Collapsibility of the nasopharyngeal airway in obstructive sleep apnea

To determine whether there is a relationship between pharyngeal airway collapsibility in awake subjects with obstructive sleep apnea (OSA) and the degree of disordered breathing during sleep, we studied 11 men with OSA and 10 normal men. Collapsibility of the nasopharyngeal airway was assessed by measuring nasopharyngeal resistance during the application of subatmospheric pressure. The pressure in a tightly fitting face mask was lowered at the end of expiration, drawing air out of the respiratory system and through the mask and a pneumotachygraph. Nasopharyngeal resistance was measured as the difference between mask and pharyngeal pressure divided by the flow rate. There was a highly significant correlation between nasopharyngeal resistance and both the number of apneas and hypopneas per hour of sleep (r = 0.71, p less than 0.001) and the number of oxyhemoglobin desaturation episodes (greater than 4%) per hour of sleep (r = 0.80, p less than 0.001). We conclude that the pharyngeal airway of awake patients with sleep apnea is more collapsible and has a higher resistance than normal when subatmospheric pressure is applied, and that the level of resistance correlates with the degree of sleep-disordered breathing.