Mark wrote:

>   The oxygen saturation and pulse rate sensors I've seen all TOO much of
> when Robin's in hospital, have a red LED and a photosensor, perhaps an
> IR pair as well, in something rather like a large plastic clothespin (I
> know what they look like but didn't feel like disassembling them while
> there <G>)
>
>   You clamp it onto a finger and watch the light conductance waveform
> for pulse rate, I know I've read before how they determine O2 saturation
> but don't remember just now.
>
Oxygenated and deoxygenated blood absorb near infra red light in two
different frequencies.   By measuring the absorbsion and taking the
ratio you can calculate the saturation percentage of the blood.   Since
the density of or mass of blood in the tissue changes during each
cardiac cycle ( that is high as the heart ejects and falling off as the
heart empties) you can also derive heart rate from this same data set.

>   I thought that the chest tubes were mainly for breathing rates, (They
> measure pressure changes from the tube's being stretched as your chest
> expands/contracts) but it's entirely possible that an FFT or high pass
> filtering or something on there - some devious wonderful trick - would
> also disclose a pulse rate?  Anyone know?
>
The devices on the jogger's chest pick up the ECG from the heart.  The
heart uses electrical energy as the cells depolarize with each
contraction.   Respiratory rates can be sensed by measuring change in
electrical impedence across the chest over time.   As the lung fills
with air impedence increases.

>   Interesting things to learn
> in this field for myself, I'm not much good on bio-sensors yet I'm
> afraid <G>
>
>   Mark
>
Mark---Be afraid be very afraid.   One screw-up or misstep in this area
and you can end up dead


John