Frequency Domain Photon Migration (FDPM) is a non-invasive infrared monitoring technology that functions by directing an intensity modulated monochromatic light source at the tissue of interest. Simultaneous determination of absorption and scattering provides the capability for non-invasive direct measurement of tissue metabolite composition. FDPM could potentially be used to monitor changes in various metabolic parameters such as methemoglobin (MetHgb) and methylene blue concentrations during treatment in vivo.
The purpose of this study is to evaluate the feasibility of FDPM to non-invasively monitor metabolic events, such as the extent of methemoglobinemia and reversal using methylene blue in vivo.
In vivo detection of methemoglobinemia was evaluated in a New Zealand Rabbit model via intravascular injection of amyl nitrite, and the effects were assessed using FDPM monitoring with a prototype device constructed in our laboratory. The FDPM data were then compared to standard arterial blood gas measurements of MetHgb using a co-oximeter.
In vivo, MetHgb concentration quantitatively measured by FDPM was compared to %MetHgb obtained through arterial blood gas measurements. Rapid development of methemoglobinemia following amyl nitrite injection was non-invasively tracked, as shown in the figureincluded.
CONCLUSIONS & CLINICAL IMPLICATIONS:
Our results demonstrate the feasibility of monitoring MetHgb levels in tissue non-invasively via FDPM. The ability to non-invasively measure metabolic parameters may someday be useful for assessing and treating conditions such as methemoglobinemia and cyanide toxicity.
N.H. El-Abbadi, TRDRP# 9RT-0094, grant monies; Air Force D/F49620-00-10371, grant monies.