The Influence of Different Breathing Frequencies on the Autonomic Nervous System

Abstract

Heart rate variability (HRV) is a marker of autonomic nervous system flexibility and stress adaptability. It reflects the natural fluctuations in the time between heartbeats and is considered an indicator of the body's capacity to regulate physiological and psychological stress. Lower HRV is generally associated with reduced adaptability and increased vulnerability to stress [1].

At the Institute of Pathophysiology, University of Ljubljana, we explored whether slow-paced breathing could induce parasympathetic activation by testing the effects of six different breathing frequencies on HRV. The main objective of the preliminary study was to find the natural resonance frequency of each subject based on the measured data and reported experiences of comfort and relaxation across different breathing rates. Additionally, we wanted to assess the level of correlation between subjects’ perceived level of comfort and the calculated natural resonance frequency.

We tested six breathing frequencies: 4.0, 4.5, 5.0, 5.5, 6.0, and 6.5 breaths per minute. For each frequency, the exhalation was set to be 20% longer than the inhalation to encourage parasympathetic activation [2]. Subjects were instructed to follow the auditory cues of a paced breathing application. Each breathing trial lasted two minutes, followed by one minute of spontaneous breathing. After each trial, participants described their experience and rated the level of breathing comfort from 0 to 7 (0 least comfortable, 7 the most). Throughout the experiment, we tracked respiratory patterns using a breathing belt while continuously measuring ECG signals to monitor heart activity and electrodermal activity (EDA) to assess skin conductance to indicate the arousal of the sympathetic nervous system.

We analyzed the data with Kubios HRV software and calculated the natural resonance frequency of each participant using the resonance frequency assessment protocol [3]. Our analysis raises questions about its authority to define a person's optimal breathing frequency. Participants largely failed to identify this frequency themselves; only one matched the analysis. As no clear correlation emerged between perceived comfort and calculated optimal frequency, subjective experience challenges our conclusions – an issue further complicated by the limited sample size (n = 8).

Further research should aim to develop a suitable long-term resonance breathing protocol that would allow users to practice breathing at their natural resonance frequency, supporting regulation of the autonomic nervous system, improvement of HRV, and overall well-being. It should also address the gap between subjective experience and analytically derived optimal frequency. 

References

[1] F. Shaffer, R. McCraty, and C. L. Zerr, “A healthy heart is not a metronome: an integrative review of the heart’s anatomy and heart rate variability,” Frontiers in Psychology, vol. 5, no. 1040, Sep. 2014. doi: 10.3389/fpsyg.2014.01040.

‌[2] A. Zaccaro et al., “How breath-control can change your life: A systematic review on psycho-physiological correlates of slow breathing,” Frontiers in Human Neuroscience, vol. 12, no. 353, pp. 1–16, Sep. 2018. doi: 10.3389/fnhum.2018.00353. 

[3] P. Lehrer et al., “Protocol for Heart Rate Variability Biofeedback Training,” Biofeedback, vol. 41, no. 3, pp. 98–109, Sep. 2013. doi: 10.5298/1081-5937-41.3.08.