lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> Gearge Braly points out that many people fly safely at SaO2's of 87%. While this may be true, we must ask whether it is desirable. On a physiologic basis, there is reason to be concerned. First, it places you at a position where you must increase cardiac output to avoid reducing mixed venous oxygen so low that shunting overtakes oxygenation. Most of us can do that, but it is one part of our reserves used up. Second, this is where the "knee" in the hemoglobin/oxygen dissociation curve is. It is a much larger distance to go from 95% to 90% SaO2 than it is to go from 92% to 87%. And that is a much larger distance than going from 90% to 85%, etc. This is counter-intuitive, but true. Essentially, once you reach the knee of the curve, your margin of safety is gone. You may be OK where you are, but it doesn't take much to make things go bad. To fly at an SaO2 of 78%-83% is IMHO foolhardy. The issue is not cardiac arrest, it is intellectual function. The brain is able to autoregulate its flow to match oxygen demand, but if there isn't enough oxygen there, the brain can't function well. And at that level of SaO2, it begins to be more difficult to move oxygen off of the hemoglobin molecule to the tissues. Yes, it does work, but the margin of safety simply is not there. No, I haven't flown at a cabin pressure altitude over 10k. But that doesn't alter the physiology. You are welcome to fly at whatever SaO2 suits you. But I won't recommend anything below 90%. Ted Noel ____________ The Bible Only --- If the Bible doesn't teach it, neither will we. --- http://www.bibleonly.org --- Webmaster --- tednoel@cfl.rr.com --- >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://members.olsusa.com/mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please remember that purchases from the Builders' Bookstore assist with the management of the LML. Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>