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.


OBJECTIVE
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.


CONCLUSIONS
Inspiratory-related upper airway dilating forces are impeded in sleep apnea patients.
Sériès
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F
Centre de Recherche, Hôpital Laval, Institut Universitaire de Cardiologie et de Pneumologie, Université Laval, Quebec City, Quebec, Canada. frederic.series@med.ulaval.ca
Vérin
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E
Similowski
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T
D003964:Diaphragm / Q000294:innervation / Q000503:physiopathology*; D004558:Electric Stimulation; D045853:Exhalation; D005260:Female; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000294:innervation / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D010791:Phrenic Nerve / Q000503:physiopathology*; D015656:Respiratory Mechanics; D012891:Sleep Apnea Syndromes / Q000503:physiopathology*; D013314:Stress, Mechanical