Evaluation of Half-Mask Gas Collection for Metabolic Measurement in the Work Place

Metabolic measurement is often important in job design and research. Metabolic measurement via indirect spirometry has traditionally used a mouth-piece nose-clip headgear (MNH) method of collecting expired gases. MNH is often uncomfortable, prohibits oral communication, may fail because of loss of nose-clip, and may interfere with or alter some work tasks because of the awkwardness of the headgear. Gas collection masks (MASK) offer the possibility of partially or totally alleviating the problems of MNH but increase the possibility of erroneous measure due to leakage. This study compared the measurement of performance and subject's subjective ratings of a typical MNH vs. MASK (Hans Rudolph model 8900 series) over a range of work loads from light to maximal in 20 well-trained subjects (M=12, F=8). Ventilation (Ve), oxygen uptake (VO₂), and respiratory exchange ratio (RER) were collected with a Sensormedics MMC-1, and heart rate (HR) with a Polar Heartwatch. Comfort was assessed with a Likert questionnaire. Results from the final work rate are shown below:

Variable Ve (L/min) VO₂ (ml/kg/min) RER HR (bpm)

MNH 105,217 52.2 1.13 187

MASK 115,281 56.6 1.09 187

Results show this MASK produced values as high as the MNH with greater subject comfort at both peak and sub-maximal work. The observed Ve in the MASK condition suggests that leakage was not problematic and there could be a tendency for the MNH to actually impede the measurement. Based on previous preliminary studies and these data, careful use of the MASK is recommended over MNH for work place metabolic or other ventilatory measurements.