Biomedical subjects
Publications and source records attributed to S Nitta.
A coronary-bronchial fistula and aneurysmal dilatation of the proximal part of the fistula was successfully closed using an autologous vein graft-coated stent (Palmaz-Schatz stent). This is the first report that demonstrates the feasibility of the vein-coated stent for the treatment of congenital disease.
For the development of a totally implantable ventricular assist system (VAS), we have been developing the vibrating flow pump (VFP), which can generate oscillated blood flow with a relative high frequency (10-50 Hz) for a totally implantable system. In this study, the effects of left ventricular assistance with this unique oscillated blood flow were analyzed by the use of nonlinear mathematics for evaluation as the whole circulatory regulatory system, not as the decomposed parts of the system. Left heart bypasses using the VFP from the left atrium to the descending aorta were performed in chronic animal experiments using healthy adult goats. The ECG, arterial blood pressure, VFP pump flow, and the flow of the descending aorta were recorded in the data recorder during awake conditions and analyzed in a personal computer system through an A-D convertor. By the use of nonlinear mathematics, time series data were embedded into the phase space, the Lyapunov numerical method, fractal dimension analysis, and power spectrum analysis were performed to evaluate nonlinear dynamics. During left ventricular assistance with the VFP, Mayer wave fluctuations were decreased in the power spectrum, the fractal dimension of the hemodynamics was significantly decreased, and peripheral vascular resistance was significantly decreased. These results suggest that nonlinear dynamics, which mediate the cardiovascular dynamics, may be affected during left ventricular (LV) bypass with oscillated flow. The decreased power of the Mayer wave in the spectrum caused the limit cycle attractor of the hemodynamics and decreased peripheral resistance. Decreased sympathetic discharges may be the origin of the decreased Mayer wave and fractal dimension. These nonlinear dynamic analyses may be useful to design optimal VAS control.
The demand of the biological system needs to be predicted to consider the quality of life (QOL) of a patient with an artificial heart system. The purpose of this study was the prediction of the imminent cardiac output and the predictive control for an artificial heart. For that purpose, autonomic nerve information was applied in this study. Nervous sympathicus action potentials were measured, and a prediction function of cardiac output was made using the sympathetic tone and preload and after-load measurement with multiple regression analysis. The predicted value showed significant correlation with the measured value after 2.9 s. Currently, however, long-term instrumentation of the nervous sympathicus potential is difficult. Thus, hemodynamic fluctuations, which recently have attracted attention, were used in this study. A prediction function using the Mayer wave, which represented nervous sympathicus, was determined. As a result, mid-term prediction became possible. Furthermore, a measurement of the vagal nerve was used as a possible long-term prediction parameter. For long-term prediction, Hurst exponent analysis was used in this study. Vagal nerve discharges in the changing position showed alteration of long-term determination. In conclusion, the future prediction control of an artificial heart takes shape using these prediction functions.
To detect useful information for an artificial heart control system, we paid attention to the autonomic nervous system. For stable recording, we used vagal nerve activity in chronic animal experiments using healthy adult goats in an awake condition because this nerve was sufficiently bold and large enough. Vagal nerve discharges were successfully recorded from awake goats. They were synchronized with respiration and responded to the hemodynamic changes induced by drug administration, suggesting that they may provide useful information for an artificial heart control algorithm. For automatic control, some time delay plays a vitally important role. Thus, predictive control for an artificial heart system may be desirable. It may be embodied by the use of autonomic nerve information.
A vibrating flow pump (VFP) can generate high frequency oscillated blood flow within 10-30 Hz by the oscillation of its central tube. A totally implantable artificial heart using a VFP is being developed as a unique type of blood pump. In this study, left ventricular (LV) assist circulation was performed using a VFP. The total vascular resistance and driving frequency of the VFP were estimated from their relationship. The effect of oscillation on the vascular system was studied by the frequency analysis method and vascular impedance. Adult goats were anesthetized by halothane using an inhaler and a left fourth thoracotomy was performed. The inflow cannula was inserted into the left ventricle, and the outflow cannula was sutured to the descending aorta. The VFP and a centrifugal pump were set in parallel for alternation and comparison. The driving frequency of the VFP was changed and included 15, 20, 25, and 30 Hz. The hemodynamic parameters were continuously recorded during experiments by a digital audio tape (DAT) data recorder. The internal pressure of the left ventricular cavity and aortic pressure were monitored by the pressure manometers continuously. One hundred percent LV assistance was judged by the separation of LV and aortic pressure. The total vascular resistance was decreased by the start of operation of each pump. The decrease during flow using the VFP was not as large as that using a centrifugal pump (CP). The arterial input impedance during oscillated blood flow by the VFP showed a slow curve appearance. It was similar to the frequency characteristics curve of natural heart beats within the lower frequencies. The study of arterial impedance may be important for the estimation of the reflection of the pulsatile wave from the arterial branch, among other things.
For development aimed at a totally implantable type ventricular assist device (VAD), the vibrating flow pump (VFP) has been developed at Tohoku University. A transcutaneous energy transmission system (TETS) using amorphous fibers was developed to power the totally implantable VAD system. The VFP works at a high frequency compared to that of a natural heart of a biological system. It is a frequency of 10-50 Hz. In this research, animal experiments with left heart bypass were carried out with healthy adult goats. For comparison between nonpulsatile flow and oscillated flow, a rotary pump (RP) and the VFP were used in the experiments. For the achievement of total left heart bypass, left ventricular approaches were carried out, and blood was pumped from the left ventricle to the descending aorta. Adequate support of the left heart was provided by both pumps. In terms of the results, the vascular resistances tended to decrease during the use of both pumps during 100% bypass driving. When we compared these pumps at the same flow rate, the resistances during RP driving were significantly smaller than those during VFP driving. These results may suggest that the influences of the VFP upon the peripheral vessels may be relatively small compared to those of the RP. This may be an important result when a stable hemodynamic condition is required during artificial circulation. The VFP was considered as a candidate for a totally implantable VAD as a result.
Nonlinearity in circulation control attracts attention because nonlinearity is thought to be essential in the function of the living body. Many investigators have pointed out that the analysis of heart rate variability in particular is important in the analysis of autonomic nerve and cardiac function evaluation. Heart rate variability shows nonlinear behavior. However, until the present, many reports have been premised on linearity; linear correlation by frequency analysis has been used by many studies. However, in terms of this methodology, there is a problem applying it to the nonlinear living body. Therefore, fractal and chaos methodology has been used. The ascertainment of cardiac function has become important in allowing the clinical stage of a ventricular assist system to be successful. The purpose of this study was cardiac function evaluation by a methodology that was premised on nonlinearity. Chaos and fractal theory was used as a nonlinear dynamic theory. As a methodology of measurement, the volume of the left ventricle was used rather than an electrocardiogram, the waveform of arterial blood pressure. The volume was measured using acoustic quantification (AQ) ultrasonic echocardiography. Using these methodologies, the time series of many patients were analyzed. For example, drug administration was attempted in this study, and it was found that some drugs like ACE inhibitors showed a significant effect upon nonlinear dynamics in the cardiovascular system. The result, which attempted cardiac function evaluation by these various methodologies, is reported.
In patients scheduled for cesarean section (c-section) using combined spinal epidural anesthesia (CSEA), we compared the cephalad spreading speed during double-segment technique (DST) with that of single-space technique (SST) of CSEA. In the patients of SST group (n = 169), a 17-G Tuohy needle was introduced at the L 3-4, and then a long spinal needle was inserted through the Tuohy needle. In the patients of DST group (n = 16), a Tuohy needle was introduced at the T 11-12, and a spinal needle was inserted at the L 3-4. After 0.3% hyperbaric dibucaine 1.0 ml was injected through the spinal needle, 1.5% mepivacaine 10 ml was injected through the epidural catheter in both the groups. The analgesic level was measured at 5-min intervals, and blood pressure and complaints of patients were also recorded. The cephalad spread of analgesia was significantly higher in DST group than in SST group at 5 and 10 min after the administration of local anesthetics. Two patients in SST group, epidural catheterization was not possible. There were no difference in the incidences of hypotension, nausea and dyspnea between the groups. We conclude from these results that DST for CSEA is preferable to SST for c-section.
We encountered three rare cases of cancer of unknown origin affecting the mediastinal and hilar lymph nodes. Patient 1 was a 63 year-old man. Chest X-ray and CT films revealed an enlarged right hilar lymph node. A right mediastinal and hilar lymphadenectomy was performed. The histological diagnosis was metastatic squamous cell carcinoma (SCC). SCC of the right upper lobe appeared 34 months after the operation, requiring a right pneumonectomy. Patient 1 was alive 43 months after his first operation. Patient 2 was a 73 year-old man in whom left mediastinal and hilar lymph node swelling had been detected. A mediastinoscopy and lymph node biopsy were performed. The histological findings resulted in a diagnosis of metastatic small cell carcinoma. Chemotherapy was initiated, and the patient was alive 5 months after the biopsy procedure, Patient 3 was a 57 year-old man in whom right mediastinal and hilar lymph node swelling had been disclosed by chest CT scans. We performed a medianosternotomy and mediastinal and right hilar lymphadenectomy. Histologically, the diagnosis was metastatic adenocarcinoma. After the operation, radiation therapy was performed on the patient's mediastinum. Patient 3 was alive 5 months after the initial operation. The patients were given diagnoses of T0N1 or T0N2 lung cancer.
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Five patients (4 men and one woman) aged 48-82 years who were suffering from superior vena cava (SVC) syndrome had Wallstent implanted percutaneously to relieve the obstruction. After stent placement, all cases received anticoagulant therapy with heparin. However one transient stent thrombosis occurred, stent placement resulted in complete relief of all patients. Wallstent placement could be an extremely useful treatment for SVC syndrome and should be the treatment of choice in all cases where SVC obstruction occurs or recurs, following chemotherapy or radiotherapy.
For the Quality of life (QOL) of patients with an artificial heart system, monitoring an information of the cardiovascular control system may be important. We have been evaluating the autonomic nervous system for that purpose. Recently, fluctuations in hemodynamic parameters including heart rate variability (HRV) were evaluated by means of spectral analysis and nonlinear mathematical analysis. Respiratory wavers in HRV were thought to reflect ongoing information of the parasympathetic nerve activity. Is it true? In order to confirm this hypothesis, we recorded vagal nerve activity directly in the chronic animal experiments. Six healthy adult goats were anesthetized with Halothene inhalation and thoracotomy were performed by the fourth lib resection during mechanical ventilation. Arterial blood pressure, right and left atrial pressures were continuously monitored with the catheter insertion. Cardiac output was measured by the electromagnetic flowmeter attached to the ascending aorta. After the chest was closed, incision was made to the left neck and left vagal nerve was separated. Stainless steel electrodes were inserted into the vagal nerve and fixed by the plasticizer. After the incision was closed, the goats were transferred to the cage and extubated after waking. Hemodynamic parameters and vagal nerve activity were measured in the awake condition. The results showed that clear observation of the autonomic nerve discharges were embodied by this experimental system. The vagal nerve discharges were synchronized with heart beat and respiration. The vagal nerve tonus was significantly influenced by the hemodynamic alteration. However in some condition, the respiratory wave was not always consistent with tonus of the vagal nerve activity, thus suggesting that we should check another information to evaluate the parasympathetic tone. We must continue this study to evaluate an autonomic nerve during artificial heart circulation.
To evaluate the influence of potassium ion concentration in an organ preservation solution on lung preservation, four types of solutions were produced. These preservation solutions consisted of sodium and potassium ions on the cation and phosphate ions on the anion with glucose. Contents of solutions were: (1) 155 mmol/l Na+, 0 mmol/l K+; (2) 150 mmol/l Na+, 5 mmol/l K+; (3) 20 mmol/l Na+, 135 mmol/l K+; and (4) 0 mmol/l Na+, 155 mmol/l K+. All four solutions possessed the same osmolarity, the same pH in the same temperature, and the same buffer action. Lungs were preserved at 7 degrees C in these solutions for 24 h and evaluated in a rat lung perfusion system with perfluorochemical emulsion. Pressure-limited perfusions with pressure-limited ventilation were carried out for 20 min before and after preservation. Thereafter, the recovery ratios of pulmonary arterial flow (Q), tidal volume (VT), oxygen tension of the pulmonary venous effluent (PPVO2), and wet-to-dry ratios were compared. The recovery ratios of Q were better in low, but not zero, potassium solutions, whereas wet-to-dry ratios were kept lower in high potassium solutions. No difference in pulmonary compliance or gas exchange was observed against a great change in potassium ion concentration. Therefore, the potassium ion concentration did not play a major role in lung preservation.
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The ultrasonic properties of the tissue elements in the aorta were measured using a scanning acoustic microscope (SAM). Twelve autopsied aortas were formalin-fixed, frozen and sectioned at 10 microm thickness and mounted on glass slides for SAM investigation. A specially developed SAM system operating in the frequency range of 100-200 MHz was employed, and color-coded images of the two-dimensional (2-D) distributions of attenuation and sound speed were displayed. The region-of-interest (ROI) for attenuation and sound speed measurements was determined by comparison of optical and acoustic images. The average value of the slope of attenuation was 0.61 dB/mm/MHz and the sound speed was 1568 m/s in the normal intima; 2.5 dB/mm/MHz, 1760 m/s in the calcificated lesion; 1.7 dB/mm/MHz and 1677 m/s in the fibrosis; and 0.34 dB/mm/MHz, 1526 m/s in the fatty material, respectively. Acoustic microscopy provides the basic data for understanding the IVUS imaging of atherosclerosis, as well as on the pathological features of atherosclerosis.
With the increase of ischemic diseases of the circulatory system in Japan, the necessity for cardiovascular intervention continues to increase. However, because intervention operations have been developed only recently, the education system for the corresponding specialists in our country has not been established yet. In this study, an intervention educational support system using a virtual reality (VR) technique was developed. Of course, intervention includes percutaneous transluminal coronary angioplasty (PTCA). PTCA is an operation enlarging the stenosis of the coronary artery with a balloon through a guide catheter. The technique that lets the guide wire for the PTCA balloon cross the stenosis is one of the most difficult. A simulation system for the manipulation of a torque device for the PTCA guide wire was developed with this technology for VR. In virtual space, reconstitution of the 3-dimensional coronary artery with atherosclerosis was performed, and the virtual PTCA system was produced experimentally. An interesting system was produced experimentally as a system for the training of doctors studying to become interventional specialists. After the system was combined with an Expert system for treating ischemic heart diseases, its usefulness was steadily increased. With the development of more sophisticated VR methodology in the future, a PTCA training system without using a patient will be embodied.
Aiming at a totally implantable ventricular assist device (VAD), a vibrating flow pump (VFP) was developed in Tohoku University. A transcutaneous energy transmission system (TETS) using an amorphous fiber was developed for the totally implantable VAD system. The VFP works with a higher frequency than the natural heart of a biological system, a frequency of 10-50 Hz. In this research, animal experiments on left heart bypass were performed with healthy goats. Blood from the apex of the left ventricle was received and was sent to the aorta so that an adequate supporting effect of the left heart was provided. In particular, the depression effect of the left ventricle was obvious. As a result, sufficient artificial heart flow was provided. For a totally implantable type VAD, left heart bypass of almost 100% may become necessary in some situations. Therefore, apex approaches of left heart bypass may be desirable. From an anatomical consideration, an apex of the heart is suitable for the VFP of this totally implantable type. In the left heart bypass for which the apex of the heart was used, an almost 100% bypass was possible. This is a requirement that is important when waiting for recovery of sufficient cardiac function. It is also important that left heart circulation is maintained fully by an artificial heart of the complete implantation type. The VFP was considered to be useful as a totally implantable type artificial heart from the results.
In the clinical application of supporting circulation, the treatment of a patient with pulmonary hypertension is very important. We developed the electromagnetically driven vibrating flow pump (VFP) as a totally implantable type ventricular assist system. The artificial heart driven by electromagnetic forces creates high speed oscillation flow around 10-50 Hz. Assistance by high-speed oscillation flow has an interesting influence on the cardiovascular system. In this study, we carried out research on the influence such oscillation flow had on the pulmonary arterial vessels, and the supporting flow wave-form that controlled pulmonary vascular resistance was considered. Six healthy adult goats of both sexes were used in the experiments. We carried out inhalation anesthesia and performed intubation. The thorax was opened through left fourth rib resection. Right heart bypass was performed from the right atrium to the pulmonary artery. The flow of right heart assistance was maintained within 20-25% of total flow. Our purpose was to add flow of a specific high frequency to the right heart circulation. The hemodynamic parameters were recorded on a magnetic tape data recorder and input into a computer through an A-D converter. A result identified was that the pulmonary vascular resistance changed according to the alteration of the driving frequency of the VFP even during the same flow assistance. The resistance of the pulmonary arterial vessels became smaller when the driving of the VFP of 30 Hz was added to the right heart circulation. This was significant even when compared with continuous flow right heart assist. The characteristics of impedance appeared to have interesting alterations as well. Control of pulmonary vascular resistance by right heart assistance becomes possible if these results are applied. Accordingly, it may become one of the choices for treatment of a patient with pulmonary hypertension.