| Research Abstract |
In this project, we investigated the relationships among variability and nonlinear dynamics of heart rate, endothelial function and circadian variation of blood pressure in various physiological and clinical conditions. The major findings are as follows :
(1) Chronic inhibition of NO synthesis by administration of N(G)-nitro-L-arginine methyl ester lead sustained hypertension and bradycardia in freely moving canines. In this condition, despite that heart rate variability assessed as standard deviation of 24-h R-R interval was increased, complexity of heart rate asses as spectral exponent of 1/f fluctuation was reduced. These indicate that variability and complexity of heart rate fluctuation show differential responses to chronic inhibition of NO synthesis and that circulatory regulation by NO may be involved in the genesis of complexity but not variability of heart rate.
(2) In patients with chronic atrial fibrillation who were followed-up for 33 months, decreased irregularity of R-R int
… More
erval assessed as approximate entropy predicted an increased risk for cardiac death, but not for fatal stroke. Although atrial fibrillation was an exclusion criteria in earlier studies of heart rate variability, nonlinear dynamics of heart rate includes prognostic information even in this condition.
(3) Well-rounded exercise training performed for 12 weeks in normotensive and mild-hypertensive elderly subjects decreased daytime blood pressure only in subjects who showed nocturnal blood pressure decline (dippers) ; however, the training did not change either daytime or nighttime blood pressure in nondipper normotensive or hypertensive subjects. Consequently, the type of circadian variation of blood pressure was unchanged by the training in any group. On the other hand, the endothelial function assessed as flow-mediated vasodilation response was reduced only in non-dipper hypertensive subjects at baseline and, only in this group, the training improved the endothelial function. Heart rate variability was unchanged by the exercise training. Less
|
