Reflex bradycardia occurring in response to diving, nasopharyngeal stimulation and ocular pressure, and its modification by respiration and swallowing.

1. Digital pressure applied to the eyes evokes reflex bradycardia in human subjects and anaesthetized dogs. The bradycardia is most pronounced when breathing stops. 2. In the dog oculo-cardiac reflex bradycardia is mediated by vegal stimulation and by sympathetic withdrawal. 3. Oculo-cardiac reflex bradycardia in the dog is reduced by central neural inspiratory activity and by the excitation of pulmonary afferents by inflation of the lungs. In human subjects it is reduced when inspiratory efforts are made against a closed glottis. 4. Nasopharyngeal stimulation with water evokes reflex bradycardia in the anaesthetized dog. This bradycardia is reduced by central neural inspiratory activity and by the excitation of pulmonary afferents by inflation of the lungs. 5. Bradycardia occurs in normal human subjects during immersion of the face in water ('diving'). This bradycardia is reduced when inspiratory efforts are made against a closed glottis. 6. Swallowing evokes transient tachycardia in human subjects. During diving or the application of ocular pressure, swallowing reduces the reflex bradycardia which these evoke.