An Evolutionary Trade-Off For Walking Upright

A research group in Japan has revealed that walking upright has made humans more prone to limb ischemia than mice.

AsianScientist (Apr. 6, 2018) – In a study published in the Journal of the American Heart Association, scientists in Japan have demonstrated that humans risked limb ischemia in exchange for bipedal walking.

Peripheral obstructive arterial disease develops when blood vessels narrow due to arteriosclerosis and blood flow in the legs (and rarely, the arms) becomes restricted. Blood flow disturbances in a limb can cause pain, numbness or coldness during physical activity. In severe cases where the tissue has gone without blood for too long, the limb may have to be amputated.

Previous clinical and animal research showed that mice sustain less tissue damage under ischemic condition than humans, but the cause of this difference was not clear. To illustrate why humans appear to be at a disadvantage, researchers from Kumamoto University, Japan, focused on collateral vessels that could bypass an obstruction of the main artery carrying blood to the limb. Using a murine hind limb ischemia model, they compared the shape of blood vessels in the hind limbs of mice with those of a patient who had peripheral obstructive artery disease.

Techniques such as radiography can be used to visualize the small blood vessels of a mouse, but such methods can only produce two-dimensional images. To obtain more detail, the researchers used micro X-ray computed tomography (CT) to generate three-dimensional images.

The micro CT scans clarified that when the hind limb of a mouse suffers from ischemia, the inferior gluteal artery expands and functions as a bypass. In human patients with peripheral obstructive artery disease, detailed diagnostic images revealed that the inferior gluteal artery also expands in response to vascular stenosis (vessel hardening).

However, the researchers also showed that the inferior gluteal artery of the mouse extends to the lower hind leg area, whereas the human inferior gluteal artery terminates much earlier at the buttock. Consequently, the mouse vascular structure is more robust against lower limb ischemia than the human vascular structure.

“Two things are believed to be the causes of the inhibited development of the inferior gluteal artery in humans,” said Assistant Professor Yuichiro Arima of Kumamoto University, who led the study. “One is that the development of the artery is restricted by the skeletal change accompanying bipedal walking, and the other is that, over time, the distance between the pelvis and the lower leg has become too far for the artery to reach.”

“In other words, evolution has increased the human risk for lower limb ischemia. This understanding is expected to lead to the development of treatments that strengthen the collateral circulation pathways for people suffering from peripheral obstructive arterial disease,” he added.


The article can be found at: Arima et al. (2018) Evaluation of Collateral Source Characteristics With 3‐Dimensional Analysis Using Micro–X‐Ray Computed Tomography.

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Source: Kumamoto University; Photo: Yuichiro Arima.
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