To most people, giraffes are majestic, long-necked animals that rank near the top of a zoo visit. But to a cardiovascular physiologist, they are fascinating. Because of their height, giraffes need a scarily high blood pressure – yet they escape the massive health problems that plague people with hypertension.
How do they do it? Giraffes have sky-high blood pressure because of their sky-high heads that, in adults, rise about 6m above the ground – a long, long way for a heart to pump blood against gravity. To have a blood pressure of 110/70 at the brain – about normal for a large mammal – giraffes need a blood pressure at the heart of about 220/180 — a pressure reading like that would cause all sorts of problems in humans — from heart or kidney failure to swollen ankles and legs. In people, chronic high blood pressure causes a thickening of the heart muscles, leading to a disease known as diastolic heart failure. Not so for giraffes. Cardiologist and evolutionary biologist Barbara Natterson-Horowitz found that their left ventricles did get thicker, but without the stiffening, or fibrosis. And the giraffe has another trick to avoid heart failure: the electrical rhythm of its heart differs from that of other mammals. In giraffes, the ventricular-filling phase of the heartbeat is extended. This allows the heart to pump more blood with each stroke, allowing a giraffe to run hard despite its thicker heart muscle. "All you have to do is look at a picture of a fleeing giraffe," Natterson-Horowitz says, "and you realise that the giraffe has solved the problem."
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Sup, Kumara
It's still in the mail
1. "Your reader should be thrilled with getting their mail within the same month let alone the same quarter," writes a reader. "In February, a friend from Toronto, Canada sent my family a card to say congratulations on the twins due in May and in a separate package a set of newborn clothes for the twins and some chocolate for the new mum. The card alone took three months and arrived a week after the babies did. The small package arrived last week after what must have been quite an adventure with the chocolates melted and two months expired. Twins are already 11 weeks old and too big for the clothes."
