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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 35  |  Issue : 3  |  Page : 1218-1223

Assessment of cognitive function in patients with sleep apnea syndrome


1 Department of Chest Disease and Tuberculosis, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Psychiatric Medicine, Faculty of Medicine, Menoufia University, Menoufia, Egypt
3 Department of Public Health and Community, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission26-May-2022
Date of Decision22-Jun-2022
Date of Acceptance26-Jun-2022
Date of Web Publication29-Oct-2022

Correspondence Address:
Mai M El-Kalashy
Shebin Elkom, Menoufia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_179_22

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  Abstract 


Background
Obstructive sleep apnea (OSA) can negatively affect patients' physical and psychological functioning, as well as their quality of life. A major consequence of OSA is impaired cognitive functioning. Indeed, several studies have shown that OSA mainly leads to deficits in executive functions, attention, and memory.
Objectives
To assess cognitive function in patients with sleep apnea syndrome.
Patients and methods
This prospective study was done on 70 patients with sleep apnea syndrome who were referred to Chest and Neurology Departments, Menoufia University Hospital, in the period from January 2021 to April 2022. The study was done after written consents from 70 patients with sleep apnea syndrome based on clinical criteria and confirmed with overnight polysomnography. They were assessed by the Montreal Cognitive Assessment questionnaire for their cognitive function, which was classified according to severity.
Results
Of 70 patients with sleep apnea syndrome, 56 (80%) patients had cognitive dysfunction. The most prevalent type of cognitive dysfunction was memory and attention (30 patients) followed by visuospatial orientation, memory, attention, and language. Cognitive dysfunction was significantly higher among diabetic patients and related to severity of apnea–hypopnea index. Cognitive dysfunction had a significant negative correlation with BMI, apnea–hypopnea index, and oxygen desaturation.
Conclusion
Cognitive dysfunction has a high incidence in patients with sleep apnea syndrome, especially obstructive type, and in obese diabetic ones. Other studies should be done on the effect of treatment of sleep apnea on reversal of the cognitive dysfunction.

Keywords: cognitive dysfunction, polysomnography, sleep apnea


How to cite this article:
Abdelaal GA, Omara HR, Abdelaty NB, El-Kalashy MM. Assessment of cognitive function in patients with sleep apnea syndrome. Menoufia Med J 2022;35:1218-23

How to cite this URL:
Abdelaal GA, Omara HR, Abdelaty NB, El-Kalashy MM. Assessment of cognitive function in patients with sleep apnea syndrome. Menoufia Med J [serial online] 2022 [cited 2024 Mar 29];35:1218-23. Available from: http://www.mmj.eg.net/text.asp?2022/35/3/1218/359468




  Introduction Top


Sleep disordered breathing (SDB) means upper airway collapse during sleep that includes many disorders [snoring, upper airway resistance syndrome, and obstructive sleep apnea (OSA)]. OSA is the commonest, affecting ~60% of older adults, especially men. The currently used International Classification of Sleep Disorders concluded that an obstructive apnea–hypopnea index (AHI) more than or equal to one event per hour on an overnight polysomnogram is diagnostic of OSA[1].

Many abnormalities are the reason for the relation between sleep efficiency, with respect to quality quantity, and SBD, and cognitive dysfunction. For example, sleep disorders have been linked to cortical thinning, a marker of cortical atrophy found in many dementia subtypes[2].

OSA and cognitive impairment interrelationship was first observed in 1980s; however, along the years with many studies on this topic, the burden, mechanism, and management of impaired cognitive functions relating to OSA are not conclusive. Overall, 59.2% of patients with OSA with high BMI had at least one cognitive disorder. So, a large, multicenter study on sleep-related cognitive dysfunctions, with and without obesity, is still needed to accurately identify all aspects of the problem[3]. The study was concerned with assessing cognitive function in patients with sleep apnea syndrome.

Objectives were to assess cognitive function in patients with sleep apnea syndrome.


  Patients and methods Top


This prospective study was done on 70 patients referred to Chest and Neurology Departments, Menoufia University Hospital, with sleep apnea syndrome in the period from January 2021 to April 2022. An informed written consent was taken from all the patients, and the study was approved by Menoufia Ethical Committee. Inclusion criteria were patients with clinical symptoms of sleep apnea (witnessed apnea during sleep, daytime sleepiness, morning headache, etc.), with confirmation and severity classified by overnight polysomnography. Exclusion criteria were any other chest disease and any neurocognitive disease. All of the patients underwent full history taking and complete general and local examination.

Full overnight polysomnography for 8 h was done. electroencephalogram, ECG, electromyography, pulse oximetry, and chest and abdominal belts were connected using Philips Sprionic Alice 6, Washington, USA, and the followed items of sleep were registered: sleep efficiency, desaturation index, AHI, and arousals. The patients with proven sleep apnea completed the Montreal Cognitive Assessment questionnaire, and patients were classified into mild, moderate, and severe according to the degree of cognitive impairment. The most recent version of the Montreal Cognitive Assessment is only a one-page 30-point test, which can be fulfilled by patients in 10 min. The short-term memory recall task (five points) was tested for two trials of knowing five nouns, and delayed recall was calculated after about 5 min of delay. Visuospatial skills were tested using a clock-drawing test (three points) and a three-dimensional cube drawing (one point). Executive functions were checked by an alternation exercise adapted from the Trail Making B task (one point), a phonemic fluency job (one point), and two-item verbal abstraction ability (two points). Attention, concentration, and working memory were assessed using a sustained attention test (target detection using tapping; one point), a serial subtraction test (three points), and digits forward and backward (one point each). Language was checked by a three-item confrontation naming test with less-familiar animals (lion, camel, and rhinoceros; three points), repetition of two syntactically complex sentences (two points), and the fluency job. Lastly, orientation to time and place was assessed (six points). It was translated in Arabic by Dr Ziad Nasreldinne, a neurologist, who graduated from the University of Sherbrooke, Québec, and did fellowship in Cognitive Neurology/Neurobehavior from UCLA[4].

Statistical analysis

Data were collected, tabulated, and statistically analyzed using an IBM personal computer with Statistical Package for the Social Sciences (SPSS), version 19 (SPSS Inc., Chicago, Illinois, USA). Quantitative data were presented in the form of mean, SD, and range, and qualitative data were presented in the form of numbers and percentages. Shapiro–Wilk test of normality was used to determine if the data were normally distributed or not. χ2 test was used for comparison between qualitative variables. Mann–Whitney test was used for comparison between two groups not normally distributed having quantitative variables. Kruskal–Wallis test is a nonparametric test used for comparison between three or more groups not normally distributed having quantitative variables. Spearman's correlation was used for correlation of two quantitative variables not normally distributed. Significance level was set at P value less than 0.05.


  Results Top


The study was conducted on 70 patients who had different degrees of OSA to assess their level of cognitive impairment. The mean age of the studied group was 49.1 years, 62.9% of patients were males, 51.4% were smoker, diabetes mellitus was present in 75.7% of patients, and hypertension was found in 78.6%. The mean BMI was 35.5 ± 5.09, and the mean neck circumference was 42.7 ± 4.22 [Table 1].
Table 1: Sociodemographic data of the studied patients (n=70)

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Regarding the degree of AHI, which is the diagnostic index of OSA in the studied group, it was found that 13 (18.6%) patients had mild OSA abnormality, 15 (15%) patients were moderate, and 42 (60%) patients had severe degree of OSA, with mean and SD of 44.4 ± 30.2, with range of 3.3–108. The mean ± SD obstructive apnea and central apnea indices were 13.5 ± 16.4 and 1.94 ± 3.09, respectively. The mean ± SD hypopnea index was 27 ± 18. The mean ± SD oxygen desaturation was 59.3 ± 34.5, with lowest oxygen saturation of 78.6. In the studied group, the mean ± SD sleep efficiency was 56.8 ± 19.5, and the mean ± SD arousal index was 37.7 ± 20.6 [Table 2].
Table 2: Sleep and oxygen saturation data of the studied patients (n=70)

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It was found that cognitive impairment in the studied group was as follows: severe cognitive dysfunction was present in 32 (45.7%) patients, moderate in 20 (28.6%), mild in four (5.7%), and normal in 14 (20%) patients, with a mean cognitive dysfunction score of 15.4 ± 7.59 [Figure 1] and [Figure 2].
Figure 1: Montreal Cognitive Assessment (MOCA) questionnaire, Arabic copy.

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Figure 2: Cognitive dysfunction among the studied group (N=70).

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Regarding the type of cognitive dysfunction, most patients (53.6%) had memory and attention affection [Table 3].
Table 3: Type of cognitive dysfunction among the studied group (n=56)

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Comparison between cognitive dysfunction and sociodemographic data of the studied patients (N = 70) showed that there was no significant relation between cognitive dysfunction and age of patients, sex, smoking, and hypertension (P > 0.05). Cognitive dysfunction was significantly higher in diabetic patients (17.6 ± 7.48 vs. 8.52 ± 0.51; P < 0.001). Moreover, there was a highly significant relation between degree of sleep apnea and cognitive dysfunction. It was higher in patients with severe OSA than those with moderate and mild OSA (P < 0.001) [Table 4].
Table 4: Comparison between cognitive dysfunction and sociodemographic data of the studied patients (n=70)

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Regarding the correlation between cognitive dysfunction and age and sleep data of the studied group, there was a significant negative correlation between cognitive dysfunction and BMI, AHI, obstructive apnea index, hypopnea index, and O2 desaturation (P < 0.05) [Table 5].
Table 5: Correlation between cognitive dysfunction and age and sleep data of the studied group (n=70)

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  Discussion Top


In this study, there was no significant relation between cognitive dysfunction and age of patients, sex, smoking, and hypertension (P > 0.05) but cognitive dysfunction was significantly higher in diabetic patients (17.6 ± 7.48 vs. 8.52 ± 0.51; P < 0.001).

Both SDB and cognitive dysfunction deteriorate by aging. Patients with SDB show cognitive abnormalities similar to those caused by the aging process. Recent studies have detected that SBD and aging behave separately, impairing cognitive function, so there is a synergistic effect of both SBD and increased age impairing the cognitive function more than each disease alone. This is caused by structural and functional brain changes, such as changes in neuronal structure without neuronal death, loss of synapses, and neuronal networks dysfunction[5].

Smokers showed faster impairment in global cognition and executive function, whereas ex-smokers for more than 10 years showed no abnormalities in cognitive function[6].

Biessels et al.[6] studied cognitive impairment in patients with type 2 diabetes mellitus and detected that they had a high incidence of Alzheimer's disease. Glucose metabolism process and metabolic disorders could be the reasons for highly affected cognitive function[7].

In this study, 56 (80%) patients with sleep apnea had cognitive dysfunction, and the most prevalent disorder (53.6%) was memory and attention affection.

Overall, 70–80% of people with dementia had an association with sleep apnea, and also SDB class increases with dementia grade, giving the hypothesis of vicious circle relationship, where each one exacerbates and correlate with the other. OSA is reported in patients with reduced attention, executive functioning, visuospatial and constructional abilities, and psychomotor speed in nondemented persons[8],[9]. Patients with OSA showed twofold to sixfold increase in mild cognitive impairment or dementia[10],[11], and earlier onset of mild cognitive impairment or dementia. Many abnormalities are the reason for the relation between sleep efficiency, with respect to quality, quantity, and SBD, and cognitive dysfunction. For example, sleep disorders have been mediated due to cortical thinning and a proof of cortical atrophy present in dementia subtypes[2],[12]. The results of a cross-sectional study of 141 cognitively normal community-dwelling older adults (median age = 82.9 years) showed that decreased cortical thickness in the lateral orbitofrontal cortex and inferior frontal gyrus was associated with increased sleep fragmentation as measured by an ACTi-graph (a wrist-worn device that records movement over several days that uses a polysomnographically validated algorithm to assess sleep–wake patterns)[13],[14].

In this study, there was a highly significant relation between degree of sleep apnea and cognitive dysfunction; it was higher in patients with severe obstructive sleep apnea (OSA) than those with moderate and mild OSP (P < 0.001).

Researchers have shown that higher AHI and respiratory disturbance index (RDI) were associated with all-cause cognitive dysfunction[15]. However, one study studied adults with mild to moderate SDB and concluded no association between SDB grade and cognitive dysfunction[16], and it reported that may be the severe cases of SDB had a negative effect on cognition.

The study design, number of patients, and different methodology may explain these results.

Theories on the link between sleep and cognition are as follows:

Controlled attention: monotonous tasks are most affected by sleep loss due to the amount of up–down control needed to sustain attention while complex/difficult functions are intrinsically motivating (i.e. down–up control)[17].

Neuropsychological: sleep loss leads to focal impairment in functions subserved by the prefrontal cortex (i.e. executive functions)[18],[19].

Vigilance/arousal: attention, which is needed for the performance of many other cognitive functions, is mediated by arousal – a common disorder of SDB[20].

Wake-state instability: cognitive deficits observed as a result of sleep loss occur owing to the interaction of the drive to maintain alertness and the homeostatic drive to initiate sleep[21].

Sleep quantity and sleep quality in early life result in cognitive function in adult life, but the mechanism is unknown[22].

In this study, there was a significant negative correlation between cognitive dysfunction and BMI, AHI, obstructive apnea index, hypopnea index, and O2 desaturation (P < 0.05) but a nonsignificant negative correlation with sleep efficiency.

Recent research detected cognitive dysfunction with high BMI[23],[24],[25]. Moreover, there was a 0.55-time higher risk when associated with SDB. SDB is higher in overweight and obese children with increasing risk of cognitive dysfunction. Changes in brain structure, especially in the frontal lobe areas, have been found in clinically overweight to obese young adults[26]. There was decreased focal gray matter amount and increased orbitofrontal white matter in adults with high BMI, which reveal that brain structural changes have a role in causing cognitive dysfunction[27].

The results showed that grade of oxygen desaturation resulted in cognitive dysfunction in attention and executive tasks, even after controlling factors as age, sex, education, and depressive symptoms. Nocturnal oxygen desaturation measurement may be a helpful method to detect a hidden reversible factor of cognitive dysfunction[28].

Hypoxia is implicated in the mechanism of a myriad of neurological diseases, such as Alzheimer's, Parkinson's, and other age-related neurodegenerative diseases[29].


  Conclusion Top


Cognitive dysfunction is highly prevalent in patients with sleep apnea syndrome, especially obstructive type, and obese diabetic ones. Other studies should be done on the effect of treatment of sleep apnea on reversal of cognitive dysfunction.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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