Cardiac Vagal Control and Respiratory Sinus Arrhythmia during Hypercapnia in Humans

Abstract

Normoxic hypercapnia may increase high-frequency (HF) power in heart rate variability (HRV) and also increase respiratory sinus arrhythmia (RSA). Low-frequency (LF) power may remain unchanged. In this study, 5-min ECG recordings (N = 10) were analyzed in time and frequency domains while human subjects breathed normoxic 5% CO 2 (5%CO 2 ) or room air (RA). Tidal volume (V T ), inhalatory (T I ), and exhalatory (T E ) times of breaths in the final minute were measured. ECG time domain measures were unaffected by CO 2 inhalation (P > 0.05). Following natural logarithmic transformation (LN), LF LN was unaltered (RA: 7.14 ± 0.95 vs. 5%CO 2 : 7.35 ± 1.12, P > 0.05), and HF LN increased (RA: 7.65 ± 1.37 vs. 5%CO 2 : 8.58 ± 1.11, P < 0.05) with CO 2 inhalation. When changes in total power (NU) were corrected, LF NU decreased (RA: 34.4 ± 22.9 vs. 5%CO 2 : 23.8 ± 23

Indirect measures of human vagal withdrawal during head-up tilt with and without a respiratory acidosis

“…In the current study there was no evidence of tachycardia during hypercapnia when supine, consistent with a previous study [23]. However, others have reported small increases in heart rate with hypercapnia [24,25,31,32].…”

“…For example, HF cardiac variability may be abolished with administration of atropine while mean heart rate remains unchanged [30]. Equally, HF cardiac variability will increase markedly with a respiratory acidosis with minimal [25] or no change [23] in R-R interval.…”

“…However, directional changes in the LF component of HRV with tilting appear equivocal, with no change [14,18,21] or an increase [19,20,22] being reported for healthy subjects. Hypercapnia has consistently been shown to increase HF cardiac variability [7,[23][24][25], suggestive of an increase in respiratory sinus arrhythmia [24,[26][27][28] but shown to have variable effects on LF variability [29].…”

Quantitative mapping of cerebrovascular reactivity using resting-state BOLD fMRI: Validation in healthy adults

“…PETCO 2 fluctuations may result in and from respiration-rate changes (Sin et al, 2012) and heart-rate variations (Brown et al, 2007). A robust relationship between PETCO 2 fluctuations and the rs-fMRI signal was first reported by Wise et al (Wise et al, 2004) and reproduced by Chang et al (Chang and Glover, 2009).…”

“…Interestingly, the effects of RVT and CRV on the rs-fMRI signal were found to mirror each other (Petridou et al, 2009) and partially colocalize (Chang et al, 2009a). At the same time, intravascular CO 2 changes are also known to modulate CRV (Brown et al, 2007).…”