Blood pressure is the force exerted by circulating blood against artery walls. This pressure is typically measured in millimeters of mercury (mmHg) and involves two numbers: systolic pressure (when the heart beats) and diastolic pressure (when the heart rests between beats). While high blood pressure can cause health issues in many species, certain animals have naturally elevated levels to suit their unique physiology. The animal with the highest blood pressure is the giraffe.
The Giraffe’s Remarkable Circulation
The giraffe’s extraordinary height, which can reach up to 20 feet, necessitates a powerful circulatory system to pump blood against gravity to its brain. Its heart generates immense pressure, leading to a blood pressure that can range from 180 to 300 mmHg, significantly higher than the average human’s 120/80 mmHg. This high pressure is essential for ensuring oxygenated blood reaches the brain, even when the head is elevated several meters above the heart.
A giraffe’s heart, weighing around 25 pounds, features an especially thick and muscular left ventricle. This powerful chamber propels blood upwards, and its wall thickness is directly related to the length of the neck. Despite this muscular thickening, giraffe hearts remain healthy, unlike in humans where such thickening often leads to cardiac problems. This resilience is partly due to a unique genetic makeup that prevents excessive connective tissue (fibrosis) from forming in the heart muscle.
When a giraffe lowers its head to drink, its body employs several adaptations to prevent a dangerous rush of blood to the brain or fainting when raising its head. The jugular veins in the neck contain a series of valves, which prevent blood from flowing backward or pooling excessively in the head. These valves help regulate blood flow and pressure during rapid head movements.
The giraffe’s circulatory system also features thick-walled arteries, which function like natural compression stockings. This prevents blood from pooling in the legs due to the extreme hydrostatic pressure. Additionally, a specialized network of blood vessels at the base of the brain, known as the rete mirabile, helps to equalize blood pressure and protect the brain from sudden changes in blood volume.
Other Animals with Notable Blood Pressure
While the giraffe holds the record for the highest blood pressure, other animals also exhibit interesting adaptations in their circulatory systems. Birds, for instance, have high blood pressure, ranging from 108 to 250 mmHg, necessary to power flight muscles and maintain high metabolic rates. Their stiffer arteries and faster heart rates support this elevated pressure.
Large mammals like elephants also have high systolic blood pressure, around 180 mmHg, to effectively pump blood through their massive bodies and long blood vessels. Similarly, some bear species, such as grizzly bears, have been recorded with systolic pressures as high as 253 mmHg. Even domestic animals like greyhounds have naturally higher blood pressure compared to other dog breeds, often exceeding 160 mmHg, due to their athletic physiology.
On the opposite end of the spectrum, some animals have remarkably low blood pressure. Turtles and tortoises, for example, exhibit resting arterial pressures as low as 15-30 mmHg. Their slow metabolism and reptilian physiology contribute to these lower values, though their blood pressure can increase with warmer temperatures. These diverse adaptations highlight the wide range of physiological strategies animals employ to maintain circulation in varying body sizes and environments.