Vigilance and attention in patients with Sleep Apnea Syndrome 31 State of research

Attention underlies performance of intellectual and everyday tasks. Depending on requirement character, novelty, intensity and level of activity, different components of attention are required.

The central nervous system activation (alertness) reflects the degree of general alertness and represents a kind of basic activation and general responsiveness. It is unconscious, and affected by the autonomic nervous system and the physiological diurnal state of the organism. Two variants of the central nervous system activation are described. The tonic activation is the stable level of attention over a long period of time. A disruption in tonic activation is manifested by a slowing of cognitive and motor processes. The tonic activation can be measured with the Multiple Sleep Latency Test MSLT (Carskadon & Dement 1977, Carskadon et al. 1986), the Maintenance of Wakefulness Test MWT (Poceta et al. 1992) or the

Pupillography (company Amtech, Weinheim, Wilhelm et al. 1998, 2001). A newer method to quantify the tonic activation is the Reading test (Erle et al. 2009).

The phasic activation is manifested in stimulus situations, in which short-term increases of the activation in the resting state are required. Limitations of the phasic activation can result in delayed reaction rapidities up to omitted reactions. The phasic activation may be tested for example in the kind of reaction time measurements, e.g. with the test battery of Zimmermann and Fimm (TAP / 1994), event-related EEG deductions or on the basis of the heartbeat rate or skin conductivity.

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Selective Attention

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Fig. 4. Proposed relationship between sleep quality and sleepiness-related restrictions during the day

Sustained attention is the ability to direct attention over a long period to one or more randomly occurring stimuli and to respond to minimal stimuli changes (Davies, Jones and Taylor 1984). Vigilance, which is a variant of sustained attention, requires long-term attention performance in minimally and irregularly occurring stimuli. As reliable indicators false (i.e. incorrectly or delayed) and omitted responses as well as reaction times can be measured as an expression of sustained attention and vigilance. Furthermore, particularly in the field of sleep medicine the Clock Test by Mackworth (1948), modified by Quatember and Maly (Sturm und Büssing, 1993), and the vigilance test "Carda" by Randerath et al. (1997, 2000) and Gerdesmeyer et al. (1997) and the sustained attention test "Carsim" by Büttner et al. (2000a/b, 2001) have been used to test the vigilance and sustained attention. Selective attention is also the ability to focus on specific relevant stimuli and to suppress simultaneously occurring irrelevant stimuli. The kind of attention function can be investigated by choice-reaction tasks or orienting responses, e.g. based on the subtest "Selective attention" to the TAP1.

Divided attention describes the capacity for serial and parallel information processing and the flexibility of selecting to switch back and forth at least two different sources of information (Sturm and Zimmermann 2000). Relevant stimuli can each occur in one or two sources of information to which the person have to respond as quickly as possible. Divided attention can be measured with dual-task activities (e.g. using the subtest "Divided attention" of the TAP). As with many sleep-related disorders, such as hypersomnias and dyssomnias, the victims suffer from, in addition to their nocturnal symptoms, increased daytime sleepiness and the tendency to fall asleep (Büttner et al. 2004b). These difficulties are in turn associated with attention-related deficits and limitations (including Gerdesmeyer et al. 1997, Müller et al. 1997, Randerath et al. 1997, 1998, Weeß 1997, Weeß et al. 1998a/b, Büttner et al. 2003b, 2004b).

1 TAP = German: Testbatterie zur Aufmerksamkeitsprüfung; English translation: Test battery for Attentional Performance

Consequence of this reduced performance include an increased risk of accidents at work and in traffic and thus a higher socio-medical risk (e.g. Bradley et al. 1985, Podszus et al. In 1986, He et al. 1988, Mitler et al. 1988, Lamphere et al. 1989, Roehrs et al. 1989, Bédard et al. 1991, Kribbs et al. 1993a/b, Gerdesmeyer et al. 1997, Randerath et al. 1997, 1998, Weeß 1997, Weeß et al. 1998a/b, Büttner et al. 2000a/b, Büttner 2001).

To explore the difficult relationship between sleep, daytime fatigue and physical and mental performance is based mainly on three conditions (Johnson 1982, Weeß 1997, Weeß et al. 1998a/b). Thus, the three mentioned above parameters will be affecting through a variety of other variables, for example by the motivation of the healthy subjects or patients, or the daily and weekly rhythm. Furthermore, daytime fatigue and performance as well as their underlying attention-related processes are complex constructs. This analysis will be complicated also by the lack of standard term uses in the medical and psychological literature (Johnson 1982, Weeß 1997, Weeß et al. 1998a/b).

There are, both in the medical and especially in sleep medicine research, a number of different research approaches and definitions regarding the attention and attention-driven processes (Rützel 1977, Rapp 1982, Brickenkamp & Karl 1986, Posner & Rafal, 1987, Säring 1988, Posner & Petersen, 1990, Posner 1995), which accentuate different characteristics and aspects of the daytime performance (James 1890, Head 1926, Mackworth JF 1956, Mackworth N 1958, Schmidtke 1965, Norman 1973, Bäumler 1974, Harnatt 1975, Rützel 1977, Brickenkamp & Karl 1986, Posner & Rafal, 1987, Säring 1988, Posner & Petersen, 1990, Rollet 1993, Schmöttke & Wiedl 1993).

Currently, in the sleep medicine literature, mainly the concept of Posner and Rafal (1987) will be used (Keller et al. 1993, Weeß 1997, Weeß et al. 1998a/b).

Also problematic are the very diverse conducted empirical analysis of attention and its components and the varying quality of the validation test procedures and instruments. Thus, inter alia vigilance covered by inappropriate (Stephan et al. 1991), too complex (Bédard et al. 1993) or timely too short (Bédard et al. 1991, 1993) test requirements (Weeß 1997, Weeß et al. 1998a/b).

To capture the tendency to fall asleep in Obstructive Sleep Apnea is conducted usually by the MSLT (Multiple Sleep Latency Test) (Poceta et al. 1992), because it correlated most strongly with the subjective state/mood of OSAS. However, through it the attention and vigilance will be detected only indirectly (Denzel et al. 1993).

For this purpose researched Denzel et al. (1993) for more suitable methods and examined in this context, two computerized neuropsychological test procedures, a vigilance and a attention test, in which the attention test was checked under three experimental conditions (visual, auditory, combined). In both the dual-task-task as well as the vigilance testing was found significant differences before and after nCPAP therapy (Denzel et al. 1993). Similar results - i.e. a significant improvement of vigilance under nCPAP - were found already by Kesper-Schwarzenberger et al. (1991), Cassel et al. (1991) and George et al. (1997; DADT)

As important criteria was found the standardization of experimental conditions (Horn et al. 1983, Denzel et al. 1993) and the design of the experimental setup (the author). Thus showed, inter alia, that an immediate auditory feedback about the correctness improved the occurred reactions improved the motivation of the patients, thereby obscuring the effects of sleep deprivation and their resulting poor performance (Wilkinson 1961, Steyvers & Gaillard 1993, Weeß 1997, Weeß et al. 1998a/b).

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