The “nasal cycle” phenomenon is widely known in the scientific community and has been subject to multiple studies. Yogis had known about it for hundreds of years and used it effectively to change the body’s temperature and one’s mental state,
At any given moment you are naturally breathing through one dominant nostril (sympathetic dominance); then sometime later the body’s central nervous system, switches to the other one. This switch happens roughly every 2-2.5 hours and continues in a rhythmical fashion. This is achieved by the stimulus of erectile tissue in the nasal cavities.
Multiple research studies show that the way your body functions is quite different based on which side of the body has sympathetic dominance.
When the sympathetic system is dominant on the right side and parasympathetic system is dominant on the left, (right nostril dominance):
Right lung dominant
Generally, more active state
Locomotor activity increased
Heart rate increased
Blood pressure increased
Respiration rate increased
Body temperature increased
Prolactin secretion reduces
When the sympathetic system is dominant on the left side and parasympathetic system is dominant on the right, (left nostril dominance):
Left lung dominant
Generally, more resting state
Locomotor activity decreased
Heart rate reduced
Blood pressure reduced
Respiration rate reduced
Body temperature reduced
Prolactin secretion increased
In the course of the day, our body alternates between more active and more restful states.
Yogis used different language to describe it this process. Yoga teaches us that our energy balance is affected by the flow of energy along major energy channels, called nadis:
Ida nadi (lunar channel) is cooling and has overall feminine quality; it terminates at the left nostril. Pingala nadi (solar channel) is heating and has an overall masculine quality; it terminates at the right nostril.
Breathing in through a nostril will emphasize the qualities of that channel; breathing out through the nostril will sedate the corresponding channel. This model is used widely in a therapeutic context.
Sometimes there might be too much heat in the system (for example, if somebody has hot flashes or feels angry/irritable), which can be helped by breathing in through the Left nostril (to stimulate the lunar channel) and out through the right (to sedate the solar channel).
When there is not enough heat in the system (for example, cold limbs, low blood pressure, depression), it can help to breath in through the Right nostril (to stimulate the solar channel) and out through the Left (to sedate the lunar channel).
What I find interesting is how we can influence sympathetic dominance. When we lie down on our left, the right nostril, (upper) will broaden, this can be evident when we are congested trying to sleep. It was once thought that this was due to gravity, but current thinking is that it is the pressure exerted on the down arm and the chest, setting up a reflex that automatically dilates the nostril that is higher and closes the one that is lower.
We can try this when we go to bed, lying on our left side for a while, 5 to 10 minutes activating the right nostril and raising the body heat, once warm and comfortable, turn over to the right, allow the left nostril to open, calming, relaxing and preparing for sleep.
Many yoga breathing techniques focus on the balance and stimulation of energy which can help deal with some of the stresses we face in modern times. These have been around for thousands of years and are now becoming relevant and recognised.