Palatopharyngeus has respiratory activity and responds to negative pressure in sleep apnoeics

The intrinsic tongue muscle, genioglossus, and soft palatal muscles, tensor palatini, levator palatini and palatoglossus, are known to exhibit phasic respiratory activity and to respond reflexly to negative pressure in man, which may be important in the maintenance of upper airway patency. We hypothesized that the palatopharyngeus muscle should also have respiratory activity and increased activity in response to negative upper airway pressure. We have, therefore, examined the palatopharyngeus and the antagonist muscle, levator palatini, in eight awake sleep apnoea patients, using bipolar electromyography during nose- or mouth-breathing in different postures, and with or without application of negative pressure. Overall, palatopharyngeus and levator palatini demonstrated phasic respiratory activity. Palatopharyngeus demonstrated increased activity in the supine compared to erect posture. Analysis by route of respiration showed palatopharyngeus to be more active in the supine posture when nose-breathing compared to mouth-breathing. Graded negative pressure application caused significant increases in palatopharyngeus and levator palatini activity when applied via the mouth. Nasal negative pressure application caused a nonsignificant trend to increasing palatopharyngeus activity with increasing negative pressure compared to a significant increase for levator palatini. We conclude that palatopharyngeus and levator palatini demonstrate respiratory activity and reflex activation in response to negative pressure. Palatopharyngeus may, therefore, have a role as an upper airway dilator. The differential response of palatopharyngeus to oral and nasal negative pressure application may be important in the pathogenesis of sleep apnoea.