Objective versus Subjective Cognitive Functioning in Patients with Obstructive Sleep Apnea

Study objectives: Previous studies have found that patients’ neurocognitive functions were affected by OSA symptoms. However, no study has focused on the subjective awareness of cognitive impairments. This study used a subjective rating scale to evaluate OSA patient perceptions of their cognitive impairments, and explore the relationship between subjective and objective cognitive functions. Methods: An independent-group design was used to compare objective and subjective cognitive performance in both the OSA and control groups. An experimental group of 19 male OSA patients and a control group of 19 normal subjects matched in age and education participated in the study. A neurocognitive test battery that measures attention, memory and executive functions, and the SCIRS (Subjective Cognitive Impairment Rating Scale) that measures subjective perception of cognitive impairments were used. Results: On the neurocognitive test measures, OSA patients demonstrated decreased performance on memory and executive function. On the subjective measures, OSA patients reported a mild to moderately negative impact on attention, memory, and emotional control due to OSA. Conclusions: The results show that OSA patients may not be fully aware of their cognitive impairments, especially with regard to their executive functions. The inconsistency suggests that including neurocognitive tests in the evaluation of sleep-related breathing disorders may provide useful information that cannot be obtained through clinical interviews. Keywords: Obstructive sleep apnea, Neurocognitive test battery, Subjective and objective cognitive functions. INTRODUCTION Obstructive sleep apnea (OSA) is characterized by episodes of complete or partial pharyngeal obstruction during sleep and is associated with frequent arousals and intermittent hypoxemia [1, 2]. OSA is highly prevalent and affects the physical and psychological well-being of the patients. According to epidemiological data, 2% of females and 4% of males suffer from OSA in Western countries [3]. East Asian populations have a similar respiratory disturbance index (RDI) but relatively smaller body mass index (BMI) than Western populations. Patients with OSA symptoms are also at a higher risk of other problems during periods of wakefulness, of which the most significant are health-related problems, drowsiness and neurocognitive impairments [4]. The neurocognitive dysfunctions have been brought to the attention of clinicians and researchers because they may have a major impact on the individual’s daily activities and occupational safety. Previous studies have used different neurocognitive tests to examine patients’ areas of functioning affected by OSA. The impact of the cognitive deficits may be easily identified *Address correspondence to this author at the Department of Psychology/The Research Center for Mind, Brain, & Learning National Chengchi University 64, Sec. 2, Chih-Nan Rd. Taipei, Taiwan 116; Tel: 886-2-29387383; 886-2-29393091; Ext: 62412; Fax: 886-2-29390644; E-mail: [email protected]: [email protected] in those with a higher apnea-hypopnea index and greater hypoxemia. Although results from previous studies are not all consistent, there seems to be more evidence to support significant deficits in cognitive processing [2, 5], sustained attention [6, 7] and executive function [8-11] in patients with more severe OSA symptoms. More specifically, impaired cognitive processing is reflected by a slowing of reaction time and increased errors. Deficient sustained attention, or what some authors call vigilance, is reflected in an inability to maintain attention over time, therefore demonstrating a slowing of response time, and increasing lapses and false responses as the task is prolonged. Impaired executive function is reflected in problems with information manipulation, inadequate planning, poor judgment, poor decision-making, inflexibility, impulsivity and difficulty maintaining motivation. All the above neurocognitive problems could influence patients’ daily functioning and professional performance. However, in light of the major impact cognitive dysfunction may have, it seems to be ignored by some OSA patients. The association between self-reported cognitive symptoms and performances on objective cognitive tests has been investigated on patients with emotional distress [12, 13], head injury [14, 15] and insomnia [16]. Some investigators found a significant relationship, but other studies have failed to find an association between objective measures of cognitive dysfunction. Despite inconsistent conclusions on the understanding of objective performance, the subjective rating and the relationship is important and provides useful information 34 The Open Sleep Journal, 2012, Volume 5 Chen et al. for future treatment. In clinical observations, the most common complaint of OSA patients is daytime sleepiness and/or fatigue [4, 17, 18]. Complaints about the impact of cognitive dysfunction are less commonly heard. Although the objective neurocognitive deficits in OSA patients are evident, no study, as far as we know, has focused on the subjective perception of neurocognitive dysfunctions and their relationship with the objective performance of OSA patients. Therefore, the present study examined both the objective and subjective aspects of neurocognitive dysfunctions in OSA patients. We planned to interview OSA patients and discuss their cognitive related symptoms, then use their description to develop Subjective Cognitive Impairment Rating Scale (SCIRS) and to test reliability and validity. The purposes of the present study were: 1) to assess objective cognitive performances in OSA patients using a neurocognitive test battery; 2) to test reliability and validity of SCIRS and measure the OSA patients’ subjective cognitive functioning; and 3) to examine the relationship between the objective and subjective measures. MATERIALS AND METHODOLOGY Subjects Participants included 19 untreated male OSA patients (age: Mean±SD=41.72±7.46 years; years of education: Mean±SD=14.67±1.94; BMI: Mean±SD= 29.06±4.13), and 19 healthy control male subjects (age: Mean±SD= 41. 58±8.28 years; years of education: Mean±SD= 14.74±1.91 years; BMI: Mean±SD=23.76±2.26). The OSA subjects were all referred to the sleep lab from the outpatients’ clinic in Chang Gung Memorial Hospital. They were all first diagnosed BUT never receive any treatment related to sleep apnea. The control subjects were recruited from the community. There were no significant differences in age, gender and years of education between the two groups. As expected, OSA patients had significant higher BMI than the control subjects (t(36)=4.88, p<.001). The inclusion criteria for participation in both groups were: Age between 30 and 55 years with no major medical disorders. All OSA patients had a polysomnography examination. Previous research has indicated that patients with more severe OSA demonstrated more deficits in neurocognitive functions. Thus, in this study, we included OSA patients with RDI above 15 (RDI: Mean±SD= 59.24±24.53). The control subjects were screened for sleep disorder breathing (SDB) with the Snore Outcome Study questionnaire (SOS) [19, 20] and a report by their bed partners about nighttime SDB-related symptoms and didn’t show any OSA related symptom. All subjects that passed the screening procedures were asked to fill out the subjective rating scales, and then underwent a neurocognitive test battery. We let subjects to decided test administering time according to their subjectively best performance time. The test session began at 9 A.M. and 2 P.M. There were 11 OAS patients and 10 control subjects started tests at 9 A.M., for the rest of the subjects started at 2 P.M. (Fig 1). MEASURES Subjective Cognitive Impairment Rating Scale (SCIRS) Since no instrument has been developed to measure the subjective perception of cognitive impairment in OSA patients, we developed the Subjective Cognitive Impairment Rating Scale (SCIRS) [21] to evaluate OSA patients’ subjective perception of their cognitive impairment (see Appendix I). To construct the SCIRS, 30 untreated OSA patients were interviewed about their daily life experiences of cognitive problems that may be related to OSA. The descriptions of cognitive problems were first categorized into three groups based on previous research findings of cognitive impairments in OSA; the groups were “attention & vigilance”, “memory & learning”, “abstract thinking & problem solving.” An additional area, “emotional control & motivation” was added since many patients reported an impact in this domain as well. The descriptions were then integrated into 28 descriptions to serve as the items of the scale. Subjects were asked to rate the impact of OSA on each item with a 5point Likert scale, ranging from 0 (no impact) to 4 (extreme impact). The scale was administered to 88 untreated OSA patients. Internal consistency of the 28 items was good for the total scale (Cronbach’s ! = .98) and all four subscales (attention & vigilance Cronbach’s ! =.91; memory & learning Cronbach’s !=.93; abstract thinking & problem solving Cronbach’s !=.95; emotional control & motivation Cronbach’s !=.95). In terms of validity, we selected two well validated and popular self-rating scales that were used to measure OSA patients sleepiness (Epworth Sleepiness Scale, ESS) [22] and quality of life (Medical Outcome Study Short Form-36, SF-36) [23] as criteria validity indexes. Table 1 shows the Pearson correlation coefficients between the scores on the SCIRS and the SF-36 and ESS; there was a small to moderate correlation with the ESS and SF-36. There Fig. (1). Research procedures. Objective
versus
Subjective
Cognitive
Functioning
in
Patients The Open Sleep Journal, 2012, Volume 5 35 was also a significantly moderate correlation between RDI and total scores of the SCIRS (r=.35, p<.01). The discriminate validity is significant in all subscales. Neurocognitive Test Battery A neurocognitive test battery was designed to assess a broad range of cognitive abilities of the subjects. The selected tests were shown to be sensitive to OSA patients’ cognitive impairments in previous studies and also demonstrated good reliability and validity in the Chinese-language version. All the tests were widely used and locally validated by some research references. Multiple Vigilance Test (MVT) The MVT was designed to assess vigilance and sustained attention [24]. Subjects were asked to attend to a specific target stimulus, while disregarding distracting non-target stimuli that were displayed on a computer screen. There were 240 stimuli, including 60 target stimuli and 180 nontarget stimuli. The inter-stimulus intervals (ISIs) varied randomly from 4 to 11 seconds. The total test lasted 30 minutes. Subjects’ reaction time and the number of misses and false alarms were recorded. The MVT was used to assess subject’s fatigue and has shown good reliability and validity [25]. Modified Paced Auditory Serial Addition Test (PASAT) The PASAT was developed by Gronwall and colleagues in 1974 to measure attention, concentration, working memory, and speed of information processing. Subjects had to add each new digit to the number immediately preceding it and give the response before the presentation of the next stimulus. In the current study, we used a modified version of the PASAT, with 61 items presented at an ISI of 2.0 seconds. The total correct number and percentage of correct responses were recorded. The PASAT was used to assess subjects’ attention process and locally validated [26]. Wechsler Memory Scale (WMS) The WMS was designed to measure various aspects of memory function [27]. It consists of 11 subtests (six primary and five optional), and provides eight primary index scores (Auditory Immediate Memory, Visual Immediate Memory, Immediate Memory, Auditory Delayed Memory, Visual Delayed Memory, Auditory Recognition Delayed Memory, General Memory and Working Memory). In the current study, we used four of the primary subtests, Logical Memory, Faces, Verbal Paired Association, and Family Pictures, and calculated seven primary index scores (except the Working Memory Index) for subsequent data analysis. The WMS was locally validated and has shown good reliability and validity [28]. Wechsler Adult Intelligence Scale -Third Edition (WAISIII) -short version The purpose of WAIS-III is to provide measures of general intellectual function [27]. The full version of the test consists of 11 subtests and can generate Verbal IQ (VIQ), Performance IQ (PIQ), and a Full Scale IQ (FIQ), as well as three index scores. In this study, we used a short version of the WAIS-III, which included six subtests (Picture Completion, Digit Symbol-Coding, Similarities, Block Design, Digit Span, and Information). The WAIS-III was locally validated and has shown good reliability and validity [29]. Wisconsin Card Sorting Test (WCST) The WCST was designed to assess the ability to form abstract concepts, to shift and to maintain cognitive sets, and to utilize feedback [27]. At first, four stimulus cards were presented to the subject. The subject was then given a stack of additional cards and asked to match each one to one of the stimulus cards. The subject was not told about the rule to match the cards; however, he or she was told whether a particular match was right or wrong. A number of different Table 1. Pearson Correlation Coefficients Between the Scores on the Subjective Cognitive Impairment Rating Scale (SCIRS) and the Scores on the Medical Outcome Study Short Form-36 (SF-36) and Epworth Sleepiness Scale (ESS) Pearson Correlation Coefficients Attention & Vigilance Memory & Learning Abstract Thinking & Problem Solving Emotional Control & Motivation Total Score ESS .414** .332** .363** .350** .373**