Tests of overall and regional lung function using xenon-133 with fixed counters were carried out on 49 patients who were judged on specified radiological grounds to have emphysema: 31 of them also had clinical evidence of chronic bronchitis. The radiological extent of the disease was classified as generalized, extensive localized or localized. The results of the tests were compared with the radiographic extent of the disease and with the local radiographic appearances. Derangements of total lung function agreed well with the radiological extent of the disease; in particular, the average level of Paco2 was lower than that predicted from the F.E.V.1 when generalized and extensive localized emphysema were present. Co-existing chronic bronchitis was associated with higher levels of Paco2. The resting Pao2 was higher if one or both lower regions were normally ventilated despite unevenness of ventilation elsewhere, emphasizing the importance of the lower lung regions in determining the overall V/Q of the lungs. Regional derangements of ventilation coincided fairly well with the radiographic distribution of vascular narrowing or loss but the blood flow was found to be diminished in less than 5% of upper and middle regions with radiological changes. Ventilation was impaired in parts of the lungs where the vascular shadows were apparently normal. This finding was attributed to the effects of chronic bronchitis, because it was also found in seven patients with this disease who did not have radiographic evidence of emphysema; in these, impairment of ventilation in the middle and lower regions was a salient feature.
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