THE PULSATILE NATURE OF THE PULMONARY CAPILLARY BLOOD FLOW*

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Abstract
The nature of the pulmonary capillary flow in man has been investigated using the body plethysmograph and various test gases. Rhythmic oscillations in the plethysmographic record during breath-holding with glottis open were shown to the synchronous in time with the cardiac cycle and to occur regardless of the density of the gas or its solubility in blood. The rhythmic oscillations in the plethysmographic record were also shown to be synchronous with those in the pneumo-tachographic record. Evidence is presented to indicate that both the plethysmographic and pneumotachographic records have a common origin in the mechanical events of the cardiac cycle rather than in the uptake of the test gas by pulsatile pulmonary capillary flow. The conclusion is reached that the pulsations in the plethysmographic record cannot be used as evidence that pulmonary capillary flow is pulsatile.