24-hour assessment of performance on a palmtop computer: validating a self-constructed test battery

Vigilanz und Fahreignung

Störungen der Vigilanz können die Fahreignung relevant beeinträchtigen. Sie können vielfältige Ursachen haben und stellen eine der Hauptursachen für Verkehrsunfälle dar. Dieser Artikel benennt die rechtlichen Grundlagen für die Beurteilung der Fahreignung, stellt Testverfahren zur Einschätzung von Vigilanzstörungen vor und erläutert ein praktisches Vorgehen unter Berücksichtigung der gesetzlichen Bestimmungen.

Circadian rhythmicity of body temperature and metabolism

This article reviews the literature on the circadian rhythms of body temperature and whole-organism metabolism. The two rhythms are first described separately, each description preceded by a review of research methods. Both rhythms are generated endogenously but can be affected by exogenous factors. The relationship between the two rhythms is discussed next. In endothermic animals, modulation of metabolic activity can affect body temperature, but the rhythm of body temperature is not a mere side effect of the rhythm of metabolic thermogenesis associated with general activity. The circadian system modulates metabolic heat production to generate the body temperature rhythm, which challenges homeothermy but does not abolish it. Individual cells do not regulate their own temperature, but the relationship between circadian rhythms and metabolism at the cellular level is also discussed. Metabolism is both an output of and an input to the circadian clock, meaning that circadian rhythmicity and metabolism are intertwined in the cell.

Integration of biological clocks and rhythms

Animals, plants, and microorganisms exhibit numerous biological rhythms that are generated by numerous biological clocks. This article summarizes experimental data pertinent to the often-ignored issue of integration of multiple rhythms. Five contexts of integration are discussed: (i) integration of circadian rhythms of multiple processes within an individual organism, (ii) integration of biological rhythms operating in different time scales (such as tidal, daily, and seasonal), (iii) integration of rhythms across multiple species, (iv) integration of rhythms of different members of a species, and (v) integration of rhythmicity and physiological homeostasis. Understanding of these multiple rhythmic interactions is an important first step in the eventual thorough understanding of how organisms arrange their vital functions temporally within and without their bodies.

Circadian Variation in Cortisol Reactivity to an Acute Stressor

To investigate the role of the circadian pacemaker in cortisol reactivity to a cold pressor challenge, 26 diurnally subjects participated in a constant-routine protocol and were divided into two groups. Group 1 started immediately after a monitored sleep period at 09:00 h, while group 2 started 12 h later. After 2 h of adaptation, a cold pressor test was presented every 3 h. The cortisol response was assessed by means of saliva samples that were taken before and after the test. The pretest samples were considered to be base-rate measures and base-rate values as subtracted from post-test values were considered as reactivity measures. Both measures showed distinct Time-of-Day variations (respectively: F(7,168) = 16.92, p < 0.001, epsilon = 0.383; and F(7,175) = 8.01, p < 0.001, epsilon = 0.523). These findings are interpreted as evidence for the existence of an endogenous circadian periodicity underlying the sensitivity of the hypothalamus-pituitary-adrenal (HPA)-axis to acute stress.

Chronic insomnia and daytime functioning: an ambulatory assessment

In this ambulatory study, the relation between daytime functioning and chronic insomnia was investigated. The study sample consisted of 39 chronic insomniacs and 20 healthy control participants. Performance (vigilance, working memory, motor control) and well-being (concentration, fatigue, mood, sleepiness) were assessed by means of a validated test battery, and intra-individual sleep variability was taken into account. Subjective well-being was found to be compromised in insomniacs as compared to control participants, but no differences in the level of performance were found. Evening cortisol levels did not indicate increased levels of arousal in the insomniacs. Although the absence of an effect of chronic insomnia on objectively measured performance may be due to experimental or statistical factors, this study hypothesizes that the insomniacs studied in the field may have been able to exert compensatory effort to overcome their self-perceived fatigue.

Personal digital assistants in health care: experienced clinicians in the palm of your hand?

Physicians and other health-care professionals are rapidly adopting personal digital assistants (PDA). Palm pilots and other hand-held computers are also increasingly popular among medical students. PDAs can be used for medical student education and physician training, daily clinical practice, and research. PDAs and their increasing integration with information technology in hospitals could change the way health care is delivered in the future. But despite the increasing use of PDAs, evidence from well-designed research studies is still needed to show how much these devices can improve the quality of care, save patients' lives, and ultimately reduce health-care expenses. In this Review of PDA use in health care, the operating systems, basic functionality, security and safety, limitations, and future implications of PDAs are examined. A personal perspective and an introduction to medical PDA applications, software, guidelines, and programmes for health-care professionals is also provided.

Chronic insomnia and performance in a 24-h constant routine study

Insomniacs report daytime functioning problems, but studies of neurobehavioral functioning in insomniacs have shown little objective evidence of impairment. In addition, very little is known about the influence of the circadian clock on performance in chronic insomniacs. In the present study, we investigated whether chronic insomnia is associated with an overall performance deficit, and what the effect is of circadian rhythmicity, under strictly controlled laboratory conditions. A 24-h experiment was carried out under constant routine conditions. Psychomotor performance, body temperature, and subjective functioning of 11 insomniacs and 13 healthy subjects were assessed. The insomniacs showed significant overall performance impairments in vigilance, working memory, and motor control. In addition, body temperature, performance and subjective functioning showed a circadian pattern similar to healthy subjects, with trough values in the late night/early morning and peak values in the early evening. Self-reported functioning among the insomniacs indicated mood disturbances, concentration problems, elevated fatigue and elevated sleepiness. The results indicated that chronic insomnia is associated with a substantial lowering of the 24-h level of performance and subjective functioning, irrespective of the type of task and/or the particular parameter, and without differential effects of circadian rhythmicity. Apparently, chronic insomnia has a negative impact upon performance as measured under strictly controlled, unmasked conditions.

Circadian variation in cardiac autonomic activity: reactivity measurements to different types of stressors

The role of endogenous circadian rhythmicity in autonomic cardiac reactivity to different stressors was investigated. A constant routine protocol was used with repeated exposure to a dual task and a cold pressor test. The 29 subjects were randomly divided into two groups in order to manipulate prior wakefulness. Group 1 started at 09:00 h immediately after a monitored sleep period, whereas group 2 started 12 h later. Measures of interbeat intervals (IBI), respiratory sinus arrythmia (RSA, a measure of parasympathetic activity), pre-ejection period (PEP, a measure of sympathetic activity), as well as core body temperature (CBT) were recorded continuously. Multilevel regression analyses (across-subjects) revealed significant (mainly 24 h) sinusoidal circadian variation in the response to both stressors for IBI and RSA, but not for PEP. Individual 24 + 12 h cosine fits demonstrated a relatively large interindividual variation of the phases of the IBI and RSA rhythms, as compared to that of the CBT rhythm. Sinusoidal by group interactions were found for IBI and PEP, but not for RSA. These findings were interpreted as an indication for endogenous circadian and exogenous parasympathetic (vagal) modulation of cardiac reactivity, while sympathetic reactivity is relatively unaffected by the endogenous circadian drive and mainly influenced by exogenous factors.

The manifestation of the motor activity circadian rhythm of blinded rats depends on the lighting conditions during lactation

The purpose of this experiment was to examine the effect of different lighting conditions during lactation on the functioning of the circadian pacemaker in the adult rat in absence of the retinal input. We reared one group of rats under constant light (LL-rats) and the other under constant darkness (DD-rats). After weaning they were placed under light-dark cycles of 24h period for 29 days to eliminate the aftereffects of the previous lighting. All the animals were then binocularly enucleated and motor activity was recorded. Results reveal that, before and after the enucleation, the expression of the circadian rhythm was stronger in DD- than in the LL-rats. Our results indicate that lighting conditions during lactation modify the functioning of the circadian pacemaker.