Carbon dioxide (CO2) monitoring in human subjects is of crucial importance in medical practice. Transcutaneous monitors based on the Stow-Severinghaus electrode make a good alternative to the painful and risky arterial “blood gases” sampling. Yet, such monitors are not only expensive, but also bulky and continuously drifting, requiring frequent recalibrations by trained medical staff. Aiming at finding alternatives, the full panel of CO2 measurement techniques is thoroughly reviewed. The physicochemical working principle of each sensing technique is given, as well as some typical merit criteria, advantages, and drawbacks. An overview of the main CO2 monitoring methods and sites routinely used in clinical practice is also provided, revealing their constraints and specificities. The reviewed CO2 sensing techniques are then evaluated in view of the latter clinical constraints and transcutaneous sensing coupled to a dye-based fluorescence CO2 sensing seems to offer the best potential for the development of a future non-invasive clinical CO2 monitor.
Significance: The arterial carbon dioxide (CO 2) partial pressure Pa CO 2 is a clinically relevant variable. However, its measurement requires arterial blood sampling or bulky and expensive transcutaneous Ptc CO 2 meters. While the spectrophotometric determination of hemoglobin species-such as oxy-hemoglobin (O 2 Hb) and deoxy-hemoglobin (HHb)-allowed for the development of pulse oximetry, the measurement of CO 2 blood content with minimal discomfort has not been addressed yet. Aim: Characterizing human carbamino-hemoglobin (CO 2 Hb) absorption spectrum, which is missing from the literature. Providing the theoretical background that will allow for transcutaneous, noninvasive Pa CO 2 measurements. Approach: A tonometry-based approach was used to obtain gas-equilibrated, lysed, diluted human blood. Equilibration was performed with both CO 2 , dinitrogen (N 2), 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 CO 2 Hb 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 CO 2 Hb 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: CO 2 Hb 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 Pa CO 2 measurement seems extremely challenging.
Cet article décrit un TP d’introduction aux systèmes embarqués réalisés avec les étudiants de Télécom Physique Strasbourg en deuxième année du cycle de formation ingénieur (BAC +4). Il vise à introduire les concepts fondamentaux des systèmes embarqués sur un exemple concret, en l’occurrence la réalisation d’une station météo, avec une approche de type projet. Les travaux pratiques se déroulent sur 2 jours (16 heures) pendant lesquels les étudiants apprennent à utiliser les fonctionnalités avancées du microcontrôleur (interruptions et timers), les protocoles de communication standards (SPI, I2C et 1-wire) et mettent en place une communication de type UART entre deux microprocesseurs.
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