Are Snoring Medical Students at Risk of Failing their Exams?

Are Snoring Medical Students at Risk of Failing their Exams? Joachim H. Ficker, 2 Gunther H. Wiest, 1 Guido Lehnert, 1 Martin Meyer, 2 and Eckhart G. Hahn 1 (1) Medical Department and (2) Institute for Medical Statistics, University of Erlangen-Nuremberg, Erlangen, Germany Study Objectives: To compare the examination results of self-reported snoring and nonsnoring medical students Design: We studied the examination scores obtained by medical students answering a multiple-choice test forming part of their final examinations. The students were asked to classify themselves as nonsnorers, occasional snorers, or frequent snorers, and to state their age, sex, height and weight. Setting: University Hospital, Erlangen, Germany Participants: 201 medical students (61% males / 39% females; mean age 24.6±2.1 years; BMI 22.4±2.5 kg/m 2 ) taking their final examinations in internal medicine. Measurements and Results: Seventy-eight students (38.8%) claimed to be nonsnorers, 99 (49.3%) occasional snorers and 24 (11.9%) frequent snorers. The mean examination scores (adjusted for age, sex, and BMI) were 69.6±9.9% for the nonsnorers, 65.3±10.0% for the occasional snorers and 62.0±8.2% for the frequent snorers (p<0.0001). 12.8% of the nonsnorers failed the exam, compared with 22.2% of the occasional snorers and 41.7% of the frequent snorers (p<0.001). Logistic regression analysis showed an association between failing the exam and snoring (p=0.013), but not between failure and age, BMI, or sex (relative risk for snorers adjusted for age, sex and BMI: 1.26; 95%-CI 1.01-1.57). Conclusions: In medical students, snoring seems to be associated with an increased risk of failing exams in a doseresponse manner, even after controlling for age, sex and BMI. For the present, the mechanisms underlying this association must remain a matter of speculation. Snoring-related sleep fragmentation ( upper airway resistance syndrome ) might be a causal factor. Key words: Snoring; cognitive function; daytime performance; sleepiness; upper airway resistance syndrome Accepted for publication September, 1998 Address correspondence and requests for reprints to Joachim H. Ficker, MD, Medical Department I, University of Erlangen-Nuremberg, Krankenhausstr. 12, 91054 Erlangen, Germany; E-mail: joachim.ficker@med1.med.unierlangen.de Snoring, whether occasional or frequent, is a common disorder affecting most adults. 1,2 It has usually been regarded as a social nuisance rather than a significant health problem. Nevertheless, snoring is an indicator of obstructive sleep apnea (OSA), and in recent years it has been shown that not only full-blown OSA 3 but even nonapneic snoring may produce substantial daytime sleepiness, subjective work performance problems, and cognitive impairment, such as deficits in attention, decreased learning ability, and reduced memory span, especially in middleaged men. 4-9 To date, however, there has been no clear evidence to indicate whether nonapneic snoring has any significant impact on the cognitive performance of young people in daily life. With this in mind, we compared the results achieved by self-reported snoring medical students taking their final examinations in internal medicine with those of students who claimed to be nonsnorers. METHODS We studied 10th-term medical students taking a multiple-choice test as part of their final examinations in internal medicine. This multiple-choice test consisted of 45 items 205

Table 1. Results: examination scores and biometric data by snoring status Nonsnorers Occasional snorers Frequent snorers Total Number of students 78 (38.8%) 99 (49.3%) 24 (11.9%) 201 (100.0%) Age 24.3 ± 1.8 24.8 ± 2.4 25.1 ±1.8 24.6 ±2.1 Sex (F/M) 28 / 50 47 / 52 3 / 21 78 / 123 BMI 21.9 ± 2.3 22.2 ± 2.5 24.3 ± 2.3 22.4 ± 2.5 Score 31.7 ± 4.2 (70.3 ± 9.2%) 29.4 ± 4.8 (65.3 ± 10.7%) 27.2 ± 4.0 (60.4 ± 8.9%) 30.0 ± 4.7 (66.7 ± 10.4%) Score adjusted for age, sex and BMI 31.3 ± 4.4 (69.6 ± 9.9%) 29.4 ± 4.5 (65.4 ± 10.0%) 27.9 ± 3.7 (62.0 ± 8.2%) 30.0 ± 4.5 (66.7 ± 10.0%) Number of failures 10 (12.8%) 22 (22.2%) 10 (41.7%) 42 (20.9%) The figures given are number of subjects (percentage of study population) or means ± SD covering a wide range of information relating to internal medicine. A 46th item was added which invited the students to answer a number of questions on a voluntary basis, with no impact on their examination results, to provide data for a scientific study. They were assured that their answers would be dealt with confidentially. The students were asked to choose one of the following three options: I have never been told that I snore, I snore occasionally, or I frequently snore. In addition they were asked to reveal their age, sex, height, and weight. The multiple-choice tests were analyzed by an investigator blinded to the answers to the 46th item. The results of the test were expressed as a score representing the number of correctly answered items, the maximum score thus being 45. Students who achieved a score of 27 (60% correctly answered items) or more passed the examination, and students scoring 26 or less failed. Statistical Methods All numbers are expressed as arithmetic means ± standard deviation (SD). Group comparisons were performed using Fisher s exact test, the Mann-Whitney U-test, or the Kruskall-Wallis test where appropriate. Quantitative analysis of scores was performed using multiple linear regression analysis and analysis of variance (ANOVA). For the regression model, age, BMI, and snoring status were used as independent factors. The ANOVA model included sex and snoring status as between-subject factors, and age and BMI as covariates. In a second approach the examination scores were recoded into a dichotomic variable ( exam failed or exam passed ). This variable was tested using a logistic regression model with age, BMI, sex, and snoring status as covariables. To calculate the risk of failing the exam we adjusted the score for age, BMI, and sex. The statistical calculations were performed with the aid of SPSS (version 7.5). For differences between groups, a two-tailed p value of less than 0.05 was considered significant. RESULTS A total of 274 students took part in the final examination, of whom 201 volunteered to participate in our study and answered the additional questions. Sixty-nine students noted that they did not wish to participate in the study, and four students ignored the 46th item. The following results are therefore based on an analysis of 201 students. These students comprised 78 (39.9%) female and 123 (60.1%) male students with a mean age of 24.6±2.1 years (21-33 years). The mean body mass index (BMI) was 22.4±2.5 kg/m 2 (17.3-29.5) kg/m 2 ) (Table 1). There were no data available on the BMIs of the students who declined to participate, but there were no differences in their gender (39.2% female/60.8% male) and age distribution (24.9±3.1 years) compared with students who participated. The mean score was 30.0±4.7 (67.8%), with 159 students (79.1%) passing and 42 (20.9%) failing the examination (Table 1). Seventy-eight students (38.8%) claimed that they never snored, 99 (49.3%) admitted to snoring occasionally, and 24 students (11.9%) admitted to snoring frequently. The demographic data of these three groups and their examination results are shown in Table 1. The mean score of the nonsnorers was significantly higher than that of the occasional snorers, which in turn was significantly higher than that of the frequent snorers (Kruskal-Wallis-Test; p<0.0001). The scores were weakly correlated with age (r=-0.17; p=0.014) and BMI (r=-0.23; p=0.01), but were independent of sex (U-test; p=0.87). Logistic regression analysis showed an association between the risk of failing the examination and snoring ( occasionally or frequently ) (p=0.013), but not between such risk and age (p=0.60), BMI (p=0.16), or sex (p=0.27). Analysis of variance (ANOVA) revealed the score to be associated with BMI (p=0.015) and especially with snoring (p=0.002), but not with age (p=0.065) or sex (p=0.27). Stepwise, forward, multiple linear regression analysis was performed without the variable sex, since the examination score had been shown by univariate anal- 206

Figure 1. Examination scores by self-reported snoring status ysis and ANOVA to be independent of gender. Only snoring status and BMI remained in the final model (r-square = 0.13). Linear regression showed a strong contribution of snoring (B=-1.97; p<0.001) and BMI (B=-0.32; p=0.04) to the examination score. No correlation between age and score was demonstrable. Of the nonsnoring students, 12.8% failed the test, compared with 22.2% of the occasional snorers and 41.7% of the frequent snorers (p<0.01; Fig. 1). Taken together, students snoring occasionally or frequently achieved a mean score of 28.9±4.8, significantly lower than that achieved by nonsnoring students (31.7±4.16 ; p<0.001). Thirty-two of the 123 snoring students (26.0%) failed their exams, while only 10 of the 78 nonsnorers (12.8%) did so (p=0.032). After adjustment of the score for age, BMI, and sex, the relative risk of snorers to fail the exam was calculated to be 1.26 (95%-CI 1.01-1.57). DISCUSSION This study is based on snoring status self-reported by the students. The question therefore arises as to whether self-reporting is sufficiently reliable. 10 The use of selfreported snoring in epidemiologic studies is well established, and the questions on snoring used in this study are very similar to those used in most major epidemiologic studies on snoring. 6,11-13 Telakivi et al, 12 who used these questions in their classic epidemiologic study on the association between snoring and blood pressure, compared the self-reported snoring status with polysomnographic findings, and reported a sensitivity of 93%. 11 Some further validation of these snoring questions is provided, for instance, by the studies of Stradling et al 6 and Wiggins et al, 14 who demonstrated a reasonably good correlation between the results of self-reporting on snoring with the results of wives reports on the snoring status of their husbands. Cuda et al 15 demonstrated a fairly high test-retest reliability of such questions. Bliwise et al, 16 who studied a middle-aged population of 1409 patients using different questions to establish their snoring status, showed that self-reported snoring correlated well with objective findings from the sleep laboratory, even in persons customarily sleeping alone. Our students were not aware of the hypothesis underlying this study, and their knowledge of the pathophysiology of sleep-related breathing disorders was certainly not sufficient for them to develop similar hypotheses postulating an association between snoring status and examination results which might have biased their answers. It might be supposed that some students hesitated to admit to snoring because of the stigma commonly attached to this condition, although they were assured that their data would be dealt with confidentially, and that their answers would have no impact on their examination results. In our study, 11.9% of the students reported snoring frequently. This is consistent with the data reported by Billiard et al, 17 who studied a population of 58,162 French draftees between 17 and 22 years of age, 13.6% of whom self-reported snoring regularly. The students snoring status determined in this study would thus seem to be reasonably reliable. The major finding of the present study is that snoring students had significantly lower scores than their nonsnoring fellows, and that their risk of failing the examination was markedly increased. The scores of students snoring occasionally were significantly lower than those of nonsnoring students, and students snoring frequently had significantly lower scores than those snoring occasionally. This seems to indicate that the severity of snoring and the examination score is linked in a doseresponse manner. These observations tend to support our hypothesis that snoring may be associated with poorer examination results. We did not perform nocturnal polysomnographies, nor did we make any further assessment of daytime function; thus, we are not able to demonstrate conclusively the pathophysiologic mechanisms underlying the observed association between snoring and reduced examination scores. For the present, therefore, these mechanisms must continue to remain a matter of speculation. In principle, it might be speculated that snoring itself was the cause of cognitive impairment in snoring individuals. On the other hand it is possible that other, not immediately obvious, factors might underlie cognitive impair- 207

ment and might also cause or aggravate snoring. For example, increased use of alcohol among snoring students might cause or aggravate snoring and be responsible for the poorer examination results. Similar effects can be expected, for instance, from drug abuse or sleep deprivation. Such confounding factors might even fully account for the observed association. Since snoring is one of the leading symptoms of OSA, it might be assumed that the snoring-student groups contained more individuals with OSA, and that OSA-related cognitive impairment thus accounted for the poorer examination scores in these groups. But the prevalence of OSA among our students with a mean age of 24.6 years is unlikely to exceed 2% to 4%. 18 This means that not more than approximately 8 of the 201 students might be expected to have full-blown OSA, a figure too low to explain the observed distinct effect on the examination results in the two groups of snorers. Thus the question arises as to how snoring might have contributed to the poorer examination scores achieved by snoring students. It is well established that snoring is associated with daytime sleepiness, even in younger individuals. In their study of more than 58,000 French draftees, Billiard et al 17 showed a significant association between snoring and daytime somnolence. Janson et al 7 demonstrated that even in the absence of sleep apnea, snoring may be a cause of excessive daytime sleepiness and fatigue, and that these symptoms can be reversed by UPPP. Even in children, snoring may be associated with reduced vigilance as well as concentration and memory problems, and it has been demonstrated that such impairment of daytime performance can be reversed when snoring is eliminated (for instance, by adenotonsillectomy). 19-21 Guilleminault et al 4,22 demonstrated that in some individuals snoring may be associated with sleep fragmentation due to transient alpha EEG arousals resulting in daytime sleepiness. This upper airway resistance syndrome might have caused a reduction in vigilance, as well as concentration and memory problems in our snoring students, which in turn might have impaired their performance during the examination. More importantly, reduced vigilance, daytime sleepiness, and concentration problems might have impaired learning efficiency throughout the year, thus preventing optimal preparation for the examination. Furthermore, some published data appear to indicate that sleep deprivation or sleep fragmentation may impair the consolidation of newly learned information and the formation of a permanent memory trace during sleep. 23-25 Again, it must be emphasized that this is an epidemiologic study and, as in most such studies, we can only demonstrate statistical links between two factors (here snoring and exam-failing ) without being able to provide proof of a causal relationship or even identify any specific causal links. Further studies are needed to identify the mechanisms underlying the observed association between snoring status and examination results in our students. CONCLUSION The results of the present study demonstrate that snoring students are indeed more likely than nonsorers to have lower examination scores and even to fail their exams. Snoring and the risk of failing examinations seem to be linked in a dose-response manner. 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