Measurement technique influences the response of transfer factor (TICO) to salbutamol in patients with airflow limitation

Abstract

Single-breath transfer factor obtained using a multibreath estimate of alveolar volume (TI) was measured before and after salbutamol in twenty patients with reversible airflow limitation. The effective breathholding time was calculated by four methods due respectively to Ogilvie and colleagues as modified by the American Thoracic Society (ATS), ATS Epidemiological Standardization Project (ESP), Jones and Meade in which allowance was made for the time of sample collection and a simplified method in which the allowance for sampling was in terms of volume, not time. Two patients could perform the test procedure only after salbutamol. Amongst the remainder the transfer factor calculated using a single-breath estimate of alveolar volume (TI') was on average 12% less then TI. Carbon monoxide transfer coefficient (KCO), TI and TI' were highest by the ESP method and lowest by the Ogilvie method. Inhalation of salbutamol (200γ) did not affect TI' by any method or TI and KCO by the Jones and Meade method but results by the other methods were reduced; in the case of the modified Ogilvie method the reduction was 3.9%. This error was due to overestimation of effective breathholding time by neglecting the reduction of 39% which occurred in the time of sample collection. The time of inspiration was unchanged whilst the time of deadspace washout was reduced by 16%. After bronchodilatation the absence of a change in TI' was due to the overestimation of effective breathholding time being offset by an increase in the proportion of alveolar volume measured by the single-breath procedure. It is concluded that for patients receiving bronchodilator therapy the transfer factor is best measured as TI using the Jones/Meade time correction. Use of TI' systematically underestimates the transfer factor of such patients.