大坂 元久

Background-Patients with a reduced nonlinear component of heart rate regulation have a poorer outcome. Methods and Results-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 (WRY). We also determined the linearity and nonlinearity of the correlation in SHR who were givers an angiotensin 11 receptor blocker, candesartan, orally for 2 weeks. The RSNA value was higher in SHR than in WRY, 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 WRY. 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 WRY. 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 driven candesartan, the RSNA value was lower, and the linearity was lower and nonlinearity higher than SHR given vehicle. Conclusions-Linear correlation between RSNA and blood pressure or renal blood flow was higher in SHR than in WRY, 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.

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 (RAI-RA2). The power spectrum of AF had a discrete peak around 17 Hz during Vs. After Vs was stopped, the discrete peak shifted from 17 Hz 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 (RAI 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.

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.

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.

Background: The triggering role of the autonomic nervous system in the initiation of ventricular tachycardia has not been established. To investigate the relationship between changes in autonomic activity and the occurrence of nonsustained ventricular tachycardia (NSVT) we examined heart rate variability (HRV) during the 2-hour period preceding spontaneous episodes of NSVT. Twenty-four subjects were identified retrospectively as having had one episode of NSVT during 24-hour Holter ECG recording. Methods: We measured the mean interval between normal beats (meanRR), the standard deviation of the intervals between beats (SD), the percentage of counts of sequential intervals between normal beats with a change of &gt 50 ms (%RR50), the logarithms of low- and high-frequency spectral components (lnLF, lnHF) of HRV for sequential 10-minute segments preceding NSVT. The correlation dimension (CDim) of HRV was calculated similarly for sequential 20-minute segments. We assessed the significance of the time-course change of each marker over the 120-minute period prior to NSVT onset. Results: MeanRR (P &lt 0.05), lnLF (P &lt 0.0001), lnHF (P &lt 0.0001), the natural logarithm of the ratio of LF to HF (ln[LF/HF] P &lt 0.05), and CDim (P &lt 0.05) showed significant time-course changes during that period, while SD and %RR50 did not. MeanRR, lnLF, lnHF, and CDim all decreased prior to the onset of NSVT, whereas ln(LF/HF) increased. We divided the subjects into two groups: one consisting of 12 patients with coronary artery disease and the second group of 12 patients without known coronary artery disease. Both groups showed significant changes (P &lt 0.05) of CDim, lnLF, and lnHF preceding the episodes of NSVT. Conclusions: Changes in the pattern of HRV prior to the onset of episodes of NSVT suggest that changes in autonomic activity may commonly play a role in the triggering of spontaneous episodes of NSVT in susceptible patients. The measured changes suggest a reduction in parasympathetic activity, perhaps in conjunction with an increase in sympathetic activity, may trigger NSVT.

The important role of alpha(1)-adrenergic receptors in the genesis of cardiac arrhythmias in ischemia and during reperfusion(1,2) has recently been elucidated. On the other hand, alpha(1)-adrenergic modulation of cardiac rhythm has promoted interest in myocardial alpha(1)-adrenoceptor research. The chronotropic action of alpha(1)-adrenergic stimulation is usually reported as inhibitory rather than excitatory.(3) However, in some species and in certain tissues, the positive chronotropic action of alpha(1)-adrenergic stimulation has also been reported. Moreover, there is an important developmental component to the alpha(1)-adrenergic receptor-effector system. Although alpha(1)-adrenergic stimulation decreases automaticity in the human atrium and in the ventricular conducting system of the adult rat,(4,5) an increase in automaticity brought about by or adrenergic stimulation was reported in isolated neonatal canine Purkinje fibers.(6) These findings suggest that the chronotropic response of cardiac tissues to alpha(1)-adrenergic stimulation changes from excitatory to inhibitory during development. This study clarifies the effect of alpha(1)-adrenergic stimulation on human sinus node automaticity, especially in relation to age.