Blue venous blood, flowing by the walls of air sacs in the lungs, absorbs oxygen from the air. Changed to arterial blood it distributes the life giving gas throughout the body. At sea level, oxygen in the lung sacs maintains a pressure of some two pounds to the square inch. At 19000 feet, as at the silver hut of the wintering party, pressure drops to less than half. Though the lungs labor mightily, with deeper and faster breaths, the supply of oxygen barely suffices even while the body rests. Hard work can not be sustained more than a few uninterrupted minutes. The right side of the heart enlarges to overcome the increased resistance in the small blood vessels of the lungs. Three air sacs symbolize the 300 million in each lungs where the blood briefly comes into contact with oxygen. Barry Bishop labors around a slope of Ama Dablam while burdened with 30 pounds of equipment. Later, in the test in the societys office, the 150 pund author bore a 210 pound man up a flight of stairs and exclaimed, this is just how I felt on Ama Dablam!!bearing 30 pounds at 19000 feet proved as difficult as carrying more than 200 pounds at sea level.
Though ballel chested natives of the andes have adopted to life at 17500 feet, scientists who wintered with mr. Bishop on Himalayan heights doubts that man can live indefinitely much higher than that. In rarefied air a climbers blood has little reserve of oxygen, and must pause every few steps to catch his breath.