Biomedical subjects

Tomoyuki Yambe

Publications and source records attributed to Tomoyuki Yambe.

At least 19 recordsLinked to original sources

PubMed2006

Passive mechanical properties of large intestine under in vivo and in vitro compression.

This paper presents experimental data obtained from both in vivo and in vitro compression of the large intestine of goat. In vivo experimental data were obtained from compression tests on the large intestine of an anesthetized goat using force-displacement acquisition equipment. In vitro experimental data were also obtained from tissue excised after the in vivo experiments, and two types of data were then compared. The results demonstrated that the stress values had a strong dependence on the compressive rate in the in vivo experiments, although such effect was not distinct in the in vitro experiments. Additionally, at a lower compression rate, the intestinal tissues were found to be stiffer in the in vitro experiments than in the in vivo ones. This paper is a preliminary report on the mechanical properties of the large intestine based on in vivo and in vitro experimental data.

Animals↗

PubMed2006

Intravascular two-dimensional tissue strain imaging.

Our goal is to achieve the precise quantitative imaging of tissue elasticity in clinical settings. In the present study, we measured basic ultrasonic characteristics of atherosclerosis by two-dimensional (2D) intravascular tissue velocity imaging. Radio-frequency (RF) signal from a clinically used IVUS apparatus was digitized at 500 MSa/s and stored in a workstation. First, the correlation coefficient between two consecutive frames was calculated in the rotational direction and the rotational disuniformity was corrected to obtain the maximum correlation coefficient. Then, the polar coordinate images were converted into rectangular coordinate images and the images were divided into 64 by 64 square shaped regions of interest (ROIs). The correlation and displacement of the ROIs between the consecutive two frames were calculated by template matching method. Two-dimensional tissue velocity was defined as the vectors of displacement of ROI with 0.7 and more correlation. IVUS studies were performed in directional coronary atherectomy (DCA) procedures. The specimens excised by DCA were stained with Elastica-Masson's trichrome staining and CD68 immunochemical staining. Eleven cases (including two no re-flow cases and one perforation case) were intraoperatively observed by IVUS and the specimens obtained by DCA were observed by optical microscopy. The specimen from homogeneous 2D strain was collagen dominant fibrosis and the specimen from a lesion with complex vectors contained CD68 positive cells and degenerated collagen fibers, which indicated the plaque was vulnerable.

Algorithms↗

PubMed2006

Ultrasonic speed microscopy for imaging of coronary artery.

We have been developing a scanning acoustic microscope (SAM) system for medicine and biology featuring quantitative measurement of ultrasonic speed and attenuation of soft tissues. In the present study, we will propose a new concept ultrasonic speed microscopy that can measure the thickness and ultrasonic speed using fast Fourier transform of a single pulsed wave instead of continuous waves used in conventional SAM systems. Six coronary arteries were frozen and sectioned approximately 10 microm in thickness. They were mounted on glass slides without cover slips. The scanning time of a frame with 300 x 300 pixels was 121 s and two-dimensional distribution of ultrasonic speed was obtained. The ultrasonic speed was 1720 m/s in the thickened intima with collagen fiber, 1520 m/s in lipid deposition underlying fibrous cap and 1830 m/s in calcified lesion in the intima. These basic measurements will help understanding echogenecity in intravascular ultrasound (IVUS) images. Imaging of coronary artery with the ultrasonic speed microscopy provides important information for study of IVUS coronary imaging.

Algorithms↗

PubMed2006

Preclinical development of SMA artificial anal sphincters.

This article presents some progress in the development for preclinical trials of an artificial anal sphincter using shape memory alloys. The novel device has been proposed and developed by the author's group at Tohoku University. It has two dominant features different from other systems, which are either clinically available or still under development. One is that a solid driving element, a combination of shape memory alloy (SMA) ribbons and silicone elastomer sheets with a layered structure, is adopted for the opening and closing functions of the artificial sphincter. The other is a sandwich mechanism for the closing of bowel to reduce the risk of buckling induced ischemia which has been reported in hydraulically driven artificial sphincters with a radial squeezing mechanism. The device has fewer parts inside the body and therefore be implanted more easily. A new design eliminating the risk of heat burns enables long-term implantation and brings the device closer to practical use. Functionality and safety of the device have been proved in three-month animal experiments.

Alloys↗

PubMed2006

Low-frequency electrical stimulation increases muscle strength and improves blood supply in patients with chronic heart failure.

BACKGROUND: This study was designed to evaluate the effects of low-frequency electrical stimulation (LFES) on muscle strength and blood flow in patients with advanced chronic heart failure (CHF). METHODS AND RESULTS: Patients with CHF (n=15; age 56.5 +/- 5.2 years; New York Heart Association III - IV; ejection fraction 18.7 +/- 3.3%) were examined before and after 6 weeks of LFES (10 Hz) of the quadriceps and calf muscles of both legs (1 h/day, 7 days/week). Dynamometry was performed weekly to determine maximal muscle strength (F(max); N) and isokinetic peak torque (PT(max); Nm); blood flow velocity (BFV) was measured at baseline and after 6 weeks of LFES using pulsed-wave Doppler velocimetry of the right femoral artery. Six weeks of LFES significantly increased F(max) (from 224.5 +/- 96.8 N to 340.0 +/- 99.4 N; p<0.001), and also PT(max) (from 94.5 +/- 41.5 Nm to 135.3 +/- 28.8 Nm; p<0.01). BFV in the femoral artery increased after 6 weeks from 35.7 +/- 15.4 cm/s to 48.2 +/- 18.1 cm/s (p<0.05); BFV values at rest before and after 6 weeks of LFES did not differ significantly. CONCLUSIONS: LFES may improve muscle strength and blood supply, and could be recommended for the treatment of patients with severe CHF.

Biomarkers↗

PubMed2006

Electrical stimulation of skeletal muscles. An alternative to aerobic exercise training in patients with chronic heart failure?

The aim of this study was to investigate whether electrical stimulation of skeletal muscles could represent a rehabilitation alternative for patients with chronic heart failure (CHF). Thirty patients with CHF and NYHA class II-III were randomly assigned to a rehabilitation program using either electrical stimulation of skeletal muscles or bicycle training. Patients in the first group (n = 15) had 8 weeks of home-based low-frequency electrical stimulation (LFES) applied simultaneously to the quadriceps and calf muscles of both legs (1 h/day for 7 days/week); patients in the second group (n = 15) underwent 8 weeks of 40 minute aerobic exercise (3 times a week). After the 8-week period significant increases in several functional parameters were observed in both groups: maximal VO2 uptake (LFES group: from 17.5 +/- 4.4 mL/kg/min to 18.3 +/- 4.2 mL/kg/min, P < 0.05; bicycle group: from 18.1 +/- 3.9 mL/kg/min to 19.3 +/- 4.1 mL/kg/min, P < 0.01), maximal workload (LFES group: from 84.3 +/- 15.2 W to 95.9 +/- 9.8 W, P < 0.05; bicycle group: from 91.2 +/- 13.4 W to 112.9 +/- 10.8 W, P < 0.01), distance walked in 6 minutes (LFES group: from 398 +/- 105 m to 435 +/- 112 m, P < 0.05; bicycle group: from 425 +/- 118 m to 483 +/- 120 m, P < 0.03), and exercise duration (LFES group: from 488 +/- 45 seconds to 568 +/- 120 seconds, P < 0.05; bicycle group: from 510 +/- 90 seconds to 611 +/- 112 seconds, P < 0.03). These results demonstrate that an improvement of exercise capacities can be achieved either by classical exercise training or by home-based electrical stimulation. LFES should be considered as a valuable alternative to classical exercise training in patients with CHF.

Bicycling↗

PubMed2006

Impact of type A behavior on brachial-ankle pulse wave velocity in Japanese.

Pulse wave velocity (PWV) is the velocity of a pulse wave traveling a given distance between 2 sites in the arterial system, and is a well-known indicator of arteriosclerosis. Brachial-ankle PWV (baPWV) is a parameter more simple to obtain, compared with the conventional PWV, and is an easy and effective means of evaluating arteriosclerosis. BaPWV can be obtained by only wrapping the four extremities with blood pressure cuffs, and it can be easily used to screen a large number of subjects. Type A behavior has been confirmed as an independent risk factor for the development of coronary heart disease. To examine the relationship between Type A behavior and arteriosclerosis, 307 normal Japanese subjects were classified into either a Type A group (n = 90) or a non-Type A group (n = 217) by using Maeda's Type A Scale. BaPWV was evaluated using a PWV diagnosis device. The baPWV in the Type A group was significantly higher than that obtained in the non-Type A group. The baPWV showed a positive correlation with age both in the Type A group and in the non-Type A group; however, the straight-line regression slope of baPWV versus age in the Type A group was significantly larger than that in the non-Type A group. Therefore, our results suggest that arteriosclerosis might be promoted earlier in subjects expressing the Type A behavior pattern. Type A behavior pattern is confirmed as a risk factor for arteriosclerosis, and may increase the risk of the cardiovascular disease related to arteriosclerosis.

Adult↗

PubMed2005

Fundamental study of ultrasonic-measurement-integrated simulation of real blood flow in the aorta.

Acquisition of detailed information on the velocity and pressure fields of the blood flow is essential to achieve accurate diagnosis or treatment for serious circulatory diseases such as aortic aneurysms. A possible way to obtain such information is integration of numerical simulation and color Doppler ultrasonography in the framework of a flow observer. This methodology, namely, Ultrasonic-Measurement-Integrated (UMI) Simulation, consists of the following processes. At each time step of numerical simulation, the difference between the measurable output signal and the signal indicated by numerical simulation is evaluated. Feedback signals are generated from the difference, and numerical simulation is updated applying the feedback signal to compensate for the difference. This paper deals with a numerical study on the fundamental characteristics of UMI simulation using a simple two-dimensional model problem for the blood flow in an aorta with an aneurysm. The effect of the number of feedback points and the feedback formula are investigated systematically. It is revealed that the result of UMI simulation in the feedback domain rapidly converges to the standard solution, even with usually inevitable incorrect upstream boundary conditions. Finally, an example of UMI simulation with feedback from real color Doppler measurement also shows a good agreement with measurement.

Aortic Aneurysm, Thoracic↗

PubMed2005

Development of the pulsation device for rotary blood pumps.

A rotary blood pump (RP) is desirable as a small ventricular assist device (VAD). However, an RP is nonpulsatile. We tried to develop a device that attaches a pulse to the RP. We also tried to develop a pulse-generating equipment that was not air-pressure driven. The ball screw motor was considered a candidate. The application of a small-sized shape memory alloy was also attempted. An electrohydraulic system was adopted, and actuator power was connected to the diaphragm. The diaphragm was placed on the outer side of the ventricle. Most RPs that have been developed all over the world drain blood from the ventricle. The wave of a pulse should be generated if a pulse is added by the drawn part. The output assistance from the outer side of the ventricle was attempted in animal experiments, and the device operated effectively. This device can be used during implantable operation of RP. This may serve as an effective device in patients experiencing problems in peripheral circulation and in the function of internal organs.

Animals↗

PubMed2005

Comparison of brachial-ankle pulse wave velocity in Japanese and Russians.

Pulse wave velocity (PWV) is a well-known indicator of arterial stiffness and a marker of the presence of vascular lesions. Cardiovascular mortality in Russia has become the highest in the world. The Japanese are enjoying long lives, and the mortality caused by cardiovascular diseases has thus far remained at lower levels than that in Russia. In this study, we focused on brachial-ankle pulse wave velocity (baPWV) obtained from normal human subjects in Russia as well as in Japan, and compared their respective cardiovascular risks. We evaluated baPWV in 337 Japanese and 138 Russian healthy subjects. The baPWV was recorded using a PWV diagnosis device. BaPWV was measured between 2 locations of the arterial tree. The baPWV in the Russian group was significantly higher than that obtained in the Japanese of two groups categorized by age (40-59 years and 60- years). Further, body mass index (BMI), systolic blood pressure (SBP) and diastolic blood pressure in the Russian group were significantly higher than those obtained in Japanese in three age groups (under 39 years, 40-59 years, and 60- years). Moreover, the baPWV indicated a positive correlation with age, BMI and SBP in both Japanese and Russians, although the increasing trend of the baPWV against age of the Russian group had a larger value than that of the Japanese. Therefore, we suggest that arterial stiffness might be promoted earlier in the Russian group, which might be the main cause of the increased cardiovascular risk in Russia.

Adult↗

PubMed2005

Non-blood contacting electro-hydraulic artificial myocardium (EHAM) improves the myocardial tissue perfusion.

Artificial heart (AH) and ventricular assist devices (VAD) are widely used in the clinical setting to assist severe heart failure patients. The concept of direct cardiac compression (DCC) has been in use for several decades and has advantages over intravascular VAD. The process involves compressing the dysfunctional heart from its epicardial surface to avoid the thromboembolic events and decrease the complications and mortality. An Electro-hydraulic Artificial Myocardium (EHAM) system was designed and fabricated by Tohoku University. This system may assist cardiac contraction and create pulsatile blood flow. The aim of this study was to clearly define the hemodynamic efficiency of the EHAM system in myocardial tissue perfusion during its application in acute animal experiment. Eight healthy adult goats were used; left lateral thoracotomy was performed and the chest was opened by the resection of the 4th and 5th ribs. Hemodynamic parameters including ECG, blood pressure and cardiac output were continuously monitored. Myocardial tissue perfusion was measured by using Omega flow laser fiber attached to the surface of the heart. During the EHAM compression, and increase in blood pressure and myocardial tissue perfusion was observed in all animals when compared with pre-assisted mode. To conclude, EHAM effectively improves myocardial tissue perfusion and increases the pressure on the initiation of direct cardiac compression immediately. Thus it can be a potentially valuable adjunct in the management of severe heart failure.

Animals↗

PubMed2005

Sound speed scanning acoustic microscopy for biomedical applications.

Since 1985, we have been developing a scanning acoustic microscope (SAM) system for biomedical use and have been investigating the acoustic properties of various organs and disease states by using this SAM system. In biomedicine, SAM is useful for intraoperative pathological examination, study of low-frequency ultrasonic images, and assessment of biomechanics at a microscopic level. Recently, we have proposed a new concept -- acoustic microscopy -- using a single pulsed wave instead of continuous waves used in conventional SAM systems. In the present study, we compared two systems by measuring the same biological material. The sound speed image obtained by sound speed microscopy corresponded well to that obtained using a conventional SAM system. Lesions with hyaline degeneration showed a lower sound speed when compared with that of normal myocardium. Frequency domain analysis of amplitude and phase by both methods also showed similar characteristics. Although the data acquisition time of one frame was greater than that in conventional SAM, the total time required for calculation was significantly shorter. The SAM system can be applied to intraoperative pathological examination.

Animals↗

PubMed2005

Detection and correction of aliasing in ultrasonic measurement of blood flows with Ultrasonic-Measurement-Integrated simulation.

Detailed information of real blood flows is essential to develop an accurate diagnosis or treatment for serious circulatory diseases such as aortic aneurysms. Ultrasonic-Measurement-Integrated (UMI) simulation, in which feedback signals from the ultrasonic measurement make the simulation converge to the real blood flow, is a key to solving this problem. However, aliasing in the ultrasonic blood velocity measurement causes UMI simulation to converge to an erroneous result. In this paper, we have investigated the detection and the correction of aliasing in UMI simulation. The artificial force in the feedback of UMI simulation can be used as an index to detect the aliasing. We have proposed two ways for the correction of the aliasing. Correction A, in which measurement velocity is replaced with the computational one at the monitoring point where the aliasing is detected, substantially improves the accuracy of UMI simulation. Correction B, in which measurement velocity is replaced with an estimated Doppler velocity, can provide exactly the same result as that of UMI simulation using the nonaliased standard solution. Although correction B gives the most accurate result, correction A seems more robust and, therefore, a beneficial choice considering the other artifacts in the measurement.

Doppler Effect↗

PubMed2004

Comparison of heart rate variability and stroke volume variability.

In order to compare the heart rate variability (HRV) and stroke volume variability (SVV), supine electrocardiographic (ECG) and the time series data of left ventricular (LV) volume recordings were taken in 12 healthy adult male volunteers. The low frequency (LF) and high frequency (HF) peaks of HRV and SVV were evaluated quantitatively by power spectral analysis. The fractal dimension (FD) of the time series data was analyzed by the box-counting method. A LF peak around 0.1 Hz and a HF peak around 0.3 Hz were as clearly observed in the SVV spectrum as in the HRV spectrum. The LF/HF ratio in SVV was significantly lower than that in HRV, while the FD was significantly higher in SVV than in HRV. No significant correlation of HF, LF or FD was observed between HRV and SVV. Our results indicate that SVV provides different information about the activity of the autonomic nervous system than HRV.

Adult↗

PubMed2004

Development of an implantable artificial anal sphincter using a shape memory alloy.

BACKGROUND/PURPOSE: The authors created a new artificial anal sphincter using a shape memory alloy (AS-SMA) to treat fecal incontinence and evaluated its validity. METHODS: AS-SMA consists of 2 Ti-Ni plates to sandwich the intestine and generates a pressure of 55 mm Hg at its resting position. With the electric power supply, the 2 metals bend to form an almondlike shape making a maximum gap of 33 mm between each other at the temperature of 55 degrees C. The device was attached to the colostomy in a piglet and was operated several times a day for 1 month. Fecal continence, bowel movements, and general condition of the piglet were recorded. After the experiment, tissue damage around the device was investigated. RESULTS: Fecal continence was obtained while the device was in the resting position. When it was operated, bowel movements were observed. The bowel movements to operations ratio was 82:105 (78%). During the experiment, the animal had neither abdominal distension nor vomiting. At the autopsy, there was mild inflammation and shallow burns around the device. No compression injury was detected. CONCLUSIONS: AS-SMA achieved fecal continence of the colostomy. With reduction of the associated side effects, it would be a potential substitute for an impaired anal sphincter.

Alloys↗

PubMed2004

A Japanese-Russian collaborative study on aging and atherosclerosis.

In Russia, the average life span is decreasing. This phenomenon has not been previously observed in the western hemisphere during periods of relative peace. Although this trend can be attributed to various causes, the available statistics suggest that approximately 55% of the total mortality in Russia at the present time is due to cardiovascular events. Similarly, cardiovascular events are also increasing in Japan and are associated with changes in eating habits. A Japanese-Russian international collaborative study was therefore initiated to investigate this. Data on 102 normal Russian subjects were obtained from a total of 345 patients treated at the Smolensk State Medical Academy outpatients' clinic. The data on the Japanese patients were collected at Tohoku University, Tohoku Rosai Hospital, and Fukuda Denshi Company. Sixty-seven healthy male Japanese volunteers were compared with 44 healthy male Russian patients. In this study, Vasera VS1000 (Fukuda Denshi, Tokyo) was utilized to measure pulse wave velocity (PWV). Linear regression analysis was performed, and the results showed that brachial-ankle PWV (baPWV) was significantly higher in the Russian compared with the Japanese study group. With regard to aging, PWV was found to increase both in the Japanese and Russian subjects, with a significant increase in the latter group during their 40s compared with the Japanese, and with this tendency being carried forward into the 50s. This may be the principal cause for the higher incidence of cardiovascular events reported among Russians. Furthermore, when a straight line regression analysis was performed, the zero axis intercept in both cases showed almost the same value. These results indicated that the PWV may be almost the same in Japanese and Russian populations at the time of birth. In conclusion, at the time of birth, there is no difference in the atherosclerotic status of Japanese and Russian infants. However, over time atherosclerosis becomes more apparent and progresses significantly in the case of Russian subjects. This finding is observed through the analysis of PWV. The present authors intend to continue their study aimed at preventing the further development of atherosclerosis through medical intervention.

Aging↗

PubMed2004

Brachio-ankle pulse wave velocity and cardio-ankle vascular index (CAVI).

In order to diagnose arteriosclerosis in any part of the body, pulse wave velocity (PWV) measurement is a useful approach. However, it is considered that the technique of PWV measurement should be simplified. A new method for measuring PWV has therefore been proposed in Japan. The PWV of the brachial artery (ba) and the ankle was measured by applying air pressure with the aid of a volume plethysmograph. Comparisons between the baPWV measurement method and the conventional method are currently being performed. Since satisfactory results have been obtained to date, baPWV has gained popularity throughout Japan. Since this method measures PWV in the arm and foot, it may be said that aortic PWV is not reflected though a large amount of past PWV measurements. BaPWV is influenced by blood pressure. With the baPWV technique, blood pressure compensation is not carried out. Furthermore, the pulse pressure is measured by air pressure; therefore any stimulus that exerts pressure on an artery may influence these results. Due to these reasons, a cardie-ankle vascular index (CAVI) has been proposed in which the pressure wave form indicating the closing of the aortic valve appears in the form of an arterial pressure wave after a fixed delay time. This delay is the time difference between the actual closing of the aortic valve and the measuring point. Prior to the introduction of baPWV, PWV was measured in the carotid artery and foot. As in traditional PWV, baPWV uses the delay time, but between the brachial artery and the ankle artery. However, the carotid artery differs from the brachial artery, and the measured value differs depending on whether the arteriosclerosis is present in the carotid artery or the brachial artery. CAVI is calculated from the ECG, PCG, brachial artery waveform and ankle artery waveform using a special algorithm. This new method represents a breakthrough in the diagnosis of atherosclerosis.

Ankle↗

PubMed2004

Addition of rhythm to non-pulsatile circulation.

The development of a rotary blood pump (RP) is desirable as it can be used as a small ventricular assistance device (VAD). However, a RP does not generate any pulse. It may be physiologically better for the patient if the RP could generate a pulse. We have attempted to develop a device that produces a pulse in the RP. Intra-aortic balloon pumping (IABP) is effective in producing a pulse. However, the IABP cannot be implanted inside the body. Therefore, an attempt was made to develop pulse-generating equipment that was not driven by air pressure. The ball screw motor was considered as a possible candidate. In the future, we plan to apply small shape memory alloys. An electrohydraulic system was adopted, and actuator power output was connected to the diaphragm. The diaphragm was placed outside the ventricle. Most RPs developed throughout the world drain blood from the ventricle. The pulse wave should be generated if a pulse is added by the part from which blood is being drawn. In this study, animal experiments were conducted and the output assistance was tested from outside the ventricle. The device operated effectively in the animal experiment. The RP can easily be equipped with this device at the time of performing the implant operation. For a patient with problems of peripheral circulation and the internal organ function, it may prove to be an effective device.

Animal Experimentation↗