A sampling method for mean alveolar gas in normal subjects and patients with respiratory disease.

The paper describes an alveolar gas sampling method based on the criterion of equality of mean alveolar (RA) and expired (RE) respiratory quotients. Expired gas is sampled at an expired volume equal to VT/2 + VD by means of a mechanical sampler controlled by an analog computer. Eleven normal subjects and 50 patients with cardiopulmonary disease have been tested. When the difference between mean alveolar and expired respiratory quotients did not exceed 0.05, the result was considered to be satisfactory. Such results have been obtained in 40 patients and all of the normal subjects. For the remaining 10 patients, either experimental error and/or particular non-homogeneities in ventilation seemed to be the cause of the unsatisfactory results. Arterial to alveolar PCO2 differences have been calculated. The mean difference in normal subjects was never negative (1.86 +/- 1.58 torr).