Effect on Costal Respiratory Movements of Division of the Phrenics Following Transection of the Midbrain. ∗

Abstract

It has been shown that section of the dorsal roots of the thoracic nerves is followed by cessation of costal respiratory movements which are promptly resumed if the phrenics are excised, the vagi and midbrain being intact. 1 (The effect of section of the dorsal roots is somewhat greater when the cervical as well as the thoracic roots are sectioned. 2 )

Section of the midbrain alone at the level of the inferior colliculi is followed by a diminution of costal movements and the rate of respiration is somewhat slowed, but remains regular.

The question arises therefore whether section of the phrenics would have the same effect on costal respiration after section of the midbrain as after section of the dorsal roots of the thoracic nerves. The observed effects of division of the phrenics subsequent to transection of the midbrain in 30 cats are:

1. An increase in the depth of the costal respiratory movements, which is to be expected.

2. The respiratory rhythm immediately becomes irregular. There may be pauses of 5 to 10 seconds followed by from 5 to 10 costal movements and a succeeding pause. In some cases the tendency to grouping is slight. The character of the individual movements may vary. Sometimes there may be a rapid abrupt inspiratory movement followed without pause by an equally abrupt expiratory movement with a rhythm of 10 to 12 a minute. A series of from one to 3 small inspiratory movements may precede the actual large abrupt inspiration. When the group character is more pronounced, the inspiration is not so abrupt and expiration follows after a more appreciable interval.

So long as the vagi are intact, section of the dorsal roots of the phrenics, following transection of the midbrain does not elicit irregular respiration.