Examination of mitral regurgitation with a goat heart model for the development of intelligent artificial papillary muscle

Annuloplasty for functional mitral or tricuspid regurgitation has been made for surgical restoration of valvular diseases. However, these major techniques may sometimes be ineffective because of chamber dilation and valve tethering. We have been developing a sophisticated intelligent artificial papillary muscle (PM) by using an anisotropic shape memory alloy fiber for an alternative surgical reconstruction of the continuity of the mitral structural apparatus and the left ventricular myocardium. This study exhibited the mitral regurgitation with regard to the reduction in the PM tension quantitatively with an originally developed ventricular simulator using isolated goat hearts for the sophisticated artificial PM. Aortic and mitral valves with left ventricular free wall portions of isolated goat hearts (n=9) were secured on the elastic plastic membrane and statically pressurized, which led to valvular leaflet-papillary muscle positional change and central mitral regurgitation. PMs were connected to the load cell, and the relationship between the tension of regurgitation and PM tension were measured. Then we connected the left ventricular specimen model to our hydraulic ventricular simulator and achieved hemodynamic simulation with the controlled tension of PMs.

A new control method depending on primary phase angle of transcutaneous energy transmission system for artificial heart

A new control method for stabilizing output voltage of the transcutaneous energy transmission system for artificial heart is proposed. This method is primary side, is outside of the body, which is not depending on a signal transmission system from the implanted device. The impedance observed from primary side changes from inductive to capacitive and the output voltage decreases drastically when the output current is large and the coupling factor is higher than that of the optimal condition. In this case, the driving frequency should be changed to higher so that the phase angle of the primary impedance is zero degree. The preliminary examination showed that this control method can enhance the output voltage limit to twice and the feasibility of the primary side control.

Elimination of Teicoplanin by Adsorption to the Filter Membrane during Haemodiafiltration: Screening Experiments for Linezolid, Teicoplanin and Vancomycin followed by in vitro Haemodiafiltration Models for Teicoplanin

Pharmaceutical agents directed against methicillin-resistant Staphylococcus aureus can be eliminated during haemodiafiltration, not only by diffusion and ultrafiltration, but also by adsorption onto haemofilters. The latter may be affected by the binding of agents to serum albumin. The present study therefore investigated the affinity of anti-methicillin-resistant Staphylococcus aureus agents (teicoplanin, linezolid, vancomycin) for haemofilters and the pharmacokinetic properties of teicoplanin during haemodiafiltration. Linezolid, teicoplanin and vancomycin were first screened for their in vitro affinity for three different kinds of filter membranes: polysulfone, polyacrylonitrile and polymethylmethacrylate. Only teicoplanin showed significant filter-binding activity. An in vitro haemodiafiltration circulation model was then developed that incorporated a one-litre beaker containing Krebs-Ringer's bicarbonate solution with/without human albumin (0 or 3 g/dl) as an artificial plasma. Teicoplanin (initial concentration 50 μg/ml, representing the maximum plasma concentration (Cmax) resulting from a typical clinical dosage) was circulated throughout the beaker. Teicoplanin concentrations in the ‘plasma’ and ultrafiltrate were determined by high performance liquid chromatography. In the screening experiment, teicoplanin was predominantly adsorbed onto polysulfone and polymethylmethacrylate membranes. Furthermore, teicoplanin was primarily eliminated by adsorption onto these filters during in vitro haemodiafiltration. Albumin significantly reduced both haemodiafiltration clearance and the adsorption-dependent elimination, although there were complex but significant interactions between albumin and the filter membrane. Elimination of teicoplanin in an in vitro haemodiafiltration model was largely due to adsorption onto polysulfone and polymethylmethacrylate haemofilters. Future clinical studies should likely be designed to evaluate present recommendations of teicoplanin dosages in patients on haemodiafiltration.

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Rotary blood pumps which have contact-less suspension are small, durable and widely used for left ventricular assist devices (LVADs). In order to design a total artificial heart (TAH) with rotary blood pumps, two pumps one for each ventricle, are controlled independently. Some of the challenges for the development of a TAH includes the requirement of a small size and the anatomical fitting of inlets and outlets which should be arranged closely on the circumference in the same direction. And they should be combined into a unit. In this paper, a helical flow total artificial heart (HFTAH) combing two centrifugal pumps with helical inlet in face is proposed in order to achieve a smaller TAH. To examine the pump performance, a preliminary test model for left ventricle was built, the size of the pump was 69.0mm in diameter and 45.0mm height. The size of the impeller was 44.0mm in diameter and 23.0mm height including a 15.0mm-height hydrodynamic bearing. The pump was externally driven by a direct current motor. 5.0L/min flow rate against 100mmHg pressure difference was obtained, where the total power consumption was 5.0W, the system efficiency was 23% with a rotational speed of 2070rpm. In this system, maximum pressure head, flow rate and efficiency were 420mmHg, 15.0L/min and 26%, respectively. In acute animal experiments with three healthy adult goats, the total biventricular bypass assist system using the pumps was able to maintain the maximum aortic flow at approximately 5.0L/min, and the pulmonary arterial flow at approximately 4.6L/min, the mean aorta pressure was 105mmHg, and the mean pulmonary artery pressure was 51mmHg. The development of the control method is undergoing, and a driving system and the pump aiming at the chronic animal experiments will be developed.

Structural design of a newly developed pediatric circulatory assist device for Fontan circulation by using shape memory alloy fiber

Total cavopulmonary connection (TCPC) is commonly applied for the surgical treatment of congenital heart disease such as single ventricle in pediatric patients. Patients with no ventricle in pulmonary circulation are treated along with Fontan algorithm, in which the systemic venous return is diverted directly to the pulmonary artery without passing through subpulmonary ventricle. In order to promote the pulmonary circulation after Fontan procedure, we developed a newly designed pulmonary circulatory assist device by using shape memory alloy fibers. We developed a pulmonary circulatory assist device as a non-blood contacting mechanical support system in pediatric patients with TCPC. The device has been designed to be installed like a cuff around the ePTFE TCPC conduit, which can contract from outside. We employed a covalent type functional anisotropic shape memory alloy fiber (Biometal, Toki Corporation, Tokyo Japan) as a servo actuator of the pulmonary circulatory assist device. The diameter of this fiber was 100 microns, and its contractile frequency was 2-3 Hz. Heat generation with electric current contracts these fibers and the conduit. The maximum contraction ratio of this fiber is about 7% in length. In order to extend its contractile ratio, we fabricated and installed mechanical structural units to control the length of fibers. In this study, we examined basic contractile functions of the device in the mock system. As a result, the internal pressure of the conduit increased to 63 mmHg by the mechanical contraction under the condition of 400 msec-current supply in the mock examination with the overflow tank of 10 mmHg loading.

Effects of combination therapy with montelukast and carbocysteine in allergen-induced airway hyperresponsiveness and airway inflammation

BACKGROUND AND PURPOSE

Montelukast and S-carbocysteine have been used in asthmatic patients as an anti-inflammatory or mucolytic agent respectively. S-carbocysteine also exhibits anti-inflammatory properties.

EXPERIMENTAL APPROACH

Ovalbumin (OVA) sensitized BALB/c mice were challenged with OVA for 3 days followed by single OVA re-challenge (secondary challenge) 2 weeks later. Forty-eight hours after secondary challenge, mice were assessed for airway hyperresponsiveness (AHR) and cell composition in bronchoalveolar lavage (BAL) fluid. Suboptimal doses of 10 mg.kg(-1) of S-carbocysteine by intraperitoneal injection (ip), 20 mg.kg(-1) of montelukast by gavage, the combination of S-carbocysteine and montelukast or 3 mg.kg(-1) of dexamethasone as a control were administered from 1 day before the secondary challenge to the last experimental day. Isolated lung cells were cultured with OVA and montelukast to determine the effects on cytokine production.

KEY RESULTS

Treatment with S-carbocysteine or montelukast reduced both AHR and the numbers of eosinophils in BAL fluid. Neutralizing IFN-gamma abolished the effects of S-carbocysteine on these airway responses. Combination of the two drugs showed further decreases in both AHR and eosinophils in the BAL fluid. Goblet cell metaplasia and Th2-type cytokines, interleukin (IL)-4, IL-5 and IL-13, in BAL fluid were decreased with montelukast treatment. Conversely, S-carbocysteine increased Th1-type cytokines, IFN-gamma and IL-12 in BAL fluid.

CONCLUSIONS AND IMPLICATIONS

The combination of two agents, montelukast and S-carbocysteine, demonstrated additive effects on AHR and airway inflammation in a secondary allergen model most likely through independent mechanisms of action.

[Thoracoplasty]

Thoracoplasty was at 1st invented for the treatment of pulmonary tuberculosis during the days when no effective chemotherapeutic drugs for tuberculosis were available. Removal of some portions of the ribs by thoracoplasty deforms the chest wall and compresses tuberculous cavities. Since the introduction of potent anti-tuberculous drugs, thoracoplasty for pulmonary tuberculosis has been obsolete. Currently, thoracoplasty is mainly applied to reduction of the volume of the pleural space in the treatment of post-resectional space problems and in the treatment of thoracic empyema. Well-planned and safe resections of the affected ribs hold the keys to successful thoracoplasty. The procedure is performed alone or with muscle flaps or with omental flap, depending on the extent of space and the presence of bronchopleural fistula. Thoracic surgeons should know the current application of thoracoplasty.

Clinical comparison of two different types of bifurcated graft for postoperative baPWV and ABI

AIM

A newly-designed bifurcated graft with the distal end larger than the conventional type has been developed. The purpose of this study was to evaluate the early results of graft replacement using this new graft, and to compare whether the new graft is more advantageous than the conventional graft in terms of peripheral blood flow and arterial stiffness.

METHODS

Records of 36 patients who underwent bifurcated graft replacement for infrarenal abdominal aortic aneurysm (AAA), from May 2003 to September 2006 were reviewed after excluding peripheral arterial disease (ABI > 0.9). Subjects were divided into two groups: group C (N.=20), with implantation of the conventional type and group N (N.=16), with implantation of the new type. We investigated changes in brachial-ankle pulse wave velocity (baPWV) and ankle-brachial pressure index (ABI), measurements being performed preoperatively and postoperatively.

RESULTS

baPWV in the postoperative group as a whole was significantly higher than in the preoperative group (P<0.05), while ABI in the postoperative group was lower than in the preoperative group (P<0.05). In group C, baPWV increased (P<0.05) and ABI decreased (P<0.05) after bifurcated graft replacement, whereas in group N, there were no significant differences in changes of baPWV and ABI.

CONCLUSIONS

This study shows that the new graft reduces the development of arterial stiffness postoperatively compared with the conventional type. These results may predict the new type graft decrease in the risk of morbidity and mortality caused by atherosclerotic disease.

Sensorless control for a sophisticated artificial myocardial contraction by using shape memory alloy fibre

The authors have been developing an artificial myocardium, which is capable of supporting natural contractile function from the outside of the ventricle. The system was originally designed by using sophisticated covalent shape memory alloy fibres, and the surface did not implicate blood compatibility. The purpose of our study on the development of artificial myocardium was to achieve the assistance of myocardial functional reproduction by the integrative small mechanical elements without sensors, so that the effective circulatory support could be accomplished. In this study, the authors fabricated the prototype artificial myocardial assist unit composed of the sophisticated shape memory alloy fibre (Biometal), the diameter of which was 100 microns, and examined the mechanical response by using pulse width modulation (PWM) control method in each unit. Prior to the evaluation of dynamic characteristics, the relationship between strain and electric resistance and also the initial response of each unit were obtained. The component for the PWM control was designed in order to regulate the myocardial contractile function, which consisted of an originally-designed RISC microcomputer with the input of displacement, and its output signal was controlled by pulse wave modulation method. As a result, the optimal PWM parameters were confirmed and the fibrous displacement was successfully regulated under the different heat transfer conditions simulating internal body temperature as well as bias tensile loading. Then it was indicated that this control theory might be applied for more sophisticated ventricular passive or active restraint by the artificial myocardium on physiological demand.

Assessment of synchronization measures for effective ventricular support by using the shape memory alloy fibred artificial myocardium in goats

Thromboembolic and haemorrhagic complications are the primary causes of mortality and morbidity in patients with artificial hearts, which are known to be induced by the interactions between blood flow and artificial material surfaces. The authors have been developing a new mechanical artificial myocardial assist device by using a sophisticated shape memory alloy fibre in order to achieve the mechanical cardiac support from outside of the heart without a direct blood contacting surface. The original material employed as the actuator of artificial myocardial assist devices was 100um fibred-shaped, which was composed of covalent and metallic bonding structure and designed to generate 4-7 % shortening by Joule heating induced by the electric current input. In this study, we focused on the synchronization of the actuator with native cardiac function, and the phase delay parameter was examined in animal experiments using Saanen goats. Total weight of the device including the actuator was around 150g, and the electric power was supplied transcutaneously. The device could be successfully installed into thoracic cavity, which was able to be girdling the left ventricle. The contraction of the device could be controlled by the originally designed microcomputer. The mechanical contraction signal input had been transmitted with the phase delay of 50-200 msec after the R-wave of ECG, and hemodynamic changes were investigated. Cardiac output and systolic left ventricular pressure were elevated with 20% delay of cardiac cycle by 27% and 7%, respectively, although there was smaller difference under the condition of the delay of over 30%. Therefore, it was suggested that the synchronization measures should be examined in order to achieve sophisticated ventricular passive/active support on physiological demand.