Many adults with hypertension have inadequate control of blood pressure. Additional treatment options, including non-pharmacologic, are necessary to provide additional options to patients. Slow breathing techniques are the most common mind-body practice in the United States, but evidence regarding long-term effects on blood pressure are lacking. This study reports the effect of long-term slow breathing on blood pressure and changes in autonomic function. We found that in healthy adults, twelve weeks of slow breathing exercises resulted in a significant decrease in blood pressure measurements. The blood pressure decrease was more pronounced among participants with elevated baseline blood pressure (SBP > 120 and/or DBP > 90) exceeding the minimum clinically important difference for blood pressure change1. Changes in blood pressure were independent to slow breathing technique (E > I versus E = I). Changes in autonomic tone including spectral analyses (HF RR and LF sys), catecholamines, Valsalva maneuver, etc. showed poor correlation to changes in blood pressure.
Slow breathing has been implemented in various ways including specific rates, use of device to provide biofeedback, and as part of other mind-body interventions such as mindfulness, t’ai chi, and meditation. Unfortunately, most of these studies had a short duration (four to eight weeks) and were done on hypertensive subjects already on medications, and used a fixed slow breathing rate (most of them 6 breaths/minute). Many studies have measured the acute effects of slow breathing on blood pressure with long-term effects not being well documented in high quality studies. Meta-analyses have examined the clinical effectiveness and quality of research regarding the effects of slow breathing on blood pressure among hypertensives19,20. Chaddha et al found 15 device-guided breathing and two yoga-based slow breathing studies examining effects on blood pressure. Nine studies lacked an active control group. The slow breathing rate varied between studies. Most studies were sponsored by the manufacturer of RESPeRate or used the BreatheMAX inspiratory device (slow loaded breathing). Compliance to breathing interventions was very high among all trials with no adverse effects. The total estimated effect of slow breathing on SBP was − 5.88 mm Hg [-8.03—3.73] with high heterogeneity among studies (heterogeneity index, I2 = 83%). Device-based slow breathing reduced blood pressure less than yoga-based (-5.28 versus − 8.45 mm Hg). Device-based slow breathing reduced DBP by -2.97 mm Hg [-4.28—1.66]. Most recently, Herawati found 20 studies that used breathing exercises to lower blood pressure. Among these studies three did not show a blood lowering effect of slow breathing. The change in blood pressure ranged from 4-54.22/3–17 mmHg for systolic and diastolic blood pressures respectively. Most studies used some kind of device (either RESPeRate, SLOWB or loaded breathing). Also, most of them used a respiratory rate of 6 breaths/minute. In five of the 20 studies some measurements of autonomic tone were performed, and the results are contradictory probably in part because the different methodologies used to determine autonomic function. Oneda et al suggests that sympathetic activity is linked to breathing frequency21, while de Barros did not find changes in blood pressure, or autonomic function22.
Our study intervention varies as compared to prior studies in several ways. First, we screened patients to determine if they would be able to adhere and perform slow breathing. Second, slow breathing was titrated to the slowest comfortable breath rather than a fixed goal of breathing. This is consistent with how slow breathing is taught amongst the tradition of slow breathing in yoga (pranayama). Among participants with the highest baseline blood pressure in our study (SBP > 120, or DBP > 90), the reduction in blood pressure (SBP − 10.3 ± 7.9, DBP − 3.8 ± 5.5 mm Hg was greater than estimated total effects reported by Chaddha et al, and equivalent or greater than single antihypertensive therapy23. Our results have several limitations, the main one was the lack of a randomized normal breathing control group to account for a possible placebo or training effect. The addition of an observational control group with repeated measurements somewhat mitigates this limitation. Furthermore, it is reassuring that significant differences in blood pressure were selectively observed in subjects with higher blood pressure. Again, the addition of a control group reduces the possibility that this was due to a regression to the mean phenomenon, Finally, we excluded patients with hypertension which may have reduced our power to see potential effects on blood pressure.
Our results confirm previous studies that show differences in autonomic modulation between groups with normal blood pressure and elevated blood pressure24. We found that at baseline, high blood pressure groups have lower vagal tone (HFRRI). We also found differences in baroreflex sensitivity between groups. Prior studies that have found an acute reduction in blood pressure with slow breathing have hypothesized that slow breathing reduces blood pressure through decreases in sympathetic activity and/or increases in vagal tone21,25,26. In our results, spectral analyses did not indicate significant changes or correlation with blood pressure reduction. One possibility for these results is that spectral analyses do not capture changes in autonomic tone sufficiently for the slow breathing intervention and that more sensitive measurements of autonomic function such as direct measurement of muscle sympathetic nerve activity may provide additional information. More likely, our negative results may be explained by the small number of subjects with elevated blood pressure, which prevented us from seeing more dramatic changes that could occur in hypertensive subjects. Another possibility is slow breathing reduces blood pressure by other mechanisms such as endothelial function, oxidative stress, renal mechanisms, or salt metabolism27. Further research into how slow breathing reduces blood pressure is necessary.
The large reductions in blood pressure we observed support the need for a larger randomized controlled efficacy trial to further examine slow breathing interventions among hypertensive adults. There is a predominance of device-guided studies, and our study adds to the limited data available regarding effects of yoga-based slow breathing on blood pressure. This study is of public health importance given that small reductions in blood pressure are associated with significant improvement in health outcomes. In pharmacological studies, a 5mm Hg reduction in SBP reduces risk of major cardiovascular events by 10%28.. Yet, anti-hypertensive medications have low adherence and side effects. Whereas the literature suggests high compliance to slow breathing intervention with no adverse effects. Lastly, the absence of changes in autonomic tone as measured by spectral analyses suggest that the cardiovascular mechanisms of slow breathing have yet to be well characterized. Further research into the mechanisms and effectiveness of slow breathing on cardiovascular health is needed.