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Pulsatile gas flow in lobar and segmental bronchi synchronous with the heart beat has been measured during routine diagnostic bronchoscopy, using a new type of flowmeter. Pulsations were detected in three-quarters of the 60 patients examined, and occurred in all parts of the lung though they were more marked on the left side. They were seen both during inspiration and expiration, but were most obvious in the postexpiratory pauses. At a given instant in the cardiac cycle, the phase of the pulsations was sometimes different in different parts of the lung, gas going into some lobes and coming out of others. Volume flow rates up to 2.5 liter/min and displaced volumes up to 5 ml were recorded. The pulsatile flow is probably caused by changes in volume of the beating heart, and by its movements within the chest so that some parts of the lung are compressed while others expand. Because of their size and frequency, the pulsations promote mixing of the anatomical dead-space gas with alveolar gas. Submitted on October 10, 1960

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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. Submitted on September 3, 1958