Single breath transfer factor measured concurrently by two methods in asthmatic and normal subjects.

, , 232-236. There have been conflicting reports that the single breath transfer factor for carbon monoxide in asthma may be normal, high or low. To resolve this point the single breath transfer factor was measured in comparable groups of asthmatic and normal subjects. Two methods of calculating the alveolar volume were used, employing multiple breath helium dilution (giving Tl) and single breath helium dilution (giving Tl′). A higher value was found for Tl than for Tl′ in the asthmatic subjects but a lower value for Tl than Tl′ in the normal subjects. These differences were significant. The largest differences were found in the asthmatic subjects with a large residual volume. There was no significant difference between the asthmatic and normal subjects in the value of Tl and Tl′. As the reports of a raised transfer factor were from workers who used Tl, and this was not confirmed by those who used Tl′, it is concluded that this apparent difference between normal and asthmatic subjects can be explained in some cases by the difference in the methods used.