Measurement of single-breath carbon monoxide transfer factor (diffusing capacity) during progressive exercise.

The transfer factor (diffusing capacity) for carbon monoxide (TLCO) is known to rise with increasing levels of work, but uncertainty remains as to the exact relationship of TLCO and the transfer coefficient (KCO) to oxygen uptake (VO2). We have studied the effects of increasing levels of work on TLCO and KCO in 22 normal male subjects using the single-breath technique and a standardized protocol. Additionally, we have investigated whether young people were different from a middle-age group, the need for carboxyhaemoglobin corrections in current smokers and non-smokers, and the variations of cardiac frequency during breath-holding. Our results show that TLCO and KCO increase in a curvilinear manner up to maximal VO2, a quadratic equation describing the relationship. There was no effect of age up to 50 years. There was no significant increase in the carboxyhaemoglobin levels, and therefore this correction is unnecessary. Cardiac frequency showed no significant variation during the breath-holding manoeuvre, except at rest and at low levels of exercise.