Abstract
The variability of heart period, measured as the time distance between two consecutive QRS complexes from the electrocardiogram (RR), was exploited to infer cardiac vagal control, while the variability of the duration of the electrical activity of the heart, measured as the time interval from Q-wave onset to T-wave end (QT), was proposed as an indirect index of cardiac sympathetic modulation. This study tests the utility of the concomitant evaluation of RR variability (RRV) and QT variability (QTV) markers in typifying cardiac autonomic control of humans under different experimental conditions and of rat groups featuring documented differences in resting sympatho-vagal balance. We considered: (i) 23 healthy young subjects in resting supine position (REST) undergoing head-up tilt at 45° (T45) and 90° (T90) followed by recovery to the supine position; (ii) 9 Wistar (WI) and 14 wild-type Groningen (WT) rats in unstressed conditions, where the WT animals were classified as non-aggressive (non-AGG, n = 9) and aggressive (AGG, n = 5) according to the resident intruder test. In humans, spectral analysis of RRV and QTV was performed over a single stationary sequence of 250 consecutive values. In rats, spectral analysis was iterated over 10-min recordings with a frame length of 250 beats with 80% overlap and the median of the distribution of the spectral markers was extracted. Over RRV and QTV we computed the power in the low frequency (LF, from 0.04 to 0.15 Hz in humans and from 0.2 to 0.75 Hz in rats) band (LFRR and LFQT) and the power in the high frequency (HF, from 0.15 to 0.5 Hz in humans and from 0.75 to 2.5 Hz in rats) band (HFRR and HFQT). In humans the HFRR power was lower during T90 and higher during recovery compared to REST, while the LFQT power was higher during T90. In rats the HFRR power was lower in WT rats compared to WI rats and the LFQT power was higher in AGG than in non-AGG animals. We concluded that RRV and QTV provide complementary information in describing the functioning of vagal and sympathetic limbs of the autonomic nervous system in humans and rats.
Highlights
Heart period, measured as the time distance between two consecutive QRS complexes from the electrocardiogram (RR), exhibits spontaneous fluctuations usually referred to as RR variability (RRV)
Box-and-whisker plots of Figure 3 show the results of RRV (Figures 3A–C) and QT variability (QTV) (Figures 3D–F) analyses performed on human data as a function of the experimental condition (i.e., resting supine position (REST), tilt at 45◦ (T45), R45, T90, and R90)
HFRR power significantly decreased during T90 and increased during R90 compared to REST (Figure 3C). μQT was significantly reduced during both T45 and T90 and did not vary during R45 and R90 (Figure 3D). σQ2 T did not change with the experimental condition (Figure 3E)
Summary
Heart period, measured as the time distance between two consecutive QRS complexes from the electrocardiogram (RR), exhibits spontaneous fluctuations usually referred to as RR variability (RRV). Short-term RRV markers in humans are mainly associated with vagal modulation given that the magnitude of RR changes is dramatically reduced by full vagal blockade (Pomeranz et al, 1985). This consideration holds in humans and in rats (Japundzic et al, 1990; Cerutti et al, 1991; Silva et al, 2017) and this analogy strengthened the use of rats as an animal model of human autonomic cardiac control. In rats the HF power of RRV was utilized to typify the autonomic response to several types of stressors either pharmacological, interventional, or social (Akselrod et al, 1987; Japundzic et al, 1990; Cerutti et al, 1991; Rubini et al, 1993; Stauss et al, 1997; Sgoifo et al, 1998, 1999; Jaenisch et al, 2011; Carnevali et al, 2013; Carnevali and Sgoifo, 2014; Silva et al, 2016, 2017)
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