Inhalation/exhalation ratio modulates the effect of slow breathing on heart rate variability and relaxation - Van Diest et al. (2014)
Key Points
Exhaling longer than inhaling leads to a greater feeling of relaxation
Breathing a 6 breaths/min with a longer exhale increases heart rate variability
Care must be taken not to hyperventilate when breathing at 6 breaths/min
The Breathing Diabetic Summary
As we’ve been learning, slow breathing increases heart rate variability (HRV). It also causes us to relax by increasing our parasympathetic tone. However, a key component of many slow breathing techniques is that the exhale is much longer than the inhale (usually twice as long). These authors wanted to tease out what is more important, slowing down the breath, or making the exhale longer than the inhale?
To answer this question, they had 23 participants follow four different breathing patterns for 5 min each to look at the effects of both breathing rate and inhale-to-exhale (i/e) ratio:
12 breaths/min, exhale longer than inhale (i/e ratio of 0.42)
12 breaths/min, inhale longer than exhale (i/e ratio of 2.33)
6 breaths/min, exhale longer than inhale (i/e ratio of 0.42)
6 breaths/min, inhale longer than exhale (i/e ratio of 2.33)
They measured several different markers of relaxation, which were much more thorough than previous studies. For example, after each 5-min session they administered two different questionnaires that aimed to more objectively measure relaxation (although that’s difficult to measure objectively). They also measured several common indices of HRV.
The results revealed that the participants reported higher feelings of pleasantness when breathing at a low i/e ratio (that is, a longer exhale). When adopting this breathing pattern (even at 12 breaths/min), they felt more in control and scored higher on relaxation, mindfulness, and positive energy. The authors suspect that the greater relaxation with the longer exhales is the result of exhaling being a passive process in which the respiratory muscles relax, whereas inhaling is an active process in which the breathing muscles contract.
Interestingly, slow breathing at 6 breaths/min only increased their reported levels of positive energy when compared to 12 breaths/min. The authors suspect that the participants might have been hyperventilating when breathing at 6 breaths/min. It takes practice to learn how to breathe at a slow rate without overcompensating. Thus, they believe that slight hyperventilation might have been the reason that the slower breathing rate didn’t elicit a greater relaxation response. They even suggested future studies monitor CO2 to ensure no hyperventilation occurs. (See Principle 1 to find out more about the importance of CO2.)
The HRV parameters revealed that i/e ratio had a much larger effect when breathing at 6 breaths/min versus 12 breaths/min. For example, when breathing at 6 breaths/min using a low i/e ratio (longer exhale), high frequency HRV and respiratory sinus arrhythmia were significantly increased. The same was not true for breathing at 12 breaths/min. Finally, low frequency HRV was increased only when breathing at 6 breaths/min, regardless of i/e ratio.
In summary, inhalation-to-exhalation ratio plays a key role in feelings of relaxation and measurements of heart rate variability. For us, this might mean we need to increase our exhalation, or at least make sure our inhales and exhales are the same length: having a longer inhalation than exhalation appears to have negative consequences. Furthermore, practicing Breathe Light (see Principle 2) before trying to practice slow breathing at 6 breaths/min (or slower) might help reduce the risk of hyperventilating by teaching us to breathe less in general.
Abstract from Paper
Slow breathing is widely applied to improve symptoms of hyperarousal, but it is unknown whether its beneficial effects relate to the reduction in respiration rate per se, or, to a lower inhalation/exhalation (i/e) ratio. The present study examined the effects of four ventilatory patterns on heart rate variability and self-reported dimensions of relaxation. Thirty participants were instructed to breathe at 6 or 12 breaths/min, and with an i/e ratio of 0.42 or 2.33. Participants reported increased relaxation, stress reduction, mindfulness and positive energy when breathing with the low compared to the high i/e ratio. A lower compared to a higher respiration rate was associated only with an increased score on positive energy. A low i/e ratio was also associated with more power in the high frequency component of heart rate variability, but only for the slow breathing pattern. Our results show that i/e ratio is an important modulator for the autonomic and subjective effects of instructed ventilatory patterns.
Journal Reference:
Ilse Van Diest, Karen Verstappen, Andre´ E. Aubert, Devy Widjaja, Debora Vansteenwegen, and Elke Vlemincx, (2014) Inhalation/exhalation ratio modulates the effect of slow breathing on heart rate variability and relaxation, Appl Psychophysiol Biofeedback, 39, 171 – 180.