INTRAPULMONARY GAS MIXING STUDIED BY THE CLOSED‐CIRCUIT HELIUM TECHNIQUE

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Abstract
Summary: Studies were made in normal subjects and in patients with various types of respiratory disease.About half the normal subjects showed relatively minor degrees of inequality of ventilation.Nine patients with pulmonary emphysema all showed markedly uneven ventilation of the lungs. The poorly ventilated space usually accounted for 50% or more of the functional residual capacity, and the tidal volume of this space was less then 4% of the volume of the space. The closed‐circuit method was modified to reveal the true functional residual capacity in severe emphysema.Three out of five patients with diffuse pulmonary sarcoidosis and three out of six patients with diffuse interstitial pulmonary fibrosis showed ventilatory inequality intermediate in degree between the normal subjects and those with emphysema. The lungs of the remaining patients in each group were evenly ventilated.Extensive bronchitis may produce a severe mixing defect, and this may be the only physiological abnormality in a patient who appears clinically to have pulmonary emphysema. The defect was reversible in one such case studied.Increase of tidal volume may lead to disproportionately great improvement in the ventilation of the poorly ventilated space.

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