A Pilot Study on the Effectiveness of Heart Rate Variability Biofeedback on Healthy Subjects

Abstract: Heart Rate Variability (HRV) is a medical term describing the heart’s natural varying time difference between heartbeats (called NN-intervals). A higher HRV i.e. a larger variability between NN-intervals is connected to healthiness, and lower HRV to unhealthy states. Biofeedback (BF) is a method that can detect and send physiological signals back to the user on a screen. Every individual has a resonant frequency, and when breathing at this frequency, the interplay between blood pressure and respiration causes HRV to increase momentarily. HRV biofeedback aims at increasing HRV, by measuring heart rhythm and respiration to guide the user in resonant breathing. This thesis had the objective to investigate the effectiveness of one 20 minutes long biofeedback session with resonant frequency breathing. The hypothesis was that the time frame would be longer than two hours. It was carried out with 12 healthy volunteers, who participated in a biofeedback session with an Android application, and afterwards 5 minutes long ECG measurements were made every half hour for two hours. A control session was held with the same participants to give the trial more scientific strength. The result showed that a 20 min resonant breathing biofeedback session can elevate Standard Deviation of NN intervals (SDNN) significantly (p < 0.05), 2 hours after the biofeedback session. The conclusion was that the hypothesis cannot be rejected, but the result is too weak to strengthen it much. Further research is needed to draw more conclusions about the time frame of HRV elevations in healthy people.