fascinating as usual gents... (I mean that in a gender neutral sense, kathy) regarding the CO blood level, can this become increased or out of normal limits by being a heavy smoker? or drinker? thanks ----- Original Message ----- From: "Benjamin Bromilow" To: Sent: Thursday, September 27, 2001 6:42 AM Subject: Re: [pic]: can you make an oxygen saturation monitor with a pic?? > Absolutely, the pulse-ox units are great for *monitoring* patients but for > diagnostic purposes we still like getting a nice arterial blood sample for > testing. If you use PulseOx units enough you'll see a huge variation in > accuracy. Often the units will consistently measure low (ie around 90%) on > patients but when you do the blood gas the sats are okay at 95%. > So if you know that someone has good saturation as they are and want to > check that they don't desaturate then fine but for diagnostic or baseline > measurements you really need some blood- even though arterial sampling is > painful > > I believe the unit takes the trough level as "finger" absorption (ie > bone/soft tissue/nail etc) and uses [peak - trough] to work out the reading. > Truly lots of black magic in it though. Often the units will display a > reasonable looking trace yet say it is poor quality. I suspect the "quality" > of the trace has little to do with the amplitude or pulse shape and more to > do with stuff we don't see on the monitor. > > Ben > ps This really is too much to do with the day job!! > pps The paediatric sensors are adhesive stick on. They get replaced > frequently. Might be able to scrounge one. The adult clip on units are > usually re-used until they are held together with tape!! > pps Personally I'd rather build a "personal" ECG machine with graphical LCD > output and rythym analysis! > ----- Original Message ----- > From: Russell McMahon > To: > Sent: Thursday, September 27, 2001 1:35 PM > Subject: Re: [pic]: can you make an oxygen saturation monitor with a pic?? > > > > > Hello Gents, > > > > > > I've recently become aware of an O2 saturation measuring device > > > used by hospitals...it appears to use two led's on the top and bottom > > > of the index finger, which then measures heart pulse and O2 saturation, > > > > > > anyone know how this works? and can it be done with a pic? > > > > > > This is known as a "Pulse Oximeter". > > Search under that name for lots of information. > > Some years ago an issue of the superb "Hewlett Packard Journal" was almost > > completely dedicated to this subject. They gave extensive information on > > what is involved. HP used to be good at this - telling you how they did it > > and what's involved indicates that they have done it so well that you > can't > > compete with them economically. Often they are right. I believe that back > > issues of the HP Journal are available on the net. > > > > The cost is not in the sensors, which are relatively simple and low cost, > > but in processing the data. A substantial amount of black magic is > involved. > > AFAIK (based on the article) the HP sensors are throw-away items designed > to > > be replaced frequently in the medical environment. > > > > The system works by using two frequencies of Infra Red. One is affected by > > an absorption line in blood due to Oxyhaemoglobin and the other isn't. The > > un-affected light gives a reference level of absorption allowing changes > in > > the other to be corrected to show only the OH level. In theory. > > > > There is substantial craft and knowledge in fitting the results to reality > > in practice. I read a paper which compared the results from a number of > > different PO sets used by doctors for patients in the Andes afair. They > > noted that the results from each varied under various combinations of > > patient, environment and true condition. ie even real tools are only a > > diagnostic guide and need to be used with care. > > > > > > > > regards > > > > Russell McMahon > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu