Equipment Note The Rapid Sampling, Storage and Analysis of Expired Air

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Abstract
1. The methods which are commonly used in work physiology for rapid sampling, laboratory storage and analysis of expired air have been examined 2. The rapid fractional sampling of expired air from both a mixing chamber and a side arm sampling device produces significant differences in [Vdot]oa values when compared to the standard Douglas method. However, provided the volume of the mixing chamber is above 4 litres, the differences are small for this technique, (293 ±18.1 mls) compared with the side arm technique (263.4± 62.9 mls), and introduce negligible error into the estimation of energy expenditure 3. The selective loss of CO2 from butyl rubber bladders, Douglas bags and syringes was found to be 0.11 per cent/hr., 0.2 per cent/hr. and 0.007 per cent/hr. respectively during the 8 hr. period. Loss of CO2 during the first 30 min was high in the case of the bladders and they were found to be very unsatisfactory storage containers. Douglas bags showed a negligible loss of CO2 during the first 2 hours, but the concentration began to fall shortly thereafter. Syringes, on the other hand, showed no appreciable decline of CO2 until after the 8th hour of storage Samples collected in glass tonometers by mercury siphoning and displacement of acidulated water still maintained their concentrations of O2 and CO2 after 56 days of storage 4. The Pauling (Beckman E2 analyser was found to be an accurate, simple and fast method of estimating the O2 concentration in expired air. The discrepancy between the methods was found to be of the order of ±0.15 vol per cent when compared with the conventional Haldane gas analysis method.