Don Callander wrote:I also remember some physiologic testing of Himalayan sherpas done at the U. of MN in the early 90's; they presented with Hgb of >20 (Hct >60) with no clotting issues.
I just found a research result which says that native Tibetans have unusually high concentration of Nitric Oxide (NO) in their blood:
I'm no medical person, but apparently NO tends to dilate blood vessels, and this increases oxygen transport starting with blood flow thru the lungs and finishing with capillaries to the muscle cells -- another reason beyond hematocrit why native Tibetans perform well at high altitude.
I've read that NO also inhibits the adhesion and clumping of platelets, which helps fight against dangerous clots in the blood vessels -- which might explain how they can tolerate high hematocrit with less risk of clotting than non-Tibetans.
Apparently lower atmospheric pressure tends to decrease NO levels in many non-Tibetans, so it might be that this decreases athletic performance at altitude more than just the reduced oxygen pressure would indicate.
A drug known to manipulate NO function is Viagra -- but I sort of heard it operates more selectively, especially in the lungs (and another organ) -- so I guess the native Tibetans are getting their result by some other means.
Of course even enhancing NO function only in the lungs could give a substantial benefit to athletic performance -- but it's not clear how that could help athletes in sea-level performance. Nevertheless it's getting studied . . .