INFLUENCE OF CERVICAL SYMPATHETIC-NERVES ON VENTILATION AND UPPER AIRWAY-RESISTANCE IN THE RAT

The cervical sympathetic trunks innervate the carotid bodies, carotid baroreceptors, thyroid gland and the upper airway mucosa, structures w hich can influence breathing and upper airway resistance. However, the ir role in the control of ventilation and upper airway patency is poor ly understood. A constant airflow was applied to the upper airway thro ugh a high-cervical tracheostomy in anaesthetized rats breathing spont aneously through a low-cervical tracheostomy, The peripheral ends of t he cut cervical sympathetic trunks were stimulated electrically and ai rflow resistance and ventilation were measured. The effects of cervica l sympathetic trunk section on ventilation were also measured in consc ious rats. In conscious rats, cutting the sympathetic trunks caused a decrease in ventilation during normoxia but only slightly affected ven tilatory responses to hypoxia and hypercapnia. In anaesthetized rats, sympathetic trunk stimulation caused an inhibition of breathing which was sometimes followed by excitation. These responses were unaffected by alpha- or beta-adrenoceptor blockade but were abolished by cutting the carotid sinus nerves. Sympathetic stimulation also caused a fall i n upper airway resistance which was reduced by bypassing the nose, una ffected by propranolol or carotid sinus nerve section and abolished by phentolamine, It was concluded that the cervical sympathetic nerves e xert important influences on ventilation and upper airway resistance.