Two minutes of slow breathing restores autonomic and respiratory balance
Key Points
Slow breathing reduces sympathetic activity and restores autonomic and respiratory balance
Slow breathing reduces blood pressure in hypertensive patients
The Breathing Diabetic Summary
I think I underlined this entire paper! Reading a paper like this always reinvigorates my love for learning about breathing. Although the focus is on hypertension, this paper had a lot of good information in general about breathing and autonomic function.
To begin, autonomic dysfunction in the form of increased sympathetic activity plays a major role in causing hypertension. Moreover, the autonomic imbalance in hypertensive patients also is associated with reduced baroreflex sensitivity (we’ve covered several papers on that: Bernardi et al. [2017], Rosengard-Barlund et al. [2011], and Bernardi et al. [2011]). This forms a negative feedback look where the reduced baroreflex sensitivity cannot suppress the increased sympathetic activity, which then elevates blood pressure, which then reduces baroreflex sensitivity further, etc.
However, slow breathing (particularly at 6 breaths/min) previously has been shown to improve baroreflex sensitivity and lower blood pressure. Therefore, the authors hypothesized that slow breathing might be very beneficial for hypertensive patients.
The study had 20 hypertensive patients and 26 healthy controls. The subjects were first instructed to rest for 30 minutes in the laboratory to become familiar with the setting. Then, they were instructed to complete the following protocol in random order: 5 minutes of spontaneous breathing, 2 minutes of slow breathing at 6 breaths/min, and 2 minutes of controlled breathing at 15 breaths/min. Various measurements were taken throughout the protocol. As we get into the results, keep in mind that the subjects only performed slow breathing for 2 minutes!
It’s probably not a surprise by now, but slow breathing significantly reduced systolic and diastolic blood pressure in the hypertensive subjects. The blood pressure of the control subjects also was reduced, but it was not statistically significant. Slow breathing also significantly increased baroreflex sensitivity in both the hypertensive subjects and the controls. During spontaneous breathing, the baroreflex sensitivity of the hypertensive subjects was lower than the controls; however, after just 2 minutes of slow breathing, their baroreflex jumped up to values similar to the controls during spontaneous breathing. Therefore, slow breathing quickly normalized the autonomic function of these hypertensive patients (similar has been seen in diabetic patients who also suffer from a lower baroreflex sensitivity).
Another interesting finding of this study was that the hypertensive patients had a higher resting breathing rate and lower end-tidal CO2, symptoms of hyperventilation. (Learn more about the importance of CO2 here.) However, slow breathing didn’t change the patients’ CO2 values. Thus, there are other mechanisms at work (besides CO2) that are leading to the improvements in autonomic function. In any case, the authors hypothesize that the resting hyperventilation is a result of the increased sympathetic activity in the hypertensive patients. This might sound familiar if you are diabetic (see more here).
Overall, this paper showed that slow breathing reduced the higher resting sympathetic activity seen in hypertensive patients, thus restoring autonomic and respiratory balance. As is usual, their words say it better than I ever could:
“Slow breathing showed the potential to be a simple and inexpensive method to improve autonomic balance and respiratory control and reduce blood pressure in hypertensive patients.”
Abstract from Paper
Sympathetic hyperactivity and parasympathetic withdrawal may cause and sustain hypertension. This autonomic imbalance is in turn related to a reduced or reset arterial baroreflex sensitivity and chemoreflex-induced hyperventilation. Slow breathing at 6 breaths/min increases baroreflex sensitivity and reduces sympathetic activity and chemoreflex activation, suggesting a potentially beneficial effect in hypertension. We tested whether slow breathing was capable of modifying blood pressure in hypertensive and control subjects and improving baroreflex sensitivity. Continuous noninvasive blood pressure, RR interval, respiration, and end-tidal CO2 (CO2-et) were monitored in 20 subjects with essential hypertension (56.41.9 years) and in 26 controls (52.31.4 years) in sitting position during spontaneous breathing and controlled breathing at slower (6/min) and faster (15/min) breathing rate. Baroreflex sensitivity was measured by autoregressive spectral analysis and “alpha angle” method. Slow breathing decreased systolic and diastolic pressures in hypertensive subjects (from 149.73.7 to 141.14 mmHg, P<0.05; and from 82.73 to 77.83.7 mm Hg, P<0.01, respectively). Controlled breathing (15/min) decreased systolic (to 142.83.9 mm Hg; P<0.05) but not diastolic blood pressure and decreased RR interval (P<0.05) without altering the baroreflex. Similar findings were seen in controls for RR interval. Slow breathing increased baroreflex sensitivity in hypertensives (from 5.80.7 to 10.32.0 ms/mm Hg; P[1]0.01) and controls (from 10.91.0 to 16.01.5 ms/mm Hg; P<0.001) without inducing hyperventilation. During spontaneous breathing, hypertensive subjects showed lower CO2 and faster breathing rate, suggesting hyperventilation and reduced baroreflex sensitivity (P<0.001 versus controls). Slow breathing reduces blood pressure and enhances baroreflex sensitivity in hypertensive patients. These effects appear potentially beneficial in the management of hypertension.
Journal Reference:
Chacko N. Joseph, Cesare Porta, Gaia Casucci, Nadia Casiraghi, Mara Maffeis, Marco Rossi, and Luciano Bernardi, (2005) Slow breathing improves arterial baroreflex sensitivity and decreases blood pressure in essential hypertension, Hypertension, 46, 714 – 718, DOI: 10.1161/01.HYP.0000179581.68566.7d.