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  • Title: [Time-sequential changes of vagal activity with aging].
    Author: Sakurabayashi T, Sawanobori T, Ishii H, Yoshizaki T, Tamura K.
    Journal: J Cardiol; 1993; 23(1):87-97. PubMed ID: 8164138.
    Abstract:
    We examined the correlation of the time-sequential variability of vagal activity with the heart, and then the circadian rhythm of vagal activity and its changes with aging were investigated. The subjects consisted of 154 healthy volunteers, 90 males and 64 females whose ages ranged from 12 to 83 years. Holter monitoring was performed continuously for 24 hours. RR interval and RR50 were measured using Ewing's method. Least square-fit of a cosine curve in a period of 24 hours of these parameters was calculated, and MESOR (midline estimating statistic of rhythm), amplitude and acrophase were determined. The results were as follows: 1. In all subjects, the circadian rhythms of the RR interval were significantly noted. MESOR, amplitude and acrophase of the RR interval were 0.83 +/- 0.07 sec (mean +/- SD), 0.16 +/- 0.06 sec and 19.6 +/- 33.8 degrees. MESOR and acrophase were not changed significantly by aging. Amplitude was significantly decreased by aging (r = -0.23, p < 0.01). 2. The circadian rhythm of RR50 was dominantly and significantly noted in 92 of 154 cases. MESOR of RR50 were 477 +/- 301 counts/hr and the amplitudes of RR50 were 319 +/- 209 counts/hr. These indices were significantly changed by aging (MESOR: r = -0.69, p < 0.01; amplitude: r = -0.51, p < 0.01). 3. Acrophase of RR50 was 30.0 +/- 47.8 degrees, and it became delayed by aging (r = 0.32, p < 0.01). In conclusion, 1) based on the cosinor analysis of time sequential changes of RR50, the circadian rhythm of cardiac vagal activity was validated. 2) Heart rate is determined chiefly by the intrinsic heart rate and the autonomic nervous system. At rest vagal activity to heart rate is dominant over sympathetic activity, and the intrinsic heart rate decreases by aging. So the fact that MESOR of RR interval was not changed by aging and that MESOR of RR50 decreased by aging indicated that vagal activity to the heart decreased with aging. 3) Vagal activity accelerated during the time between midnight and early morning.
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