Characterization of obstructive nonapneic respiratory events in moderate sleep apnea syndrome

Obstructive nonapneic respiratory events (ONAREs, i.e., obstructive hypopne as [OHs] and respiratory effort related arousals [RERAs]) are clinically im portant as producing sleep fragmentation but are much more difficult to det ect and classify than obstructive apneas. We characterized 1,061 ONAREs in 15 unselected patients with moderate sleep apnea-hypopnea syndrome (OSAHS) according to the 1999 American Academy of Sleep Medicine (AASM) Task Force recommendations concerning accurate skills for respiratory measurements (i. e., pneumotachograph and esophageal pressure [Pes]) and definitions of resp iratory events. OHs were defined as greater than or equal to 50% decrease i n flow or <50% but <greater than or equal to>30% decrease in flow associate d with either a desaturation of greater than or equal to3% or a cortical ar ousal. RERAs corresponded to a less than 30% decrease in flow associated wi th an arousal. OHs represented a large majority of the events (79.9%, n = 8 48). Among the events demonstrating a 30 to 50% reduction in flow (n = 392) , the occurrence of a cortical arousal permitted the classification of 246 events as OHs (62.8%). RERAs represented only 5.3% of the events. Finally 1 4.8% of the events were classified as indeterminate owing to a <50% and <gr eater than or equal to>30% airflow decrease without arousal or desaturation or an airflow decrease less than 30% without arousal. The same level of Ap es was observed at the end of OHs and RERAs (21.9 +/- 5.5 versus 18.9 +/- 5 .7 cm H2O respectively [NS]) whereas the reduction in flow was as expected, higher for OH (57.9 +/- 10.7 versus 21.3 +/- 4.9%). In a population of mod erate OSAHS, OH represented the dominant type of ONAREs when RERAs should b e considered as specific but relatively rare respiratory events. The occurr ence and the recognition of a microarousal represented the key associated f actor for classifying respiratory events as hypopneas. The high rate (15%) of unclassified events demonstrated some limitations in the AASM Task Force recommendations for definitions of respiratory events. Similar levels of D elta Pes found at the end of RERAs and OHs, although the reduction in flow was higher for OHs, suggest that different levels of collapsibility can exi st throughout the night in a given patient.