Dr Trevor Day - Respiratory and Cardiovascular Physiologist.
It’s three in the morning and I’ve woken up, unable to breathe.
We are staying in a place called Gorak Shep, at the head of the Khumbu Valley in Nepal. It may as well be the moon – we are surrounded by dust and rock, our lodgings aside a frozen lake. Everest Base Camp is less than two kilometers away, and later (but still before dawn) our troop of twenty three hikers, mostly physiology students who are doubling as researchers and study participants, will climb to Kala Patthar (5643 metres, 18,514 feet), a landmark overlooking Base Camp with views of the Everest summit. Before we depart, however, we are all required to have our weight, blood pressure, resting heart rate, oxygen saturation, respiratory rate and end-tidal CO2 measured and recorded.
This battery of measures is the brainchild of cardiorespiratory researcher Trevor Day, Associate Professor of Physiology at Mt Royal University, Canada and the overseer of this expedition to the top of the world – a 120 kilometer round trip from Lukla at the base of the valley to Everest Base Camp and back.
Peculiar things happen when you’re up this high, where the partial pressure of oxygen is a little more than half that at sea level – several compensatory physiological mechanisms are required to maintain adequate oxygen supply to the tissues. As we trudge up the mountain, Trevor gives me the rundown on acclimatization...
“As we ascend, we sensitize our receptors that detect low oxygen, so therefore we breathe more when we are exposed to a low oxygen stimulus.”
“We make more red blood cells, so the ratio of red cells to our total plasma goes up as well and that helps with our oxygen carrying capacity. Our blood pressure goes up, our cardiac output goes up”.
Excess CO2 is also expired as a side effect of the increased breathing. Curiously, this molecule serves as a trigger for the impulse to breathe, and its paucity leads to the strangely contrary periodic breath-hold phenomenon I’ve been experiencing.
This normal acclimatization process is fairly well understood but what Trevor is really interested in is how such a response begins to unravel at these altitudes.