Patterns of gas flow in the upper bronchial tree

¹ Department of Medicine, Postgraduate Medical School, Hammersmith Hospital, London, England

Patterns of gas flow in the upper bronchial tree have been studied by observing the flow of dye and different gases through a lung cast, and by measurements made on open-chested dogs and on human beings at bronchoscopy. Flow is completely laminar throughout the bronchial tree at low expiratory flow rates (up to 10 l/min.) and completely turbulent, proximal to the segmental bronchi, at high flow rates (80 l/min.). Both at low and high expiratory flow rates, gas from segmental bronchi was not uniformly mixed in the lobar or main bronchi which they supplied. The composition of a catheter sample in these airways would therefore not be representative of the alveolar gas in the corresponding lobe or lung unless the alveolar gas in all areas distal to the sampling tube was homogeneous. Penetration of the left upper lobe bronchus by gas from the lower lobe was demonstrated in the model and a normal subject at bronchoscopy.