Abstract
An instrument for measuring low rates of biological O2exchange using an open-flow gas analysis system is described. A novel differential O2sensor that is capable of measuring as little as 0.4 Pa O2against a background of ambient air (20,900 Pa O2), yet has a dynamic range of ±2000 Pa O2(i.e., ±ca. 2% O2) is described. Baseline drift was typically less than 0.025 Pa min−1. The differential O2sensor was incorporated into a respiratory quotient/photosynthetic quotient analyzer that contained other environmental sensors for atmospheric pressure, absolute O2and CO2concentration, temperature of the differential O2sensor block, and differential pressure between reference and sample streams. Protocols for how these sensors can be used to calibrate the differential O2sensor and to improve its stability with time are described. Together, the differential O2sensor, the environmental sensors, and the simple calibration techniques allow for simultaneous, noninvasive, and accurate measurements of O2and CO2exchange in tissues with metabolic rates as low as about 0.1 μmol O2or CO2h−1. Example data are provided in which O2differentials of 3 to 41 Pa O2were measured in an open-flow system.
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