Measurement of acetylene in breath by ultraviolet absorption spectroscopy: Potential for noninvasive cardiac output monitoring

A new, miniaturized, noninvasive instrument for rapid acetylene analysis in breath gas is described. Acetylene is a blood-soluble gas and for many years its uptake rate during rebreathing and/or nonrebreathing tests has been used to calculate the volume of lung tissue as well as the flow rate of blood through the lungs. The instrument relies on dispersive UV absorption spectroscopy as its measurement principle and is employed in an extractive (side-stream) configuration. The analyzer afforded fast (276+/-43 ms, 0%-90%, at 2 L min(-1) flow rates), interference-free detection of acetylene, with signal-to-noise ratios in excess of 50. Comparison tests with a mass spectrometer using calibration gas samples gave an excellent correlation {[C2H2](MS) = 0.999.[C2H2](UV), R-2 = 1.000}, which validated the linearity and accuracy of the UV system. A similar level of correlation between these devices also was observed during human subject C2H2 uptake tests, with both instruments sampling a common extracted gas stream {[C2H2](UV) = 0.940.[C2H2](MS), R-2 = 0.998}. These results indicate that a miniature, low-cost, rugged, ultraviolet spectrometer system measuring acetylene holds promise for human breath analysis in a clinical setting. (C) 2003 American Institute of Physics.