Postural Apnea in the Duck.

Abstract

Aside from the apnea which is produced in the duck by submergence or by pouring water over its nostrils, one can also obtain a complete cessation of respiration when the duck is held in the air in certain definite positions. This applies especially to the position of the head in space. We fully confirmed Huxley 1 , 2 , 3 and Paton 4 in that whenever the vertex of the head is directed downward, whether the body is in the prone or supine position, apnea ensues. Like Huxley, we observed a very marked slowing of the heart accompanying apnea.

If the duck is placed on its back, the neck will be curved so that the head is held in the air in normal position with the beak directed towards the tail (labyrinthine righting reflexes on the head). Under these conditions respiration is normal. When the head is bent backward so that the vertex is directed downward, respiration stops and the apnea continues as long as the forced position of the head is maintained. Occasionally the animal struggles for a moment or two and it appeared as if it might make some respiratory movements during the struggle. By connecting the head of the duck with the Benedict portable respiration apparatus, we convinced ourselves that these movements usually do not involve any respiration. Occasionally they are accompanied by expiratory movements, and more rarely by inspiratory movements. Whenever there is a respiratory movement, it is always followed by a temporary acceleration of the slowed heart. These occasional respirations apparently suffice to keep the duck alive under these circumstances and some animals were subjected to incomplete postural apnea of as long as 30 minutes' duration. However, 2 of our animals succumbed to postural apnea, death being preceded by a few terminal expiratory movements.