Asana and Pranayama and the Respiratory System
Excerpt from 70 glorious years of yogacharya BKS Iyengar
(commemoration volume)
It has been mentioned earlier that certain āsanas produce a reflex action in the autonomic system, thereby increasing the supply of oxygenated blood to an organ.
In a standing position the heart has to push, pump blood against gravity towards the head, while gravity takes care of the flow towards the feet. Hence the tone of the blood vessels is different in the cephalic and caudal sides of the body.
In Savāsana, the heart pushes the blood with equal force towards both ends since both, the legs and the head are on gravity par.
In Sirsāsana while the vessel tone is diminished towards the legs it is increased towards the head.
In Sarvangāsana it is somewhat diminished on the side of the head, whereas in Sirsāsana it is increased.
We are talking here of the venous blood return. Twisting poses have a counter stimulating effect on the gastrointestinal vascularity.
The way blood flows towards the heart is very important. When standing, the venous blood has to ascend towards the heart against gravity and therefore, the tone of the venous blood vessels must be perfect. Any loss of tone in these vessels creates stasis of the venous blood in the pelvis and legs, leading to various diseases. The well-known prominent varicose veins seen on some people, are often due to constant standing.
Different prānāyāmas done in different asānas further make a qualitative change in the functioning of an organ. Prānāyāma with the help of the vocal, gastric and pelvic diaphragms has a positive effect on the bioenergy, making it flow smoothly through the central canal of the spinal cord (susumna) towards the cerebrum (sahasrāra), which is the ultimate aim of the yoga student.
In the sitting position, the tone of the private diaphragm must be maximum while the vocal diaphragm is optimally relaxed. In Halasāna, the pelvic diaphragm is totally released while the vocal diaphragm is kept passive. In Setubandha, it is the diaphragm (the gastric diaphragm) which is relaxed while the other two, the pelvic and vocal diaphragms, are passive.
Good tonicity in the vessels is maintained by the automatic nervous system via the sympathetic and parasympathetic nerve supply. Excessive tone or tension in the blood vessels indicates hypertension, while insufficient tonicity means hypotension, in other words, high and low blood pressure.
Paraphrasing...
Blood pressure changes depending on our activities, for instance it is different when we do physical exercises, during the ingestion of food or due to emotions. In normal people, the autonomic nervous system synchronises the pressure in the different vessels without the knowledge of the conscious brain.
Blood pressure also response to external causes which are unavoidable.
However, it is the internal environment which is the primary factor, responsible for the changes in the tone of our veins and arteries.
Nature constantly tries to adjust to these different disorders with it stress-response phenomena.
However, there are limits to how far these chaotic conditions can go and the internal balance be maintained or re-established. A time may come when the stress reactions cannot cope with the conditions, and diseases set in, giving rise to various psychosomatic disorders.
The regular practise of asānas and pranayama can help our physical and mental condition, invigorates the body and can also help us in facing the challenges in our lives.