Comparing the Effects of Square, 4-7-8, and 6 Breaths-per-Minute Breathing Conditions on Heart Rate Variability, CO2 Levels, and Mood.

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Square and 4-7-8 breathing are popularly promoted by psychotherapists but have little empirical support. We hypothesized that breathing at 6 breaths per minute (bpm) would improve HRV, reduce blood pressure, and improve mood more than either square or 4-7-8 breathing. We also hypothesized square and 4-7-8 breathing would increase end-tidal CO2 (PETCO2). Eighty-four college students (60% female) had HRV measured at baseline and during 1) square breathing, 2) 4-7-8 breathing, 3) 6bpm with a 4:6 inhale-to-exhale ratio, and 4) 6bpm with a 5:5 ratio. We used a 3-lead electrocardiogram to measure HRV and a capnometer to measure PETCO2. We measured mood using the Scale of Positive and Negative Experience (SPANE) after each breathing condition. We used a repeated measures mixed effects model to examine the effects of each breathing technique on HRV, blood pressure, mood, and PETCO2 levels. Breathing at 6bpm increased HRV measures more than square or 4-7-8 breathing with small to medium effects. None of the breathing conditions resulted in meaningful changes in blood pressure or mood. Unexpectedly, breathing at 6bpm led to mild over-breathing. While various breathing techniques are used in psychotherapy, their relative efficacy remains unclear. This study found that breathing at 6bpm is likely more effective at increasing HRV than square or 4-7-8 breathing, albeit with a higher risk of over-breathing. Future studies could examine whether these effects hold over multiple weeks of breathing practice and attend to the effects of different breathing techniques on CO2 levels.