We drove it in the following four conditions: (A) continuous mode at 1500 rpm, (B) counterpulse mode (systolic 1500 rpm, diastolic 2500 rpm), (C) continuous mode at 2000 rpm, and (D) counterpulse mode (systolic 2000 rpm, diastolic 2500 rpm). Data concerning the rotation speed, pump flow, left ventricular pressure, aortic pressure, and pressure head (i.e., aortic pressure-left ventricular pressure) in each condition were collected. After data collection, we analyzed pump flow, and calculated its forward and backward flow. Counterpulse mode decreased the amounts of pump backward flow compared with the continuous mode [mean backward flow, -4, -1, -0.5, 0 l/min, in (A), (B), (C), and (D) conditions, respectively]. The actual amounts of mean backward flow can be different from those in clinical situations; however, this novel drive mode for rotary pumps can relatively decrease pump backward flow during pump weaning and can be beneficial for safe and proper pump-off trials. Further investigations in in vivo settings are currently ongoing.