长颈鹿如何应对高血压
文章来源：BBC
由于它们的身高，长颈鹿需要非常高的血压——但它们却避免了困扰高血压患者的巨大健康问题。他们是如何做到的呢？
Because of their height, giraffes require scarily high blood pressures – yet they escape the massive health problems that plague people with hypertension. How do they do it?
对大多数人来说，长颈鹿只是可爱的长颈动物，它们在动物园参观或照片野生动物园的愿望清单中名列前茅。但对于心血管生理学家来说，还有更多值得爱的地方。事实证明，长颈鹿已经解决了一个每年导致数百万人死亡的问题：高血压。到目前为止，科学家们仅部分了解他们的解决方案，涉及加压器官、改变心律、血液储存——以及支持长袜的生物学等价物。
To most people, giraffes are merely adorable, long-necked animals that rank near the top of a zoo visit or a photo-safari bucket list. But to a cardiovascular physiologist, there's even more to love. Giraffes, it turns out, have solved a problem that kills millions of people every year: high blood pressure. Their solutions, only partly understood by scientists so far, involve pressurised organs, altered heart rhythms, blood storage – and the biological equivalent of support stockings.
长颈鹿的血压很高，因为它们的头很高，在成年人中，它们高出地面约 6m（19 英尺）——这是心脏对抗重力泵血的一段很长很长的路。为了让大脑血压达到 110/70——对于大型哺乳动物来说是正常的——长颈鹿需要大约 220/180 的心脏血压。它不会让长颈鹿感到不安，但这样的压力会给人们带来各种各样的问题，从心力衰竭到肾功能衰竭，再到脚踝和腿部肿胀。
Giraffes have sky-high blood pressure because of their sky-high heads that, in adults, rise about 6m (19ft) 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. It doesn't faze the giraffes, but a pressure like that would cause all sorts of problems for people, from heart failure to kidney failure to swollen ankles and legs.
在人类中，慢性高血压会导致心肌增厚。每次中风后，心脏的左心室变得更加僵硬，无法再次充盈，从而导致一种称为舒张性心力衰竭的疾病，其特征是疲劳、呼吸急促和运动能力下降。目前美国 620 万例心力衰竭病例中有近一半是由这种类型的心力衰竭引起的。
In people, chronic high blood pressure causes a thickening of the heart muscles. The left ventricle of the heart becomes stiffer and less able to fill again after each stroke, leading to a disease known as diastolic heart failure, characterised by fatigue, shortness of breath and reduced ability to exercise. This type of heart failure is responsible for nearly half of the 6.2 million heart failure cases in the US today.
长颈鹿的血压异常高，但似乎不会给它们带来健康问题（图片来源：C. Aalkjær & T. Wang / AR Physiology 2020）
当哈佛大学和加州大学洛杉矶分校的心脏病学家和进化生物学家芭芭拉·纳特森-霍洛维茨 (Barbara Naterson-Horowitz) 检查长颈鹿的心脏时，她和她的学生发现它们的左心室确实变厚了，但没有发生在人类身上的硬化或纤维化。研究人员还发现，长颈鹿的五个与纤维化相关的基因发生了突变。为了与这一发现保持一致，2016 年检查长颈鹿基因组的其他研究人员发现了几种与心血管发育和血压和循环维持相关的长颈鹿特异性基因变异。2021 年 3 月，另一个研究小组报告了与纤维化有关的基因中的长颈鹿特异性变异。
When cardiologist and evolutionary biologist Barbara Natterson-Horowitz of Harvard and UCLA examined giraffes' hearts, she and her student found that their left ventricles did get thicker, but without the stiffening, or fibrosis, that would occur in people. The researchers also found that giraffes have mutations in five genes related to fibrosis. In keeping with that find, other researchers who examined the giraffe genome in 2016 found several giraffe-specific gene variants related to cardiovascular development and maintenance of blood pressure and circulation. And in March 2021, another research group reported giraffe-specific variants in genes involved in fibrosis.
长颈鹿还有一个避免心力衰竭的技巧：它的心脏电节律与其他哺乳动物不同
The giraffe has another trick to avoid heart failure: the electrical rhythm of its heart differs from that of other mammals
长颈鹿还有另一个避免心力衰竭的技巧：它的心脏电节律与其他哺乳动物不同。纳特森-霍洛维茨发现，在长颈鹿中，心跳的心室充盈期延长了。（她的研究还没有发表。）这使得心脏在每次中风时泵出更多的血液，尽管长颈鹿的心肌较厚，但它仍然可以努力奔跑。“你所要做的就是看一张逃跑的长颈鹿的照片，”纳特森-霍洛维茨说，“你就会意识到长颈鹿已经解决了这个问题。”
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, Natterson-Horowitz found. (Neither of her studies has been published yet.) 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."
纳特森-霍洛维茨现在将注意力转向长颈鹿似乎已经解决的另一个问题：怀孕期间的高血压，这种情况被称为先兆子痫。对于人类，这会导致严重的并发症，包括肝损伤、肾功能衰竭和胎盘脱落。然而，长颈鹿似乎过得很好。Naterson-Horowitz 和她的团队希望研究怀孕的长颈鹿的胎盘，看看它们是否具有允许这一点的独特适应性。
Natterson-Horowitz is now turning her attention to another problem that giraffes seem to have solved: high blood pressure during pregnancy, a condition known as preeclampsia. In people, this can lead to severe complications that include liver damage, kidney failure and detachment of the placenta. Yet giraffes seem to fare just fine. Natterson-Horowitz and her team are hoping to study the placentas of pregnant giraffes to see if they have unique adaptations that allow this.
患有高血压的人也容易在腿部和脚踝处出现恼人的肿胀，因为高压迫使水从血管中流出并进入组织。但是你只需要看看长颈鹿修长的腿就知道它们也解决了这个问题。“为什么我们看不到腿肿的长颈鹿？它们是如何抵御下面巨大压力的？” 丹麦奥胡斯大学的心血管生理学家 Christian Aalkjær 问道，他在 2021 年生理学年度评论中写到了长颈鹿对高血压的适应。
People who suffer from hypertension are also prone to annoying swelling in their legs and ankles because the high pressure forces water out of blood vessels and into the tissue. But you only have to look at the slender legs of a giraffe to know that they've solved that problem, too. "Why don't we see giraffes with swollen legs? How are they protected against the enormous pressure down there?" asks Christian Aalkjær, a cardiovascular physiologist at Aarhus University in Denmark who wrote about giraffes' adaptations to high blood pressure in the 2021 Annual Review of Physiology.
长颈鹿用护士对病人使用的相同技巧来减少肿胀：支撑丝袜
Giraffes minimise swelling with the same trick that nurses use on their patients: support stockings
至少在某种程度上，长颈鹿通过护士对病人使用的相同技巧来减少肿胀：支撑丝袜。在人身上，这些是紧身、有弹性的紧身裤，可压缩腿部组织并防止体液积聚。长颈鹿通过紧密包裹致密的结缔组织来完成同样的事情。Aalkjær 的团队通过在四只因其他原因被麻醉的长颈鹿的腿上注射少量盐水溶液来测试这种效果。研究小组发现，与颈部注射相比，成功的注射需要在小腿上施加更大的压力，这表明包裹物有助于防止渗漏。
In part, at least, giraffes minimise swelling with the same trick that nurses use on their patients: support stockings. In people, these are tight, elastic leggings that compress the leg tissues and prevent fluid from accumulating. Giraffes accomplish the same thing with a tight wrapping of dense connective tissue. Aalkjær's team tested the effect of this by injecting a small amount of saline solution beneath the wrapping into the legs of four giraffes that had been anesthetised for other reasons. Successful injection required much more pressure in the lower leg than a comparable injection in the neck, the team found, indicating that the wrapping helped resist leakage.
一看长颈鹿修长的腿，就会发现它们没有高血压人类常见的脚踝肿胀（图片来源：Getty Images）
Aalkjær 和其他人发现，长颈鹿的膝盖附近也有厚壁动脉，可以作为流量限制器。这可以降低小腿的血压，就像花园软管的扭结导致水压下降超过扭结一样。然而，目前尚不清楚长颈鹿是否会根据需要打开和关闭动脉以调节小腿压力。“想象一下，当长颈鹿一动不动地站在那里时，它会关闭膝盖下方的括约肌，这会很有趣，”Aalkjær 说。“但我们不知道。”
Giraffes also have thick-walled arteries near their knees that might act as flow restrictors, Aalkjær and others have found. This could lower the blood pressure in the lower legs, much as a kink in a garden hose causes water pressure to drop beyond the kink. It remains unclear, however, whether giraffes open and close the arteries to regulate lower-leg pressure as needed. "It would be fun to imagine that when the giraffe is standing still out there, it's closing off that sphincter just beneath the knee," says Aalkjær. "But we don't know."
Aalkjær 还有一个关于这些非凡动物的问题。当长颈鹿弯腰喝水后抬起头时，大脑的血压会急剧下降——这是许多人突然站起来时头晕的更严重的版本。长颈鹿为什么不晕倒？
Aalkjær has one more question about these remarkable animals. When a giraffe raises its head after bending down for a drink, blood pressure to the brain should drop precipitately – a more severe version of the dizziness that many people experience when they stand up suddenly. Why don't giraffes faint?
至少部分答案似乎是长颈鹿可以缓冲这些突然的血压变化。在麻醉的长颈鹿身上，它们的头部可以用绳索和滑轮升起和降下，Aalkjær 发现当头部向下时，血液会积聚在颈部的大静脉中。这可以储存超过一升（0.2 加仑）的血液，暂时减少返回心脏的血液量。由于可用的血液较少，当头部向下时，心脏在每次搏动时产生的压力较小。当头部再次抬起时，储存的血液会突然涌回心脏，心脏会以有力的高压中风做出反应，帮助将血液泵送到大脑。
At least part of the answer seems to be that giraffes can buffer these sudden changes in blood pressure. In anesthetised giraffes whose heads could be raised and lowered with ropes and pulleys, Aalkjær has found that blood pools in the big veins of the neck when the head is down. This stores more than a litre (0.2 gallons) of blood, temporarily reducing the amount of blood returning to the heart. With less blood available, the heart generates less pressure with each beat while the head is down. As the head is raised again, the stored blood rushes suddenly back to the heart, which responds with a vigorous, high-pressure stroke that helps pump blood up to the brain.
目前尚不清楚这是否会发生在清醒、自由移动的动物身上，尽管 Aalkjær 的团队最近记录了植入自由移动的长颈鹿的传感器的血压和流量，他希望尽快得到答案。
It's not yet clear whether this is what happens in awake, freely moving animals, though Aalkjær's team has recently recorded blood pressure and flow from sensors implanted in free-moving giraffes and he hopes to have an answer soon.
那么——我们能从长颈鹿身上学到医学知识吗？这些见解还没有产生特定的临床治疗。但这并不意味着他们不会，Natterson-Horowitz 说。尽管一些适应可能与人类的高血压无关，但它们可能有助于生物医学科学家以新的方式思考这个问题，并为这种非常常见的疾病找到新的方法。
So – can we learn medical lessons from giraffes? None of the insights have yet yielded a specific clinical therapy. But that doesn't mean they won't, says Natterson-Horowitz. Even though some of the adaptations are probably not relevant for hypertension in humans, they may help biomedical scientists think about the problem in new ways and find novel approaches to this far-too-common disease.
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