RESPIRATORY AND CARDIOVASCULAR INTERACTIONS IN DUCKS - EFFECT OF LUNG DENERVATION ON INITIATION OF AND RECOVERY FROM SOME CARDIOVASCULAR-RESPONSES TO SUBMERGENCE

Lung denervation in ducks, by sectioning all vagal branches to 1 lung following mid-cervical vagotomy on the other side, resulted in immediate bradycardia and fall in breathing frequency. Some 3-5 wk after lung denervation, breathing frequency was within the normal range but the lung inflation reflex, present in unilaterally vagotomized sham-operated ducks, was abolished. During 2 min dives there were no significant differences between sham-operated and denervated ducks in heart rate [HR], arterial blood pressure [BP], blood gas tensions and pHa [arterial pH]. During recovery from diving, HR increased more slowly in denervates and breathing rate was significantly below that attained by shams, although tidal volume rose to a maximum of 225% of the pre-dive value in denervates in contrast to a maximum increase of 139% of pre-dive in sham-operated ducks. Both sham-operated and denervated ducks exhibited a significant fall in diastolic BP 60 s after emergence. A single passive lung inflation with air during a dive caused a significant increase in HR in normal and sham-operated but not denervated ducks. Addition of 60 .+-. 4 mmHg PCO2 [CO2 tension] to the inflating gas prevented this cardio-acceleration. In unoperated, sham-operated and denervated animals, a significant increase in HR occurred with the 1st voluntary breath terminating a dive, even if the animal was surfaced into air containing 60 .+-. 4 mmHg PCO2. Respiratory motor neuron activity was monitored in an intercostal nerve of paralysed ducks either on unidirectional ventilation or during asphyxia. Cardio-acceleration and hypertension accompanied each inspiratory burst. The increase in HR was 43.9 .+-. 3.2% of the maximum possible change which could have occurred (i.e., maximum rate in that duck minus the pre-burst rate). Increases in HR usually preceded those in BP although only the former were abolished by bilateral vagotomy. Denervation of the lungs had no obvious effect on the initiation of the cardiovascular responses to diving. Termination of these responses can be achieved either by feedback from pulmonary receptors or central irradiation of impulses from respiratory to cardiovascular controlling neurons.