13 de outubro de 2010

Blood Pressure and Inversions

By Roger Cole

I have high blood pressure that is controlled by medication. Is it safe to practice inversions, particularly Shoulderstand and Headstand? —Diane Kane, Kirkland, Washington

Roger Cole’s reply:

You should check with your doctor about your individual case, but standard medical advice for people whose blood pressure is controlled on medication is to engage in exercise and other healthy activities that a person with normal blood pressure would do. Therefore, it seems reasonable that you can safely introduce inversions if you do so gradually. In fact, inversions trigger several reflexes that temporarily reduce blood pressure, so theoretically, regular practice may enhance treatment of your high blood pressure. Note, however, that people whose high blood pressure is not under control should bring the pressure down first by other means before practicing inversions.

First, let me explain how inversions affect blood pressure. In an inverted posture, gravity causes pressure to increase inside the blood vessels (arteries, veins, and capillaries) of the head and neck. The vessels of the brain and eyes are largely protected from this pressure increase because they are bathed in fluid—cerebrospinal fluid inside the skull and vitreous humor in the eyes—the pressure of which also increases during inversions: The pressure of the fluid pushing in on the blood vessel walls from outside counteracts the pressure of the blood pushing out on the vessel walls from inside.

Blood vessels that lie outside of the skull and eyes, such as those supplying the inner lining of the nose, do not have this protection. Instead, many are protected by local reflexes that respond to elevated blood pressure by contracting muscles in the vessel walls. This contraction prevents the vessel walls from being overstretched. If inversions are introduced gradually, you are in theory systematically strengthening the vessel wall muscles by challenging them to contract against greater and greater pressure.

How much blood pressure increases in the head during an inversion depends mainly on two factors: how far above the head the heart is, and how far above the heart the legs and trunk are. Therefore, a mildly inverted posture like Adho Mukha Svanasana (Downward-Facing Dog), which lifts the heart only a little above the head and does not elevate the legs, only increases pressure in the head a little. Supported Setu Bandha Sarvangasana (Bridge Pose, lying on bolsters, legs horizontal, feet at hip level) increases pressure in the head somewhat more because the legs and trunk are slightly above the heart, and the heart is slightly above the head. Salamba Sarvangasana (Shoulderstand) increases pressure in the head still more, because the legs and trunk are raised to their maximum vertical position above the heart, and the heart is raised somewhat higher above the head than in Setu Bandha. Sirsasana (Headstand) increases blood pressure in the head the most, because the legs and trunk are maximally elevated and the head is as far below the heart as it can get.

To safely practice inversions, I recommend that you introduce them over several months, starting with mild or partial inversions first, then gradually attempting steeper inversions, and moving on to Headstand last.

Roger Cole, Ph.D., is a certified Iyengar Yoga teacher and a research scientist specializing in the physiology of relaxation, sleep, and biological rhythms. He trains yoga teachers and students in the anatomy, physiology, and practice of asana and pranayama. He is based at North County Yoga Center in Solana Beach, California, and teaches workshops worldwide.

Nenhum comentário:

Postar um comentário

Aguarde. Sua mensagem será postada em breve!

Atenção: não permitimos comentários que agridam ou ofendam pessoas, instituições, organizações governamentais, entre outros.