Motohisa Osaka

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

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Publications (27)56.51 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.
    Heart rhythm: the official journal of the Heart Rhythm Society 04/2014; · 4.56 Impact Factor
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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.
    Heart Rhythm. 01/2014;
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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.
    Hypertension Research 12/2011; 35(2):132-41. · 2.79 Impact Factor
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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.
    Journal of Artificial Organs 06/2011; 14(2):133-9. · 1.41 Impact Factor
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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.
    Circulation Journal 09/2010; 74(9):1906-15. · 3.58 Impact Factor
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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.
    Circulation Journal 11/2008; 72(11):1867-73. · 3.58 Impact Factor
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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.
    Hypertension Research 11/2008; 31(10):1941-51. · 2.79 Impact Factor
  • Motohisa Osaka
    Journal of Nippon Medical School 11/2007; 74(5):330-1.
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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.
    07/2007;
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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
    AIP Conference Proceedings. 04/2004; 708(1):306-309.
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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".
    Biomedecine [?] Pharmacotherapy 11/2003; 57 Suppl 1:122s-125s. · 2.07 Impact Factor
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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.
    Physical Review E 05/2003; 67(4 Pt 1):041915. · 2.31 Impact Factor
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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.
    Physica D Nonlinear Phenomena 04/2003; 178(s 1–2):118–126. · 1.67 Impact Factor
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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.
    Circulation 08/2002; 106(5):620-5. · 15.20 Impact Factor
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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.
    Japanese Circulation Journal 03/2001; 65(2):111-6.
  • Motohisa Osaka, Nobuyasu Ito
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    ABSTRACT: To determine the attractor dimension of chaotic dynamics, the box-counting method has the difficulty in getting accurate estimates because the boxes are not weighted by their relative probabilities. We present a new method to minimize this difficulty. The local box-counting method can be quite effective in determining the attractor dimension of high-order chaos as well as low-order chaos.
    International Journal of Modern Physics C 12/2000; 11:1519-1526. · 0.62 Impact Factor
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    ABSTRACT: Some string dynamics which are expected to show non-trivial correlations are proposed and studied. It is because we were motivated by the observation that some DNA sequences show spatial 1f correlation. Our model is based on a rule by which one string is split into two parts in the middle and another string is inserted between them when the strings are made longer. The basic model shows long-range correlations with a structure characteristic of cyclic patterns on the log-log plot of the spectrum. The effects of string cross-over and point-mutation are also studied. The cross-over destroys the structures appearing in the basic model and makes 1f-like correlation clear. The point-mutation makes the power spectrum flat as is expected from the white-noise nature. The analogy of the cross-over model with real DNA evolution dynamics is suggested.
    Physica D Nonlinear Phenomena 01/1999; 125(1):142-154. · 1.67 Impact Factor
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    ABSTRACT: T-wave alternans and QT dispersion were compared as predictors of the outcome of electrophysiologic study and arrhythmia-free survival in patients undergoing electrophysiologic evaluation. T-wave alternans was a highly significant predictor of these 2 outcome variables, whereas QT dispersion was not.
    The American Journal of Cardiology 12/1998; 82(9):1127-9, A9. · 3.21 Impact Factor
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    ABSTRACT: A mutual information (MI) method for assessment of the relationship between hemodynamic variables was proposed and applied to the analysis of heart rate (HR), arterial blood pressure (BP), and renal sympathetic nerve activity (RSNA) in artificial heart-implanted dogs to quantify correlation between these parameters. MI measures the nonlinear as well as linear dependence of two variables. Simulation studies revealed that this MI technique furnishes mathematical features well suited to the investigation of nonlinear dynamics such as the cardiovascular system and can quantify a relationship between two parameters. To constitute a model free of the natural heart, two pneumatically actuated ventricular assist devices were implanted as biventricular bypasses in acute canine experiments. RSNA was detected with the use of bipolar electrodes attached to the renal sympathetic nerve. Analysis of data during control revealed that correlation between HR and RSNA was higher than that between HR and BP and that between RSNA and BP (P < 0.05). Although RSNA seemed to fluctuate noncorrelatedly with BP in higher pacing rates, the MI values between them disclosed their strong correlation. Surprisingly, correlation between RSNA and BP was stronger during a pacing rate of 60 beats/min than during higher pacing rates and control (P < 0. 05). It is suggested that the baroreflex system may be susceptible to pacing rates during the total artificial heart state. We calculated the time delay between HR and RSNA, between RSNA and BP, and between HR and BP by regarding a time delay at which the maximum MI value between each pair of parameters was given as a physiological delay. Our results indicate that RSNA leads BP, BP leads HR, and RSNA leads HR during control (P < 0.05). We conclude that this method could provide a powerful means for measuring correlation of physiological variables.
    The American journal of physiology 11/1998; 275(4 Pt 2):H1419-33. · 3.28 Impact Factor
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    ABSTRACT: The frequency of ventricular premature beats (VPBs) has been related to the risk of mortality. However, little is known about the temporal pattern of occurrence of VPBs and its relationship to autonomic activity. Hence, we applied a general correlation measure, mutual information, to quantify how VPBs are generated over time. We also used mutual information to determine the correlation between VPB production and heart rate in order to evaluate effects of autonomic activity on VPB production. We examined twenty subjects with more than 3000 VPBs/day and simulated random time series of VPB occurrence. We found that mutual information values could be used to characterize quantitatively the temporal patterns of VPB generation. Our data suggest that VPB production is not random and VPBs generated with a higher value of mutual information may be more greatly affected by autonomic activity.
    Methods of Information in Medicine 01/1998; 36(4-5):257-60. · 1.08 Impact Factor

Publication Stats

129 Citations
56.51 Total Impact Points

Institutions

  • 2008–2014
    • Nippon Veterinary and Life Science University
      Edo, Tōkyō, Japan
  • 2011
    • National Defense Medical College
      • Division of Nephrology
      Tokorozawa, Saitama-ken, Japan
  • 1993–2007
    • Nippon Medical School
      • • Department of Life Information Sciences
      • • Nippon Medical School Hospital
      • • Department of Internal Medicine
      Tokyo, Tokyo-to, Japan
  • 2002
    • Keio University
      • Department of Internal Medicine
      Tokyo, Tokyo-to, Japan
  • 1995–1998
    • Massachusetts Institute of Technology
      • Division of Health Sciences and Technology
      Cambridge, MA, United States