RESPIRATORY AROUSAL INDEX AND CRANIOFACIAL ABNORMALITIES IN UARS:
INDICATORS FOR NCPAP USEFULNESS
Helmut S. Schmidt, Brian P. Berendts, and Robert M. Hinkle
The Ohio Sleep Medicine Institute, and Dublin Oral and Facial Surgery Inc.
Columbus, Ohio U.S.A

Treatment of UARS with NCPAP is considered by many unjustified due to the very low or "normal " apnea + hypopnea index (A+HI). This has led us to identify a new measure of sleep disordered breathing (SDB) that more accurately assesses clinical impact and treatment response.

21 patients with UARS (14 male, 7 female), mean age 46.6 years, were selected on the basis of having had a baseline nocturnal polysomnogram (NPSG), a cephalometric x-ray, and were free of sleep altering medications. NPSG was scored to include a respiratory arousal index (RAI - number of inspiratory associated arousals per hour of sleep). Inspiratory arousals were scored according to AASM criteria1, with two modifications: arousals were counted in stage REM regardless of changes in chin EMG, and K-complexes were included as part of the arousals if present immediately prior to, during, or following the alpha burst activity. Twelve patients had MSLT’s with a mean sleep onset latency of 6.4 minutes; none qualified for narcolepsy.

Mean age was 46.6 years (± 9.8) with a mean body mass index (BMI) of 30.1kg/m² (± 5.3). Mean A+HI was only 2.4 (± 1.6), though the mean RAI was 34.2 (± 10.6). On average < 2% of sleep time was spent at SaO2 levels < 90%. The posterior airway space (PAS) was the most strikingly abnormal, with mandibular hypoplasia also notable. PAS correlated inversely with RAI (r = -0.5693 p < 0.01). In addition, RAI, as defined above was also highly correlated with other indicators of sleep fragmentation. This suggests that as the PAS narrows, the inspiratory associated arousals, i.e. the RAI increases and sleep architecture becomes more fragmented. The mean effective CPAP was 7.6 cm H20 (± 2.9, range 4-12). A narrow therapeutic window (NTW) was strongly suggested in approximately 50% of patients. Our clinical experience also suggests that the NTW-CPAP phenomenon may relate to the extent of the patient’s pre-existing craniofacial abnormalities and the potential for CPAP failure.

Conclusions: RAI, as opposed to A+HI, should be used as an indicator of breathing induced fragmentation of sleep and appropriate NCPAP use in UARS. RAI is the preferred measure of severity of SDB and an essential indicator of treatment effectiveness. The NTW-CPAP concept should be taken into consideration during routine clinical CPAP titrations and as a potential cause for CPAP failure.

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¹ Guilleminault C. et. al EEG arousals: Scoring Rules and Examples, A Preliminary Report from the Sleep Disorders Atlas Task Force of American Academy of Sleep Medicine. Sleep, 1992, 15(2):173-184.