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imginit

Development Team Member
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Posts: 7
 #1 
Just to make sure I understand:

tHb is used to determine the amount of hemoglobin that is being looked at.  From the oxygenated Hb vs the deoxygenated Hb, the sm02 can be calculated.  

Roger

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Posts: 266
 #2 
Here's some equations and terminology to help my reply

Oxy Hemoglobin Concentration = O2Hb = The grams of oxygenated hemoglobin per deciliter of tissue
Deoxy Hemoglobin Concentration = HHb = The grams of deoxygenated hemoglobin per deciliter of tissue

Total Hemoglobin Concentration = O2Hb + HHb = The total grams of hemoglobin per deciliter of tissue

SmO2= 100 * O2Hb / (O2HB + HHB) = Percentage of hemoglobin that is oxygenated

Moxy measures SmO2 in an absolute sense.  An SmO2 of 60 means that 60% of the hemoglobin is oxygenated.

Moxy's THb measurement is only a relative indication of changes in the Total Hemoglobin concentration. If the Moxy THb goes up, that indicates that the total hemoglobin concentration in the muscle went up. However, we can't say anything about the absolute value of the total hemoglobin concentration.

The reason for this limitation is that the Moxy sensor can't distinguish between a low hemoglobin concentration in the muscle and a thick fat layer.

An imperfect analogy that I sometimes use is to think of looking at a stop light off in the distance on a foggy day.  It's easy to tell if the light is red or green even if its just all a blur.  However, it's much more difficult to tell if it is a bright light that is far away or a dim light that is closer.  SmO2 is measured by a color change in the hemoglobin so that is easy to measure through the fat (fog). Total hemoglobin is a quantitative measurement of the amount of light absorber under the unknown fat layer thickness which makes it much more difficult.
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