Aspiring climbers should be aware of three factors relating to hypoxia that can reduce their risk of altitude sicknesses and make climbing safer:
1. How the body detects hypoxia
Your body has oxygen sensors to detect hypoxia. These sensors are mitochondria, tiny intracellular powerhouses that trigger adaptive responses to boost oxygen uptake and delivery to vital organs.
In the carotid body — a tiny sensor in the carotid artery — and in the lung’s pulmonary arteries, mitochondria produce signalling molecules (called oxygen radicals) that trigger responses. These responses include neurotransmitter release, contraction of lung blood vessels and changes in gene expression.
The carotid body samples blood headed to the brain and, if it is acidic or hypoxic, signals the brain to increase the depth and rate of breathing. This is a helpful response because it increases ventilation, bringing more oxygen into your body.
A similar sensor in the lung’s pulmonary arteries constricts those arteries in response to hypoxic air (hypoxic pulmonary vasoconstriction, or HPV). HPV is helpful when lung hypoxia involves only a segment of lung, as in pneumonia. But at altitude, where the entire lung is filled with hypoxic air, HPV raises the pressure in the pulmonary arteries, which promotes fluid leakage from blood vessels into the airways, causing HAPE.
2. Acclimatization is key to surviving hypoxia
Slow ascent gives oxygen sensors time to condition climbers to function in the rarified air at altitudes like Kilimanjaro. The first adaptation, carotid body activation, happens quickly: breathing increases within minutes of hypoxic exposure.
Hours later, gene and protein expression changes. This is due to activation of transcription factors that control genes’ on and off switches. One such transcription factor that is activated by hypoxia, named HIF-1, . More erythropoietin means more production of hemoglobin and red blood cells which increases the blood’s oxygen-carrying capacity.
Third, with a slow climb and sustained hypoxia, , preventing pulmonary hypertension and HAPE. Our guides were very familiar with the necessity of acclimatization, and cheered us on with the refrain “Pole pole,” Swahili for “slowly slowly.”
Going slowly reduces the risk of developing acute mountain sickness. Like the parable of the tortoise and the hare, it , whose bravado and strength allow rapid ascent, rather than slow-moving seniors. In addition to going “pole pole,” one can improve the chances of summiting by choosing a longer route (on Kilimanjaro, ideally a six- or seven-day ascent, like the Lemosho route) and following a “climb high, sleep low” philosophy: Hike to a higher altitude each day and then descend to your campsite.
