Xref: utzoo sci.bio:4848 sci.med:24560
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!ub!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.bio,sci.med
Subject: Re: Hemoglobin Saturation Curve
Summary: Variation caused by pH and temperature
Keywords: hemoglobin saturation curves
Message-ID: <4899@kitty.UUCP>
Date: 25 Apr 91 02:51:26 GMT
References: <6523@husc6.harvard.edu>
Followup-To: sci.bio,sci.med
Organization: Recognition Research Corp., Clarence, NY
Lines: 32

In article <6523@husc6.harvard.edu> shahn@hstbme.mit.edu (Sam Hahn) writes:
>Does anyone know of an equation that describes the oxygen 
>saturation/desaturation curve for hemoglobin? Surprisingly, none of my 
>biochemistry or physiology texts seems to have a reference for an actual 
>quantitative relationship between oxygen pressure and hemoglobin 
>saturation.
>
>I have tried curve fitting a standard saturation curve with very 
>unsatisfactory results so any help would be appreciated.

	Hemoglobin saturation in % plotted against PO2 varies depending
upon both pH and temperature.  If you look in one of the more complete
physiology texts, such as "Human Physiology" by Mountcastle, you will
see *families* of curves, with significanly different curves resulting
from pH variations of as little as 0.1 pH unit.  You will also see
different curves depending upon temperature, but temperature variation
is not much of a problem in say, a clinical setting.

	Therefore, your curve fitting may be unsatisfactory due to pH
(and possibly temperature) variation.

	It would have been helpful if you had described your application.
For example, in the case of an oximeter, curve fitting is not much of a
problem since pH and temperature is largely compensated after calculations
are performed with both the visible light and NIR spectrophotometric
absorption versus saturation curves.  Using just two fitted curves (the
visible and NIR), oxygen saturation can be measured to within 2% - which
is really pretty good.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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