Vagal blockade using atropine sulfate significantly decreased all heart rate variability indexes, particularly high-frequency power (P<0.001), which then increased linearly during recovery.
Do heart rate variability indexes accurately reflect vagal effects on the heart during recovery from vagal blockade?
Heart rate variability indexes, particularly high-frequency power, are predominantly under vagal control and increase linearly as vagal blockade decreases.
p-value: p=<0.001
Heart rate variability (HRV) has been widely used as a measure of vagal activation in physiological, psychological, and clinical examinations. We studied the within-subject quantitative relationship between HRV and vagal effects on the heart in different body postures during a gradually decreasing vagal blockade. Electrocardiogram and respiratory frequency were measured in subjects (8 endurance athletes and 10 participants of nonendurance sports) in supine, sitting, and standing postures before the blockade, under vagal blockade (atropine sulfate, 0.04 mg/kg), and four times during a 150-min recovery from the blockade. Fast Fourier transform was used to calculate low-frequency power (LFP, 0.04-0.15 Hz), high-frequency power (HFP, 0.15-0.40 Hz), and total power (TP, 0.04-0.40 Hz). A within-subject linear regression analysis of recovery time on each HRV index was conducted. Complete vagal blockade decreased all HRV significantly, particularly HFP (P < 0.001). A linear fit explained a large portion of the within-subject variance between recovery time and natural log-transformed (ln) HRV indexes in every posture, with coefficients of determination (R2) in the supine posture means (SD): 98 (SD 2)% for mean R-R interval, 87 (SD 10)% for lnLFP, 87 (SD 13)% for lnHFP, and 91 (SD 10)% for lnTP. Neither body posture nor endurance-training background had an impact on R2 values. There was marked between-subject variation in the R2 values, slopes, and intercepts. In conclusion, all HRV, particularly HFP, is predominantly under vagal control. Within subjects, lnLFP, lnHFP, and lnTP increased linearly with the gradually decreasing vagal blockade in all postures.
Martinmäki et al. (Tue,) conducted a other in Healthy subjects (n=18). Atropine sulfate (vagal blockade) vs. Baseline (before blockade) was evaluated on Heart rate variability (HRV) indexes (LFP, HFP, TP) (p=<0.001). Vagal blockade using atropine sulfate significantly decreased all heart rate variability indexes, particularly high-frequency power (P<0.001), which then increased linearly during recovery.