Armstrong's Line
The phenomena of blood boiling at high altitude is a fact. It is due to gas (Boyle's) laws. At about 62,000 feet, air comes out of solution (blood). This altitude is also known as the Armstrong's Line. This is why pilots who fly the U-2 and SR-71 high altitude a/c has to wear a full pressure suit, to avoid this unpleasant event. Colonel Joseph Kittinger, the man who did the world's highest altitude parachute jump at 102,800 feet also had to wear a pressure suit when he leaped off from the balloon!