Immediate response to expiratory threshold load

Abstract

In anesthetized rabbits, cats and dogs the end-inspiratory volume referred to normal FRC (ΔVe.i.) of the first breath during expiratory threshold load (ETL) was greater than control ΔVe.i. The increase of ΔVe.i. was roughly proportional to the increase of end-expiratory volume relative to normal FRC (ΔVe.e.) caused by ETL. During squeezing of the rib cage or of the abdomen or after cordotomy at T 1 the phenomenon occurred nearly to the same extent. This suggests that afferent impulses from the chest wall are not essential in determining the phenomenon. The first inspiration during ETL occurred after a delay that was roughly proportional to the increase of ΔVe.e.: the arterial P CO 2 however, was not significantly increased at the time of the first inspiration during ETL. After bilateral vagotomy the first inspiration during ETL was no longer increased. An explanation of the increased ΔVe.i. of the first inspiration during ETL is provided on the basis of the vagal dependent tidal volume-inspiratory duration characteristic of the respiratory center.