# Instrumentation for the breath-by-breath determination of oxygen and carbon dioxide based on nondispersive absorption measurements

#### Abstract

The development of instrumentation capable of the breath-by-breath monitoring of oxygen and carbon dioxide is described. The instrumentation is based on nondispersive absorption measurements, with oxygen being measured by vacuum ultraviolet absorption and carbon dioxide by infrared absorption. Oxygen- and carbon dioxide-filled discharge lamps were originally used as the selective sources for the absorption measurements. Unfortunately, the lamps did not provide sufficient wavelength selectivity which resulted in nonlinear calibration plots of low sensitivity. Consequently, a carbon-dioxide discharge lamp coupled with an interference filter provided the desired selectivity for the measurement of carbon dioxide while a xenon discharge lamp provided the required selectivity for the measurement of oxygen concentration. Accurate and precise determinations of oxygen and carbon dioxide were obtained over the desired concentration ranges. The equations for comparison of computed (y) versus prepared (x) concentrations were y = 1.00x $-$ 0.13% (r$\sp2$ = 0.998) for oxygen over a concentration range of 20 to 100% oxygen, and y = 1.07x $-$ 0.04% (r $\sp2$ = 0.998) for carbon dioxide over a concentration range of 1 to 8% carbon dioxide. The resolution of the measurement for oxygen was $\pm$0.6% while the resolution of the measurement for carbon dioxide was $\pm$0.4%. The instruments had the rapid response necessary for breath-by-breath measurements. Other respiratory gases did not interfere with the measurement of either oxygen or carbon dioxide. The anesthetic gases, nitrous oxide and halothane, did not interfere with the measurement of carbon dioxide. They did interfere with the measurement of oxygen, however. When present at typical anesthetic concentrations, their absorbance will have to be taken into account.

#### Degree

Ph.D.

Pardue, Purdue University.

#### Subject Area

Analytical chemistry

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