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The giraffe paradox

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The gentle giant intrigues scientists by the way it maintains its blood pressure

On September 29, World Heart Day, organisations across India held camps to help the public “know their numbers” — blood pressure (BP), blood sugar and body weight. An analysis of the readings taken by the Rotary Club camps showed results that matched larger epidemiology studies: one of three people had elevated BP and one of five had elevated blood sugar.

A BP of 120/80 mmHg (millimetre mercury) or below is considered normal. More than 140/90, signifying Stage 1 hypertension, and more than 160/100, signifying Stage 2, can damage the brain, eyes, heart and kidneys.

When studying blood pressure, scientists have been intrigued by the giraffe, the gentle giant of Africa. How does it pump blood through its body that rises to 18 feet? With what force does it pump blood up the six-foot-long neck to its brain? What protects the giraffe from giddiness as it bends down to drink water and then lifts its head up? Despite standing almost all the time, why doesn’t a giraffe faint? The answers to these questions hold answers to protect human beings from brain haemorrhage due to high BP and fainting due to low BP.

A strong heart

The giraffe’s strong heart generates a pressure of 300 mmHg needed to pump blood all the way up its long neck. Yet, when scientists measured the BP in its brain, it was a constant 120/80 mmHg. A network of blood vessels in the upper neck helps reduce the BP.

Galen, an ancient Greek physician and philosopher, named it rete mirabile (pronounced “reete meerabil”), meaning “wonderful net”. The network and valves in major veins maintain a constant pressure in the giraffe’s brain even when it stoops to drink water and lifts its neck up to its full height.

No protective mesh

Human beings lack this stabilising mesh and need to protect the brain by other means — avoiding tobacco, consuming less salt, coping with stress, taking medicines and above all by detecting hypertension through periodic check-ups. The giraffe doesn’t have these complications!

Standing still for long, weak leg muscles and the effects of some medicines can cause pooling of blood in the legs, lowering the BP. Getting up from bed suddenly, stiff arteries, and reduced water intake can sometimes cause a significant drop in BP on standing up. Whatever the cause, dizziness due to low BP is often relieved by allowing blood to flow freely into the brain by making the patient lie flat on the ground. Lifting the legs facilitates the flow of blood.

Giraffes do not faint because blood does not pool in their legs. We can avoid fainting by drinking enough water, toning the leg muscles by exercise, and moving the feet while sitting or standing for long. Lying down flat at the onset of dizziness can prevent a fall.

vijayacardio@gmail.com

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Printable version | Dec 6, 2019 1:41:40 AM | https://www.thehindu.com/opinion/open-page/the-giraffe-paradox/article29744413.ece

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