REFLEX RELATIONSHIPS BETWEEN THE CERVICAL ESOPHAGUS AND THE RESPIRATORY SYSTEM IN CATS

The present study focused on reflex relationships between the esophagu s and the respiratory system in cats, namely the changes in airway ton e and pulmonary circulation elicited by mechanical or acid (pH 2) stim ulation of esophageal afferents. One-minute of sustained distension of the cervical esophagus increased tracheal pressure (PTr), decreased p ulmonary artery pressure (PPA) and to a higher extent pulmonary blood flow (QPA) and lowered arterial blood pressure (Pa). This was associat ed with significant variations in arterial blood gases (increased PaO2 and decreased PaCO2). Acid stimulation of the cervical esophagus caus ed a marked increase in PTr and a modest fall in QPA. In both circumst ances, cervical bivagotomy abolished PTr changes, whereas the changes in pulmonary hemodynamics but not in Pa were then accentuated. Further cervical sympathectomy suppressed the vascular response. These observ ations show the existence of reflex influences of esophageal afferents on the control of airway tone and pulmonary vascular resistance. The vagus nerve is the efferent arm of the bronchomotor reflex whereas mod ulation of the sympathetic control of pulmonary circulation seems to b e responsible for the changes in pulmonary hemodynamics.