Breathing at a rate of 5.5 breaths per minute with equal inhalation-to-exhalation ratio increases heart rate variability - Lin et al. (2014)
Slow breathing at 5.5 or 6 breaths/min significantly improves heart rate variability (HRV)
And equal inhale-to-exhale ratio causes greater improvements in HRV than shorter inhales followed by longer exhales
The Breathing Diabetic Summary
We have seen in previous studies that slow breathing increases heart rate variability (HRV) (see examples here and here). Breathing at a rate of ~5-6 breaths/min seems to elicit the greatest response with respect to HRV. However, as we have noted, there are many ways to achieve these breathing rates. Russell et al. (2017) showed that including a rest period after exhalation improved some aspects of HRV, whereas continuous breathing with equal inhales and exhales improved others. The goal of this study was similar to that of Russell et al. (2017), except that they chose to examine how 4 different breathing patterns affected HRV (none of which included a post-exhalation pause).
The four breathing patterns they examined were:
6 breaths/min, 5 sec inhale, 5 sec exhale
6 breaths/min, 4 sec inhale, 6 sec exhale
5.5 breaths/min, ~5 sec inhale, ~5 sec exhale
5.5 breaths/min, ~4 sec inhale, ~6 sec exhale
Previous studies have been inconclusive about which pattern is best for HRV. As previously stated, some find that longer exhales are better, while others show that equal inhale-to-exhale ratios are better. This study hoped to shed light on which is best.
Forty-eight college students participated in the study; however, one subject’s data was excluded, so there were 47 participants in the analysis. After 10 min of seated rest, each of the breathing protocols above were performed for 2 min, with a 1 min break in between each trial.
All four of the breathing patterns significantly increased 3 different aspects of HRV from their baseline values: SDNN, low frequency HRV, and the low frequency to high frequency ratio. They also found that all 4 breathing patterns led to higher levels of relaxation compared to at baseline during spontaneous breathing.
Comparing the different breathing patterns directly, they found that breathing at 5.5 breaths/min with equal inhale-to-exhale ration elicited the greatest positive response in HRV. The authors suspect that breathing with an equal inhale-to-exhale ratio might cause a greater increase in vagal tone and baroreflex, leading to greater HRV. However, it is important to note that all 4 breathing patterns significantly increased HRV. So, if you find breathing slowly with an extended exhale to be more comfortable, you can be sure that you are still significantly increasing HRV.
Overall, this paper showed that slow breathing significantly increased several aspects of HRV. Moreover, they showed that using an equal inhale-to-exhale ratio might cause a greater positive response with respect to HRV than a shorter inhale followed by a longer exhale. However, for us, the important take-home message is that we can significantly improve our HRV in just 2 min by simply breathing at a rate of 5.5 or 6 breaths/min. Let’s start today and improve this important overall marker of health!
Abstract from Paper
Objectives: Prior studies have found that a breathing pattern of 6 or 5.5 breaths per minute (bpm) was associated with greater heart rate variability (HRV) than that of spontaneous breathing rate. However, the effects of combining the breathing rate with the inhalation-to-exhalation ratio (I:E ratio) on HRV indices are inconsistent. This study aimed to examine the differences in HRV indices and subjective feelings of anxiety and relaxation among four different breathing patterns.
Methods: Forty-seven healthy college students were recruited for the study, and a Latin square experimental design with a counterbalance in random sequences was applied. Participants were instructed to breathe at two different breathing rates (6 and 5.5 breaths) and two different I:E ratios (5:5 and 4:6). The HRV indices as well as anxiety and relaxation levels were measured at baseline (spontaneous breathing) and for the four different breathing patterns.
Results: The results revealed that a pattern of 5.5 bpm with an I:E ratio of 5:5 produced a higher NN interval standard deviation and higher low frequency power than the other breathing patterns. Moreover, the four different breathing patterns were associated with significantly increased feeling of relaxation compared with baseline.
Conclusion: The study confirmed that a breathing pattern of 5.5 bpm with an I:E ratio of 5:5 achieved greater HRV than the other breathing patterns. This finding can be applied to HRV biofeedback or breathing training in the future.
I.M. Lin, L.Y. Tai, and S.Y. Fan, (2014) Breathing at a rate of 5.5 breaths per minute with equal inhalation-to-exhalation ratio increases heart rate variability, International Journal of Psychophysiology, 91, 206 – 211, http://dx.doi.org/10.1016/j.ijpsycho.2013.12.006.