DIFFERENTIAL RESPIRATORY MUSCLE RECRUITMENT INDUCED BY CLONIDINE IN AWAKE GOATS

The purpose of this study was to test the hypothesis that dysrhythmic breathing induced by the alpha(2)-agonist clonidine is accompanied by differential recruitment of respiratory muscles. In adult goats (n = 1 4) electromyographic (EMG) measurements were made from inspiratory mus cles (diaphragm and parasternal intercostal) and expiratory muscles [t riangularis sterni (TS) and transversus abdominis (Abd)]. EMG of the t hyroary-tenoid (TA) muscle was used as an index of upper airway (glott al) patency. Peak EMG activities of all spinal inspiratory and expirat ory muscles were augmented by central and peripheral chemoreceptor sti muli. Phasic TA was apparent in the postinspiratory phase of the breat hing cycle under normoxic conditions. During dysrhythmic breathing epi sodes induced by clonidine, TS and Abd activities were attenuated or a bolished, whereas diaphragm and parasternal intercostal activities wer e unchanged. There was no tonic activation of TS or Abd EMG during apn eas; however, TA activity became tonic throughout the apnea. We conclu de that 1) alpha(2)-adrenoceptor stimulation results in differential r ecruitment of respiratory muscles during respiratory dysrhythmias and 2) apneas are accompanied by active glottic closure in the awake goat.