Motohisa Osaka

Nippon Veterinary and Life Science University, Edo, Tokyo, Japan

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Publications (30)72.83 Total impact

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    ABSTRACT: Causative arrhythmias of sudden cardiac arrest (SCA) are changing in this age of improved coronary care. We examined the frequency of terminal arrhythmias and the electrical events prior to SCA. We analyzed 24-h Holter recordings in 132 patients enrolled from 41 institutions who either died (n = 88) or had an aborted death (n = 44). The Holter recordings were performed for diagnosing and evaluating diseases and arrhythmias in those without any episodes suggestive of SCA. In 97 (73%) patients, the SCA was associated with ventricular tachyarrhythmias and in 35 (27%) with bradyarrhythmias. The bradyarrhythmia-related SCA patients were older than those with a tachyarrhythmia-related SCA (70±13 years vs. 58±19 years, p<0.001). The most common arrhythmia for a tachyarrhythmia-related SCA was ventricular tachycardia degenerating to ventricular fibrillation (45%). The bradyarrhythmia-related SCA was caused by asystole (74%) or atrioventricular block (26%). Spontaneous conversion was observed in 37 (38%) patients with ventricular tachyarrhythmias. Of those, 62% of the patients experienced symptoms including syncope, chest pain or convulsion. A multivariate logistic analysis revealed that the independent predictors of mortality for tachyarrhythmia-related SCAs were an advanced age (odds ratio: 95% confidence interval, 1.04: 1.02-1.08) and ST elevation within the hour before the SCA (3.54: 1.07-13.5). In contrast, the presence of preceding torsades de pointes was associated with spontaneous conversion (0.20: 0.05-0.66). The most frequent cause of an SCA remains ventricular tachyarrhythmias. Advanced age and ST elevation before the SCA are risk factors for mortality in tachyarrhythmia-related SCAs.
    No preview · Article · Apr 2014 · Heart rhythm: the official journal of the Heart Rhythm Society
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    ABSTRACT: Background Causative arrhythmias of sudden cardiac arrest (SCA) are changing in this age of improved coronary care. Objectives We examined the frequency of terminal arrhythmias and the electrical events prior to SCA. Methods We analyzed 24-h Holter recordings in 132 patients enrolled from 41 institutions who either died (n = 88) or had an aborted death (n = 44). The Holter recordings were performed for diagnosing and evaluating diseases and arrhythmias in those without any episodes suggestive of SCA. Results In 97 (73%) patients, the SCA was associated with ventricular tachyarrhythmias and in 35 (27%) with bradyarrhythmias. The bradyarrhythmia-related SCA patients were older than those with a tachyarrhythmia-related SCA (70±13 years vs. 58±19 years, p<0.001). The most common arrhythmia for a tachyarrhythmia-related SCA was ventricular tachycardia degenerating to ventricular fibrillation (45%). The bradyarrhythmia-related SCA was caused by asystole (74%) or atrioventricular block (26%). Spontaneous conversion was observed in 37 (38%) patients with ventricular tachyarrhythmias. Of those, 62% of the patients experienced symptoms including syncope, chest pain or convulsion. A multivariate logistic analysis revealed that the independent predictors of mortality for tachyarrhythmia-related SCAs were an advanced age (odds ratio: 95% confidence interval, 1.04: 1.02-1.08) and ST elevation within the hour before the SCA (3.54: 1.07-13.5). In contrast, the presence of preceding torsades de pointes was associated with spontaneous conversion (0.20: 0.05-0.66). Conclusions The most frequent cause of an SCA remains ventricular tachyarrhythmias. Advanced age and ST elevation before the SCA are risk factors for mortality in tachyarrhythmia-related SCAs.
    No preview · Article · Jan 2014
  • Motohisa Osaka
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    ABSTRACT: The FitzHugh-Nagumo model of nerve conduction is also used as a model of cardiac excitability. We propose the replacement of a gating variable of the conductance of K+ current with Ca2+ current as a slow variable of the model, in which plays a key role in the cardiac action potential. Since ion currents conduct transversely as well as longitudinally through gap junctions between myocytes, particularly in ischemia, a respective diffusion term is involved to both equations of a fast variable and a slow variable. We show that only a small increase of a coefficient of the diffusion term of Ca2+ current may cause cardiac instabilities, which are presumed to cause breakup of conduction and finally a lethal arrhythmia, ventricular fibrillation. Particularly, these instabilities do not occur without the diffusion term of Ca2+ current.
    No preview · Article · Feb 2013
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    Motohisa Osaka

    Preview · Chapter · Jan 2012
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    ABSTRACT: Accentuated sympathetic nerve activity (SNA) is a risk factor for cardiovascular events. In this review, we investigate our working hypothesis that potentiated activity of neurons in the rostral ventrolateral medulla (RVLM) is the primary cause of experimental and essential hypertension. Over the past decade, we have examined how RVLM neurons regulate peripheral SNA, how the sympathetic and renin-angiotensin systems are correlated and how the sympathetic system can be suppressed to prevent cardiovascular events in patients. Based on results of whole-cell patch-clamp studies, we report that angiotensin II (Ang II) potentiated the activity of RVLM neurons, a sympathetic nervous center, whereas Ang II receptor blocker (ARB) reduced RVLM activities. Our optical imaging demonstrated that a longitudinal rostrocaudal column, including the RVLM and the caudal end of ventrolateral medulla, acts as a sympathetic center. By organizing and analyzing these data, we hope to develop therapies for reducing SNA in our patients. Recently, 2-year depressor effects were obtained by a single procedure of renal nerve ablation in patients with essential hypertension. The ablation injured not only the efferent renal sympathetic nerves but also the afferent renal nerves and led to reduced activities of the hypothalamus, RVLM neurons and efferent systemic sympathetic nerves. These clinical results stress the importance of the RVLM neurons in blood pressure regulation. We expect renal nerve ablation to be an effective treatment for congestive heart failure and chronic kidney disease, such as diabetic nephropathy.
    Preview · Article · Dec 2011 · Hypertension Research
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    ABSTRACT: Artificial pancreas technology, involving "closed-loop" controls with real-time blood glucose monitoring, has been increasing in reliability as its potential for clinical use and application grows. One such device, based on this technology, is the STG-22 (Nikkiso Co., Ltd., Tokyo, Japan) artificial pancreas apparatus. In order to assess the reliability and accuracy of the device for measuring blood glucose, it is important to compare its readings to those obtained using a 'gold standard' method, such as the hexokinase method. Therefore, in the present study, canine blood [glucose] measurements using the STG-22 were compared to those obtained using a previously established commercial reagent, Quickauto-Neo GLU-HK. Furthermore, two different sample types (whole blood versus plasma constituent) were compared to determine which sample type results in more accurate and optimal readings with the STG-22. Given that the STG-22 was not primarily designed for canine blood samples, results for canine blood samples were not accurate. Measurements performed by the STG-22 with whole blood were significantly lower than reference [glucose] counterparts. Alternatively, an opposite trend was observed with plasma measurements that were significantly higher. A conversion format using the following formula, Hexokinase [glucose] = STG-22 [glucose] × 1.407 + 1.532, was observed with canine samples in our study.
    Full-text · Article · Jun 2011 · Journal of Artificial Organs
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    ABSTRACT: No reliable precursor of sudden cardiac death is known. Holter electrocardiograms of 34 patients experiencing a cardiac event (event group, 20 deaths) were compared with 191 controls (no event group). The event group included 25 patients with ventricular fibrillation or acute myocardial infarction (AMI), and 9 with cardiac arrest due to complete atrioventricular block. The logarithms were calculated of the moving average of 5 successive values for the low-frequency component (LF), the high-frequency component (HF), and the ratio LF/HF of heart rate variability: ln(LF), ln(HF) and ln(LF/HF). A V-shaped trough appeared in the curve of ln(LF/HF) [sV-trough] or ln(HF) [pV-trough] before such an event in 31 patients in the event group. The V-trough was marked by a small variation lasting 2 h, an abrupt descent lasting 30 min, and a sharp ascent for 40 min. An sV-trough was observed in 22 patients before the onset of ventricular fibrillation or AMI. A pV-trough was observed in all 9 patients before the onset of complete atrioventricular block. In the no event group, an sV-trough and a pV-trough were observed in 10 subjects (5%) and 20 subjects (10%), respectively. The positive predictive accuracy of an sV-trough for ventricular fibrillation or AMI and that of a pV-trough for complete atrioventricular block was 88% and 100%, respectively. A previously unidentified V-trough of autonomic activity is a potential precursor of lethal events.
    No preview · Article · Sep 2010 · Circulation Journal
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    ABSTRACT: Approximately 5% of motor vehicle deaths are assumed to be occur because of a cardiac event thought to be triggered by multiple factors. One important factor is an imbalance of sympathetic and parasympathetic nervous activities, which can be measured by analyzing heart rate variability (HRV). Therefore, a system has been developed to make electrocardiographic (ECG) recordings outside the driver's awareness from the steering wheel (steering-ECG) with an algorithm to remove noise. Steering-ECG and ECG from a chest lead (chest-ECG) were recorded simultaneously in 10 normal subjects while they were driving for 90 min. For each of 4 parameters (instantaneous heart rate, low- and high-frequency components of HRV, and the ratio of these components in all subjects), mutual information was used to examine whether the fluctuation from the steering-ECG resembled that from the chest-ECG. The mutual information of each parameter was larger than 0.047 with 95% confidence interval (mutual information values vary from 0 to 1; threshold of significance: 0.047). Hence, the fluctuation of each steering-ECG parameter resembled its chest-ECG counterpart. This system heralds a new driver-safety strategy by reporting alteration of autonomic nervous activity during driving.
    No preview · Article · Nov 2008 · Circulation Journal
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    ABSTRACT: The nonlinearity of cardiovascular regulation is higher in normal physiology, whereas several diseases are characterized by a reduction in this nonlinearity. Reduced nonlinearity of heart rate regulation is a robust risk factor for high mortality in patients with myocardial infarction. We investigated the changes in linear and nonlinear correlations of cardiovascular regulation after administering drugs in hypertensive diabetic rats. Type 1 diabetes was induced in rats by intraperitoneally injecting spontaneously hypertensive rats with streptozotocin. The animals were then divided into 4 groups and each group was given vehicle, candesartan, amlodipine, or insulin for 2 weeks. Blood pressure, heart rate, renal sympathetic nerve activity, and renal blood flow were simultaneously recorded in the conscious state, and the linear and nonlinear correlations were compared by using coherence and the mutual information method. Candesartan and amlodipine decreased blood pressure to a similar extent, but renal sympathetic nerve activity was significantly lower in the candesartan group than in the vehicle group. The renal sympathetic nerve activity in the insulin group was also lower than in the vehicle group. There were no significant differences in linear correlation among the 4 groups. In contrast, the nonlinear correlations between renal sympathetic nerve activity and blood pressure in the candesartan group and the insulin group were significantly higher than in the vehicle group. Candesartan and insulin decreased renal sympathetic nerve activity and increased the nonlinearity. These results suggest that reducing the activity of renin-angiotensin system and insulin that lowers blood glucose level may improve autonomic nervous system dysfunction and neurohumoral regulation of the cardiovascular system in diabetic hypertensive rats.
    Preview · Article · Nov 2008 · Hypertension Research
  • Motohisa Osaka
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    ABSTRACT: Nowadays various fields, such as physics, chemistry, biology, and economics, have been linked under the regime of nonlinear dynamics. Medicine is no exception. One of the hottest topics in circulatory medicine is to discover a marker that indicates cardiac sudden death. Fractal is a noted concept of nonlinear dynamics and may be a marker. It means self-similarity. Although a phenomenon that has a fractal nature looks complicated, its origin is a simple universal law.
    No preview · Article · Nov 2007 · Journal of Nippon Medical School
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    ABSTRACT: Some cases of traffic accidents are assumed to be due to the occurrences of cardiac events during driving, which are thought to be induced by imbalance of autonomic nervous activities. These can be measured by analyzing heart rate variability. Therefore, we developed a new system of steering-wheel electrocardiogram with a soft-ware to remove noises. We compared the trends of sympathetic and parasympathetic nerve activities measured from the steering-wheel electrocardiograms with those recorded simultaneously from chest leads. For each parameter of instantaneous heart rate, low- or high-frequency component of heart rate variability in all the cases, the trend from the steering-wheel electrocardiogram resembled that from the chest-lead electrocardiogram. In 3 of 7 subjects, the trend of LF/HF showed a strong relationship between the steering-wheel electrocardiogram and the chest-lead electrocardiogram. Our system will open doors to a new strategy to keep a driver out of a risk by notifying it while driving.
    No preview · Article · Jul 2007
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    ABSTRACT: The mechanism of 1/f scaling of heartbeat intervals remains unknown. We recorded heartbeat intervals, sympathetic nerve activity, and blood pressure in conscious rats with normal or high blood pressure. Using nonlinear analyses, we demonstrate that the dynamics of this system of 3 variables is low‐order chaos, and that sympathetic nerve activity leads to heartbeat interval and blood pressure changes. It is suggested that 1/f scaling of heartbeat intervals results from the low‐order chaos of these variables and that impaired regulation of blood pressure by sympathetic nerve activity is likely to cause experimentally observable steeper scaling of heartbeat intervals in hypertensive (high blood pressure) rats. © 2004 American Institute of Physics
    No preview · Article · Apr 2004

  • No preview · Article · Feb 2004 · Journal of Hypertension

  • No preview · Article · Feb 2004 · Journal of Hypertension
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    ABSTRACT: Where is the place which should be helped in a patient with congestive heart failure? The answer may be contraction of the heart. At Tohoku University, development research of "the artificial myocardium" has been conducted, using a ball screw type electromagnetic motor. Furthermore, super-miniaturization is being attempted at present. Thus, a system with shape memory alloy is being developed. The cooling speed problem was solved by the application of the Peltier element. A drive at a speed equal to that of a heartbeat was realized by the application of this system. At present, a ventricular assist device is used for patients waiting for a heart transplant in Japan. An air driven type system disturbs a patient's QOL remarkably because it is connected to the drive device. With our concept, energy is provided by using the electromagnetic force from outside of the body by the use of transcutaneous energy transmission system. Magnetic shielding by amorphous fibers was used at Tohoku University to improve the total efficiency. A natural heart can alter the cardiac output corresponding to the demand. Artificial internal organs must participate in the system of the living body, too. Tohoku University has developed a resistance based artificial heart control algorithm, which simulated a baroreflex system to cope with every demand. Nano level sensing equipment is now under development at Tohoku University. At present, development is being conducted aiming at an "intelligent artificial myocardium".
    No preview · Article · Nov 2003 · Biomedecine [?] Pharmacotherapy
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    ABSTRACT: The mechanism of 1/f scaling of heartbeat intervals remains unknown. We recorded heartbeat intervals, sympathetic nerve activity, and blood pressure in conscious rats with normal or high blood pressure. Using nonlinear analyses, we demonstrate that the dynamics of this system of three variables is low-order chaos, and that sympathetic nerve activity leads to heartbeat interval and blood pressure changes. It is suggested that impaired regulation of blood pressure by sympathetic nerve activity is likely to cause experimentally observable steeper scaling of heartbeat intervals in hypertensive (high blood pressure) rats.
    Preview · Article · May 2003 · Physical Review E
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    ABSTRACT: Although there exist several different models for the excitability of cardiac and nerve cells, the number of ionic currents that determine this excitability is not clearly known. On the other hand, the chaotic behavior of excitable cells has recently been demonstrated. The science of complex dynamics provides tools for the reconstruction of the original dynamics from a time series of observed data. We determined the degrees of freedom for the excitability of a single cardiac pacemaker cell by chaotic analysis of a time series of action potentials (APs) recorded from the rabbit sinus node. We provide evidence that at least 12 variables are needed to determine the AP. From our findings, we conclude that a new model for the cardiac pacemaker mechanism may be needed, because previous models could deal only with fewer than 12 variables. Our approach based on our observation of a time series offers a powerful tool for constructing a model for the underlying biological mechanism.
    No preview · Article · Apr 2003 · Physica D Nonlinear Phenomena
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    ABSTRACT: Objective: Patients with reduced nonlinear component of heart rate regulation show a poor prognosis. We previously reported that the linear correlation between renal sympathetic nerve activity (RSNA) and blood pressure (BP) was significantly higher and the nonlinear correlation was lower in spontaneously hypertensive rats (SHR) than in Wistar-Kyoto rats. This time, we examined whether the linear and nonlinear correlation between RSNA and BP would change in SHR treated with angiotensin II receptor blocker (candesartan) or calcium channel blocker (amlodipine) orally for 2 weeks. Further, to elucidate mechanisms underlying the reduced linearity by amlodipine, we examined whether the linear and nonlinear correlation between RSNA and BP would change in SHR treated with amlodipine and L-NAME orally for 2 weeks. Methods: By recording BP, RSNA, heart rate, and ipsilateral RBF simultaneously in conscious state, we compared the linear (coherence of transfer function) and nonlinear (mutual information method) correlations between RSNA and BP in SHR treated with drugs. 〈 Protocol 1 〉 candesartan (1mg/kg/day, n = 13), amlodipine (5mg/kg/day, n = 7) or vehicle (n = 7) was given orally for 2 weeks to SHRs. 〈 Protocol 2 〉 combination of amlodipine (5mg/kg/day) and L-NAME (1.5mg/kg/day, n = 9), amlodipine (5mg/kg/day, n = 7), or vehicle was given orally for 2 weeks to SHRs. Results: 〈 Protocol 1 〉Mean RSNA was significantly decreased in candesartan group despite the lower BP and larger RBF, whereas RSNA did not decrease in the amlodipine group. The coherence (the linearity) between RSNA and BP at 0-1.0 Hz was significantly reduced in both candesartan and amlodipine groups compared with vehicle group. In contrast, mutual information of the correlation between RSNA and BP increased in both candesaratan and amlodipine groups. 〈 Protocol 2 〉 The coherence between RSNA and BP was significantly higher and mutual information was lower in SHR treated with amlodipine plus L-NAME compared with SHR treated with only amlodipine. Conclusions: The data regarding candesartan suggest that blockades of the reninangiotensin system and sympathetic nervous system contribute to the reduced linearity and increased nonlinearity. However, since this is not the case with amlodipine, increased nitric oxide contributed to the improved neural regulation by the calcium channel blocker. Since potentiated sympathetic nerve activity and high linearity are risk factors for cardiovascular events, drugs that reduce sympathetic nerve activity and normalize the neural regulation are beneficial to prevent cardiovascular events in hypertensive patients.
    No preview · Article · Jan 2003
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    ABSTRACT: Patients with a reduced nonlinear component of heart rate regulation have a poorer outcome. We investigated whether a nonlinear correlation between renal sympathetic nerve activity (RSNA) and blood pressure or renal blood flow is reduced in conscious, spontaneously hypertensive rats (SHR) by comparing them with normotensive Wistar-Kyoto rats (WKY). We also determined the linearity and nonlinearity of the correlation in SHR who were given an angiotensin II receptor blocker, candesartan, orally for 2 weeks. The RSNA value was higher in SHR than in WKY, and coherence peaks of transfer function were found at 0.05 and 0.80 Hz (ie, below respiratory- and cardiac-related fluctuations). The coherence (linearity) of the transfer function was significantly higher and gain was smaller in SHR than in WKY. Because mutual information values (linear and nonlinear correlation) were similar in both strains, we found the nonlinear correlation to be lower in SHR than in WKY. Time delay values calculated by the mutual information method demonstrated that RSNA preceded blood pressure and renal blood flow by 0.5 to 1.0 s. In SHR given candesartan, the RSNA value was lower, and the linearity was lower and nonlinearity higher than SHR given vehicle. Linear correlation between RSNA and blood pressure or renal blood flow was higher in SHR than in WKY, whereas the nonlinear correlation was lower. Oral treatment with candesartan increased the nonlinearity and reduced the linearity in SHR. Increased RSNA and the renin-angiotensin system may be responsible for the lower nonlinearity and higher linearity in hypertension.
    Preview · Article · Aug 2002 · Circulation
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    ABSTRACT: Atrial fibrillation (AF) is often described as a disorganized phenomenon, but many features that qualitatively suggest an underlying order have recently been reported. The present study aimed to disclose this underlying order of AF in a quantitative manner, using a new method of mutual information (MI), which is a measure for gauging the general correlation between 2 time series. Frequency analysis and the MI method were used to analyze 5 epicardial potentials on both atria during AF induced by vagal stimulation (Vs) in 15 dogs. Unipolar electrodes were placed on the right atrial appendage (Rap), the high right atrium (HRA), and the left atrial appendage (Lap). The other 2 electrodes were placed equidistantly between HRA and Rap (RA1-RA2). The power spectrum of AF had a discrete peak around 17Hz during Vs. After Vs was stopped, the discrete peak shifted from 17Hz to 7 Hz on all epicardial leads. Taking RA2 as a reference, MI was calculated between RA2 and each of the other electrodes. The MI values (0.066+/-0.005) were greater than 0.047 (the critical value for correlated data) even during Vs. The MI values increased significantly from the highly active process of AF during Vs to the less active one (0.126+/-0.006) before termination of AF. In addition, the MI values increased more at the electrodes close to RA2 (RA1 and Rap) than at those far from it (HRA and Lap). These findings suggest that multiple wavelets, which are not random, progressively organize into a few major waves toward the termination of AF; therefore, AF is not a random phenomenon in this model.
    No preview · Article · Mar 2001 · Japanese Circulation Journal

Publication Stats

280 Citations
72.83 Total Impact Points

Institutions

  • 2008-2014
    • Nippon Veterinary and Life Science University
      Edo, Tokyo, Japan
  • 1995-2007
    • Nippon Medical School
      • • Department of Life Information Sciences
      • • Institute of Gastroenterology
      • • Nippon Medical School Hospital
      • • Department of Internal Medicine
      Edo, Tokyo, Japan
    • Massachusetts Institute of Technology
      • Division of Health Sciences and Technology
      Cambridge, MA, United States