Physiology of Yoga

In the previous post, we discussed how pranayama (yogic breathwork) can be utilized to help increase energy and build internal heat when the body is feeling sluggish. However, sometimes (especially during the holiday season) our days can leave us feeling spread thin and exhausted as we rush about, juggling several commitments. At the end of the day, we are left feeling exhausted, yet still wound-up and unable to relax. This dichotomy is a result of an overactive nervous system, specifically the sympathetic branch, which is responsible for preparing our body for action. When we are constantly darting about our days from obligation to obligation, we never give our bodies a chance to relax and switch to parasympathetic control. Maintaining a balance between these two systems is crucial, not only for our mental health, but also for optimal functioning of several of our physiological systems. While we might not be able to abandon our commitments, yoga offers breathing practices, such as nadi shodhana, which can be incorporated throughout the day to help maintain balance and calm the internal seas.

Nadi shodhana, or alternate-nostril breathing, is a pranayama practice traditionally cited in yogic texts for calming the mind and body. Also known as “channel-clearing breath,” this practice is attributed with the ability to help open and clear the central channel of the body. To perform the practice, come to a comfortable seat and place the tip of the index and middle fingers of the right hand in between the eyebrows, the right ring and little fingers on the left nostril, and the right thumb on the right nostril. The ring and little fingers are used to open or close the left nostril, while the thumb is used for the right nostril.

To begin, use the thumb to close the right nostril while breathing gently out the left. Next, take a full breath in through the left and then close the left nostril gently with the ring and little fingers. Remove the right thumb from the right nostril and breathe out through the right. Finally, breathe in through the right and exhale out the left. This completes one round of nadi shodhana. Repeat this complete cycle for at least ten rounds, but continue it for up to fifteen minutes to reap greater benefits.

So how exactly does this alternate breathing bring the body back into balance and help calm the inner storm? Nadi shodhana helps calm several of our physiological systems, but, most notably, the cardiovascular system. The cardiovascular system is composed of the heart and all of the blood vessels (arteries, capillaries, and veins) and is responsible for delivering oxygen and nutrients to all of the body’s tissues. While practicing this deep breathing does not necessarily increase the oxygen saturation of the blood (normal, healthy individuals already have about 98 percent saturation), it does help decrease blood pressure and lower heart rate, two metrics that are chronically increasing in today’s society, making this practice invaluable. Through activation of the vagus nerve, nadi shodhana sets a cascade in motion (described previously) to release parasympathetic neurotransmitters such as Acetylcholine (ACh) from neurons. Once ACh is released in the target tissue, physiological changes occur to bring the body into a more relaxed state.

In the heart, cholinergic neurons (branches of the vagus nerve) innervate the cardiac muscle tissue. When activated, these neurons release ACh, which binds to specialized docking stations in the heart, called muscarinic receptors. Muscarinic receptors are concentrated in specific locations (the SA and AV nodes) responsible for generating the electrical conduction and “beat” of the heart. When ACh binds, it causes the frequency of electrical firing to decrease in the SA node and slows electrical conduction from the AV node, thus slowing the heart rate. Additionally, these muscarinic receptors inhibit the release of the excitatory neurotransmitter, norepinephrine, thus allowing the “rest and digest” response to take precedence over excitatory mechanisms.

Similarly, when ACh reaches the muscle walls of the arteries, a relaxation response is initiated through the binding of ACh to specific docking stations (muscarinic receptors). Once bound to these receptors, a chain of dominoes begins to fall, resulting in the release of chemicals and activation of enzymes (such as nitric oxide and guanylyl cyclase) in the blood stream. This release causes the vessel walls to dilate and blood pressure to decrease, illustrating a biological application of Bernoulli’s principle. This can be visualized by imagining a flowing river.If there is a steady flow of water and the river banks suddenly widen, the velocity and pressure of the water will decrease, as there is more space for the water to fill. This happens inside our arteries as well. Initiated by the release of ACh, arterial walls relax and dilate, giving the blood more space to flow, allowing blood pressure to decrease, and blood to move more freely throughout the vessels of the body.  Given this effect, it is not surprising that nadi shodhana was nicknamed the “channel clearing” breath.

We have all experienced the effects of being overbooked and stretched in many directions. When we enter these time periods when there doesn’t seem to be enough hours in the day, our nervous system revs up, throwing our body into overdrive. If we do not actively work toward rebalancing our system, the pendulum can become stuck, leaving us with that feeling of being too exhausted to fall asleep. Incorporating a simple pranayamic practice such as nadi shodhana into our day can help give our overactive systems a break and restore a calmer, more focused state of being. The next time you find yourself with a list that seems to be endless, give yourself permission to take five minutes to calm the internal seas. You will move forward with increased fluidity and focus, making your day a little less daunting.