Measuring hemoglobin spectra: searching for carbamino-hemoglobin.

Abstract

.Significance: The arterial carbon dioxide () partial pressure is a clinically relevant variable. However, its measurement requires arterial blood sampling or bulky and expensive transcutaneous meters. While the spectrophotometric determination of hemoglobin species—such as oxy-hemoglobin () and deoxy-hemoglobin (HHb)—allowed for the development of pulse oximetry, the measurement of blood content with minimal discomfort has not been addressed yet.Aim: Characterizing human carbamino-hemoglobin () absorption spectrum, which is missing from the literature. Providing the theoretical background that will allow for transcutaneous, noninvasive measurements.Approach: A tonometry-based approach was used to obtain gas-equilibrated, lysed, diluted human blood. Equilibration was performed with both , dinitrogen (), and ambient air. Spectrophotometric measurements were carried out on the 235- to 1000-nm range. A theoretical background was also derived from that of pulse oximetry.Results: The absorption spectra of both and HHb were extremely close and comparable with that of state-of-the-art HHb. The above-mentioned theoretical background led to an estimated relative error above 30% on the measured amount of in a subject’s blood. Auxiliary measurements revealed that the use of ethylene diamine tetraacetic acid did not interfere with spectrophotometric measurements, whereas sodium metabisulfite did.Conclusions: absorption spectrum was measured for the first time. Such spectrum being close to that of HHb, the use of a theoretical background based on pulse oximetry theory for noninvasive measurement seems extremely challenging.