The Upper Airway Resistance Syndrome: Level of negative intrathoracic pressure

The Upper Airway Resistance Syndrome: Level of negative intrathoracic pressureBerry and Light reported similar findings after occluding the inspiratory limb of a tight-fitting face mask in six young normal male subjects during sleep; arousal occurred at similar Pes nadirs in all subjects under both normoxic and hyperoxic conditions. Hy-peroxic airway occlusions resulted in a longer time to arousal after occlusion without a significant change in the respiratory rate, implying a slower change in the Pes nadir with each inspiration. An increased rate of negative inspiratory pressure generation in the breaths just preceding arousal was also found. The authors concluded that the Pes nadir threshold for arousal was constant, despite alterations in its rate of change induced by hyperoxia.
These investigations support the belief that the level of negative intrathoracic pressure generated (as reflected by the Pes nadir) is the primary physiologic change inducing arousal. Other factors (including changes in oxygenation, hypercapnea, time since the previous awakening, total sleep time [TST], and temporal proximity to REM) probably modify this response secondarily. Therefore, these secondary factors may account for the variations in the arousal threshold seen between different individuals, and for the changes in the arousal threshold seen in the same individual at different times during sleep. The mechanism of arousal would be further illuminated by the precise identification of the origin and afferent pathways involved in the detection of this threshold. inhalers for asthma

The mechanoreceptors in the respiratory muscles, chest wall, and lower and upper airways have been suggested as potential loci for the generation of afferent CNS input leading to arousal. The data in this area, much of it from animal studies, have been conflicting and inconclusive. The results from two recent investigations deserve mention, however. Bas-ner and colleagues noted an increased time to arousal following external airway occlusion in subjects wearing full face masks after their nasal and oropharyngeal mucosa had been anesthetized with 4% lidocaine. Similarly, Berry et al found decreased genioglossus activity during obstructive apneas, increased apnea duration, and greater Pes nadirs prior to apnea termination after anesthesia of the upper airway with 4% lidocaine.


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