**2.1 State of research**

#### **2.1.1 Sleep Apnea Syndromes and neuropsychological disorders**

In addition to nocturnal Sleep Apnea Syndrome symptoms there are a lot of daytime symptoms. It is assumed that the reduced sleep quality, arising out of deep sleep or REM-

Central Europe (0.006 %) and the USA (0.06-0.1 %) are located in the middle. 3. *Sleep Apnea Syndromes* (SAS) are common disorders, which are characterized by repeated oropharyngeal occlusions occurring during the sleep time (sleep-related breathing problems, intermittent hypoxemia) and may be associated with suppression of SWS sleep (disrupted and fragmentized sleep architecture). Due to intermittent hypoxemia and disrupted sleep architecture, SAS leads to impaired daytime functioning in various (neuro)psychological and affective domains and has been associated with increased morbidity and mortality, principally from adipositas,

cardiovascular and neurological diseases.

physical pain or discomfort.

2. attention deficit, 3. memory dysfunction, 4. executive dysfunction, 5. driving difficulties,

**2.1 State of research** 

1. excessive daytime sleepiness

6. motivation and emotional deficits,

professional and in the ability to drive motor vehicles.

7. psychiatric consequences (e.g. depression, anxiety) and 8. lack of ability to recognize the effects of behaviour.

The exact prevalence of the general population is unknown. Great differences exist in its appearance frequency. So the frequency of Japan is 0.16 % and of Israel 0.0002 %.

The prevalence of moderate SAS (AHI >15/h) is 9% in male and 4% in female, respectively. 25-30 % Sleep Apnea Syndromes were described at patients with hypertension and 35-45 % with patients with on the left heart-failure. The SAS frequency increases with an advancing age and reaches their peak at the age from 50 to 70 years. 80% of the patients suffer under excessive daytime sleepiness and a reduced sustained attention. Resulting from this it comes to performance losses both

*Fragmentation of sleep* and *increased frequency of arousals* occur in association with this three disorders and a number of other sleep disorders as well as with medical disorders involving

In this chapter, the author will describe neuropsychological dysfunctions/courses and

There are wide varieties of difficulties in assessment, treatment and rehabilitation for cognitive

In our studies we used neuropsychological and neuropsychiatric methods in different patient groups in a sleep laboratory. Over the past five years we have been testing and treating more than 2000 patients with different sleep disorders and more than 5000 neurological patients. During admission to the clinic, all patients were selected according to their clinical diagnosis (ICD-10) and were examined neurologically, (neuro)psychologically, psychiatrically and medically. The test persons must not suffer from any severe psychiatric disorders. The study

impairment, psychiatric disorders and behavioural disability after sleep disorders.

was carried out involving randomly selected patients with sleep disorders.

**2.1.1 Sleep Apnea Syndromes and neuropsychological disorders** 

**2. Excessive daytime sleepiness in patients with Sleep Apnea Syndrome** 

In addition to nocturnal Sleep Apnea Syndrome symptoms there are a lot of daytime symptoms. It is assumed that the reduced sleep quality, arising out of deep sleep or REM-

neuropsychiatric syndromes due sleep disorders which were characterized by

suppression, resulting in increased nocturnal arousal responses, or constantly occurring waking or a reduced relaxation function (Weeß et al. 1998a/b) and cognitive damage caused by intermittent hypoxia (Montplaisir et al. 1992). As the main symptom is excessive daytime sleepiness (EDS) is considered.

It is also assumed that the OSAS accompanying Insomnia and sleepiness influence cognitive functions (Jennum et al. 1993). As reported by Schwarzenberger et al. (1987) that patients with EDS have complaints and problems in situations of physical rest and during prolonged monotonous concentration tasks. A study by Kales (1985) showed that 76% of OSAS patients have cognitive deficits in the areas of thinking, learning ability, memory, communication and the ability to learn new information. Naëgelé et al. (1995) were able to establish in Sleep Apnea Syndrome patients that they were reduced at executive functions when these tasks involve the acquisition of information to memory processing. Another study by Cassel et al. (1995) showed that Sleep Apnea Syndrome patients have a reduced non-verbal performance and processing speed. Regarding the central nervous system activation (*alertness*), selective attention and sustained attention in Sleep Apnea Syndrome patients Kotterba et al. (1998) found, that they were impaired, and that they have a reduced vigilance (Barbè et al. 1998).

The cause of cognitive and neuropsychological deficits in the EDS itself, the sleep fragmentation and arousals and nocturnal hypoxemia are discussed (Findley et al. 1986, Greenberg et al. 1987, Guilleminault et al. 1988, Colt et al, 1991, Bédard et al. 1991, Roehrs et al. 1995).

### **2.1.2 Causes of neuropsychological deficits (Büttner 2001, 2009)**

Two concepts play a central role, first, the hypoxia and the other the disturbed sleep architecture in the causes of the neuropsychological and/or cognitive deficits in Sleep Apnea Syndrome patients.

Both factors appear usually occur together, so that it is hardly possible to separate the two. Several studies confirm the link between *nocturnal oxygen desaturation* and neuropsychological deficits. Greenberg et al. (1987) showed, for example, that the nocturnal hypoxia is the cause of the neuropsychological deficits and daytime sleepiness. In another study conducted by Findley et al. (1986) showed that there is a correlation between hypoxia during sleep and wakefulness with the degree of cognitive impairment, but not between sleep fragmentation and the cognitive functions. In a study of Kotterba et al. (1998), various neuropsychological parameters correlate with the degree of hypoxia, but not with the arousal index and AHI. Montplaisir et al. (1992) describe the nocturnal hypoxia as the best predictor for both daytime alertness as well as daytime sleepiness.

For other investigators, the cause of the neuropsychological deficits such as those of daytime sleepiness exist in the *disruption of sleep patterns* or *sleep fragmentation*, accompanied by a reduction in the proportion of REM and slow wave sleep. According to Bonnet et al. (1985) healthy persons' sleep fragmentation leads to neuropsychological impairment. Other researchers such as Telakivi et al. (1988) and Guilleminault et al. (1988) find that sleep fragmentation has an important impact on neuropsychological deficits. This allowed Guilleminault et al. (1988) to conclude in a study that the sleep fragmentation would be the best predictor of the occurrence of daytime fatigue is, and that there is no relationship between daytime sleepiness and respiratory parameters such as RDI or oxygen desaturations. This could confirm also by Colt et al. (1991) in a study. Nocturnal hypoxias were induced during a night under nCPAP therapy and, no effect on daytime sleepiness

The Effects of Sleep-Related Breathing Disorders on Waking Performance 121

George et al. (1987) took up this assumption and investigated the accident probability of 27 suspected OSAS patients. In 93% of patients were entered injuries in the accident register of *Motor Vehicle Branch* of Manitoba (Canada), but only 54% of the control group participants. Unfortunately, in seven patients, the polysomnographic confirmation of the diagnosis and the information on the period of specified accidents are missing (George et al. 1987, Cassel et al. 1991a/b, Weeß 1997, Weeß et al. 1998 a/b). Findley et al. (1988b) found that 29 OSAS patients (AHI> 5) a three-fold increased probability of accidents compared to all license holders of Virginia (USA), and even a seven-fold increased compared to a control group (n = 35). However, Findley et al. didn't give the information whether the OSAS diagnosis was already known in the survey (Findley et al. 1988b, Cassel et al. 1991a/b, Weeß 1997, Weeß et al. 1998 a/b). Later studies and studies by Cassel et al. (1991a/b, 1996), the ATS (1994) and Krieger et al. (1997) confirmed these findings. Thus, patients with Sleep Apnea Syndrome seem increasingly to suffer from severe fatigue and falling asleep while driving (see also George et al. 1987, 1996b, Findley et al. 1988b). With increasing impairment of those affected persons by the symptoms of Obstructive Sleep Apnea are also accumulated self-inflicted, sustained attention-related injuries (Cassel et al. 1991a/b, 1996, ATS 1994, Kruger et al. 1997). According to Young et al. (1997), the relative risk of an accident within five years, causing increased for men with sleep-related breathing disorders by factor of 3. Several studies show a minimum of a 2-fold to 3-fold, up to 7-fold increased risk of accidents (George et al. 1987, 1999, Findley et al. 1988, 2000, Horne & Reyner 1995, Wu & Yan-Go 1996, Young et al. 1997, Barbé et al. 1998, Terán-Santos et al. 1999, Horstmann et al. 2000, LLoberes et al. 2000, Sharma & Sharma 2008). For example, George et al. (1999) investigated the relationship between accident rates and the number of traffic offenses in OSAS patients, with the result that the frequency of accidents and the number of traffic violations during a period of five

A special group in this context represent professional drivers, bus and truck drivers, because they spend a lot of professional time on the road and also with some larger vehicles usually dangerous cargo or other people, so that probably occur in an accident caused considerable damage and injury. These people have to suffer through their work and the associated lifestyle at increased risk of interference with OSAS. Thus for example truck drivers have a very irregular sleep-wake rhythm (Stradling 1989, Stoohs et al. 1995). In 1994 Stoohs et al. researched the influence of sleep-disordered breathing (SDB) and obesity among commercial drivers of large trucks. Drivers with SDB cause twice as many accidents per 1000 driven miles, than that without SDB, and obesity, the accident rate still increased. Accidents caused by overtiredness-related un-roadworthy and related offenses are likely among professional

drivers having accepted a level that is comparable to the drunken crime (Meyer 1990).

The diagnosis of central nervous system stimulation as well as the diagnosis of daytime sleepiness has therefore central importance in the sleep medical field. Thus, the daytime sleepiness is on the one hand understood as an important symptom of non-restorative sleep, but on the other hand can also be closed due to their expression on the severity of this sleep disorder. Ultimately, their diagnostic evaluation is also an important criterion for therapy

The sleepiness-related medical history or diagnosis is used to assess the clinical and social impact of daytime sleepiness. In particular, the severity and the social and medical risk will be assessed. It can also be used as parameters of the differential diagnosis of fatigue. This anamnesis can be supported by the use of orienting processes or by the method of screening.

years was significantly higher compared to a control group.

evaluation.

could be found. So it was adopted by this study that the day's fatigue does not caused by a decrease of intermittent nocturnal oxygen saturation, but rather by the sleep fragmentation.

Bédard et al. (1991) suggested it was an *interaction of both factors*; both sleep fragmentation and nocturnal hypoxia were of great importance in the emergence of decreased vigilance or neuropsychological deficits, with the hypoxia seemingly playing a larger role in severe cases. In addition, the *daytime sleepiness* itself is responsible for the cognitive deficits (Roehrs et al. 1995).

Other assumptions are that neither the disturbed sleep architecture nor nocturnal hypoxias play a role for the neuropsychological deficits in OSAS. Thus Ingram et al. (1994) showed that there are no differences in vigilance between OSAS patients and normal subjects. The reduction of vigilance could be determined by age. Research of Kotterba et al. (1998) and Büttner et al. (2004b) were able to contradict these suggestions, as they found differences of vigilance between OSAS patients and healthy individuals, but no age differences. Severity of OSAS, as measured by the AHI or RDI, or nCPAP compliance may also play a role (Cassel et al. 1989, Engleman et al. 1993, John (et al.) 1991, 1992, 1993).

#### **2.1.3 Daytime sleepiness, fall asleep and driving performance (Büttner 2001, 2009)**

The ability to drive safely and without accident needs sustained attention and alertness (Guilleminault et al. 1978, Bradley et al. 1985, Podszus et al. 1986, Findley et al. 1988a/b, 1989b, 1990, 1991, 1995, He et al. 1988, Mitler et al. 1988, Lamphere et al. 1989, Roehrs et al. 1989, Bédard et al. 1991, Cassel et al. 1991a/b, 1993, 1996, Kribbs et al. 1993a/b, ATS 1994, Martin et al. 1996, Gerdesmeyer et al. 1997, Krieger et al. 1997, Randerath et al. 1997, 1998, Weeß 1997, Weeß et al. 1998a/b).

Increased daytime sleepiness is one of the most common causes of road accidents. Driver fatigue is the cause in up to 25% of highway accidents (Langlois et al. 1985, Pack et al. 1994, Horne et al. 1995). A study of 67 671 non-alcohol-related car accidents in France in the years 1994-1998 showed that the risk of accidents involving fatalities or serious injuries in fatiguerelated accidents is increased as compared to non-fatigue-related accidents significantly (Philip 2000). An analysis of fatal accidents on highways in Bavaria in 1991 showed that 49 of 204 accidents (24%) caused by falling asleep at the wheel (Langwieder et al. 1994). Obstructive Sleep Apnea Syndrome is again one of the most common causes of daytime sleepiness is increased (American Thoracic Society 1994, McNicholas, 1999).

Reliable data on sleepiness-related causes of accidents due to the German data protection regulations is not available and caused on it the published data's are very inconsistent: According to Seko et al. (1986) 45% of all fatal road accidents were caused by falling asleep at the wheel or a micro-sleep, but declared by the Federal Statistical Office at Wiesbaden (1988) only 0.5% of all traffic accidents (Seko et al. 1986, Federal Statistical Office Wiesbaden 1988, Cassel et al. 1993). A study of Zulley et al. showed that 38% in all traffic accidents on Bavarian highways were due vigilance reduction and 24% of all serious accidents (Zulley et al. 1995).

The sleep-related vigilance and sustained attention losses were intensified, especially exacerbated by the effects of biological rhythms (Hildebrandt et al. 1974, Hildebrandt 1976, Mitler 1991, Cassel et al. 1991c, 1993, Zulley 1995).

As early as 1955 Prokop and Prokop discussed regarding traffic safety and the importance of fatigue and falling asleep, but without to discuss the sleep-related aspects or causes (Prokop & Prokop 1955, Cassel et al. 1993). At first in 1978 Guilleminault et al. showed a possible increased risk for patients with sleep-disordered breathing (Guilleminault et al. 1978, Cassel et al. 1991a/b).

could be found. So it was adopted by this study that the day's fatigue does not caused by a decrease of intermittent nocturnal oxygen saturation, but rather by the sleep fragmentation. Bédard et al. (1991) suggested it was an *interaction of both factors*; both sleep fragmentation and nocturnal hypoxia were of great importance in the emergence of decreased vigilance or neuropsychological deficits, with the hypoxia seemingly playing a larger role in severe cases. In addition, the *daytime sleepiness* itself is responsible for the cognitive deficits (Roehrs

Other assumptions are that neither the disturbed sleep architecture nor nocturnal hypoxias play a role for the neuropsychological deficits in OSAS. Thus Ingram et al. (1994) showed that there are no differences in vigilance between OSAS patients and normal subjects. The reduction of vigilance could be determined by age. Research of Kotterba et al. (1998) and Büttner et al. (2004b) were able to contradict these suggestions, as they found differences of vigilance between OSAS patients and healthy individuals, but no age differences. Severity of OSAS, as measured by the AHI or RDI, or nCPAP compliance may also play a role (Cassel et

**2.1.3 Daytime sleepiness, fall asleep and driving performance (Büttner 2001, 2009)**  The ability to drive safely and without accident needs sustained attention and alertness (Guilleminault et al. 1978, Bradley et al. 1985, Podszus et al. 1986, Findley et al. 1988a/b, 1989b, 1990, 1991, 1995, He et al. 1988, Mitler et al. 1988, Lamphere et al. 1989, Roehrs et al. 1989, Bédard et al. 1991, Cassel et al. 1991a/b, 1993, 1996, Kribbs et al. 1993a/b, ATS 1994, Martin et al. 1996, Gerdesmeyer et al. 1997, Krieger et al. 1997, Randerath et al. 1997, 1998,

Increased daytime sleepiness is one of the most common causes of road accidents. Driver fatigue is the cause in up to 25% of highway accidents (Langlois et al. 1985, Pack et al. 1994, Horne et al. 1995). A study of 67 671 non-alcohol-related car accidents in France in the years 1994-1998 showed that the risk of accidents involving fatalities or serious injuries in fatiguerelated accidents is increased as compared to non-fatigue-related accidents significantly (Philip 2000). An analysis of fatal accidents on highways in Bavaria in 1991 showed that 49 of 204 accidents (24%) caused by falling asleep at the wheel (Langwieder et al. 1994). Obstructive Sleep Apnea Syndrome is again one of the most common causes of daytime

Reliable data on sleepiness-related causes of accidents due to the German data protection regulations is not available and caused on it the published data's are very inconsistent: According to Seko et al. (1986) 45% of all fatal road accidents were caused by falling asleep at the wheel or a micro-sleep, but declared by the Federal Statistical Office at Wiesbaden (1988) only 0.5% of all traffic accidents (Seko et al. 1986, Federal Statistical Office Wiesbaden 1988, Cassel et al. 1993). A study of Zulley et al. showed that 38% in all traffic accidents on Bavarian highways were due vigilance reduction and 24% of all serious accidents (Zulley et al. 1995). The sleep-related vigilance and sustained attention losses were intensified, especially exacerbated by the effects of biological rhythms (Hildebrandt et al. 1974, Hildebrandt 1976,

As early as 1955 Prokop and Prokop discussed regarding traffic safety and the importance of fatigue and falling asleep, but without to discuss the sleep-related aspects or causes (Prokop & Prokop 1955, Cassel et al. 1993). At first in 1978 Guilleminault et al. showed a possible increased risk for patients with sleep-disordered breathing (Guilleminault et al.

sleepiness is increased (American Thoracic Society 1994, McNicholas, 1999).

Mitler 1991, Cassel et al. 1991c, 1993, Zulley 1995).

1978, Cassel et al. 1991a/b).

al. 1989, Engleman et al. 1993, John (et al.) 1991, 1992, 1993).

Weeß 1997, Weeß et al. 1998a/b).

et al. 1995).

George et al. (1987) took up this assumption and investigated the accident probability of 27 suspected OSAS patients. In 93% of patients were entered injuries in the accident register of *Motor Vehicle Branch* of Manitoba (Canada), but only 54% of the control group participants. Unfortunately, in seven patients, the polysomnographic confirmation of the diagnosis and the information on the period of specified accidents are missing (George et al. 1987, Cassel et al. 1991a/b, Weeß 1997, Weeß et al. 1998 a/b). Findley et al. (1988b) found that 29 OSAS patients (AHI> 5) a three-fold increased probability of accidents compared to all license holders of Virginia (USA), and even a seven-fold increased compared to a control group (n = 35). However, Findley et al. didn't give the information whether the OSAS diagnosis was already known in the survey (Findley et al. 1988b, Cassel et al. 1991a/b, Weeß 1997, Weeß et al. 1998 a/b). Later studies and studies by Cassel et al. (1991a/b, 1996), the ATS (1994) and Krieger et al. (1997) confirmed these findings. Thus, patients with Sleep Apnea Syndrome seem increasingly to suffer from severe fatigue and falling asleep while driving (see also George et al. 1987, 1996b, Findley et al. 1988b). With increasing impairment of those affected persons by the symptoms of Obstructive Sleep Apnea are also accumulated self-inflicted, sustained attention-related injuries (Cassel et al. 1991a/b, 1996, ATS 1994, Kruger et al. 1997).

According to Young et al. (1997), the relative risk of an accident within five years, causing increased for men with sleep-related breathing disorders by factor of 3. Several studies show a minimum of a 2-fold to 3-fold, up to 7-fold increased risk of accidents (George et al. 1987, 1999, Findley et al. 1988, 2000, Horne & Reyner 1995, Wu & Yan-Go 1996, Young et al. 1997, Barbé et al. 1998, Terán-Santos et al. 1999, Horstmann et al. 2000, LLoberes et al. 2000, Sharma & Sharma 2008). For example, George et al. (1999) investigated the relationship between accident rates and the number of traffic offenses in OSAS patients, with the result that the frequency of accidents and the number of traffic violations during a period of five years was significantly higher compared to a control group.

A special group in this context represent professional drivers, bus and truck drivers, because they spend a lot of professional time on the road and also with some larger vehicles usually dangerous cargo or other people, so that probably occur in an accident caused considerable damage and injury. These people have to suffer through their work and the associated lifestyle at increased risk of interference with OSAS. Thus for example truck drivers have a very irregular sleep-wake rhythm (Stradling 1989, Stoohs et al. 1995). In 1994 Stoohs et al. researched the influence of sleep-disordered breathing (SDB) and obesity among commercial drivers of large trucks. Drivers with SDB cause twice as many accidents per 1000 driven miles, than that without SDB, and obesity, the accident rate still increased. Accidents caused by overtiredness-related un-roadworthy and related offenses are likely among professional drivers having accepted a level that is comparable to the drunken crime (Meyer 1990).

The diagnosis of central nervous system stimulation as well as the diagnosis of daytime sleepiness has therefore central importance in the sleep medical field. Thus, the daytime sleepiness is on the one hand understood as an important symptom of non-restorative sleep, but on the other hand can also be closed due to their expression on the severity of this sleep disorder. Ultimately, their diagnostic evaluation is also an important criterion for therapy evaluation.

The sleepiness-related medical history or diagnosis is used to assess the clinical and social impact of daytime sleepiness. In particular, the severity and the social and medical risk will be assessed. It can also be used as parameters of the differential diagnosis of fatigue. This anamnesis can be supported by the use of orienting processes or by the method of screening.

The Effects of Sleep-Related Breathing Disorders on Waking Performance 123

The Stanford Sleepiness Scale (SSS) of Hoddes et al. (1973) is a scale on which momentary alertness can be assessed on a grading of 1 to 7 and thus serves to assess the circadian variations in daytime sleepiness. The scale describes gradual gradations of awareness; it varies between very alert and drowsy conditions. The alertness descriptions are also described, each with typical sensations (e.g. *some slack*, *slows*, *woozy*) characterized. Studies on the sensitivity of the scale showed that ratings in 15-minute intervals represent discrete changes in the degree of alertness. According to the response ratings point values are

The Multiple Sleep Latency Test by Carskadon and Dement (1977) recorded the sleep latency lying down and is recommended for the investigation of daytime sleepiness in OSAS patients in the ICSD-2. The MSLT is based on the assumption that a strong

For a long time the MSLT has been considered a gold standard for the investigation of daytime sleepiness (Carskadon et al. 1986). The MSLT (as well as the Maintenance of Wakefulness Test (MWT)) is often used to determine the alertness with expert's investigations, e.g. to assess the driving ability (Poceta et al. 1992). Five times a day electrophysiological recordings (C3/A2, C4/A1, EOG, EMG) are performed in 2-hour intervals. The first time of measurement should be from 1.5 to 3 hours after waking. The patient lies in a darkened room and is asked to fall asleep. During the test procedure, the

A pathological fall asleep exists, when the medium sleep latency is < 5 minutes (Richardson et al. 1982). The gray area is between 5-10 minutes and > 10-20 minutes is a normal finding. But are also divergent standard values of 5-8 minutes; thereby establishing of normal values is equivalent to a kind of "rule of thumb" (Guilleminault et al. 1994, van den Hoed et al. 1981, Johns 2000). Although the MSLT perform and should be evaluated strictly according to objective criteria and standardized, it seems to have low implementation objectivity, because the results of individual tests vary greatly (Danker-Hopfe et al. 2006). As other reasons for the inconsistent individual test results Thorpy (1992) describes the different day times and measuring times and not objectified sleep deprivation and sedative or stimulating effects of drugs. In spite of these influences, however satisfactory test-retest reliabilities of rtt = .65 to .97 (van den Hoed et al. 1981, Zwyghuizen-Doorenbos et al. 1998) have been found. Another problem of MSLT is the limited external generalization of daytime sleepiness in everyday situations (Johns 1994). The assumption that the MSLT describe daytime sleepiness - as reflection of everyday life - Johns (2000) keeps being wrong. As a predictor of MSLT is therefore not own, regardless how strict standards and criteria were met. In considering of the relationship between ESS and MSLT are unsatisfactory correlation of r = .27 (p <.001) or on those that are not significant (Mitler et al 1998.). Reasons for the inconsistent correlations are different: Either there are satisfactory (significant) correlations when all patients fell asleep in all MSLT times or when the patients rarely slept or not fell

The Maintenance of Wakefulness Test of Poceta et al. (1992) examines the ability to stay awake in a sleep-inducing situation. The patient sits in a darkened room on a comfortable

**2.3 Stanford Sleepiness Scale (SSS)** 

**2.4 Multiple Sleep Latency Test (MSLT)** 

patient is monitored with a video recording.

asleep (Chua et al. 1998).

**2.5 Maintenance of Wakefulness Test (MWT)** 

assigned for each time interval, which are then summated.

physiological sleepiness can reduce the sleep latency (Arand et al. 2005).

It is used especially in the assessment of type and of frequency about the tendency to fall asleep, micro-sleep episodes and monotony intolerance at work (especially in monitoring activities) and to capture the possibility of active participation in road traffic and other social situations (Walsleben 1992, Weeß 2011).

The *Epworth Sleepiness Scale* (ESS), the *Stanford Sleepiness Scale* (SSS), the *Multiple Sleep Latency Test* (MSLT) and the *Maintenance Wakefulness Test* (MWT) are among the methods that are most widely used for the investigation of daytime sleepiness in sleep disorders. The ESS reflects the global and subjective severity of daytime sleepiness in eight different situations and activities of daily living. The SSS is, however, to capture subjective circadian fluctuations of daytime sleepiness. To objective capture electrophysiological and standardized tests are often, such as the MSLT and the MWT used to determine the degree of alertness on the basis of tonic activation.

If, on the basis of questionnaire data and medical history of sleeping on the basis of suspicion that a pathological daytime sleepiness (Table 1) exists, then objective analysis methods can be used to measure sleepiness-related functions.


Table 1. Sleepiness functions

#### **2.2 Epworth Sleepiness Scale (ESS)**

The Epworth Sleepiness Scale (ESS) of Johns (1991) is very often used as a screening method for detecting the global daytime sleepiness and fall asleep in sleep disorders, especially used in hypersomnias. It is asked retrospectively, how high is the probability to fall asleep in eight everyday situations. The scale has a 4-step response format, in which values between 0 and 3 (0 = never to 3 = strongly agree) must be marked and results are added up a total maximum value of 24.

Following Johns (1991, 1992, Johns & Hocking 1997) a cut-off value ≥ 11 indicates a pathological daytime sleepiness. Standardization studies for the German-speaking countries were presented by Büttner et al. (2004c) and Sauter and colleagues (2007). The study found that 85% of healthy persons achieved a total value < 10, which corresponds to the calculated cut-off values in other studies (Johns 1991, Johns & Hocking 1997). The test-retest reliability of the ESS was calculated by Johns (1994) and based on a survey after five months in 87 healthy medical students. It was rtt = .82 (p <.001), even the quality of internal consistency was confirmed (Cronbach's alpha = .88 (p <.001).

The ESS has in spite of it being subjective and a global assessment of daytime sleepiness (Johns 2000) has a very good validity. At a cut-off value > 10 it shows a high sensitivity of 93.5% and - high specificity 98.4%. The ESS is thus a highly reliable and valid procedure. The short implementation time and simple evaluation makes it very economical and cost effective. In addition, it can also be used for measuring the effectiveness of nCPAP therapy.

Nevertheless the ESS does not lend itself to capture gradually different levels of sleepiness (Sangal et al. 1997b) and that four of the eight items have very low selectivity (Rühle et al. 2005).
