Role of peripheral and central chemosensitive afferents in the control of depth and frequency of breathing.

In anaesthetized cats the response to hypercapnia was studied during normoxia, hypoxia (increased peripheral chemosensitive afferents, IPA) and after carotid sinus denervation (decreased peripheral chemosensitive afferents, DPA) in terms of: (a) central output to the inspiratory muscles, (b) bulbopontine respiratory activity and (c) threshold-inhibition curve for termination of inspiration (Vr/Ti relationship). IPA increased, whereas DPA decreased the central output, as estimated from the rate of change of the subatmospheric pressure developed in the trachea during occlusion of the airways. IPA and DPA did not modify the bulbo-pontine rhythm, as estimated from the timing of occluded breaths (phasic vagal afferents nil), nor the Vt/Ti relationship, both of which have been shown to vary as a function of PACO2. It is concluded that peripheral chemosensitive afferents influence only the output of the respiratory centres, whereas central chemosensitive afferents influence also the bulbo-pontine respiratory rhythm and the threshold inhibition curve for termination of inspiration.