Variable site of airway narrowing among obstructive sleep apnea patients

The purpose of this was to determine whether the site of physiological narrowing within the upper airway was uniform or differed among patients with obstructive sleep apnea. Inspiratory pressures were measured with an esophageal balloon catheter and three catheters located at different sites along the upper airway: supralaryngeal airway, oropharynx, and nasopharynx. Peak inspiratory pressure differences between catheters allowed assessment of pressure gradients across three airway segments: lungs-larynx-retroepiglottal airway (esophageal-supralaryngeal pressure), hypopharynx (supralaryngeal-oropharynx pressure), and transpalatal airway (oropharynx-nasopharynx pressure). In five patients, hypopharyngeal obstruction was present, and in four patients no hypopharyngeal obstruction existed. In these four patients the site of obstruction was located at the level of the palate. In a given subject, the site of obstruction was the same during repeated measurements. The presence or absence of hypopharyngeal narrowing during sleep was not predictable from gradients measured across different segments of the upper airway during wakefulness. We conclude that the site of physiological upper airway obstruction varies among patients with obstructive sleep apnea and is not predictable from pressure measured during wakefulness. We speculate that uvulopalatopharyngoplasty may not relieve obstructive apneas in patients with hypopharyngeal obstruction. </jats:p

Respiratory muscle activity during sleep-induced periodic breathing in the elderly

During spontaneous sleep-induced periodic breathing in elderly subjects, we have found that tidal volume oscillations are related to reciprocal oscillations in upper airway resistance. The purpose of this study was to address the mechanism of the relationship between oscillations in tidal volume and upper airway resistance in elderly subjects with sleep-induced periodic breathing. We hypothesized that the spontaneous periodic breathing observed in non-rapid-eye-movement (NREM) sleep in elderly subjects would be closely related to fluctuations in upper airway resistance and not to changes in central motor drive to ventilatory pump muscles. Therefore, in eight healthy elderly subjects, we measured costal margin chest wall peak moving time average electrical inspiratory activity (CW EMG), ventilation variables, and upper airway resistance during sleep. Five of eight subjects had significant sine wave oscillations in upper airway resistance and tidal volume. For these five subjects, there was a reciprocal exponential relationship between peak upper airway inspiratory resistance and tidal volume or minute ventilation [r = -0.60 +/- 0.20 (SD) (P &lt; 0.05) and -0.55 +/- 0.26 (P &lt; 0.05), respectively], such that as resistance increased, ventilation decreased. The relationship between CW EMG and tidal volume or minute ventilation was quite low (r = 0.12 +/- 0.32 and -0.07 +/- 0.27, respectively). This study demonstrated that oscillations in ventilation during NREM sleep in elderly subjects were significantly related to fluctuations in upper airway resistance but were not related to changes in chest wall muscle electrical activity. Therefore, changes in upper airway caliber likely contribute to oscillations in ventilation seen during sleep-induced periodic breathing in the elderly. </jats:p