Static lung volumes in healthy subjects assessed by helium dilution during occlusion of one mainstem bronchus

Single lung function is usually assessed by radioisotopes or, more rarely, by bronchospirometry in which a double lumen catheter is used to separate ventilation of the two lungs. The latter is more precise but less comfortable. An alternative bronchoscopic method is described for determining the volume of a single lung.

One mainstem bronchus was temporarily occluded with an inflatable balloon during fibreoptic bronchoscopy in 12 healthy volunteers aged 18-29 years. The functional residual capacities (FRC) of the right, left, and both lungs were measured in duplicate by closed circuit helium dilution. Supplementary vital capacity (VC) manoeuvres permitted calculation of single lung capacities (TLC) and residual volumes (RV).

The standard deviation of a single determination of capacities of the right, left, and both lungs were: TLC, 80, 96, and 308 ml; VC, 56, 139, 171 ml; FRC, 131, 74, and 287 ml; RV, 112, 185, and 303 ml, respectively. The sum of the right and left unilateral TLC was not different from bilateral TLC (6.12 v 5.95 l) and the sum of the unilateral FRC was not different from the bilateral FRC (2.60 v 2.78 l). The sum of the unilateral VC was lower than bilateral VC (4.52 v 4.80 l), that of the unilateral RV was higher than bilateral RV (1.60 v 1.16 l). For all subdivisions of lung volume, the right lung was larger than the left. The most common complaint was substernal discomfort during complete exhalation. Oxygen saturation rarely fell below 90%.

Temporary occlusion of a mainstem bronchus in normal subjects is safe, relatively simple, and allows fairly precise and accurate measurements of unilateral static lung volumes. Occlusion at TLC, however, probably prevents proper emptying of the non-occluded lung.