During slow-paced breathing between 4.6 to 6.5 bpm, you can examine your client's raw heart rate (HR) and respiration waveforms, autonomic, time- and frequency-domain measurements, and client self-reports.
Check the Raw Waveforms
1. Breathing should follow the pacing display.
2. HR and respirometer peaks and troughs should coincide.
3. The heart rate and respirometer waveforms should be rhythmic and ocean-like.
4. HR peak-to-trough differences (i.e., respiratory sinus arrhythmia; RSA) should increase.
Check the Metrics 1. End-tidal CO2 (i.e., the percentage of CO2 in exhaled air at the end of exhalation) should fall between 35 and 45 mmHg.
2. Hand temperature may increase while skin conductance level decreases.
3. HR Max - HR Min and RMSSD should increase.
4. Low-frequency (LF) power should increase, centered near 0.1 Hz, ideally with a single peak (see the left spectral plot; Lehrer & Gevirtz, 2014).
Check Your Client's Experience 1. Your client enjoyed low-and-slow breathing. 2. Training did not feel effortful. 3. Your client did not experience negative reactions. Summary
HRV biofeedback with slow-paced breathing can immediately increase RSA 4-10 times compared with resting baselines. Graphic adapted from Gevirtz et al. (2016).
Caption: The red waveform shows HR oscillations while resting without breathing instructions or feedback. The blue waveform shows HR oscillations with HRV biofeedback and breathing from 4.5-6.5 bpm. Likewise, autonomic, time-domain, and frequency-domain measurements will likely change while your client breathes slowly. Changes in vagal tone (i.e., parasympathetic activity) and other HRV metrics during resting conditions may take weeks to months of HRV biofeedback training with daily practice. Although we train to increase LF power during slow-paced breathing, the natural log of high-frequency band power indexes vagal tone during resting baselines (i.e., breathing ~12-16 bpm with no feedback; Shaffer & Ginsberg, 2017). Full stop: do not expect to see increased LF power at rest. To Learn More
References
Gevirtz, R. N., Lehrer, P. M., & Schwartz, M. S. (2016). Cardiorespiratory biofeedback. In M. S. Schwartz & F. Andrasik (Eds.). Biofeedback: A practitioner’s guide (4th ed.). The Guilford Press.
Lehrer, P. M., & Gevirtz, R. (2014). Heart rate variability: How and why does it work? Frontiers in Psychology. https://doi.org/10.3389/fpsyg.2014.00756
Shaffer, F., & Ginsberg, J. P. (2017). An overview of heart rate variability metrics and norms. Frontiers in Public Health. https://doi.org/10.3389/fpubh.2017.00258