Monday, February 9, 2009

Cheyne-Stokes respiration and the Potala

Days remaining before I leave warm and sunny Arizona for the Himalayas: 49. Simulated altitude at which I am sleeping with my hypoxic generator: 14,500 feet. Today's training: 60 high-intensity minutes on the elliptical machine, 60 high-intensity minutes on the step climber, and four sets of 10 leg presses @ 400 pounds.

One of the many things that makes high-altitude mountaineering dangerous is Cheyne-Stokes respiration , an abnormal pattern of breathing characterized by oscillation of ventilation between apnea and tachypnea, to compensate for changing serum partial pressures of oxygen and carbon dioxide. The condition was named after John Cheyne and William Stokes, the physicians who first described it in the 19th century. This abnormal pattern of breathing, in which breathing is rapid for a period and then absent for a period, can be seen in patients with heart failure, strokes, traumatic brain injuries, and brain tumors. In some instances, it can occur in otherwise normal people during sleep at high altitudes. Maybe it's because I've had more than my fair share of traumatic brain injuries, concussions too numerous to catalog, but in this case I'm pretty sure the culprit is high altitude. Suffice it to say that I'm very familiar with Cheyne-Stokes respiration, because that's what I do when I ascend too rapidly on a mountain-climbing expedition. I got hit with it pretty bad last night, having adjusted the simulated altitude at which I am sleeping with my hypoxic generator from 12, 100 feet to 14,500 feet. I hardly slept at all. The physiology is complex, but the basic idea is that there are two ways in which the human brain regulates autonomic breathing. One, the more primitive version, makes us breathe when the partial pressure of oxygen is too low. The other, a more advanced, finely tuned adaptation, regulates our breathing as a function of the partial pressure of carbon dioxide. What happens at extreme altitude is that the body is fooled by the partial pressure of carbon dioxide into thinking that it has enough oxygen, which is decidedly not true, but you stop breathing anyway until the more primitive regulatory function--the one that works on the basis of whether there is enough oxygen--basically says "What the bleep?" What results is a disturbed pattern of breathing in which you stop breathing for a while, gasp for air, stop breathing again, gasp for more air, ad infinitum. The problem is that you typically wake yourself up every time you gasp for air, so when you finally get up after a fitful night's sleep, you feel completely exhausted. One of the benefits of my previous high-altitude mountaineering experience is that I've learned how my body responds to high altitude. That's why it is so essential for me to acclimatize with my hypoxic breathing generator well in advance of leaving for Everest. It's very rough every time I increase the altitude, but my body does get used to it, and by the end of the 8-day cycle I'm using to stage altitude increases, I'm sleeping reasonably well through the night and feeling more rested in the morning. Why go through all of this? I get to climb Everest! And on the way there I get to stop in Lhasa, Tibet and see the Potala, the palace of His Holiness the Dalai Lama before his exile 50 years ago.

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