Indirect calorimetry estimates energy expenditure from measurement of
respiratory gas exchange volumes. This paper considers the design and
evaluation of an indirect calorimeter, the Europa GEM, suitable for us
e in nutritional research. The calorimeter is of the ventilated hood,
flow-through type and is intended for use with spontaneously breathing
patients. Our aim was to develop an accurate, flexible instrument wit
h a high level of automation. Performance was assessed in a laboratory
simulation using reference gas injections (n = 24) producing a mean e
rror of 0.3 +/- 2% in oxygen consumption (V over dot O-2), 1.8 +/- 1%
in carbon dioxide production (V over dot CO2) and 1.4 +/- 1.5% in resp
iratory quotient (RQ). In order to investigate the effect of FeCO2 on
error multiplication a further subdivision (n = 8) of tests at FeCO2 =
0.5%, 0.75% and 1% was made by modulating the air Bow through the hoo
d. However, the predicted increase in system accuracy with increasing
FeCO2 was not apparent in practice.