“…The latter uses measurements of VCO 2 together with an estimated respiratory quotient (RQ) value of 0.85 and an estimated 13 C fractional recovery value of 0.7 to calculate energy expenditure via the Weir equation as previously described 18,19 . In order to validate IRIS® measurements, a 10 ml sample from each breath bag was aspirated (using a 3-way tap and syringe) into 12 ml Exetainer® vials (Labco Ltd, Buckinghamshire, UK) which were measured using continuous flow isotope ratio mass spectrometry (IRMS, AP2003, Analytical Precision Ltd, Northwich, Cheshire, UK) against a calibrated reference gas, and the results expressed as % relative to Pee Dee Belemnite, an international standard of known 13 C composition. Statistical analyses were performed using IBM SPSS Statistics® for Windows™ v19 software (IBM SPSS Statistics, Feltham, UK).…”