Effect of breathing, pressure and posture on palatoglossal and genioglossal tone

1. Patency of the upper airway is critical to respiration. Although about half of patients with the sleep apnoea/hypopnoea syndrome obstruct their upper airway at the retropalatal level, the respiratory actions of the palatal muscles have been little studied. We have therefore tested the hypothesis that the nasopharyngeal dilator muscle palatoglossus is activated during inspiration and by negative pressure. 2. Using intramuscular wire electrodes inserted perorally, we have compared the response of palatoglossus and genioglossus to breathing, posture change and airway negative pressure in 10 normal awake subjects before and after topical anaesthesia. The results are expressed as a percentage of maximal electromyogram. Data were analysed by repeated-measures analysis of variance. 3. Inspiratory activity was exhibited by both genioglossus [inspiratory, 10% +/- 2% (SEM); expiratory, 6% +/- 1%, P = 0.001] and palatoglossus (inspiratory, 16% +/- 5%, expiratory, 10% +/- 3%, P = 0.016), but only genioglossus exhibited increased activity on lying (supine 10% +/- 2%, erect 6% +/- 1% maximum, P = 0.01). 4. One hundred milliseconds after negative pressure application, activity increased in both genioglossus (7% +/- 2% and 13% +/- 3% respectively, P = 0.02) and palatoglossus (8% +/- 2% and 23% +/- 6% respectively, P < 0.001). After lignocaine surface anaesthesia to the nose and pharynx both genioglossus and palatoglossus still increased their activity in response to negative upper airway pressure, the extent of the increase being decreased for palatoglossus (P = 0.02) but not for genioglossus. 5. Thus, palatoglossus has respiratory activity and is activated by negative upper airway pressure.

Effect of posture on upper airway dimensions in normal human

Posture has a major effect on breathing during sleep. Snoring, hypopneas, and apneas are all more common lying than sitting and more common supine than in a lateral lying position. Because the effect of the lateral lying position on upper airway caliber has not previously been studied, we examined this in 20 normal awake subjects and also determined the effect of neck position. The acoustic reflection technique was used. Pharyngeal cross-sectional areas (CSA) fell significantly from the sitting to supine position (oropharyngeal junction, from 1.65 +/- [SEM] 0.6 cm to 1.31 +/- 0.07 cm), but there was no difference in CSA between the supine and lateral positions for oropharyngeal junction (1.36 +/- 0.06 cm), mean pharyngeal area, maximal pharyngeal area, or pharyngeal volume. Neck hyper-extension significantly increased pharyngeal CSA (e.g., oropharyngeal junction null position 1.51 +/- 0.08, hyper-extension 1.94 +/- 0.11 cm), but there was no significant effect of neck flexion on airway CSA. These results confirm that in normal awake subjects, pharyngeal areas are smaller lying than sitting but also showed no significant difference between CSA in the supine and lateral lying positions. The study also demonstrates that the upper airway caliber increases with neck extension in conscious adults.

Effect of posture and breathing route on genioglossal electromyogram activity in normal subjects and in patients with the sleep apnea/hypopnea syndrome

Patients with the sleep apnea/hypopnea syndrome (SAHS) often have more apneas supine that sitting. We have shown radiologically that although the retropalatal airway narrows on lying down, the retroglossal airway widens. We have thus investigated the effect of posture on genioglossal EMG activity in 10 normal subjects and 10 patients with SAHS (58 +/- 29 SD apneas + hypopneas/h) using peroral intramuscular EMG electrodes. Data were analyzed by three-way analysis of variance, with diagnosis, posture, and route as factors. Peak inspiratory and tonic expiratory genioglossal EMG were both than sitting, with no significant difference between normal subjects and SAHS higher (p < 0.001) supine patients, although there was a trend (p < 0.09) toward the supine posture having a greater effect on peak inspiratory EMG in the SAHS patients. There was no significant effect of breathing route on either peak inspiratory (p > 0.9) or tonic expiratory (p > 0.8) genioglossal EMG, but there were significant differences between the groups (p < 0.01), the SAHS patients having higher and the normal subjects lower EMG tone with nasal in comparison with oral breathing on both inspiration and expiration. This study therefore shows that both body posture and breathing route are important determinants of genioglossal EMG tone.

Acoustic reflectometry for airway measurements in man: implementation and validation

A practical implementation of acoustic reflectometry for determining airway areas in routine clinical use is described. Advances over previous systems include portability, free breathing during measurements, no need to equilibrate with helium/oxygen, and real-time display of airway areas. Validation of the reflectometer with an airway model gave accuracies and reproducibilities (coefficient of variation (CV)) in the range 5-10%. With human volunteers, the within-run CV was typically 10%, and the day-to-day CV was 20%. The effect of breathing pattern on airway areas is demonstrated. In ten normal volunteers, acoustic and magnetic resonance imaging (MRI) methods of assessing pharyngeal and glottal areas were compared. The results (mean +/- SD) for the oropharynx were 1.0 +/- 0.3 cm2 acoustically and 0.9 +/- 0.5 cm2 by MRI (p = 0.77). The corresponding figures for glottal areas were 1.3 +/- 0.3 cm2 and 1.1 +/- 0.4 cm2 (p = 0.09).

Clinical value of polysomnography

Polysomnography is used increasingly to investigate patients with possible sleep apnoea/hypopnoea syndrome (SAHS), but it has not been assessed critically. We thus examined prospectively the value of electrophysiological and respiratory monitoring in 200 consecutive adults (163 men, 37 women; mean [SD] age 50 [13] years) having polysomnography. At polysomnography, 91 patients had SAHS (greater than 15 apnoeas + hypopnoeas [A + H] per h asleep) and 11 had periodic limb-movement disorder. Recording sleep electrophysiologically was of no diagnostic value and SAHS could be as accurately defined by A + H per time in bed as by A + H per time asleep. 66% of patients with SAHS could be diagnosed with oximetry alone, but many of the undiagnosed patients had moderately severe SAHS and benefited from treatment. Neurophysiological sleep recording is unnecessary and oximetry alone is of limited value in the overnight investigation of patients suspected of having SAHS.