Forces produced by high acceleration overdistend one part and compress
another part of the lungs. Blood flow diminishes in some parts of the
lungs and increases in others. Fluid leaks from the blood into the
tissues and into the air sacs in parts of the lungs. These effects cause
difficulty in breathing, low arterial oxygen saturation, and impaired
consciousness during high sustained acceleration and, to a lesser
extent, after its cessation. They must be considered when selecting the
best gas to be breathed, since a high partial pressure of oxygen is
favorable for consciousness, but a low inert-gas concentration during
acceleration is unfavorable for rapid lung recovery afterward.