Impediment in upper airway stabilizing forces assessed by phrenic nerve stimulation in sleep apnea patients.

BACKGROUND

The forces developed during inspiration play a key role in determining upper airway stability and the occurrence of nocturnal breathing disorders. Phrenic nerve stimulation applied during wakefulness is a unique tool to assess Upper airway dynamic properties and to measure the overall mechanical effects of the inspiratory process on UA stability.

OBJECTIVES

To compare the flow/pressure responses to inspiratory and expiratory twitches between sleep apnea subjects and normal subjects.

METHODS

Inspiratory and expiratory twitches using magnetic nerve stimulation completed in eleven untreated sleep apnea subjects and ten normal subjects.

RESULTS

In both groups, higher flow and pressure were reached during inspiratory twitches. The two groups showed no differences in expiratory twitch parameters. During inspiration, the pressure at which flow-limitation occurred was more negative in normals than in apneic subjects, but not reaching significance (p = 0.07). The relationship between pharyngeal pressure and flow adequately fitted with a polynomial regression model providing a measurement of upper airway critical pressure during twitch. This pressure significantly decreased in normals from expiratory to inspiratory twitches (-11.1 +/- 1.6 and -15.7 +/- 1.0 cm H2O respectively, 95% CI 1.6-7.6, p < 0.01), with no significant difference between the two measurements in apneic subjects. The inspiratory/expiratory difference in critical pressure was significantly correlated with the frequency of nocturnal breathing disorders.

CONCLUSION

Inspiratory-related upper airway dilating forces are impeded in sleep apnea patients.