University of Denver Autumn 2024

Being high in the sky is hard If you’ve ever hiked one of Colorado’s fourteeners, you know climbing isn’t just taxing on your muscles—it’s hard on your lungs, too, with less oxygen in your lungs and bloodstream. “The summit of a fourteener has 60% of [the oxygen] that is available at sea level, so every breath you take, you're only taking in 60% of that oxygen,” Velotta says. “If you drive to the summit of Mount Blue Sky, or if you hike up to it, you're gasping for breath.” But despite this challenge, deer mice needed to find a place to live where predators were few and far between—like the summits of mountains—so they adapted to operate on less oxygen. Mammals combine oxygen with food to make energy, and less oxygen means less energy. When you’re summiting a fourteener, your body has to work harder; you breathe more heavily, you get dehydrated. And your body makes more red blood cells. When humans have too many red blood cells floating around in their veins, it can lead to some serious problems. For one, it can make blood thick and viscous, like molasses. But it can also do damage in other ways. “All the blood vessels that carry blood through your lungs start to constrict; they get smaller and tighter, and nobody wants that,” Velotta says. “It causes a lot of problems downstream. It could lead to acute mountain sickness and hypoxic pulmonary edemas, which is basically fluid in your lungs. And it can also lead to chronic disease.” Humans who live at high altitudes are prone to these problems. Most people who make their homes in the Andes have chronic mountain sickness. The hallmark symptom is polycythemia—thickening of the blood—which can cause pulmonary hypertension and stroke. But here’s the interesting thing about those high-altitude mice Velotta is studying: They don’t have any of those issues. “They actually breathe slower and deeper, which is a way more effective way of breathing. They have as few red blood cells as anyone would at sea level. They don't get high blood pressure. And we want to know how they do that.”

Top: Velotta Lab PhD student Sarah Senese says working in such a beautiful place never gets old. Bottom: Velotta and Senese set up equipment that helps them take crucial measurements from the deer mice they capture.

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