Volume and ventilation of air sacs in ducks studied by inert gas wash-out

Abstract

Volume and ventilation of the air sacs were determined in spontaneously breathing domestic ducks by an inert gas wash-out technique. A known quantity of helium was injected via a catheter into an air sac and initial concentration as well as time course of subsequent wash-out were monitored by a mass spectrometer. Data were analyzed on the basis of single-compartment or two-compartment models according to whether the wash-out curves showed one or two exponentials. Whereas all air sacs studied (interclavicular, prethoracic, postthoracic and abdominal) had similar volumes, the prethoracic and the postthoracic sacs were found to receive about 3 times as much ventilation as the interclavicular sac or the abdominal sacs. The functional inhomogeneity, as indicated by bi-exponential wash-out kinetics, was most pronounced in the interclavicular air sac. During artificial ventilation the total air sac volume was increased, both volume and ventilation were shifted towards the caudal (postthoracic and abdominal) air sacs, and inhomogeneity of the air sacs was reduced. The physiological significance of the results, particularly with respect to gas exchange, will be discussed.