Phrenic output changes due to progressive airway denervation in rabbits.

The experiments were performed with thirteen anaesthetized rabbits breathing spontaneously through the larynx. Phrenic output was measured during tidal respiration in control conditions and in the course of progressive denervation of the laryngeal and tracheobronchial compartments. We have analysed changes in amplitude and the rate of rise of the integrated phrenic neurogram as well as the changes in TI, TE, TT and f of the respiratory timing after superior laryngeal nerves (SLN-s) section, section of the recurrent laryngeal nerves (RLN-s) and step-wise complete midcervical vagotomy. Nerve sections were performed by two methods: 1) bilateral SLN-s, RLN-s and cervical vagal neurotomy (horizontal method); 2) right-sided neurotomies of SLN, RLN and vagus followed by left-sided neurotomies of these nerves (vertical method). Laryngeal deafferentation did not greatly affect respiratory variables. Unilateral and especially bilateral vocal cord paralysis prolonged the respiratory cycle with enhanced TI/TT ratio, increased amplitude and rate of rise of the integrated phrenic neurogram. Maximum values of all parameters (the rate of rise excluded) were achieved after complete midcervical vagotomy. Of the two methods of denervation, the right-sided followed by left-sided denervation led to better adaptation of the organism to the respiratory disturbance (smaller changes in TI and TE compared with the control values). Denervation by the 'horizontal' method (paired section of the nerves) led to an abrupt failure of effective ventilation.