A RESPIRATORY REFLEX ORIGINATING FROM THE THORACIC WALL OF THE DOG

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Abstract
Respiratory arrest was produced in dogs by the continuous intraven. injn. of 2.5% Na pentothal. A mouth hook, delivering 10 1. of 02/min., was used and oxy-genation maintained by "diffusion" respiration. They found in 60 intact dogs so anesthetized are flexogenous zone in the region of the maximal cardiac impulse and in the "corresponding area of the right chest. When this area was lightly palpated, powerful reflex respiration was elicited if the animal was not too profoundly depressed by the anesthesia. It could be shown, in 23 dogs, whose respiration was studied with recording spirometer, that the thoracic reflex was able to elicit respiratory responses with depths of anesthesia in which tongue traction and anal stretching were not effective. The adequate stimulus is light pressure. The ensuing respiration is smooth, largely diaphragmatic, and inspiration is accompanied by abduction of the vocal cords. The respiratory response moves a large volume of gas. Fatigue of the reflex may occur, but sensitivity is quickly restored. In extremely deep anesthesia, the reflex cannot be elicited but it reappears before the resumption of spontaneous respiration. The reflex was also demonstrated in rabbits under pentothal anesthesia, and in dogs under CHC13 anesthesia. Anatomical dissection in 9 dogs showed that the trigger points of the reflex are the distal end and the tendon of the scalenus medius muscle and the proximal end and the tendon of the rectus abdominis muscle. The reflex is susceptible to inhibition, and may disappear in severe hypoxia or shock.

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