APPLICATION OF NEGATIVE EXPIRATORY PRESSURE DURING EXPIRATION AND ACTIVITY OF GENIOGLOSSUS IN HUMANS

The application of negative expiratory pressure (NEP) at end expiratio n has been shown to cause reflex-mediated activation of the geniogloss us muscle in awake humans. To test whether a reflex contraction of pha ryngeal dilator muscles also occurs in response to NEP applied in earl y expiration, the effect on genioglossus muscle reflex activity of NEP pulses of 500 ms, given 0.2 s after the onset of expiration and durin g the end-expiratory pause, was assessed in 10 normal awake subjects a t rest. The raw and integrated surface electromyogram of the genioglos sus (EMGgg) was recorded with airflow and mouth pressure under control conditions and with NEP ranging from -3 to -10 cmH(2)O. Intraoral EMG gg was also recorded under the same experimental conditions in two sub jects. The application of NEP at the end-expiratory pause elicited a c onsistent reflex response of EMGgg in seven subjects with a mean laten cy of 68 +/- 5 ms. In contrast, when NEP was applied at the onset of e xpiration, EMGgg reflex activity was invariably observed in only one s ubject. No relationship was found between steady increase or abrupt fa ll in expiratory flow and the presence or the absence of a reflex acti vity of genioglossus during sudden application of NEP at the beginning of expiration. Our results show that a reflex activity of genioglossu s is elicited much more commonly during application of NEP at the end rather than at the onset of expiration. These findings also suggest th at when NEP is applied in early expiration to detect intrathoracic flo w limitation the absence of upper airways narrowing does not imply the occurrence of a reflex-mediated activation of genioglossus and vice v ersa.