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bobbyjobling

Development Team Member
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Posts: 219
 #1 

The conventional method to display O2Hb and HHB doesn’t really help with the interpretation of blood flow. As you can see from the picture below, it is difficult to make any assumptions on blood flow as O2HB and HHB looks similar in the shape but inverted.

O2Hb HHB.png 

It is far better to use SmO2 and THB.
SmO2 THb.png 

Why?..... I believe the data is “lost” in the THb value as most of it is not needed……we are just interested in the shape. So let’s remove most of the value but still maintain the shape range of THb. The NewTHb value can then be used to calculate the NewO2Hb and NewHHB
THb New O2Hb HHb.png 

SmO2 New O2Hb HHB.png
I think this is a far better way to show the O2Hb and HHB.
One,more example
SmO2 THb 2.png 

And using the new O2Hb HHB
newO2Hb HHB.png 
and the old way to show O2Hb & HHB
O2Hb HHB 2.png 


Roger

Moderator
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Posts: 266
 #2 
Thanks for posting this topic.  It's good to understand this issue.

SmO2 has useful accuracy on a 0% to 100% scale.  When you see 10%, you know that almost all of the hemoglobin and myoglobin has released their oxygen.

THb is arbitrarily scaled.  It goes up when it should go up and down when it should go down but the magnitude of the number isn't useful.  You can only use it for trends.

The scale on the THb value was intentionally selected to give the nearly symmetric O2Hb and HHb curves.  This is done so the mean value is large relative to the variations.

If you subtract a fixed number from the THb (It looks like you subtracted ~12 from the old THb to get your new THb), you get a situation where the THb variations are large relative to the mean.  This has no effect on the THb interpretation, but it does mess with the O2Hb and HHb interpretation.

When you use the smaller THb value to calculate O2Hb and HHb, you can change the slope of the O2Hb or HHb line from positive to negative.  You can see that this happens on the last 2 graphs that  you show.  If you look to the right of the 12:14:24 time grid line, you can see that the O2Hb shape is quite different between the two graphs.

Moving the THb closer to 0 is great for autoscaling the THb graph to be able to see the variations, but you need to be careful about using this value to calculate O2Hb and HHb.

This is why I generally advocate just using SmO2 and THb.  SmO2 is accurate by itself.  The THb trend will not have the wrong slope (e.g. it won't show increasing when it's actually decreasing).  However, depending on how you scale the THb, the O2Hb and HHB could have the wrong slope so that makes interpretation more difficult.
bobbyjobling

Development Team Member
Registered:
Posts: 219
 #3 
Yes I agree with your statement, it is to be used with care and understanding the limitations of it helps. The value I subtract is based on a percentage of the mean which I can change if it doesn't make sense, but it appears to help. I normally come to the same conclusion when compared to Smo2 THB ...

A few questions I would like to know; what is the average contribution / ratio of myoglobin to hemoglobin? Do we measure mostly hemoglobin or myoglobin? And would myoglobin volume change with muscle compression?
All of the oxygen is transported by the hemoglobin. Would the desaturation of myoglobin oxygen follow closely with the depletion of hemoglobin oxygen, so that they both move in the same direction with minimal time delays.
I know that oxygen dissociation curve is different but also the environmental partial pressure of the oxygen range where the myoglobin and hemoglobin resides is different. Just wondering if knowing an approximate ratio would help with interpretations.
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