Sirshasana is not dangerous if it is developed gradually over a period of time, and providing the basic rules are carefully followed. Many people are apprehensive, suspicious and disinclined to do it.
It is often pointed out that it seems unnatural to invert the body for a period of time and if it were necessary then we would walk about on our hands. Well, maybe. But man is also designed to do a lot of physical exercise and not sit in one position for protracted lengths of time. Vigorous and regular exercise speeds up the blood circulation and ensures that the brain receives sufficient well oxygenated blood. Exercise also prevents blood stagnating in the lower parts of the body such as the legs; lack of exercise, which is the characteristic of modern city dwelling man, leads to varicose veins, haemorrhoids and general inefficiency of the organs of the body.
So sirshasana is in a sense an unnatural method of combating an unnatural lifestyle. Apart from this, however, sirshasana is an excellent method of bringing about calmness and concentration in preparation for meditative practices.
Sirshasana – Scientific experiments
Various experiments have been conducted to measure the changes that occur within the body during the practice of sirshasana. These confirm scientifically what we have discovered from personal experience.
X-rays taken during the practice of sirshasana have shown a considerable shift of the diaphragm, changes in the longitudinal and transverse dimensions of the heart, and widening of the arteries and veins leading to and from the lungs, especially in the upper lobes. The significance is that more blood is travelling to and from the lungs, increasing oxygenation. The upper lobe which usually is not well oxygenated by a normal breath, is washed free of stagnant blood.
The tests clearly indicate that the amount of air breathed per minute (minute ventilation) during the performance of sirshasana was considerably reduced. The frequency of respiration (the number of breaths per minute) was lowered. Oxygen consumption by the tissues increased and the amount of oxygen exhaled was less, indicating that the transfer of oxygen to the blood is greatly increased.
There was an increase in the leucocyte (white blood cell) count, implying that the body’s ability to withstand and resist infection is increased as the white blood cells are used to destroy bacteria and other foreign objects in the body.
These tests are significant and apply if the individual is completely relaxed. If the practitioner is tense or stressed while performing sirshasana, then it is possible to obtain contradictory results.
From these experiments we can conclude that sirshasana allows for a greater possibility of adaptive mechanisms in respect to circulation and respiration.
In the future, no doubt, more intricate experiments will be carried out to record and map out the actual blood flow changes in the brain; how the blood flow to the pituitary and pineal is modified and how it improves their functional efficiency; how other organs of the body are influenced and so forth. The influence of sirshasana on brain waves would also be an interesting scientific experiment. There is much scope for these kinds of tests and they would put the physical benefits obtainable from sirshasana on a firm scientific basis.