Abstract
BackgroundUpper airway collapse does not occur during wake in obstructive sleep apnea patients. This points to wake-related compensatory mechanisms, and possibly to a modified corticomotor control of upper airway dilator muscles. The objectives of the study were to characterize the responsiveness of the genioglossus to transcranial magnetic stimulation during respiratory and non-respiratory facilitatory maneuvers in obstructive sleep apnea patients, and to compare it to the responsiveness of the diaphragm, with reference to normal controls.MethodsMotor evoked potentials of the genioglossus and of the diaphragm, with the corresponding motor thresholds, were recorded in response to transcranial magnetic stimulation applied during expiration, inspiration and during maximal tongue protraction in 13 sleep apnea patients and 8 normal controls.Main ResultsIn the sleep apnea patients: 1) combined genioglossus and diaphragm responses occurred more frequently than in controls (P < 0.0001); 2) the amplitude of the genioglossus response increased during inspiratory maneuvers (not observed in controls); 3) the latency of the genioglossus response decreased during tongue protraction (not observed in controls). A significant negative correlation was found between the latency of the genioglossus response and the apnea-hypopnea index; 4) the difference in diaphragm and genioglossus cortico-motor responses during tongue protraction and inspiratory loading differed between sleep apnea and controls.ConclusionSleep apnea patients and control subjects differ in the response pattern of the genioglossus and of the diaphragm to facilitatory maneuvers, some of the differences being related to the frequency of sleep-related events.
Highlights
Upper airway collapse does not occur during wake in obstructive sleep apnea patients
In obstructive sleep apnea syndrome (OSAS) patients as compared to controls, tongue protraction has an enhanced facilitatory effect on the genioglossus response to transcranial magnetic stimulation (TMS), inspiratory maneuvers facilitate the response of the genioglossus in terms of latency, amplitude and motor threshold, and tongue protraction cross-facilitates the response of the diaphragm
This study provides a strong clue to a modification in the corticomotor control profile of certain upper airway muscles in OSAS during wakefulness
Summary
Upper airway collapse does not occur during wake in obstructive sleep apnea patients. Respiratory Research 2009, 10:74 http://respiratory-research.com/content/10/1/74 awake OSAS patients This points to wake-related neuromuscular compensatory mechanisms, and possibly, to OSAS-specific changes in the cortical motor control of the upper airway dilators. These muscles obey brainstem automatic respiratory commands and in behavioral and voluntary commands, suprapontine in origin, that involve their somatotopic representation within the primary motor cortex. Both the bulbar and the cortical commands to the upper airway muscles converge to "peripheral" motoneurones where they are integrated and modulate one another [7], as it is the case at the spinal level for phrenic motoneurones [8-10] This cross-modulation can be studied through the analysis of the electromyographic responses to transcranial magnetic stimulation (TMS) and of the effects of voluntary and involuntary muscle activations on these responses. In normal individuals, that the response of the genioglossus to TMS is differently influenced by respiratory and non-respiratory maneuvers [7], with a pattern of change that is distinct from that of the diaphragm [7]
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