During these breathing events, blood oxygen saturation (SaO2) can drop to dangerously low levels, resulting in increased respiratory effort and arousals from sleep to resume breathing. Recurrent hypoxemia and fragmented sleep are significant consequences of the disorder.3 The primary daytime sequelae of the disorder include excessive daytime sleepiness, mood changes, and self-reported cognitive problems. OSAHS is also associated with an increased risk of co-morbid medical illnesses, such as hypertension and vascular disease, making it a potentially costly disorder.4,5 Neuropsychological Consequences of OSA and the Effects of Treatment Decreased mental acuity can have significant negative consequences for occupational performance, automobile safety, and educational pursuits. Most studies of cognition in OSAHS have focused on attention and vigilance because these are the primary complaints reported by OSAHS patients. Studying multiple cognitive domains in a single sample, however, allows for comparisons between these domains and between assumed brain regions, which can lead investigators to develop a more comprehensive neurofunctional theory of OSAHS.

The neuropsychological literature on OSA from 1985 to 2002 has recently been reviewed.6 All studies that utilized clinically common measures of cognitive functioning with published normative data were reviewed. This was done to assure that reliable and valid measures were being used that would be easily comparable with studies of other cognitively impaired populations. Two primary questions were asked.

Are Patients with OSAHS Cognitively Impaired? In general, it was found that language is spared in OSAHS. Interestingly, several group comparison studies found that global cognitive functioning was spared; however, global cognitive improvement following treatment was noted in the majority of treatment studies. Only one study made both inter- and intra- group comparisons to compare first untreated apnea patients with controls and then pre-post treatment changes in the apnea group.7 The study found no differences between untreated apnea patients and controls on the Wechsler Adult Intelligence Scale- Revised (WAIS-R) full scale IQ or verbal IQ, but reported a significantly lower WAIS-R performance IQ in the untreated apnea patients. This latter deficit improved significantly with treatment. Thus, apnea patients may exhibit relatively few deficits in the global cognitive domain when compared with normal controls, but treatment may produce improvements in performance within subjects. It is difficult to determine why these improvements would exist, especially since the array of tests included in this domain is quite vast.

Attention/vigilance, executive functioning, and memory were impaired in the majority of studies reviewed.Attention/vigilance was the most commonly assessed cognitive construct in OSAHS, and multiple studies assessing sustained attention using tests developed in the sleep field (e.g. Psychomotor Vigilance Test (PVT);8 Steer Clear have found deficits in this domain9,10).Thus, attention/vigilance appears to be the most consistently affected cognitive domain in these patients. The relationships between OSAHS and measures of executive functioning and memory have been less thoroughly studied. Both of these cognitive domains present a challenge to investigators in that they are quite complex. For example, executive functioning can be tested using measures of set shifting (e.g.Trails B), working memory (e.g. the Wisconsin Card Sorting Test), and verbal fluency (e.g. controlled oral word association) among others. All are accepted tests of -executive functioning-, but each tests a distinctly different aspect of the various functional systems that lie within the frontal lobes of the brain. Because they Neuropsychological Consequences of Obstructive Sleep Apnea - Considerations for Treatment Mark S Aloia, PhD, is Assistant Professor in the Department of Psychiatry and Human Behavior at Brown Medical School in Providence, RI. He is a member of the American Academy of Sleep Medicine and the International Neuropsychological Society, among other organizations. Dr Aloia has authored over 25 peer-reviewed publications and is principal investigator on several National Institutes of Health (NIH) grants. He has mentored several young investigators and has been recognized as an outstanding research mentor at Brown University. He received his doctoral degree in clinical psychology with a specialization in neuropsychology.

2 B USINESS BRIEFING: US RESPIRATORY CARE 2005 Reference Section represent different sub-systems, performance on these tests is likely to be less consistent in any single cohort than multiple tests of a different domain, such as attention. Memory testing suffers from the same methodological concerns, although to a lesser degree.

In this case, test performance can be impaired for a number of reasons that would implicate distinctly different brain regions. Despite these limitations, patients with OSAHS appear to perform more poorly on tests of executive functioning and memory than matched controls do. Clearly, these findings have implications for the potential involvement of certain brain regions in this disorder. It is, however, difficult to determine the degree to which attention and executive functioning,which are frontally mediated,contribute to impairments in memory.

Although assessed less frequently than most other domains, psychomotor functioning and construction were impaired in OSAHS patients relative to normal controls in the majority of studies reviewed.

Interestingly, these domains have rarely been discussed as primary sources of impairment in this population.

The mechanism for psychomotor dysfunction in OSAHS is not obvious. Certainly, excessive sleepiness could result in slow motor performance, which would result in deficits on psychomotor tasks. However, if this were the case, tests of fine motor coordination (e.g.

grooved pegboard) should be impaired to the same degree as tests of simple motor speed (e.g. finger tapping). All four studies assessing fine motor coordination found OSAHS patients to be impaired relative to control subjects,7,11-13 while neither study examining motor speed identified impairments.13,14 Deficits on tests of fine motor coordination suggest the possible involvement of specific brain regions (e.g. the basal ganglia) in OSAHS that have not previously been the focus of investigation.15 The constructional findings are more complex and have not been addressed specifically in the literature. Executive and motor coordination problems could account for a large percentage of the variance in constructional performance in this population; however, studies are needed to address this question directly.

Does Treatment for OSAHS Improve Cognition? Identifying the pattern of cognitive impairment in patients with untreated OSAHS can lead investigators to hypothesize about the etiology of cognitive deficits in this population. In particular, it would be interesting to identify whether those cognitive functions related most to hypoxemia were also least likely to remit with treatment. This would suggest lasting effects of hypoxemia on cognitive functions via specific brain regions. However, the above findings do not present a clear and consistent pattern of deficits in OSAHS.The most consistent findings may be in the domains less frequently tested (e.g. psychomotor functioning and construction). In fact, the findings of relatively consistent deficits in fine motor coordination and construction raise some interesting questions about the possible brain regions involved in the disorder.