Inter- and intra-individual variation of carbon monoxide production in young healthy males

Duplicate studies of endogenous CO production (Vco) were performed in three groups of young healthy males. In group A (eleven subjects) Vco studies were performed with an interval of approximately 1 week. In group B (ten subjects) duplicate studies were done on the same day and in group C (ten subjects) duplicate studies were also done on the same day but with the subjects strictly resting between determinations. The error of the single determination estimated from duplicate measurements (formula: see text) was +/-4.3 mumol/mmol TBH.day (TBH = total body haem) in group A and +/-3.7 and +/-1.0 in group B and C, respectively. Thus the intra-individual variation in Vco was considerably diminished when the duplicate determinations were performed with the subjects strictly resting between determinations. A possible explanation for this might be less variation in blood flow or metabolic processes in tissues engaged in haem breakdown in the resting group compared with the other groups.