Single-exhalation method for study of lobar and segmental lung function by mass spectrometry in man

A single-exhalation method, based on a modification of the conventional single-breath technique, was applied to study lung function in normal subjects during fiberoptic bronchoscopy. After a single inspiration of a test gas mixture (1% He, 1% C2H2, 0.07% C18O in air), the test gas concentrations were continuously monitored during subsequent slow exhalation, using a respiratory mass spectrometer that sampled either at the lips (Whole-lung test) or, through the bronchoscope, at various sites within the bronchial tree (Regional test). Changes in concentrations of the test gases with time allowed estimation of alveolar ventilation (Va), blood flow (Q), and diffusing capacity (DLCO), per unit accessible lung volume (Va). In the Whole-lung test, both DLCO and Q agreed closely with values obtained in the same subject by a rebreathing method. No differences were observed between the upright and the lateral decubitus positions. In teh Regional test, VA/VA, DLCO/VA and Q/VA were larger in the dependent than in the upper lung, when sampling was from the main bronchi in the lateral decubitus positions. Sampling from lobar bronchi in the upright position revealed an increase from top to bottom in VA/VA, DLCO/CA and Q/VA, this being most marked for Q. These results are compatible with the regional variations that have been shown by radioactive techniques and have been attributed to gravitational forces. The method appears to be suitable for the study of lobar and segmental lung function in patients with lung disease.