> -----Original Message-----
> From: piclist-bouncesKILLspamMIT.EDU
> [.....piclist-bouncesKILLspam.....MIT.EDU] On Behalf Of Russell McMahon
> Sent: 2006 Jul 03, Mon 05:59
> To: PIC List
> Subject: [EE] Caphograph design
>
> I wish to build a Capnograph.
> Don't know what that is?
> I didn't either until yesterday - even though I wanted one.
> It's an instrument to measure exhaled CO2 content.
> Exhaled CO2 content is typically in the range 2% - 10.% Y.CO2.M.V.
>
> Real ones cost real money.
> Most straight forwards method is measuring absorption at about 4.2 -
> 4.3 nm where CO2 has an absorption peak.
> This usually involves producing light which includes this
> wavelength and then filtering it with a suitable filter.
> These are commonly enough avail;able due to their use in
> Automotive gas analysers, and, not surprisingly, in
> Capnographs. Such filters are nastily  expensive - typically
> hundreds of dollars. This is a 'discretionary'
> project and while such a cost is bearable it would be much
> better if a cheaper solution was available.
>
> One possible solution is the use of a diffraction grating or
> possibly a prism.
>
> Other people may have alternative innovative suggestions for
> addressing the 4.2 nm line approach OR may have alternative
> methods. I want a potentially "breath by breath" response and
> ideally electronic logging so chemical means are unlikely to
> be useful.
>
> I can imagine a "colour wheel" approach where CO2 is absorbed
> on a substrate causing eg colour change, read by a sensor and
> then regenerated by eg heating, all on a rotating wheel,
> might provide a viable real time solution. How one achieves
> such a colour or other change I don't yet know.
>
> Pushing that a little further, exhaled air could be bubbled
> through a solution causing transparency change and light
> occlusion and the solution subsequently regenerated. Much
> messier than I would like, but such "idea starters" may lead
> to other things.
>
> FWIW the End Tidal value (the CO2 level at the end of
> exhalation)  is an amazingly sensitive and valuable indicator
> for many medical situations. ET value gives far faster
> response than Pulse Oximiter blood oxygen readings to
> oxygenation changes (one breath versus a minute plus), is a
> sadly accurate indicator of resuscitation prospects and a
> good indicator of whether resuscitation is working (reading
> at 20 minutes resus gives near certain indication of
> death/life prospects). It's invaluable as an intubation
> indicator and monitor for patients during critical transfers.
>
>
>
>
>         Russell McMahon
>
>
>

> I wish to build a Capnograph.
> Don't know what that is?
> I didn't either until yesterday - even though I wanted one.
> It's an instrument to measure exhaled CO2 content.
> Exhaled CO2 content is typically in the range 2% - 10.%
> Y.CO2.M.V.
>
> Real ones cost real money.
> Most straight forwards method is measuring absorption at about 4.2 -
> 4.3 nm where CO2 has an absorption peak.
> This usually involves producing light which includes this wavelength
> and then filtering it with a suitable filter. These are commonly
> enough avail;able due to their use in Automotive gas analysers, and,
> not surprisingly, in Capnographs. Such filters are nastily
>  expensive - typically hundreds of dollars. This is a 'discretionary'
> project and while such a cost is bearable it would be much better if a
> cheaper solution was available.
>
> One possible solution is the use of a diffraction grating or possibly
> a prism.
>
> Other people may have alternative innovative suggestions for
> addressing the 4.2 nm line approach OR may have alternative methods. I
> want a potentially "breath by breath" response and ideally electronic
> logging so chemical means are unlikely to be useful.
>
> I can imagine a "colour wheel" approach where CO2 is absorbed on a
> substrate causing eg colour change, read by a sensor and then
> regenerated by eg heating, all on a rotating wheel, might provide a
> viable real time solution. How one achieves such a colour or other
> change I don't yet know.
>
> Pushing that a little further, exhaled air could be bubbled through a
> solution causing transparency change and light occlusion and the
> solution subsequently regenerated. Much messier than I would like, but
> such "idea starters" may lead to other things.
>
> FWIW the End Tidal value (the CO2 level at the end of exhalation)  is
> an amazingly sensitive and valuable indicator for many medical
> situations. ET value gives far faster response than Pulse Oximiter
> blood oxygen readings to oxygenation changes (one breath versus a
> minute plus), is a sadly accurate indicator of resuscitation prospects
> and a good indicator of whether resuscitation is working (reading at
> 20 minutes resus gives near certain indication of death/life
> prospects). It's invaluable as an intubation indicator and monitor for
> patients during critical transfers.
>
>
>
>
>         Russell McMahon
>
>
>

> I wish to build a Capnograph.
> Don't know what that is?
> I didn't either until yesterday - even though I wanted one.
> It's an instrument to measure exhaled CO2 content.
> Exhaled CO2 content is typically in the range 2% - 10.%
> Y.CO2.M.V.
>
> Real ones cost real money.
> Most straight forwards method is measuring absorption at about 4.2 -
> 4.3 nm where CO2 has an absorption peak.
> This usually involves producing light which includes this wavelength
> and then filtering it with a suitable filter. These are commonly
> enough avail;able due to their use in Automotive gas analysers, and,
> not surprisingly, in Capnographs. Such filters are nastily
>  expensive - typically hundreds of dollars. This is a 'discretionary'
> project and while such a cost is bearable it would be much better if a
> cheaper solution was available.
>
> One possible solution is the use of a diffraction grating or possibly
> a prism.
>
> Other people may have alternative innovative suggestions for
> addressing the 4.2 nm line approach OR may have alternative methods. I
> want a potentially "breath by breath" response and ideally electronic
> logging so chemical means are unlikely to be useful.
>
> I can imagine a "colour wheel" approach where CO2 is absorbed on a
> substrate causing eg colour change, read by a sensor and then
> regenerated by eg heating, all on a rotating wheel, might provide a
> viable real time solution. How one achieves such a colour or other
> change I don't yet know.
>
> Pushing that a little further, exhaled air could be bubbled through a
> solution causing transparency change and light occlusion and the
> solution subsequently regenerated. Much messier than I would like, but
> such "idea starters" may lead to other things.
>
> FWIW the End Tidal value (the CO2 level at the end of exhalation)  is
> an amazingly sensitive and valuable indicator for many medical
> situations. ET value gives far faster response than Pulse Oximiter
> blood oxygen readings to oxygenation changes (one breath versus a
> minute plus), is a sadly accurate indicator of resuscitation prospects
> and a good indicator of whether resuscitation is working (reading at
> 20 minutes resus gives near certain indication of death/life
> prospects). It's invaluable as an intubation indicator and monitor for
> patients during critical transfers.
>
>
>
>
>        Russell McMahon
>
>
>