Posted for "Bryan Burr" <bjburr@mwheli.com>:

 Mark,
 Thank you for that post and explanation.  I have been using a cannula
 over 18,000 feet.  Now I will change my ways.  I have the mask but it is
 so inconvenient.  But not that inconvenient.
 
 Bryan
 N132BB
 LNCE
 
 -----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of
 Marvin Kaye
 Sent: Tuesday, September 12, 2006 8:06 AM
 To: Lancair Mailing List
 Subject: [LML] Re: High Altitude Oxygen Failure
 
 Posted for "Mark Sletten" <marknlisa@hometel.com>:
 
  Listers,
  
  Please be careful here... There is an altitude at which the ambient
 pressure
  is low enough that oxygen exchange in the blood does not occur. I
 don't
  believe Lorn is advocating the use of a cannula above 18,000 feet, but
 just
  in case someone else gets the impression he, or, here's why you
 shouldn't...
  
  
  As you climb, the percentage of oxygen in the air remains constant,
 but as
  ambient pressure is drops, there is less oxygen overall. That problem
 can be
  overcome by adding oxygen to the ambient air -- most supplemental
 oxygen
  system manufacturers do this by squirting oxygen up your nose via a
 cannula.
  
  But, that solution doesn't address the *OTHER* problem with altitude,
 lower
  pressure. Let me give an example: Gas pressure is what holds the
 carbon
  dioxide in the liquid of a soda -- the can is pressurized (try to
 squeeze
  one before opening it). When you pop the top, you reduce the pressure
 on the
  liquid such that the gas escapes -- you get bubbles.