Bandhas are a group of physical locks which allow the practitioner to control different organs of the body and their nerves. The word bandha means to hold or tighten'. These locks, created by contracting different areas such as the throat, abdomen and perineum, massage the physical organs and release psychic energy by the stimulation of chakras and prana. They help to redirect prana and strengthen the whole body.
In a report on the effect of bandhas on heart rate, pulse rate and pulse pressure, K.B. Gopal, S. Lakshman and M. Batmanabne from the Dept. of: Biology and Anatomy, Jawaharlal Institute of Post Graduate Medical Education and Research, Pondicherry, India have made some interesting findings. These highlight the effects of yoga in the possible treatment of blood pressure.*1
The report states that during the tests made on eighteen trained yoga students, the cardiovascular system was affected in a beneficial manner by lowering of the heart rate and blood pressure within physiological limits. Gopal et al. have observed that this could be due to increased peripheral blood flow while performing bandhas in conjunction with pranayama. This implies that there is a lessening of the sympathetic nervous stimulation of the peripheral blood vessels which leads to relaxation of mind and body.
According to Gopal et al. in jalandhara bandha (locking of the throat centre) the pressure receptors in the carotid artery are not stimulated. However, the carotid artery is stretched due to forward bending of the neck and elevation of the ribs which increase the diameter of the base of the neck. This, he believes, contributes to the lowering of blood pressure in normal people (not in hypertension).
Increased diameter of the chest (thoracic cage volume) is also caused by uddiyana bandha (abdominal contraction). According to experimental evidence these also contribute to lowering of the blood pressure. Though these techniques are not applicable to the treatment of hypertension, they can be utilised to prevent high blood pressure.
*1. "Some Anatomical Observations on Hatha Yoga: Bandhas, an Anatomical Study" 'Ind. J. Med. Sc. 26, 9'.