Effect of Division of Dorsal Roots of Cervical Nerves Upon Diaphragmatic Respiratory Movements

Abstract

In a study of the neuro-muscular mechanism of respiration, carried out on cats, it has been observed that, in many cases, division of the vagi is followed not only by a marked decrease of the respiratory rate, but also by a diminution in amplitude of diaphragmatic movements, while costal movements increase in depth. Subsequent section of the dorsal cervical (phrenic) nerve roots in these cats is attended by very little further change in respiratory rate or movement.

When, on reversing the order of experimental procedure, the dorsal roots of the cervical nerves (iii, iv, v, vi) are divided first, both a diminution in amplitude of diaphragmatic contractions and slowing in rate ensues, and subsequent division of the vagi brings about almost no further change in respiratory rate.

That respiratory impulses to the diaphragm may still bring about increased depth of diaphragmatic movement after section of the dorsal roots of the cervicals, has been shown by division of the dorsal spinal nerve roots of the intercostals in the thoracic region with the resulting diminution in costal movement. Under such conditions, there is an increase in the magnitude of diaphragmatic movement. This is similar to the increase in costal movements observed by us some years ago when, after division of the dorsal spinal nerve roots in the thoracic region, the phrenics were excised and an increase in the magnitude of costal movement was observed. 1

The fact that diaphragmatic movement and not costal, is- diminished in magnitude by division of the vagi, appears to indicate a closer relationship of the vagi to the phrenics than to the thoracic roots of the nerves concerned in the control of costal respiratory movements. These latter appear to have central stations as high as the posterior corpora quadrigemina, section behind which affects costal respiratory movement to a much greater extent than diaphragmatic. 2