- Bob Holmes
- From “Knowable Magazine”
Image source,Getty Images
The giraffe’s neck is very long, so it needs to maintain a very high blood pressure
Because giraffes are too tall, their blood pressure is terribly high, but they avoid a large number of health problems that plague hypertensive patients. How is this done?
For most people, the giraffe is just a cute long-necked animal, which ranks high on the zoo or wild animal photo list. But for cardiovascular physiologists, there is more to appreciate. Facts have proved that giraffes have solved a problem that kills millions of people every year: high blood pressure. As for the solution, scientists have only understood part of it so far, involving compression of organs, altered heart rhythm, blood storage-and the biological equivalent of leggings stockings.
Giraffes have high blood pressure because their heads are ridiculously high. Adult giraffes have their heads about 6 meters (19 feet) above the ground-a long way for the heart to pump blood against gravity. The blood pressure of the giraffe’s brain must reach 110/70 (which is equivalent to the normal level of large mammals), and the blood pressure of the heart must reach about 220/180. Giraffes will not be frightened by such pressure, but such pressure can cause a variety of problems for people, including heart failure and kidney failure to swelling of the ankles and legs.
For humans, chronic hypertension can cause the heart muscle to thicken. After each stroke, the left ventricle becomes stiff and cannot be filled again, leading to diastolic heart failure, which is characterized by fatigue, shortness of breath, and decreased exercise capacity. This type of heart failure accounts for nearly half of the 6.2 million heart failure cases in the United States today.
Image source,Reuters
When Harvard University and UCLA cardiologist and evolutionary biologist Barbara Natterson-Horowitz examined the giraffe’s heart, she and her students discovered that the giraffe’s left The ventricles did thicken, but there was no hardening or fibrosis that the human heart would have. The researchers also found that five genes related to fibrosis have been mutated in giraffes. Consistent with this finding, other researchers examined the giraffe’s genome in 2016 and found several giraffe-specific genetic variants that are related to cardiovascular development, blood pressure and the maintenance of circulation. In March 2021, another research team discovered a giraffe-specific genetic variation associated with fibrosis.
The giraffe has another trick to avoid heart failure: its electrical rhythm of the heart is different from that of other mammals. Naterson-Horowitz discovered that the ventricular filling period of giraffes is prolonged. (Neither of her studies have been published yet.) This allows the heart to pump more blood every time it beats, so even though the giraffe has a thicker heart muscle, it won’t die if it runs quickly. Naterson Horowitz said: “You only have to look at a photo of a giraffe running away and you will realize that the giraffe has solved the problem.”
Naterson-Horowitz now turns his attention to another problem that giraffes have solved: high blood pressure during pregnancy, a disease called preeclampsia (also known as pregnancy toxemia). For people, this can lead to serious complications, including liver damage, kidney failure, and placental detachment. But the giraffe seems to be doing well. Naterson-Horowitz and her team hope to study the placenta of pregnant giraffes to see if they have unique adaptability.
People with high blood pressure are also prone to annoying swelling in the legs and ankles because the high pressure forces water out of the blood vessels and into the tissues. But you only need to look at the slender legs of giraffes to know that they also solve this problem. “Why can’t we see giraffes with swollen legs? How do they resist the tremendous pressure there?” asked Christian Aalkjær, a cardiovascular physiologist at Aarhus University in Denmark . He focused on the adaptability of giraffes to hypertension in the 2021 Annual Review of Physiology.
At least to a certain extent, the giraffe uses the same trick nurses use on patients to reduce swelling: leggings and stockings. For people, these are tight, elastic leggings that can compress leg tissues and prevent fluid accumulation. Giraffes use tight connective tissue to accomplish the same thing. Akjeel’s team tested this effect by injecting a small amount of saline solution into the legs of four giraffes under the wrapper. The giraffes were anesthetized for other reasons. The research team found that a successful injection of the calf requires more pressure than a neck injection, which suggests that the wrap helps prevent leakage.
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A glance at the slender legs of giraffes tells that their ankles do not show the swelling that is common in human hypertensive patients.
Akjeel and other researchers found that giraffes also have thick-walled arteries near their knees, which may act as airflow restriction. This may lower the blood pressure of the lower extremities, just as the water pressure drops after a soft hose is kinked. However, it is unclear whether the giraffe will open and close the arteries as needed to regulate the pressure on the calf. Akjeel said: “Imagine a giraffe standing there motionless, it will close the sphincter muscle under the knee, which is very interesting. But we don’t know.”
Akjeel still has a question about these extraordinary animals. When a giraffe raises its head after bending over to drink water, the blood pressure of the brain drops sharply-this is the more severe dizziness that many people experience when they suddenly stand up. Why don’t giraffes faint?
Part of the reason is that giraffes can cushion sudden changes in blood pressure. On giraffes under anesthesia, their heads can be raised and lowered with ropes and pulleys. Akjeel found that when the head hangs down, there is a pool of blood in the large veins of the neck. This can store more than 1 liter (0.2 gallon) of blood, temporarily reducing the amount of blood returning to the heart. Since there is less blood available, when the head hangs down, the heart produces less pressure every time it beats. When the head is raised again, the stored blood will suddenly rush back to the heart, and the heart will make a powerful, high-pressure response to help pump blood to the brain.
It is unclear whether this will happen to awake, free-moving animals, although Akjeel’s team recently recorded blood pressure and flow from sensors implanted in free-moving giraffes, and he hopes to get answers soon. .
So, can we learn medical lessons from giraffes? These insights have not yet produced specific clinical treatment methods. But that doesn’t mean it won’t, Naterson Horowitz said. Although some of these adaptive abilities may not be related to human hypertension, they may help biomedical scientists think about this problem in new ways and find new ways to treat this common disease.