Changes in transfer factor of the lung in response to bronchodilatation

Measurement of the transfer factor for carbon monoxide (T-LCO) is a widely used clinical lung function test. Although it is frequently applied in pati ents with bronchial obstruction, there is little information on the effects of bronchodilatation on the test. We therefore measured T-LCO in 40 patien ts before and after inhalation of terbutaline. T-LCO was measured with the single-breath technique in 20 patients and with the intra-breath technique in 20 patients. T-LCO was also measured in 20 healthy subjects with the sin gle-breath technique. Forced expiratory volume (FEV1) increased from 2.9 +/ - 1.1 to 3.2 +/- 1.2 l in patients with bronchial obstruction in response t o terbutaline inhalation. T-LCO increased from 8.2 +/- 2.6 to 8.6 +/- 2.7 m mol min(-1) kPa(-1) (P< 0.001) and alveolar volume (V-A) from 5.74 +/- 1.21 to 5.90 +/- 1.21 l (P<0.001). There was no difference between the single-b reath and the intra-breath techniques. There was little change in FEV1 in t he healthy subjects in response to terbutaline. T-LCO increased from 10.2 /- 2.1 to 10.5 +/- 2.2 mmol min(-1) kPa(-1) (P< 0.01), but there was no cha nge in V-A. The increase in T-LCO in patients map partly be explained by im proved distribution of the inhaled gas. In healthy subjects, terbutaline ma y increase pulmonary capillary volume. We conclude that bronchodilatation r esults in a small increase in T-LCO in patients with light to moderate bron choconstriction as well as in healthy subjects. The effect is small and sho uld in most cases be simple to account for in the interpretation of pulmona ry tests, provided the patient's treatment is known.