Cognitive function in the sleep apnea/hypopnea syndrome (SAHS)

The magnitude, determinants and reversibility of cognitive deficits associa ted with the sleep apnea/hypopnea syndrome (SAHS) are of clinical and resea rch interest. A quantitative overview of impairment effect sizes (ESs) from case-control studies of cognitive performance in SAHS suggests that defici ts broadly worsen with disease severity, with large average values for atte ntional (ES approximate to 1.0 SD units) and executive (ES approximate to 0 .9 SD units) cognitive scores, and moderate values for memory-related (ES a pproximate to 0.6 SD units) performance scores. A study of determinants of cognitive outcomes conducted in 150 patients with SAHS (AHI 5+ and greater than or equal to 2 symptoms) showed significant but weak associations betwe en a cognitive 'intellectual ability' component score (CS) and both AHI (r= -0.14) and minimum oxygen saturation (r=0.15), linking increasing disease s everity with poorer performance. A somewhat stronger correlation between a cognitive 'response slowing' CS and a 'wakefulness' CS was observed (r=-0.3 4). That sleepiness as well as hypoxemia might contribute to cognitive defi cit has also been suggested by experimental sleep fragmentation in normals, producing small to moderate impairments (average ES approximate to 0.3 SD units) in attention-biased scores. The reversibility of attentional cogniti ve deficits has been investigated through a meta-analysis of randomized pla cebo-controlled crossover studies of CPAP treatment, involving 98 SAHS pati ents (AHI 5+ and greater than or equal to 2 symptoms). While cognitive outc omes showed at least trends towards better performance on CPAP than on plac ebo (p less than or equal to 0.1), the ESs of cognitive enhancements follow ing CPAP were small (average ES approximate to 0.2 SD units). This may be d ue either to the relatively mild study population, suboptimal CPAP use or t o an irreversible component in cognitive impairment in SAHS.