September 2008 Issue

Handling Heat

Excellent article by Tom Turner in July’s issue ("Hot And High How-To") but a couple of things come to mind. First, in the sidebar Cruise Considerations, you infer that a high density altitude decreases the available amount of oxygen for breathing. This is technically true, but the difference is so small it is hardly worth considering. Obviously, if one feels the need for it oxygen should be taken regardless of altitude, density or otherwise. A pulse oximeter is a huge help here, and the basic guideline is to maintain a saturation level that is within 10 percent of sea level saturation to avoid judgment impairment. Dr. Jack Hastings, former author of the American Bonanza Society’s Aeromedical column, and a past president of the group, was kind enough to research and answer my question concerning density altitude and human saturation. Briefly stated, he said that oxygen saturation in the human body is dependant upon the "partial pressure" of oxygen in the atmosphere to create the osmotic exchange in the lungs. That partial pressure is only slightly affected by density altitude, and therefore insignificant.

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