Time-Domain HRV During Slow Breathing Tracks Vagal, Not Sympathetic, Modulation: A Pharmacological Challenge.
Year: 2025
Type: preprint
Abstract: Time-domain heart rate variability (HRV) metrics are widely used to infer autonomic function and serve as indicators of vagal influence during a wide range of breathing conditions; however, their specificity to parasympathetic modulation under slow-paced breathing remains unclear. Building on prior pharmacological work, this study tested whether RMSSD, pNN50, SDNN, as well as exploratory Toichi nonlinear metrics, index vagal activity during slow respiration by using pharmacological manipulations. Six healthy adults completed eleven 1-minute breathing trials (4–9 breaths per minute) following administration of saline, esmolol (β-adrenergic blockade), or glycopyrrolate (muscarinic blockade). The researcher delivering the treatment was not blinded to assess safety for participants, but participants were blinded along with the analysis team. Parasympathetic blockade significantly suppressed all HRV metrics and increased heart rate, whereas sympathetic blockade had no effect. The effects of breathing rate, and the interaction of breathing rate with drug condition were non-significant, indicating that drug effects on HRV were consistent across respiratory conditions. These findings support the interpretation of time-domain HRV indices as reflecting predominantly parasympathetic rather than sympathetic activity, across a wide range of paced breathing conditions in controlled laboratory settings.
Institution: University of Arizona
Language: English
Subfield: Cardiology and Cardiovascular Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W4416149044