The impact of controlled breathing on autonomic nervous system modulation: analysis using phase-rectified signal averaging, entropy and heart rate variability

<i>Objective.</i>The present study investigated how breathing stimuli affect both non-linear and linear metrics of the autonomic nervous system (ANS).<i>Approach.</i>The analysed dataset consisted of 70 young, healthy volunteers, in whom arterial blood pressure (ABP) was measured noninvasively during 5 min sessions of controlled breathing at three different frequencies: 6, 10 and 15 breaths min^-1. CO₂concentration and respiratory rate were continuously monitored throughout the controlled breathing sessions. The ANS was characterized using non-linear methods, including phase-rectified signal averaging (PRSA) for estimating heart acceleration and deceleration capacity (AC, DC), multiscale entropy, approximate entropy, sample entropy, and fuzzy entropy, as well as time and frequency-domain measures (low frequency, LF; high-frequency, HF; total power, TP) of heart rate variability (HRV).<i>Main results.</i>Higher breathing rates resulted in a significant decrease in end-tidal CO₂concentration (<i>p</i>< 0.001), accompanied by increases in both ABP (<i>p <</i>0.001) and heart rate (HR,<i>p <</i>0.001). A strong, linear decline in AC and DC (<i>p <</i>0.001 for both) was observed with increasing breathing rate. All entropy metrics increased with breathing frequency (<i>p <</i>0.001). In the time-domain, HRV metrics significantly decreased with breathing frequency (<i>p <</i>0.01 for all). In the frequency-domain, HRV LF and HRV HF decreased (<i>p</i>= 0.038 and<i>p</i>= 0.040, respectively), although these changes were modest. There was no significant change in HRV TP with breathing frequencies.<i>Significance.</i>Alterations in CO₂levels, a potent chemoreceptor trigger, and changes in HR most likely modulate ANS metrics. Non-linear PRSA and entropy appear to be more sensitive to breathing stimuli compared to frequency-dependent HRV metrics. Further research involving a larger cohort of healthy subjects is needed to validate our observations.