Analysis Of The Characteristics Of Cognitive Impairment In Patients With Obstructive Sleep Apnea

Under the modern lifestyle, more and more people began to complain about the insufficient sleep that fails to meet their physiological need. Insufficient sleep fatigues the body, which forces people to increase the caloric intake and further leads to obesity and Obstructive sleep apnea hypopnea syndrome (OSAHS). Obstructive sleep apnea hypopnea syndrome (OSAHS) refers to a sleep disorder characterized by intermittent apneas and reduced airflow during sleep, which are caused by complete or partial obstructions of the upper airway. These respiratory events occur during sleep and seriously affect people’s sleep quality, resulting in intermittent hypoxia, microarousals or arousals, sleep fragmentation, and sleep deprivation. All these conditions may exert damage to the brain and induce a decline in cognitive function. Having a serious impact on human health, OSAHS, which is featured by extensive affected population and wide age span with especially higher incidence rate in the elderly population, acts as an independent risk factor for hypertension, diabetes, as well as cardiovascular and cerebrovascular events. As one of the main causes of daytime sleepiness, sleep fragmentation is also the main clinical manifestation of OSAHS, and the OSAHS-related daytime sleepiness elevates the risk of road traffic incidents by 2-7 times. Despite of the increasingly strengthened health awareness, 80% of people remain undiagnosed and untreated.Objective:Based on patients admitted to the sleep center, this study is designed to understand their general characteristics of obstructive sleep apnea hypopnea syndrome (OSAHS) and features of sleep structure, breathing and hypoxia as showed by polysomnography (PSG), explore the changes in their cognitive function including memory, attention, verbal, visuospatial and executive functions, as well as analyze the main forms of sleep disorder influencing cognitive function.Methods:A retrospective analysis was conducted for the clinical data of obstructive sleep apnea hypopnea syndrome patients admitted to our department, who visited the SleepMedicine Center, Provincial Hospital Affiliated to Shandong University from June 2014 to January 2016 and had been diagnosed by polysomnography (PSG). Five hundred and seventy-nine cases of eligible patients with mild, moderate and severe OSAHS were enrolled and monitored by the polysomnography (PSG) using Compumedics E-Series system, Grael system, and Philiphs Alice 5 system. OSAHS was defined as at least 10 seconds of airflow decline> 90%, accompanied by sustained or increased respiratory effort. Hypopnea (obstructive) was defined as at least 10 seconds of airflow decline≥30%, accompanied by 3% decrease in oxyhemoglobin saturation or microarousal. The frequency of respiratory events was measured via apnea hypopnea index (AHI), which is calculated by dividing the number of respiratory events by the number of hours of sleep. Statistics was carried out in terms of following monitoring indicators, including AHI, oxygen desaturation index (ODI), obstructive apnea index (OAI), hypopnea (obstructive) index (HI), the ratio of sleep duration with blood oxygen<90% to the total sleep time (SLT90%), longest apnea time (LAT), minimum oxyhemoglobin saturation at night (SaO2min), average oxyhemoglobin saturation at night (SaO2ave), microarousal index, ratio of N1+N2:N3+REM sleep, and Epworth sleepiness scale scoring. The OSAHS patients were assessed using neuropsychological scales to observe their polysomnography characteristics and changes in cognitive function, includingMini-Mental state examination (MMSE), California verbal learning test California(CVLT), verbal fluency test(VFT), digit span test(DST), clock drawing test(CDT), trail making testthus(TMT),further investigating the association between different monitoring indicators and these changes in cognitive function.Results:According to the observation findings of general information characteristics in the mild, moderate and severe OSAHS groups, those cases from the sleep laboratory were featured by a significantly higher proportion of severe OSAHS than mild and moderate OSAHS and a significantly lower proportion of mild OSAHS than moderate and severe OSAHS. The 579 enrolled patients, including 489 males and 90 females, showed a male-female ratio of 5.43:1, suggesting that the affected patients were dominated by male gender. The ages of onset ranged from 35 to 65 years with the median age of 49 years; no significant difference in age was observed between three groups, and the highest prevalence was found in the young and middle-aged adults. BMI values found a gradually growing trend from mild to severe OSAHS, and there was a significant difference in BMI values between the severe OSAHS group and the mild OSAHS group (P<0.05). Similarly, neck circumference values also found a gradually growing trend from mild to severe OSAHS and showed a significant difference between the severe OSAHS group and the mild OSAHS group (P<0.05). The difference in waist circumference values was statistically significant between the moderate group and the mild group (P<0.05), so was the case between the severe group and the mild and moderate groups.The results of PSG monitoring and sleepiness scale assessment were compared between three groups in terms of AHI, ODI, OAI, HI, SLT90%, LAT, SaO2min, SaO2ave, microarousal index, ratio of N1+N2:N3+REM sleep, and ESS scoring. Compared with the mild and moderate groups, the monitored AHI, ODI, OAI and LAT were significantly enhanced in the severe group, indicating statistically significant differences; these indicators in the moderate group were higher than those in the mild group with statistical significance (P<0.01). HI was elevated in the severe and moderate groups compared with that in the mild group, suggesting a statistically significant difference (P<0.01); no significant difference was observed between the moderate and severe groups. Compared with the mild and moderate groups, the values of SLT90% and SaO2ave were increased in the severe group, demonstrating statistically significant differences (P<0.01); no statistically significant difference was reported between the mild and moderate groups. In the severe group, SaO2min values, microarousal index, ratio of N1+N2:N3+REM sleep, and ESS scores were increased compared with the mild and moderate groups, and the differences were statistically significant (P<0.0\); these indicators were higher in the moderate group than those in the mild group, showing statistical significance as well.According to the assessment results of MMSE, VFT, DST, CDTMMSE, VFT, DST and CDT in the mild, moderate and severe OSAHS groups that were divided based on their AHI degree, MMSE, DST and CDT scores in the severe OSAHS group were obviously changed compared with the mild and moderate groups, which suggested statistically significant differences (P<0.01); a statistically significant difference in DST was reported between the moderate and mild groups (P<0.05), while no statistically significant differences were seen in MMSE and CDT scores between them (P>0.05). The difference in VET was not statistically significant between three group (P>0.05). The CVLT scoring results have been shown in Figure 1. According to the results, the intra-group data analysis indicated no statistically significant differences between three groups in free memory 1, free memory 5, total memory scores, free recall B, short-delay free recall, and short-cued free recall. However, compared with the mild and moderate groups, the long-delay free recall and long-cued free recall were remarkably reduced in the severe OSAHS group with statistical significance (P<0.01), while the differences between the mild and moderate groups were not statistically significant. The completion rate results of TMT scale scoring showed a statistically significant difference in the TMT-A and TMT-B subgroups of severe OSAHS group compared with the mild and moderate OSAHS groups (P<0.01), while no statistical significance was reported between the mild and moderate groups.SLT90%, LAT, microarousal index, ratio of N1+N2:N3+REM sleep and ESS scores were divided respectively into five groups according to their exceeded values above the mean level of severe OSAHS patients so as to compare the changes in cognitive function between these groups. It was found that all of above five indicators were associated with impaired MMSE, DST, CDT, CVLT (long-delay free recall), TMT completion rate and number of time consuming, but the inter-group exhibited no statistically significant differences.Conclusion:Based on the data of patients with explicitly confirmed OSAHS, who were diagnosed and treated in the sleep center and underwent complete sleep respiratory monitoring, this paper has conducted a statistics on their general information, various indicators of sleep respiratory monitoring and neuropsychological scale scores, observed their general characteristics of OSAHS and features of sleep respiratory monitoring, evaluated multiple neuropsychological aspects, and compared the characteristics of cognitive impairment and possible related factors between different types of patients. Through analyzing the results, the following conclusions are drawn out:(1) Male patients are significantly more than female ones, where the former mainly suffer severe OSAHS while the later are mainly affected by mild-moderate OSAHS. OSAHS is positively correlated with neck circumference, waist circumference and BMI, and patients with severe OSAHS exhibit a slightly longer history of illness. (2) In these patients, the intermittent hypoxia and disordered sleep structure are exacerbated as AHI increases, where severe OSAHS is associated with obstructive apnea to a great extent while moderate OSAHS with hypopnea events. Intermittent hypoxia is developed earlier in moderate OSAHS patients suffering serious disordered sleep structure, suggesting that the cognitive impairment of moderate OSAHS may be more likely related to disordered sleep structure as well as daytime drowsiness and sleepiness. During the progress from mild to severe OSAHS, the disorder of sleep structure proves to be an important factor first affecting cognitive function. Given that hypoxia can cause permanent damage to the corresponding brain region, the early diagnosis and clinical intervention of OSAHS is of great significance for correcting the disordered sleep structure and reversing the cognitive impairment. (3) Severe OSAHS is associated with impaired MMSE, long-delay memory, attention, visuospatial and executive functions, while the verbal fluency and immediate recall are relatively retained. Moderate OSAHS is only correlated with attention damage and free of significant impairments in memory, visuospatial and executive functions. Disordered sleep structure (fragmented sleep and reduced deep sleep) may be related to the attention damage, which is probably the first cognitive impairment developed in OSAHS patients.