Percutaneous intravascular micro-axial blood pump: current state and perspective from engineering view.

The utilization of a minimally invasively placed catheter-mounted intravascular micro-axial flow blood pump (IMFBP) is increasing in the population with advanced heart failure. The current development of IMFBPs dates back around the 1990s, namely the Hemopump with a wire-drive system and the Valvopump with a direct-drive system. The wire-drive IMFBPs can use a brushless motor in an external console unit to transmit rotational force through the drive wire rotating the impeller inside the body. The direct-drive IMFBPs require an ultra-miniature and high-power brushless motor. Additionally, the direct-drive system necessitates a mechanism to protect against blood immersion into the motor. Therefore, the direct-drive IMFBPs can be categorized into two types of devices: those with seal mechanisms or those with sealless mechanisms using magnetically coupling. The IMFBPs can be classified into two groups depending on their purpose. One group is for cardiogenic shock following a heart attack or for use in high-risk percutaneous coronary intervention (PCI), and the other group serves the purpose of acute decompensated heart failure. Both direct-drive IMFBPs and wire-drive IMFBPs have their own advantages and disadvantages, and efforts are being made to develop and improve, and clinically implement them, leveraging their own strengths. In addition, there is a possibility that innovative new devices may be invented. For researchers in the field of artificial heart development, IMFBPs offer a new area of research and development, providing a novel treatment option for severe heart failure.

Development and initial performance of a miniature axial flow blood pump using magnetic fluid shaft seal.

In this study, we developed a new catheter-mounted micro-axial flow blood pump (MFBP) using a new miniature magnetic fluid shaft seal (MFSS). The prototype of the catheter-mounted MFBP had a maximum diameter of 8 mm and a length of 50 mm. The new MFSS composed a neodymium magnet ring, an iron ring, and a magnetic fluid particularly designed for the MFSS. The new MFSS had outer and inner diameters of 4.0 mm and 2.6 mm, respectively, and a length of 3.0 mm. The sealing pressure of the MFSS was calculated to be 432 mmHg using FEM (Finite Element Method) result; therefore, the MFSS had sufficient sealing pressure for the catheter-mounted MFBP. The friction loss of the MFSS included the friction owing to the viscosity of the magnetic fluid and the magnetic force between the iron ring and ring magnet. The total friction loss of the MFSS was 0.08-0.09 W in the pump operational speed range from 22,000 to 35,000 rpm. From the in vitro experimental results, the catheter-mounted MFBP using the MFSS had a pump output of 3 L/min. against a differential pressure of 60 mmHg, and the pump characteristics of the MFBP were almost the same as those of Impella 5.0.

Shear stress evaluation on blood cells using computational fluid dynamics.

BACKGROUND: Thrombus formation and hemolysis are important factors in developing blood pumps and mechanical heart valve prostheses. These phenomena are induced by flow properties. High shear stress induces platelet and red cell damage. Computational fluid dynamics (CFD) analysis calculates shear stress of fluid and particle pathlines of blood cells. OBJECTIVE: We studied blood cell damage in a blood pump by using CFD analysis and proposed a method for estimating blood damage. METHODS: We analyzed a pulsatile blood pump that was developed as a totally implantable left ventricular assist system at Tokai University. Shear stress on blood cells throughout pulsatile blood pumps were analyzed using CFD software. RESULTS: Based on the assumption that the effect of shear stress on platelets is accumulated along the trace, we proposed a method for estimating blood damage using the damage parameter D. Platelet damage parameter is calculated regardless of the division time 𝛥t which is dependent on the calculation time step. The results of the simulations are in good agreement with Giersiepen's equation obtained from the experiments. CONCLUSION: The history of shear stress on a particle was calculated using CFD analysis. The new damage parameter D yields a value close to that of Giersiepen's equation with small errors.

In vitro performance of trans-valve left ventricular assist device installed at aortic valve position.

In this study, we developed a trans-valve left ventricular assist device (LVAD) that unites a rear-impeller axial-flow blood pump (AFBP) and a polymer membrane valve placed at the aortic valve position. The diameter and length of the rear impeller AFBP was 12 and 63 mm, respectively. The polymer membrane valve was similar to the jelly-fish valve consisting of a valve leaflet made of silicone rubber (thickness 0.5 mm), valve ring (diameter: 25 mm), and valve spokes. The trans-valve LVAD was examined in a mock circulation. An implantable pulsatile flow (PF) VAD was connected to an atrial reservoir to simulate the left ventricle (LV), and the Hall valve was worn in the inflow port, and the trans-valve LVAD was placed in the outflow port as an outflow valve. When the motor rotational speed increased to 26 400 rpm, the mean aortic flow increased from 4.2 to 5.3 L/min, mean aortic pressure increased from 83.4 to 100 mm Hg, and mean motor current of the implantable PF VAD decreased from 1.18 to 0.94 A (unloading effect on LV -21%). The energy equivalent pressure increased from 85.2 to 102 mm Hg, and surplus hemodynamic energy (SHE) decreased by -15.4% from the baseline. In conclusion, the trans-valve LVAD has an advantage of preserving pulsatility without any complicated mechanism and is a novel and promising LV support device.

Development of rear-impeller axial flow blood pump for realization of axial flow blood pump installed at aortic valve position.

In this study, rear-impeller axial flow blood pumps (RIAFBP) were developed to realize a trans-valve axial ventricular assist device (VAD) which consists of the latter blood pump and a polymer monomembrane aortic valve, such as the jellyfish valve. The motor of the RIAFBP is installed in the left ventricle, and its impeller is placed at the aortic valve position. In the prototype RIAFBP, the rotation of the motor is sustained by polyethylene bushings. The RIAFBP has a length of 50 mm and diameter of 19.6 mm. The miniature RIAFBP has the same construction as that of the prototype; however, it employs a ceramic bearing and fin bearing to improve endurance and to reduce blood stagnation. The miniature RIAFBP has a length of 63 mm and diameter of 12 mm. Both RIAFBPs were examined by an in vitro experiment using a 33% glycerin solution. The prototype RIAFBP achieved a maximum pump outflow of 8.5 L/min against a pump head of 100 mm Hg at a rotational speed of 12 000 rpm. The miniature RIAFBP achieved 7 L/min against a pump head of 70 mm Hg at a rotational speed of 21 600 rpm. In conclusion, the miniature RIAFBP has enough pump performance to realize the trans-valve axial VAD.

Histological investigation of the titanium fiber mesh with one side sealed with non-porous material for its application to the artificial heart system.

In this study, we investigated tissue-inducing characteristics of a titanium fiber mesh disk with one surface sealed with a non-porous material. We used sintered titanium fiber mesh (Hi-Lex Co., Zellez™, Hyogo, Japan) having a titanium fiber diameter of 50 µm and volumetric porosity of the titanium fiber mesh of 87% with an average pore size of 200 µm. The titanium fiber mesh is disk-shaped with a dimeter of 5 mm and a thickness of 1.5 mm. One side of the titanium fiber mesh disk was sealed with silicone rubber adhesive that has no venomousness and the sealed titanium fiber mesh disks were implanted in rats under the skin of the dorsal region, and they were extracted in the 4th and 12th postoperative weeks. We investigated the distribution of capillaries; also we estimated the extent of the spread of oxygen from capillaries using the diffusion equation. Microscopic observation showed that the distribution of capillaries was mainly confined to the area around the sealed titanium fiber mesh disk and that connective tissue inside the sealed titanium fiber mesh disk seemed to be in a poor condition. From estimation of the extent of the spread of oxygen from capillaries, an area in which oxygen was poorly supplied may exist in the center of the sealed titanium fiber mesh disk. In conclusion, for application of the sealed titanium fiber mesh to an artificial heart system, the thickness of the titanium fiber mesh is an important factor for keeping the inside tissue in a healthy condition.

Measurement of hemodynamic changes with the axial flow blood pump installed in descending aorta.

We have developed various axial flow blood pumps to realize the concept of the Valvo pump, and we have studied hemodynamic changes under cardiac assistance using an axial flow blood pump in series with the natural heart. In this study, we measured hemodynamic changes of not only systemic circulation but also cerebral circulation and coronary circulation under cardiac support using our latest axial flow blood pump placed in the descending aorta in an acute animal experiment. The axial flow blood pump was installed at the thoracic descending aorta through a left thoracotomy of a goat (43.8 kg, female). When the pump was on, the aortic pressure and aortic flow downstream of the pump increased with preservation of pulsatilities. The pressure drop upstream of the pump caused reduction of afterload pressure, and it may lead to reduction of left ventricular wall stress. However, cerebral blood flow and coronary blood flow were decreased when the pump was on. The axial flow blood pump enables more effective blood perfusion into systemic circulation, but it has the potential risk of blood perfusion disturbance into cerebral circulation and coronary circulation. The results indicate that the position before the coronary ostia might be suitable for implantation of the axial flow blood pump in series with the natural heart to avoid blood perfusion disturbances.

Electrical characteristic of the titanium mesh electrode for transcutaneous intrabody communication to monitor implantable artificial organs.

We have developed a tissue-inducing electrode using titanium mesh to obtain mechanically and electrically stable contact with the tissue for a new transcutaneous communication system using the human body as a conductive medium. In this study, we investigated the electrical properties of the titanium mesh electrode by measuring electrode-tissue interface resistance in vivo. The titanium mesh electrode (Hi-Lex Co., Zellez, Hyogo, Japan) consisted of titanium fibers (diameter of 50 µm), and it has an average pore size of 200 µm and 87 % porosity. The titanium mesh electrode has a diameter of 5 mm and thickness of 1.5 mm. Three titanium mesh electrodes were implanted separately into the dorsal region of the rat. We measured the electrode-electrode impedance using an LCR meter for 12 weeks, and we calculated the tissue resistivity and electrode-tissue interface resistance. The electrode-tissue interface resistance of the titanium mesh electrode decreased slightly until the third POD and then continuously increased to 75 Ω. The electrode-tissue interface resistance of the titanium mesh electrode is stable and it has lower electrode-tissue interface resistance than that of a titanium disk electrode. The extracted titanium mesh electrode after 12 weeks implantation was fixed in 10 % buffered formalin solution and stained with hematoxylin-eosin. Light microscopic observation showed that the titanium mesh electrode was filled with connective tissue, inflammatory cells and fibroblasts with some capillaries in the pores of the titanium mesh. The results indicate that the titanium mesh electrode is a promising electrode for the new transcutaneous communication system.

Initial Acute Animal Experiment Using a New Miniature Axial Flow Pump in Series With the Natural Heart.

We have advocated an axial flow blood pump called "valvo pump" that is implanted at the aortic valve position, and we have developed axial flow blood pumps to realize the concept of the valvo pump. The latest model of the axial flow blood pump mainly consists of a stator, a directly driven impeller, and a hydrodynamic bearing. The axial flow blood pump has a diameter of 33 mm and length of 74 mm, and the length of anatomical occupation is 33 mm. The axial flow blood pump is anastomosed to the aorta with polytetrafluoroethylene (PTFE) cuffs worn on the inflow and outflow ports. Dp-Q curves of the axial flow blood pump are flatter than those of ordinary axial flow pumps, and pump outflow of 5 L/min was obtained against a pressure difference of 50 mm Hg at a rotational speed of 9000 rpm in vitro. The axial flow blood pump was installed in a goat by anastomosing with the thoracic descending aorta using PTFE cuffs, and it was rotated at a rotational speed of 8000 rpm. Unlike in case of the ventricular assistance in parallel with the natural heart, pulsatilities of aortic pressure and aortic flow were preserved even when the pump was on, and mean aortic flow was increased by 1.5 L/min with increase in mean aortic pressure of 30 mm Hg. In conclusion, circulatory assistance in series with the natural heart using the axial flow blood pump was able to improve hemodynamic pulsatility, and it would contribute to improvement of end-organ circulation. .

Passive magnetic bearing in the 3rd generation miniature axial flow pump-the valvo pump 2.

The new miniature axial flow pump (valvo pump 2) that is installed at the base of the ascending aorta consists of a six-phase stator, an impeller in which four neodymium magnets are incorporated, and passive magnetic bearings that suspend the impeller for axial levitation. The impeller is sustained by hydrodynamic force between the blade tip of the impeller and the inner housing of the stator. The passive magnetic bearing consists of a ring neodymium magnet and a columnar neodymium magnet. The ring neodymium magnet is set in the stationary side and the columnar neodymium magnet is incorporated in the impeller shaft. Both neodymium magnets are coaxially mounted, and the anterior and posterior passive magnetic bearings suspend the impeller by repulsion force against the hydrodynamic force that acts to move the impeller in the inflow port direction. The passive magnetic bearing was evaluated by a tensile test, and the levitation force of 8.5 N and stiffness of 2.45 N/mm was obtained. Performance of the axial flow pump was evaluated by an in vitro experiment. The passive magnetic bearing showed sufficient levitation capacity to suspend the impeller in an axial direction. In conclusion, the passive magnetic bearing is promising to be one of levitation technology for the third-generation axial flow blood pump.

Measurement of electrode-tissue interface impedance for improvement of a transcutaneous data transmission using human body as transmission medium.

The electrical property between an electrode and skin or tissue is one of the important issues for communication performance of the transcutaneous communication system (TCS) using a human body as a conductive medium.In this study, we used a simple method to measure interface resistance between the electrode and skin on the surface of the body. The electrode-electrode impedance was measured by a commercially available LCR meter with changes in the distance between two electrodes on an arm of a healthy male subject, and we obtained the tissue resistivity and electrode-skin interface resistance using the cross-sectional area of the arm.We also measured transmission gain of the TCS on the surface of the body, and we investigated the relationship between electrode-skin interface resistance and transmission gain. We examined four kinds of electrodes: a stainless steel electrode, a titanium electrode, an Ag-AgCl electrode and an Ag-AgCl paste electrode. The stainless steel electrode, which had lower electrode-skin resistance, had higher transmission gain.The results indicate that an electrode that has lower electrode-skin resistance will contribute to improvement of the performance of the TCS and that electrode-skin interface resistance is one of valuable evaluation parameters for selecting an optimum electrode for the TCS.

A magnetic fluid seal for rotary blood pumps: image and computational analyses of behaviors of magnetic fluids.

A magnetic fluid (MF) seal has excellent durability. The performance of an MF seal, however, has been reported to decrease in liquids (several days). We have developed an MF seal that has a shield mechanism. The seal was perfect for 275 days in water. To investigate the effect of a shield, behaviors of MFs in a seal in water were studied both experimentally and computationally. (a) Two kinds of MF seals, one with a shield and one without a shield, were installed in a centrifugal pump. Behaviors of MFs in the seals in water were observed with a video camera and high-speed microscope. In the seal without a shield, the surface of the water in the seal waved and the turbulent flow affected behaviors of the MFs. In contrast, MFs rotated stably in the seal with a shield in water even at high rotational speeds. (b) Computational fluid dynamics analysis revealed that a stationary secondary flow pattern in the seal and small velocity difference between magnetic fluid and water at the interface. These MF behaviors prolonged the life of an MF seal in water.

Evaluation of titanium mesh electrode using for transcutaneous intrabody communication by tissue-electrode impedance.

We developed a new transcutaneous communication system (TCS) that uses the human body as a conductive medium for monitoring and controlling an artificial heart and other implanted artificial organs in the body. The TCS is able to transmit data between everywhere on the surface of the body and everywhere inside the body, however poor contact between tissue and the electrode influences on communication performance. Thus in this study, we have developed a titanium mesh electrode for the internal transmission electrode. The titanium mesh electrode has advantages of histocompatibility and mechanical stable contact to the tissue by infiltration of the tissue into the titanium mesh like as an extracellular matrix. There titanium mesh electrodes were implanted separately into the dorsal region of the rats under the skin and the electrical performance of the titanium mesh electrode was evaluated by means of measuring the electrode-tissue boundary resistance. In vivo experimental results showed that the titanium mesh electrode had stable mechanical contact to tissue and lower electrode -tissue boundary resistance. In conclusion, the titanium mesh electrode showed excellent histocompatibility it realized stable contact to tissue as anchor, and it had superior electrical property. Thus the titanium mesh electrode is suitable for an internal electrode of the TCS to monitor artificial organs implanted into the body.

A magnetic fluid seal for rotary blood pumps: Behaviors of magnetic fluids in a magnetic fluid seal.

A magnetic fluid (MF) seal has excellent durability. The performance of an MF seal, however, has been reported to decrease in liquids (several days). We have developed an MF seal that has a shield mechanism. The seal was perfect for 275 days in water. To investigate the effect of a shield, behaviors of MFs in a seal in water were studied both experimentally and computationally. (a) Two kinds of MF seals, one with a shield and one without a shield, were installed in a centrifugal pump. Behaviors of MFs in the seals in water were observed with a video camera and high-speed microscope. In the seal without a shield, the surface of the water in the seal waved and the turbulent flow affected behaviors of the MFs. In contrast, MFs rotated stably in the seal with a shield in water even at high rotational speeds. (b) Computational fluid dynamics analysis revealed that a stationary secondary flow pattern in the seal and small velocity difference between magnetic fluid and water at the interface. These MF behaviors prolonged the life of an MF seal in water.

Transcutaneous communication system using the human body as conductive medium: influence of transmission data current on the heart.

We developed a new transcutaneous communication system (TCS) that uses the human body as a conductive medium for monitoring and controlling artificial hearts and other artificial organs in the body.In this study, the physiological effect of data current discharged into the body during data transmission was evaluated by an animal experiment using a goat. The external and internal units of the new TCS each mainly consist of a data transmitter and a data receiver. The data transmitter has an amplitude shift keying (ASK) modulator (carrier frequencies: 4 and 10 MHz) and an electrode.The internal unit of the TCS was fixed on the pericardium and the external unit was placed on the left ear, and each transmitter discharged an ASK-modulated current of 7 mA (RMS) into the conscious goat. The TCS was able to transmit data for 4 weeks under full duplex communication with a transmission rate of 115 kbps. On the 28th postoperative day, an electrocardiogram was measured during data transmission. Cardiac rhythm and waveform of the electrocardiogram were not changed before and during bidirectional data transmission. Also, no adverse effect on the heart was observed by autopsy.

A new transcutaneous bidirectional communication for monitoring implanted artificial heart using the human body as a conductive medium.

A transcutaneous communication system (TCS) is a key technology for monitoring and controlling artificial hearts and other artificial organs in the body. In this study, we developed a new TCS that uses the human body as a conductive medium. Direct data exchange provides a higher level of communication security compared to that of wireless methods without physical constraints such as an external wire. The external and internal units of the new TCS each consist mainly of a data transmitter and a data receiver. The data transmitter has an amplitude shift keying (ASK) modulator (carrier frequencies: 4 and 10 MHz) and an electrode. The ASK-modulated data current is led into the body through the electrode, and it flows back to the energy source through the body, the data receiver, and the earth ground that includes all conductors and dielectrics in the environment that are in close proximity to the patient. Performance of the TCS was evaluated by a communication test on the surface of the human body and in an animal experiment using a goat. The TCS was able to transmit data concurrently for 4 weeks between everywhere on the surface of the body and everywhere inside the body under full-duplex communication at a transmission rate of 115 kbps. The power consumption of each TCS unit was 125 mW with an ASK-modulated current of 7 mA (root-mean-square). While further study is required to secure its safety, the newly developed TCS has promise to be a next-generation transcutaneous communication device.

Prevalence of organic colonic lesions in patients meeting Rome III criteria for diagnosis of IBS: a prospective multi-center study utilizing colonoscopy.

BACKGROUND: It remains unknown whether the Rome III criteria can exclude organic colonic lesions prior to the diagnosis of irritable bowel syndrome (IBS). We evaluated the colonoscopy results of patients meeting the Rome III criteria for the diagnosis of IBS to determine the presence of organic colonic lesions. METHODS: This study was prospectively conducted at 17 centers in Japan. We enrolled 4528 patients who underwent diagnostic colonoscopy examinations. The diagnosis of IBS was evaluated by questionnaire results according to the Rome III criteria. RESULTS: We evaluated 4178 patients (350 were excluded because of incomplete data or previous colonic surgery), of whom 203 met the Rome III criteria (mean age 57.9 years; range 14-87 years) prior to the diagnostic colonoscopy examination. We identified organic colonic diseases in 21 of these 203 patients (10.3 %) , and these disease were also identified in 338 (8.5 %) of 3975 patients who did not fulfill the Rome III criteria. There were no differences in regard to the prevalence of organic colonic diseases between patients who did and did not fulfill the Rome III criteria. CONCLUSIONS: The prevalence of organic colonic diseases in patients who met the Rome III criteria was at an acceptably low level, indicating that the Rome III criteria are adequately specific for the diagnosis of IBS without performing a colonoscopy examination.

Interface of data transmission for a transcutaneous communication system using the human body as transmission medium.

We have been developing a new transcutaneous communication system (TCS) that uses the human body as an electrical conductive medium. We studied an interface circuit of the TCS in order to optimize the leading data current into the human body effectively. Two types of LC circuits were examined for the interface circuit, one was an LC series-parallel circuit, and the other was a parallel-connected LC circuit. The LC series-parallel circuit connected to the body could be tuned to a resonant frequency, and the frequency was determined by the values of an external inductor and an external capacitor. Permittivity of the body did not influence the electrical resonance. Connection of the LC series-parallel circuit to the body degraded the quality factor Q because of the conductivity of the body. However, the LC parallel-connected circuit when connected to the body did not indicate electrical resonance. The LC series-parallel circuit restricts a direct current and a low-frequency current to flow into the body; thus, it can prevent a patient from getting a shock. According to the above results, an LC series-parallel circuit is an optimum interface circuit between the TCS and the body for leading data current into the body effectively and safely.

A magnetic fluid seal for rotary blood pumps: effects of seal structure on long-term performance in liquid.

A magnetic fluid (MF) seal enables mechanical contact-free rotation of the shaft and hence has excellent durability. The performance of an MF seal, however, has been reported to decrease in liquids. We developed an MF seal that has a "shield" mechanism, and a new MF with a higher magnetization of 47.9 kA/m. The sealing performance of the MF seal installed in a rotary blood pump was studied. Three types of MF seals were used. Seal A was a conventional seal without a shield. Seal B had the same structure as that of Seal A, but the seal was installed at 1 mm below liquid level. Seal C was a seal with a shield and the MF was set at 1 mm below liquid level. Seal A failed after 6 and 11 days. Seal B showed better results (20 and 73 days). Seal C showed long-term durability (217 and 275 days). The reason for different results in different seal structures was considered to be different flow conditions near the magnetic fluid. Fluid dynamics near the MF in the pump were analyzed using computational fluid dynamics (CFD) software. We have developed an MF seal with a shield that works in liquid for >275 days. The MF seal is promising as a shaft seal for rotary blood pumps.

Basic study of a transcutaneous information transmission system using intra-body communication.

The transcutaneous communication system (TCS) is one of the key technologies for monitoring and controling artificial hearts and other artificial organs in the body. In this study, we have developed a new TCS that uses the human body as a conductive medium. Having no energy conversion from electric currents into electromagnetic waves and light provides energy-saving data transmission with a simple electrical circuit. Each unit of the TCS mainly consists of two electrodes, an amplitude shift keying (ASK) modulator and an ASK demodulator (carrier frequency: 4 and 10 MHz). A resonant frequency of an L-C tank circuit including the capacitance component of the body is tuned into each carrier frequency in order to apply the data current effectively into the body. Performance of the TCS was evaluated by a communication test on the surface of a human body. The TCS was able to transmit 3,315 bytes of data bi-directionally at a transmission rate of 115 kbps from a left wrist to a right forearm, to an abdomen and to a left calf without communication error. The power consumption of each TCS unit was 125 mW with an ASK modulated current of 7 mA (RMS). While further study is required to secure its safety, the TCS promises to be a next-generation transcutaneous communication device.