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Sleepiness
Sleep Medicine Reviews, Vol. 2, No. 1, pp l-2, 1998
SLEEP MEDICINE Ireviews/
GUEST EDITORIAL
Sleepiness Who’d be interested in sleep if it weren’t for its effects on wakefulness (or sleepiness, or performance capacity)? Yet, sleep itself attracts much more attention and effort than sleepiness. One reason may be the purported relation between sleep and mortality/ morbidity, although the connections aren’t that obvious. Another reason may be the amazing lack of sleepiness in patients such as insomniacs. A third reason may be the unclear situation with regard to what sleepiness is, and how it should be measured. On the other hand, the recent years have seen an increased interest in sleepiness, often related to the effects of sleep apnoea or work scheduling. The interest is apparently due to the realization that safety may be impaired under these conditions. Such links are well established today [1,2] and one might suspect that they will expand in importance in the future. Thus, our aging and increasingly sedentary society is very likely to result in an increased prevalence of sleep apnoea. Similarly, there is a steady rise in work around-the-clock and in automated (boring) work tasks, and the roads are increasingly crowded by long-haul transport trying to live up to just-in-time requirements. In addition, the tendency of concentrating the responsibility for large economical and human values on single, vulnerable, individuals is making the costs of minor lapses of attention prohibitive [3]. Thus, sleepiness prevention or alertness enhancement is becoming of paramount interest in many areas of society. So, we need information on alertness promoting work schedules, strategies for fatigue countermeasures, improved treatment of disorders of excessive sleepiness, ways of identifying individuals at risk, and, importantly, ways of measuring sleepiness and identifying critical levels of alertness. Against the background above, the paper by Johns in this issue, is very timely. It brings to attention the less than satisfactory state of knowledge with respect to the concept of sleepiness. Thus, for example, we use four to five different ways of measuring sleepiness physiologically and many more ways to measure it subjectively or behaviourally. The effect is too slow in its progression-results from different labs cannot be directly compared and integretion of knowledge is difficult. This diversity is characteristic for a young research area, but usually one particular method will gain more success than others, and will start to attract followers and turn into the gold standard. We have seen this development for the multiple sleep latency test (MSLT), and it has certainly become the dominating measure of sleepiness. But, as Johns argues, it is fraught with problems (including low correlations with other measures), as are the other physiological measurement methods, as well as those using subjective or behavioural approaches.
Correspondence to be addressed to: Torbjorn Akerstedt, IPM/Karolinska 17177 Stockholm, Sweden. email: [email protected] 1087-0792/98/010001+02$12.00/0
Institute, Box 230,
0 1998 W.B. Saunders Company Ltd
2
Guest Editorial
Incidentally, my own bias is that sleepiness is an attempt to turn the CNS over to sleep, and that it reflects an effort at resistance. Those who do not fight back will not experience any sleepiness. So, in my view, sleepiness should be measured (polysomnographically), with eyes open, in a boring, well-controlled situation. Under such conditions there will be a high correlation between EEG changes (increased alpha/ theta activity), subjective sleepiness and performance [4]. Interestingly, the Epworth Sleepiness Scale, developed by Johns, is, in a way, as much a “gold standard” in the subjective measurement of sleepiness as is the MSLT. And, it has its weaknesses in its hypothetical nature, and it may be difficult to apply to the third of the population that work irregular hours. And, of course, all questionnaires are subjected to easy simulation or dissimulation, making them invalid for identifying individuals at risk, at least if there is any advantage in being at risk or not at risk. Johns also touches upon the issue of awareness of one’s own sleepiness. This is a very important point, since one would normally have to rely on this ability for safe behaviour and also because the legal systems of many countries assumes that the driver is in fact able to estimate his/her level of sleepiness. As yet, however, there has been very little research into this area. In his review, Johns brings up the very important need for rethinking sleepiness, emphasizing contextual factors. Obviously, whatever the background of circadian phase or sleep loss that may be responsible for sleepiness, much of it may be masked by the demands of the particular situation-a measure of sleepiness is pointless without the particulars of the situation in which it was obtained. This also has repercussions on sleepiness measurement-one may have to use a battery of tests to get reasonably useful results. This contextual thinking is further developed into a four-process model of sleepiness, that builds on the assumption of a wake drive and a sleep drive and two subdivisions of each. While the reader may not immediately accept all aspects of this theoretical model as the final truth, he/she may use it, as it is intended, to start a bit of rethinking, which is long overdue. TorbjGrn Akerstedt Stockholm
References 1 Dinges DF. An overview of sleepiness and accidents. J Sleep Res 1995; 4 (Suppl. 2): 4-14. 2 Akerstedt T. Work hours, sleepiness and the underlying mechanism. 1 Sleep Res 1995; 4 (Suppl. 2): 15-22. 3 Leger D. The cost of sleep-related accidents: A report for the National Commission on Sleep Disorders Research. Sleep 1994; 17: 84-93. 4 Akerstedt T, Gillberg M. Subjective and objective sleepiness in the active individual. Inf J Neurosci 1990; 52: 29-37.
SLEEP MEDICINE Ireviews/
GUEST EDITORIAL
Sleepiness Who’d be interested in sleep if it weren’t for its effects on wakefulness (or sleepiness, or performance capacity)? Yet, sleep itself attracts much more attention and effort than sleepiness. One reason may be the purported relation between sleep and mortality/ morbidity, although the connections aren’t that obvious. Another reason may be the amazing lack of sleepiness in patients such as insomniacs. A third reason may be the unclear situation with regard to what sleepiness is, and how it should be measured. On the other hand, the recent years have seen an increased interest in sleepiness, often related to the effects of sleep apnoea or work scheduling. The interest is apparently due to the realization that safety may be impaired under these conditions. Such links are well established today [1,2] and one might suspect that they will expand in importance in the future. Thus, our aging and increasingly sedentary society is very likely to result in an increased prevalence of sleep apnoea. Similarly, there is a steady rise in work around-the-clock and in automated (boring) work tasks, and the roads are increasingly crowded by long-haul transport trying to live up to just-in-time requirements. In addition, the tendency of concentrating the responsibility for large economical and human values on single, vulnerable, individuals is making the costs of minor lapses of attention prohibitive [3]. Thus, sleepiness prevention or alertness enhancement is becoming of paramount interest in many areas of society. So, we need information on alertness promoting work schedules, strategies for fatigue countermeasures, improved treatment of disorders of excessive sleepiness, ways of identifying individuals at risk, and, importantly, ways of measuring sleepiness and identifying critical levels of alertness. Against the background above, the paper by Johns in this issue, is very timely. It brings to attention the less than satisfactory state of knowledge with respect to the concept of sleepiness. Thus, for example, we use four to five different ways of measuring sleepiness physiologically and many more ways to measure it subjectively or behaviourally. The effect is too slow in its progression-results from different labs cannot be directly compared and integretion of knowledge is difficult. This diversity is characteristic for a young research area, but usually one particular method will gain more success than others, and will start to attract followers and turn into the gold standard. We have seen this development for the multiple sleep latency test (MSLT), and it has certainly become the dominating measure of sleepiness. But, as Johns argues, it is fraught with problems (including low correlations with other measures), as are the other physiological measurement methods, as well as those using subjective or behavioural approaches.
Correspondence to be addressed to: Torbjorn Akerstedt, IPM/Karolinska 17177 Stockholm, Sweden. email: [email protected] 1087-0792/98/010001+02$12.00/0
Institute, Box 230,
0 1998 W.B. Saunders Company Ltd
2
Guest Editorial
Incidentally, my own bias is that sleepiness is an attempt to turn the CNS over to sleep, and that it reflects an effort at resistance. Those who do not fight back will not experience any sleepiness. So, in my view, sleepiness should be measured (polysomnographically), with eyes open, in a boring, well-controlled situation. Under such conditions there will be a high correlation between EEG changes (increased alpha/ theta activity), subjective sleepiness and performance [4]. Interestingly, the Epworth Sleepiness Scale, developed by Johns, is, in a way, as much a “gold standard” in the subjective measurement of sleepiness as is the MSLT. And, it has its weaknesses in its hypothetical nature, and it may be difficult to apply to the third of the population that work irregular hours. And, of course, all questionnaires are subjected to easy simulation or dissimulation, making them invalid for identifying individuals at risk, at least if there is any advantage in being at risk or not at risk. Johns also touches upon the issue of awareness of one’s own sleepiness. This is a very important point, since one would normally have to rely on this ability for safe behaviour and also because the legal systems of many countries assumes that the driver is in fact able to estimate his/her level of sleepiness. As yet, however, there has been very little research into this area. In his review, Johns brings up the very important need for rethinking sleepiness, emphasizing contextual factors. Obviously, whatever the background of circadian phase or sleep loss that may be responsible for sleepiness, much of it may be masked by the demands of the particular situation-a measure of sleepiness is pointless without the particulars of the situation in which it was obtained. This also has repercussions on sleepiness measurement-one may have to use a battery of tests to get reasonably useful results. This contextual thinking is further developed into a four-process model of sleepiness, that builds on the assumption of a wake drive and a sleep drive and two subdivisions of each. While the reader may not immediately accept all aspects of this theoretical model as the final truth, he/she may use it, as it is intended, to start a bit of rethinking, which is long overdue. TorbjGrn Akerstedt Stockholm
References 1 Dinges DF. An overview of sleepiness and accidents. J Sleep Res 1995; 4 (Suppl. 2): 4-14. 2 Akerstedt T. Work hours, sleepiness and the underlying mechanism. 1 Sleep Res 1995; 4 (Suppl. 2): 15-22. 3 Leger D. The cost of sleep-related accidents: A report for the National Commission on Sleep Disorders Research. Sleep 1994; 17: 84-93. 4 Akerstedt T, Gillberg M. Subjective and objective sleepiness in the active individual. Inf J Neurosci 1990; 52: 29-37.