Significance: The arterial carbon dioxide (CO2) partial pressure PaCO2 is a clinically relevant variable. However, its measurement requires arterial blood sampling or bulky and expensive transcutaneous PtcCO2 meters. While the spectrophotometric determination of hemoglobin species—such as oxy-hemoglobin (O2Hb) and deoxy-hemoglobin (HHb)—allowed for the development of pulse oximetry, the measurement of CO2 blood content with minimal discomfort has not been addressed yet. Aim: Characterizing human carbamino-hemoglobin (CO2Hb) absorption spectrum, which is missing from the literature. Providing the theoretical background that will allow for transcutaneous, noninvasive PaCO2 measurements. Approach: A tonometry-based approach was used to obtain gas-equilibrated, lysed, diluted human blood. Equilibration was performed with both CO2, dinitrogen (N2), 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 CO2Hb 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 CO2Hb 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:CO2Hb 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 PaCO2 measurement seems extremely challenging.

中文翻译：

---

测量血红蛋白谱：搜索氨基甲酸血红蛋白

意义：动脉二氧化碳 (CO2) 分压 PaCO2 是一个临床相关变量。然而，它的测量需要动脉血样或体积庞大且昂贵的经皮 PtcCO2 测量仪。虽然分光光度法测定血红蛋白种类——如氧合血红蛋白 (O2Hb) 和脱氧血红蛋白 (HHb)——允许发展脉搏血氧饱和度，但尚未解决测量 CO2 血液含量时带来的不适感。目的：表征人类氨基甲酸血红蛋白 (CO2Hb) 吸收光谱，这是文献中缺失的。提供允许经皮、无创 PaCO2 测量的理论背景。方法：基于眼压计的方法用于获得气体平衡、裂解、稀释的人血。用 CO2、二氮 (N2)、和环境空气。分光光度测量在 235 至 1000 nm 范围内进行。理论背景也来自脉搏血氧饱和度测定法。结果：CO2Hb 和 HHb 的吸收光谱非常接近，与最先进的 HHb 的吸收光谱相当。上述理论背景导致受试者血液中测量的 CO2Hb 量的估计相对误差超过 30%。辅助测量表明，使用乙二胺四乙酸不会干扰分光光度测量，而焦亚硫酸钠会干扰。结论：首次测量到CO2Hb吸收光谱。这种光谱接近 HHb 的光谱，使用基于脉搏血氧饱和度理论的理论背景进行无创 PaCO2 测量似乎极具挑战性。