Summary
The Naked Scientists explore the science of high altitude through Cambridge University researcher Andrew Murray and trekker Laura Soule, who climbed to Everest Base Camp at 5,300 meters. Murray explains the physiology of altitude adaptation: oxygen is critical for ATP production, and at altitude the body compensates by breathing harder, increasing red blood cells, and shifting blood pH. Laura monitored her own blood oxygen, heart rate, urine pH, and sense of smell throughout the trek. Her blood oxygen dropped to 79% of normal at the highest point, heart rate increased 10-20 BPM even at rest, and urine pH spiked with each altitude gain before normalizing. The research team found that blood oxygen content is maintained up to 7,000 meters through increased red blood cells, though each cell carries less oxygen. After acclimatization, descent felt dramatically easier. The episode also covers unrelated science news about evolution, looming sounds, and embryonic stem cells.
Key Points
- Oxygen fuels ATP production in nearly every tissue; reduced oxygen at altitude means less available energy
- The body adapts by breathing harder, increasing red blood cells, and adjusting blood pH through the kidneys
- Blood oxygen content is maintained up to about 7,000 meters through more red blood cells compensating for each carrying less oxygen
- Urine becomes alkaline at altitude as kidneys excrete bicarbonate to compensate for respiratory alkalosis
- Acute mountain sickness symptoms include severe headache, nausea, and disorientation from reduced oxygen to the brain
- Blood oxygen can drop to 79% of normal at 5,300 meters; resting heart rate increases 10-20 BPM
- There is no way to predict how well you will respond to altitude without actually going there
- Acclimatization makes descent dramatically easier; what was hard going up feels easy coming down
Key Moments
How oxygen deprivation triggers altitude adaptations
Cambridge researcher Andrew Murray explains that oxygen is critical for ATP production. At altitude, the body compensates by breathing harder and increasing red blood cells, though thicker blood becomes harder to push through capillaries.
"Oxygen is absolutely critical for almost every process in the body. Just about every tissue uses oxygen to make energy in the form of ATP, the universal energy currency of the cell. And if oxygen levels fall, the amount of ATP that can be produced and the amount of energy available to the cell is reduced."
Blood oxygen maintained up to 7,000 meters through red blood cell increase
Research samples taken up to 8,400 meters showed that blood oxygen content is maintained up to about 7,000 meters because increased red blood cell count compensates for each cell carrying less oxygen. Urine becomes alkaline as kidneys excrete bicarbonate to counteract respiratory alkalosis.
"We took samples as high as 8,400 metres, and interestingly enough, we found that even up to about 7,000 metres, the blood oxygen content was maintained, by which I mean you had more red blood cells, each of them was carrying less oxygen, but the fact that there was more of them meant that the total amount of oxygen in your blood was the same."
Real-world altitude monitoring on Everest Base Camp trek
Laura Soule monitored her physiology trekking to Everest Base Camp at 5,300 meters. Blood oxygen dropped to 90% of normal after an 800-meter altitude gain in one day, heart rate increased 10-20 BPM at rest, and urine pH spiked with each altitude jump before normalizing.
"Now that sounds like that was an enormous change in altitude in one day, 794 metres. Yes, it really was a big jump up that day. It was quite hard work and you really saw it in the experiments that we were doing. My blood oxygen level had dropped down to about 90% of what it normally is, which is quite a big difference."
