Pulse oximetry works by sending red and infrared light through blood vessels and measuring the absorption of the two wavelengths of light by hemoglobin. Blood also contains other proteins such as heme peroxidases which also absorb light at slightly different wavelengths. However, given that Hemoglobin is present in a much larger concentration, would it even be possible to detect other heme peroxidases through the method used in pulse oximetry even if they had different peaks?
It is a novel question no doubt . Please go through -https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwi65a_Jsv_1AhUfzzgGHQ-YCZkQFnoECAYQAQ&url=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fbooks%2FNBK470348%2F&usg=AOvVaw2_r6r3aQVdi6yRm0mrBW_s in detail . If the condition of pulse oximetry satisfies for the detection of other heme - peroxidases .
Dear William Raskopf ,
the challenge here is that in the absorption bands/peaks are quite broad.
Thus one will have a quite strong overlap of spectra. For the case of pulse oximetry there is a cross-over point of the attenuation at about 800nm for Oxy- (HbO2) and Dexy- (Hb) Hemoglobin.
See for example:
https://de.wikipedia.org/wiki/Datei:Oxy_and_Deoxy_Hemoglobin_Near-Infrared_absorption_spectra.png
So here one has to set one optical filter around 690nm and another at around 850 nm or even up to 1000nm and more to have strong differences in the optical signals arising from these substances.
For the case of another material (e.g. your 'heme peroxidases'), which will have a quite lower concentration compared to HbO2 +Hb in the blood, you have to find an optical window, which provides very low attenuation for HbO2+Hb but strong attenuation for the heme peroxidases.
You should share absorption spectra of heme peroxidases in comparison with HbO2 and Hb. Maybe there is a chance for setting additonal filter combinations...
By the way; about which differences in concentrations we have to consider?
heme peroxidases vs. HbO2+Hb
Dear Dr William Raskopf . No. See the following useful RG link: Article Pulse oximetry: Fundamentals and technology update
Thank you to everyone for the answers.
Gerhard Martens thank you for the detailed answer, the difference in concentration is quite large, around 200-400 picomolar heme peroxidase compared to around 10mM for hemoglobin. The absorption spectrums for most heme peroxidases are quite similar to hemoglobin, however, the current one I am studying (myeloperoxidase) has a significant red shift in its peaks when in a reduced form, so perhaps that would work, I will link the paper containing the spectrums below. There is a significant discrepancy at 472nm (since the red-shifted MPO has a peak here while hemoglobin has one near 430nm), however, this may not work in a pulse oximetry setting since green light doesn't penetrate the skin as well as red or IR. There is also a discrepancy at 625nm (since hemoglobin normally has this peak at 570nm instead), maybe this would work?
Myeloperoxidase Red-Shift: https://pubmed.ncbi.nlm.nih.gov/8020506/
Hemoglobin Spectra for Reference: https://omlc.org/spectra/hemoglobin/
Thanks William Raskopf ,
for feed back.
I see, the concentrations are quite different, around 5 orders of magnitude; that is a lot and has to be compensated somehow.
Unfortunately the full-text paper on Myeloperoxidase Red-Shift does not open here yet. So I cannot see the magnitudes of the molar extinctions.
When we would like to 'see' that myeloperoxidase in the presence of HbO2 +Hb we
a) have to go the a point in the spectrum, which is independent on the 'oxidation state' of Hb; that means that we have to go to a cross-over point of the extinctions for HbO2 and Hb, such as at about 800nm, or 600nm or about 400nm.
b) However one has to take a point in the spectrum, at which the one has the lowest extinction (but not a peak) for HbO2 +Hb to have sufficient transparent conditions for the detection of myeloperoxidase. So, to my opinion, only the 800nm are the best choice. The extinction here is about 700/cm/M.
c) With respect to myeloperoxidase, we have to compare the extinction of myeloperoxidase there (at 800nm) with the 700/cm/M.
In oder to have a chance for myeloperoxidase to be seen in an optical transmission experiment in the presence of HbO2+Hb, its extinction has to be about 5 orders of magnitude larger than 700/cm/M (due to the differences in concentrations)
So, does the myeloperoxidase has got such a high extinction there in the regime of around 700*105/cm/M ? (or even higher?)
I do not think so...
That is a very, very strong requirement.
Best regards
G.M.
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