Posted 09.26.2017 | by AMRA

Many forms of meditation, including mindfulness meditation, make use of the breath as a point of attentional focus. Research has shown that meditation on the breath reduces respiration rate, heart rate and blood pressure, and increases heart rate variability. Are these physiological changes the result of the cognitive and affective aspects of maintaining a meditative focus, or are they simply the consequences of breathing more slowly?

Bernardi et al. [Psychophysiology] investigated the long- and short-term respiratory and cardiovascular effects of meditation in experienced meditators and controls. In so doing, the researchers hoped to disentangle the physiological effects of slowed breathing from those of a maintained meditative focus.

The researchers recruited 41 participants (22% male, average age = 34 years) with prior meditation experience and 39 meditation-naive (54% male, average age = 25 years) controls. All of the meditators were beginning-to-intermediate yoga practitioners, although some had additional experience with vipassana, mindfulness, transcendental, or mantra meditation.

The researchers instructed participants to lie down quietly on their backs with eyes closed while their heart rate, respiration, blood pressure, and arterial, tissue, and brain oxygen levels were monitored under a series of different conditions. The conditions were: 1) baseline measures of normal respiration, 2) two different periods of “paced breathing” during which participants synchronized their breathing to the beats of a metronome to achieve rates of 15 and 6 breaths per minute, 3) two different periods of metronome-paced breathing while silently reciting a mantra, known as “mantra meditation” (also at 15 and 6 breaths per minute), and 4) a five-minute body scan meditation.

The meditators differed from the controls on a variety of measures across all conditions. They tended to have significantly higher levels of blood oxygen saturation (partial η2=0.19), brain oxygenation (partial η2=0.19), finger tissue oxygenation (partial η2=0.21), lower systolic blood pressure (partial η2=0.07), and slower baseline respiration levels (partial η2=0.28).

The body scan significantly decreased blood oxygen saturation in meditators and controls (partial η2=0.36), while paced breathing without mantra significantly increased blood oxygen saturation for both groups. Paced breathing with mantra lessened the extent to which blood oxygen saturation increased.

Paced breathing by itself, and mantra and body scan meditations by themselves, all significantly lowered brain oxygenation. Adding a mantra to paced breathing lowered brain oxygenation more than paced breathing alone. A similar pattern was observed for finger oxygenation, although it failed to reach significance.

Controls automatically took deeper breaths when breathing at 15 breaths per minute, but meditators did not. Adding a mantra lessened this deepening effect for controls. Both meditators and controls took deeper breaths while breathing at 6 breaths per minute, but adding a mantra lessened this effect for both groups. Breathing tended to be shallower during the body scan meditation, especially for control participants.

While paced breathing without mantra did not affect heart rate, the body scan and paced breathing with mantra slowed the heart rate (partial η2=0.32). This effect carried over into a final “at rest” recording period after all interventions were completed. Only paced breathing without mantra increased heart rate variability (partial η2=0.42), and none of the conditions acutely affected blood pressure.

The results indicate that meditation induces a hypometabolic state characterized by decreased blood oxygenation, reduced ventilatory stimulus, and reduced heart rate. None of these changes are attributable to changes in respiration rate. On the other hand, the increased heart rate variability sometimes observed in meditation may simply be the result of slowed breathing.

The results also show that long-term meditation (at least in the context of yoga practice) helps optimize cardiovascular function as evidenced by increased blood oxygenation, slowed respiration rate, and lower systolic blood pressure.

The fact that all of the meditators were yoga practitioners limits generalization about the long-term cardiovascular benefits of meditation for other types of meditation practitioners. The meditation and control groups differed in age, sex, smoking history, and physical activity. The researchers addressed this by performing supplementary analyses on a reduced sample of meditators and controls matched on age and sex that showed the same pattern of results.

Reference:

Bernardi, N. F., Bordino, M., Bianchi, L., & Bernardi, L. (2017). Acute fall and long-term rise in oxygen saturation in response to meditation. Psychophysiology.

[Link to abstract]