Postural effects on pharyngeal protective reflex mechanisms

Abstract

Study objectives: Pharyngeal muscle dilators are important in obstructive sleep apnea pathogenesis because the failure of protective reflexes involving these muscles yields pharyngeal collapse. Conflicting results exist in the literature regarding the responsiveness of these muscles during stable non-rapid eye movement sleep. However, variations in posture in previous studies may have influenced these findings. We hypothesized that tongue protruder muscles are maximally responsive to negative pressure pulses during supine sleep, when posterior tongue displacement yields pharyngeal occlusion.

Design: We studied all subjects in the supine and lateral postures during wakefulness and stable non-rapid eye movement sleep by measuring genioglossus and tensor palatini electromyograms during basal breathing and following negative pressure pulses.

Setting: Upper-airway physiology laboratory of Sleep Medicine Division, Brigham and Women's Hospital.

Subjects/participants: 17 normal subjects.

Measurements and results: We observed an increase in genioglossal responsiveness to negative pressure pulses in sleep as compared to wakefulness in supine subjects (3.9 percentage of maximum [%max] +/- 1.1 vs 4.4 %max +/- 1.0) but a decrease in the lateral decubitus position (4.1 %max +/- 1.0 vs 1.5 %max +/- 0.4), the interaction effect being significant. Despite this augmented reflex, collapsibility, as measured during negative pressure pulses, increased more while subjects were in the supine position as compared with the lateral decubitus position. While the interaction between wake-sleep state and position was also significant for the tensor palatini, the effect was weaker than for genioglossus, although, for tensor palatini, baseline activity was markedly reduced during non-rapid eye movement sleep as compared with wakefulness.

Conclusion: We conclude that body posture does have an important impact on genioglossal responsiveness to negative pressure pulses during non-rapid eye movement sleep. We speculate that this mechanism works to prevent pharyngeal occlusion when the upper airway is most vulnerable to collapse eg, during supine sleep.

Figure 1

Example of raw data showing the negative pressure reflex. The figure shows data from an individual illustrating a pulse of negative pressure delivered during early inspiration in stable non-rapid eye movement sleep. The choanal pressure reflects the magnitude of the stimulus, while the epiglottic pressure reflects the extent to which the pressure pulse is transmitted through the pharynx (measure of collapsibility). The reflex activity of the genioglossus (GG) and tensor palatini (TP) is greater in the supine posture than in the lateral decubitus position. As well, the pharynx is more collapsible supine since less of the choanal pressure is transmitted in this position as compared with the lateral decubitus.

Figure 2

Genioglossus Group Data. This figure illustrates group data for genioglossus electromyogram (GGEMG) activity during basal breathing (2A) and following negative pressure pulses (NPP) expressed both as an absolute change (Δ, 2B) and as a percentage increase (%increase) (2C). w refers to wakefulness; s, stable non-rapid eye movement sleep; %maximum, percentage of maximum.

Figure 3

Tensor Palatini Group Data. This figure illustrates group data for tensor palatini electromyogram (TPEMG) activity during basal breathing (3A) and following negative pressure pulses expressed both as an absolute change (Δ, 3B) and as a percentage increase (%increase) (2C). w refers to wakefulness; s, stable non-rapid eye movement sleep; %maximum, percentage of maximum.