Comparison of the response of diaphragm and upper airway dilating muscle activity in sleeping cats

Abstract

The steady state and transient effects of hyperoxic hypercapnia on the electromyographic activities of the genioglossus (GG), posterior cricoarytenoid (PCA), and diaphragm (D) were studied in cats instrumented with chronically implanted electrodes during non-rapid eye movement sleep. Hypercapnia (inhalation of 3.4 and 7.4% CO 2 in O 2) increased the phasic electrical activity occurring during inspiration of all three muscles. Activities of the PCA and D increased in a parallel fashion with increasing CO 2. The GG responded to steady state CO 2 inhalation alinearly, with larger increases in activity occurring when CO 2 was raised from 3.4 to 7.4% than when CO 2 was increased from 0 to 3.4%. When gas mixtures containing CO 2 were given, the GG reached its new steady state level more slowly than the D or PCA, and when CO 2 was rapidly removed from the inspired gas mixture, the GG attained its steady state sooner than the D. These results suggest that in sleeping cats, hypercapnia does not affect either transient or steady state responses of the GG in the same way as the D or the PCA. These differences seem to be explained largely by different threshold characteristics of hypoglossal and phrenic neurons.