W.J. (Bill) Dean (U.K.). wrote:
Peter Saundby has put the following posting on the U.K. u.r.a.s.:

Following the string on oxygen systems, pilots intending to fly at altitude
should be very wary of relying upon oxymetry devices intended for clinical
use to confirm in the air that they are adequately oxygenated. Professor
John Ernsting, long of the RAF Institute of Aviation Medicine gave a
presentation on their limitations at the recent International Congress of
Aerospace Medicine in Warsaw. These devices have been used by pilots of
unpressurised aircraft to monitor the adequacy of their oxygen supply or to
assess the performance of emergency oxygen systems. The problem is that
when suffering a degree of hypoxia there is a tendency to hyperventilate and
the consequent reduction of carbon dioxide will increase the stability of
oxy-haemoglobin. While blood saturation appears adequate, too little oxygen
will be released to the brain. This theory was confirmed by experiment in a
chamber; therefore extreme caution should be exercised when using oximetry
at altitude because it can offer a false assurance.

Lower pH, resulting from hyperventilation, decreases hemoglobin's
affinity for O2. The rest makes sense (higher affinity, higher measured
saturation level, and yet poor O2 delivery in tissues). Could it be
*hypo* ventilation. Do you have any references we could read.

Shawn