The Effects of an Acute Bout of Controlled Breathing on Short‐Term Heart Rate Variability

Abstract

Heart rate variability (HRV) is a non‐invasive measurement of the autonomic nervous system (ANS) which uses the frequency and time domains of an ECG to determine the magnitude of sympathetic and parasympathetic activity. Decreased HRV has been associated with several disease conditions whereas increased HRV indicates increased parasympathetic drive, which attenuates physiological and psychological stress conditions. The short‐term HRV, 5‐minute, average, denotes the temporal and dynamic functioning of the ANS and can be used to monitor acute changes in allosteric load.ObjectiveTo determine the effect of an acute bout of controlled breathing on the frequency and time domain measures of HRV.MethodsTwenty‐nine subjects (19.4 ± 0.8 yrs) volunteered for the meditation activity. The subjects attended a familiarization session to give informed consent, adjust to the lab setting, and to practice a guided breathing technique, 5 breaths/min (4 second inhale, 2 second hold, 6 second exhale). The subjects returned to the lab for a 15‐minute experimental protocol during which, they sat quietly breathing normal for 5 minutes to establish a baseline, followed by 5 minutes of the guided breathing protocol and finishing the protocol with 5 minutes of normal breathing.The ECG recorded continuously over the 15‐minute protocol using a Polar H10 heart rate monitor. The raw data was downloaded into a commercially available HRV software program and the 5‐minute average for heart rate (HR), low frequency (LF), high frequency (HF), peak HF/LF ratio, and root mean square of the standard deviation (rMSSD) were calculated for baseline, guided breathing and recovery periods.Results5 minutes of guided breathing elicited significant differences in measures within the frequency domain (HF and LF) and the time domain (rMSSD) heart rate variability. HF baseline was 52.4 ± 20.9 nu significantly decreased to 18.8 ±10.1 nu following controlled breathing, and significantly increased to 36.6 ± 13.3 nu during the recovery. LF baseline was measured at 48.6 ± 22.6 nu, increased to 81.2 ± 10.1 nu during controlled breathing and returned to 63.4 ± 17.3 nu during recovery. The rMSSD baseline was 64.9 ± 36.4. It increased significantly by 18.9% to 79.6 ± 37.8 and returned to baseline measures 60.7 ± 35.7 following the breathing exercise.DiscussionThe frequency domains of HF (parasympathetic) and LF (sympathetic) appear to respond in the opposite direction from the anticipated change in parasympathetic activity; however, these changes are indicative of slow controlled breathing. Within the time domain rMSSD has been identified as an indicator of short‐term parasympathetic activity, specifically vagal nerve activation. The rMSSD results demonstrated that controlled breathing provided significant parasympathetic response during the controlled breathing technique; however, the acute increase in activity was not sustainable past the breathing intervention.