A MODIFIED PHOTOACOUSTIC AND MAGNETOACOUSTIC MULTIGAS ANALYZER APPLIED IN GAS-EXCHANGE MEASUREMENTS

The feasibility of replacing a conventional mass spectrometer (MS) wit h a specially modified multicomponent (O-2, CO2, Freon 22, and SF6) ac oustic infrared and paramagnetic (IR/PM) gas analyzer in inert gas-reb reathing and metabolic gas exchange measurements has been investigated . Rebreathing variables were determined simultaneously with the MS and IR/PM analyzers in duplicate measurements at rest and during submaxim al exercise in 10 subjects. The differences (means +/- SD, IR/PM - MS) were 0.028 +/- 0.048 liters [functional residual capacity (FRC)], 0.1 8 +/- 0.38 l/min [cardiac output (Qc)], -0.006 +/- 0.030 l/min [O-2 co nsumption (VO2)], and -33 +/- 108 ml [combined lung tissue and capilla ry blood volume (Vti,c)]. The coefficients of variation on repeated es timates were 5.8% (FRC), 5.4% (Qc), 6.2% (VO2), and 17% (Vti,c) with t he IR/PM analyzer and 5.9% (FRC), 4.2% (Qc), 5.0% (ire,), and 9.8% (Vt i,c) with the MS. The differences (IR/PM-MS) obtained in mixed-expirat e measurements were -0.006 +/- 0.020 l/min (VO2) and 0.020 +/- 0.021 l /min (CO2 production). Breath-by-breath estimates of VO2 and CO2 produ ction with the IR/PM analyzer were, on average, 2.4 and 4.4% higher th an the MS estimates, respectively. Our results demonstrate that the IR /PM gas analyzer, when appropriately modified, can substitute for a co mplex MS in a variety of noninvasive pulmonary gas exchange measuremen ts.