Periodic limb movements both in non-REM and REM sleep: relationships between cerebral and autonomic activities.

OBJECTIVE: To investigate the temporal relationship between cerebral and autonomic activities before and during periodic limb movements in NREM and REM sleep (PLMS). METHODS: Patterns of EEG, cardiac and muscle activities associated with PLMS were drawn from polysomnographic recordings of 14 outpatients selected for the presence of PLMS both in NREM and REM sleep. PLMS were scored during all sleep stages from tibial EMG. Data from a bipolar EEG channel were analyzed by wavelet transform. Heart rate (HR) was evaluated from the electrocardiogram. EEG, HR and EMG activations were detected as transient increase of signal parameters and examined by analysis of variance and correlation analysis independently in NREM and REM sleep. Homologous parameters in REM and NREM sleep were compared by paired t-test. RESULTS: The autonomic component, expressed by HR increase, took place before the motor phenomenon both in REM and NREM sleep, but it was significantly earlier during NREM. In NREM sleep, PLM onset was heralded by a significant activation of delta-EEG, followed by a progressive increase of all the other bands. No significant activations of delta EEG were found in REM sleep. HR and EEG activations positively correlated with high frequency EEG activations and negatively (in NREM) with slow frequency ones. CONCLUSIONS: Our findings suggested a heralding role for delta band only in NREM sleep and for HR during both NREM and REM sleep. Differences in EEG and HR activation between REM and NREM sleep and correlative data suggested a different modulation of the global arousal response. SIGNIFICANCE: In this study, time-frequency analysis and advanced statistical methods enabled an accurate comparison between brain and autonomic changes associated to PLM in NREM and REM sleep providing indications about interaction between autonomic and slow and fast EEG components of arousal response.

[Commuting accidents: the influence of excessive daytime sleepiness. A review of an Italian Police officers population]. / Infortuni in itinere: ruolo della sonnolenza in una popolazione di operatori della Polizia di Stato.

Commuting accidents (CA) play an important role in many systems of workers' compensation insurance and with good reason, as they generally bring about more serious consequences in terms of permanent disablement and death than ordinary occupational accidents; this usually leads to high social costs. Nevertheless, research investigations aimed at studying the possible causes underlying the phenomenon are not available in medical literature. Objective of the present study is to evaluate whether excessive daytime sleepiness (EDS) might influence the occurrence of CA. 463 CA occurred to 411 police officers in northern Italy during the period 1999 - 2002 were collected; 51.9% of the subjects were working on shifts, 48.1% were non-shift workers. The study was carried out by submitting a self-administered questionnaire to gather information on age and physical characteristics, working conditions, sleep-related problems and accidents occurrence; EDS was measured by the Epworth Sleepiness Scale (ESS). A large number of workers (36%) complained of EDS; a strict significant relationship between shift - work condition and the presence of EDS was found, thus suggesting that CA are significantly influenced by EDS. The shift work schedule adopted by Italian Police might be accountable for the disruption of the balance between circadian and homeostatic factors.

[Shift-work seniority increases the severity of sleep disorders. Comparison of different categories of shift-workers]. / L'anzianità di turnismo aumenta la gravità dei disturbi del sonno. Confronto fra diverse categorie di turnisti.

Shift-work disrupts the sleep-wake cycle and could bring about sleep disorders and excessive daytime sleepiness. We studied two samples of shift-workers, a group of 178 nurses and one of 174 police officers, all working in the town of Palermo (Italy); their answers to a sleep disorder questionnaire were scored and added in order to create a Sleep Disorder Score (SDS). The SDS cut-off value, discrimining pathological values from physiological ones, was settled a-priori. In both groups SDS did not depend on sex, age, weight, height nor on working seniority, but it increased non linearly (cubic form) with shift-work seniority. In nurses this mathematical description of SDS exceeded the cut-off value after 15 years of shift-work seniority; in police officers it settled asymptotically under the critical value. This could be ascribable both to the different composition in sex of the two samples (nurses: 49% F-51% M vs. police officers: 6% F-94% M) both to the self-selection process that seems to undergo police officers (nurses do not leave shift-work because of salary incentives).

Brain function and effects of shift work: implications for clinical neuropharmacology.

Night or shift work is to a relevant extent unavoidable, suits a growing preference for flexibility and is predicted to spread. However, a significant percentage of shift workers report discomfort or health problems and they often (15-20% of cases) move to different occupations. Apart from social implications, the issue has medical and scientific relevance, with evidence suggesting that the circadian rhythm phases are neither equivalent nor interchangeable with respect to function and performance. Shift work may affect the gastrointestinal and cardiovascular functions, alter the hormonal and sleepiness cycles, favor sleep disturbances of medical relevance, interfere with behavior and social life and increase the risk of accidents (e.g. road accidents). The implications for clinical (neuro)pharmacology are relevant and, in several instances, critical. Shift work can interfere with mechanisms regulating drug kinetics in peripheral compartments and action at selective brain sites, either directly or through effects on the gastrointestinal/hormonal cycles. In this paper, the relevant literature is reviewed and original data on the effects of shift work are reported. Basic and clinical research should take into account the possible effects on drug action of an active life and working schedule in inappropriate phases of the circadian cycles and the risk of inadequate drug dosing or unexpected abnormal action in subjects under long-term or chronic treatment. A scientific approach, action by the scientific community involved in pharmacological research and monitoring by the regulating agencies are advisable. Regulation may help reduce the medical and social impact and improve quality of life.

Absence of sleep EEG markers in fatal familial insomnia healthy carriers: a spectral analysis study.

OBJECTIVES: Fatal familial insomnia (FFI) is linked to a mutation at codon 178 (C178) of the prion protein gene (PRNP). FFI is pathologically characterized by selective atrophy of the anteroventral and mediodorsal thalamic nuclei and clinically by loss of sleep, dysautonomia and motor signs. A key early polysomnographic sign of the disease onset is the loss of sleep spindling (sigma activity, SA). In FFI the loss of SA leads to the spectral representation of a sudden slow wave activity (SWA) increase from an awake state, the reaching of a stable plateau without oscillations, followed by abrupt fall down to REM sleep. We evaluated the presence of differences in the spectral sleep EEG pattern in FFI relatives carriers (C178(pos)) or non-carriers (C178(neg)) of the C178 mutation. METHODS: Seventeen healthy relatives of FFI patients, 8 carriers of the C178 FFI mutation in a preclinical condition and 9 non carriers, underwent two-night polysomnography. The absolute and relative EEG power of the 4 main bands (delta: SWA, 0.5-4.0 Hz; theta: TB, 4.5-8 Hz; alpha: AB, 8.5-12 Hz; sigma: SA, 12.5-16 Hz) has been studied for the total sleep time, the period of delta increase after sleep onset, and the period of delta plateau. Multiple regression has been applied to investigate relations between the power of the bands studied and 3 parameters: age, the gender of the subjects and the C178 genotype. RESULTS: Our study could not show evidence of differences in the sleep EEG composition between carriers and non-carriers of the C178 FFI mutation. CONCLUSIONS: The spectral analysis techniques we used were not able to disclose sleep EEG markers linked to the FFI C178(pos) in the preclinical condition. Key sleep EEG alteration become evident only at the clinical onset of the disease.

Temporal relationship of generalized epileptiform discharges to spindle frequency activity in childhood absence epilepsy.

OBJECTIVE: The hypothesis that the two main synchronizing mechanisms (spindle and delta oscillations) acting during non-rapid eye movement sleep show opposite relationship with the distribution of generalized epileptiform discharges (GEDs) during sleep was evaluated. METHODS: We studied the temporal relationship between the distribution of sleep GEDs and the dynamics of Sigma Activity (SA, 12-16 Hz) and Delta Activity (DA, 0.5-4.5 Hz) in 5 children affected by childhood absence epilepsy. RESULTS: Using correlation techniques, we found a high and positive correlation between GEDs and SA, while DA resulted negatively correlated with GEDs. CONCLUSION: Sleep generalized spike-and-slow-waves seems to be produced when spindle synchronizing mechanisms are active while DA production seem to exert an inhibiting role. Such a feature seems to be common to other childhood partial and undetermined epileptic syndromes.

Hypersomnia in the Prader Willi syndrome: clinical-electrophysiological features and underlying factors.

OBJECTIVE: Excessive daytime sleepiness is a common symptom in Prader Willi syndrome (PWs). Sleep disordered breathing (SDB) and narcoleptic traits such as REM sleep onsets (SOREMPs) have been reported in these subjects. We evaluated nighttime and daytime sleep patterns in patients with PWs in order to clarify the nature of their hypersomnia. DESIGN AND METHODS: We performed overnight continuous EEG-polysomnographic studies (with breathing monitoring included) in 14 subjects (6 M,8 F; mean age 17 years, range 8-37) affected by PWs unselected for sleep disturbances. Ten patients underwent a Multiple Sleep Latency Test (MSLT) the day following the nocturnal sleep studies. Patients assessment was completed by means of immunogenetic characterization. RESULTS: Nocturnal polysomnographic investigation documented sleep related breathing abnormalities such as central apneas, hypopneas or hypoventilation which mainly occurred during REM sleep in 8 subjects and did not cause sleep disruption. Only 4 subjects presented an increase in the Respiratory Disorder Index (RDI) slightly above the normal limits. In 8 subjects out of 10, with and without SDB, the mean daytime sleep latency could be considered abnormal according to the Tanner staging of pubertal development. Five patients showed at least two SOREMPs at MSLT. Subjects with and without SOREMPs had, respectively, a mean age of 18.6 SD 7.9 (4 M, 1 F) and 14.5 SD 2.9 (4 F, 1 M). The paternal deletion:uniparental dysomy ratio at genotypic characterization was 4:1 and 3.5:1 in subjects with and without SOREMPs, respectively. No patient presented DR-15 nor Dq-6. CONCLUSIONS: Excessive sleepiness is a frequent disturbance in PWs. Subgroups of PW patients show hypersomnolence and SOREMPs. Sleep disordered breathing appears to have a limited role in the genesis of hypersomnia which not seems on the other hand attributable to the coexistence of narcolepsy phenotype. Hypersomnia in PW syndrome is likely to mainly be attributable to a primary hypothalamic dysfunction. The potential interacting role of other factors such as subjects age, sex and genetic pattern is suggested and deserve further investigation.

Distribution of epileptiform discharges during nREM sleep in the CSWSS syndrome: relationship with sigma and delta activities.

PURPOSE: The EEG pattern of epilepsy with continuous spike-waves during slow wave sleep (CSWSS) is characterized by an almost continuous activation of spike-and-slow-wave complexes during nREM sleep with a marked reduction of EEG abnormalities during REM sleep and the awake state. Experimental studies indicate that normal sleep oscillations that during nREM sleep lead to the appearance of spindles and delta waves on scalp EEG might develop into paroxysmal synchronization. Spectral analysis enables the quantitative description of the dynamics of delta (Delta Activity, DA, 0.5-4.5 Hz) and sigma activity (SA, 12-16 Hz) and can be used to assess the relationship between SA, DA and epileptiform discharges (EDs) during sleep. METHODS: We analyzed the EDs distribution during sleep in five children affected by CSWSS. We used a model of the evolution of power of DA and SA to which the time series of EDs could be fitted. RESULTS: We found a high and positive correlation between EDs and SA. DA resulted negatively correlated with EDs. CONCLUSION: Our data suggest that neural mechanisms involved in the generation of sleep spindles facilitate EDs production in the CSWSS syndrome. Such a mechanism seems to be an age related phenomenon shared by other epileptic syndromes of childhood.

The contributing role of sleepiness in highway vehicle accidents.

STUDY OBJECTIVE: To evaluate the contributing role of sleepiness in Italian highway vehicle accidents during the time span 1993-1997. DESIGN: We analyzed separately the hourly distribution of accidents ascribed by police officers univocally to sleepiness and the rest. PATIENTS: N/A. INTERVENTIONS: N/A. MEASUREMENTS: Using a polynomial regression, we evaluated the relation between accidents (whether sleep-ascribed or not) and sleepiness as derived from a 24-hour sleep propensity curve. The relation between sleep-influenced and non-sleep influenced accidents was analysed using a linear regression. RESULTS: The rate of non-sleep ascribed accidents is closely related with sleep propensity and bears a strong similarity with the pattern of sleep-ascribed accidents. A close relationship between the curves of non-sleep ascribed accidents and sleep-ascribed accidents is confirmed. The regression coefficient, which can be seen as the ratio between the quota of accidents that can be considered as sleep affected and those actually ascribed to sleepiness, results in a value of 5.83. Considering that the rate of sleep ascribed accidents is 3.2%, we can calculate the quota of sleep influenced accidents out of those not officially ascribed to sleepiness as 18.7% reaching an estimate of accidents related in some way to sleepiness equal to 21.9%. CONCLUSIONS: Our indirect estimate of sleep influenced accidents approaches data reported by other European countries and highlights the importance of sleepiness as a direct and/or contributing factor in vehicle accident rates.

Nocturnal sleep features in narcolepsy: a model-based approach.

The internal structure of night sleep in subjects with narcolepsy significantly differs as compared to the controls. The differences consist in the presence of sleep onset REM periods (SOREMPs) and in a longer duration (120 minutes versus 90 minutes) of the NREM-REM cycles. Another difference consists in the lack of increase in REM sleep duration during the night, cycle after cycle. These characteristics, taken as a whole, suggest that the sleep structure of narcoleptic patients is due to an imbalance between the homeostatic process and the enhanced pressure of REM inducing mechanisms. With regard to the intrasleep dynamics the current extension of the Two-process model cannot give a satisfactory explanation because REM sleep is included as an external trigger with no intrinsic rhythmic property. Neurobiologic studies lead to consider the REM cyclic occurrence as the result of reciprocal interaction between two populations of REM-ON and REM-OFF cells. The introduction in the Two-process-model extended to the intra-night dynamics of an ultradian oscillator, based on a REM-ON--REM-OFF reciprocal interaction, allows the theoretical possibility to simulate a SOREMP. This revised model accounts for the progressive extension of REM sleep-periods duration in the course of the night. The sleep structure of narcoleptic patients can be simulated leaving unaltered the pressure of the homeostatic process and enhancing the REM inducing pressure. Such an enhanced REM pressure can be achieved by increasing the value of the numerical coefficient, which represents the strength of connection between the two types of REM-ON and REM-OFF cells. This modification allows not only to obtain a stronger ultradian oscillator but also a longer periodicity of REM sleep occurrence. By coupling the homeostatic process, considered as normal, to such a modified ultradian oscillator, our model can explain the intra-night sleep dynamics of narcoleptic subjects. A REM-ON REM-OFF dysregulation can be hypothesized to explain the pathophysiological basis of nocturnal sleep features in narcolepsy.

Sleep related vehicle accidents on Italian highways.

Sleepiness has been identified as a significant risk factor for vehicle accidents, and specific surveys are needed for Italy. The aim of this study was to assess incidence and characteristics of sleep-related vehicle-crashes on Italian highways. The database of the Italian National Institute of Statistics (1993-1997) was the source for the survey (50859 accidents with 1632 (3.2%) ascribed to sleep by the police). The distribution of accidents was evaluated by means of the analysis of variance considering the year, the day of the week, the age and the time of day and their interactions as main factors. The relative risk of sleep-related accidents was also evaluated with reference to the relative traffic density as estimated by the Italian Highways Society. The counts of sleep-related accidents, and even more the relative risk, revealed the presence of peaks and troughs in zones at a higher level of sleepiness and alertness respectively. Death of the driver occurred in 11.4% of sleep related accidents versus 5.6% in general accidents. The great majority of sleep-related accidents occurred to drivers under 35 (61.4%) mainly during the night with an increasing trend in the yearly number of sleep-related accidents, especially on weekends. Therefore sleepiness appears a remarkable risk factor and, in our opinion, its incidence as sole or contributory cause of accidents on Italian highways is still underestimated.

Sleepiness in a population of Italian shiftwork policemen.

The aim of this study was to evaluate the effects of shiftwork on sleepiness, sleep disorders and sleep related accidents in a population of policemen. Data concerning age and physical characteristics, working conditions, sleep problems and accidents were collected by a questionnaire. Sleepiness was evaluated by the Epworth Sleepiness Scale (ESS) while the presence of sleep disorders was evaluated by a score (SD-score) drawn from indicators of insomnia, breathing disorders, periodic limb movements-restless leg syndrome and hypersomnia. The effects of age, gender, body mass index, working condition and seniority on ESS, SD-score and accidents were analysed by linear and logistic regression. Participants were 1280 policemen: 611 shiftworkers and 669 non-shiftworkers. The ESS scores were not higher in shiftworkers than in non-shiftworkers, but the SD-score was found to be significantly influenced by shiftwork condition and seniority. The occurrence of sleep-related accidents was found to have been significantly increased for shiftworkers and related to the presence of indicators of sleep disorders. The sleepiness could be underestimated or even overcome by the influence of stressing conditions. However our data should alert occupational health physicians for the diagnosis and prevention of possible lurking intrinsic sleep disorders likely to influence health problems and risk of accidents in shiftworkers.

Sleep EEG synchronization mechanisms and activation of interictal epileptic spikes.

OBJECTIVE: The temporal course of sleep interictal epileptic discharges (IEDs) has been studied focusing their relationship with the temporal course of the main sleep-EEG frequency bands that is thought to reflect the action of different synchronization neural mechanisms. The existence of a mutually exclusive mechanism between spindles and delta waves should be reflected in a mutually exclusive facilitation of IEDs activation by slow wave activity (SWA) and sigma activity (SA) during synchronized NREM sleep. METHODS: We reanalyzed data from 19 children and 15 adult patients affected by different partial epileptic syndromes. The temporal series of SWA, SA and theta band (TB), derived from spectral analysis, were obtained from a spike-free and pathologic alteration-free derivation, controlateral to the most active lead, where the IEDs count was performed. Relationships between SA, SWA and TB and time series of IEDs were tested by means of correlation techniques after data normalization. RESULTS: A positive correlation of spike distribution with SWA time course has been found in the majority of adults. Only a few adult patients showed IEDs that were correlated with SA or TB. Conversely SA was shown to be positively correlated with spiking in many different epileptic syndromes of childhood. Moreover, in the contest of the NREM sleep cycle an inverse relationship between the SWA and SA mode of spike activation has been detected. CONCLUSIONS: Overall results give evidence that 3 main rhythmic spectral components that characterize sleep EEG can exert positive influences on IEDs production. Our studies demonstrate that within NREM sleep the facilitating influences on IEDs production exerted separately by either spindle activity or delta synchronization mechanisms can be detected. Moreover, a mutually exclusive mechanism between SA and SWA oscillations is detectable in the opposite relationship of the correlation between IEDs and the two bands in the central part of the NREM cycle.

Relationship of sigma activity to sleep interictal epileptic discharges: a study in children affected by benign epilepsy with occipital paroxysms.

INTRODUCTION: By applying spectral analysis techniques we recently showed that Interictal Epileptic Discharges (IEDs) are modulated by sleep spindle synchronization mechanisms (sigma activity, SA, 12. 0-16.0 Hz). This finding applies to both benign epilepsy of childhood with rolandic spikes (BECRS), to symptomatic epilepsy of childhood strongly activated by sleep and to the Landau-Kleffner syndrome. These results are quite different from those found in adult partial epileptic patients where slow wave activity (SWA, 0. 5-4.5 Hz) plays the main role in the modulation of IEDs during sleep. This finding could suggest that the activation of IEDs by spindle activities could be an age-related feature of epilepsy. In order to verify this hypothesis we studied a group of epileptic children performing a polysomnographic study on five patients with BEOP strongly activated by sleep. METHODS: We performed overnight continuous EEG-polysomnographic studies in five patients (mean age 6. 0+/-2.5). The IEDs count was performed on the most active occipital lead. The temporal series of SWA and SA values, derived from spectral analysis, were obtained from a spike-free central, controlateral lead. Relationships between SA, SWA and time series of IEDs were tested by means of correlation techniques after data normalization. RESULTS: Our results revealed a significantly higher correlation between IEDs and SA with respect to SWA in all subjects, in total sleep time. When the analysis was limited only to NREM sleep the correlation between sigma and IEDs was even more impressive. CONCLUSIONS: Data suggest that also in BEOP the spindle generating mechanism modulates the IEDs during sleep. This mechanism seems to be an age-dependent phenomenon with no relation whatsoever either with the type of epilepsy or with the brain region.

Sleep-EEG modulation of interictal epileptiform discharges in adult partial epilepsy: a spectral analysis study.

INTRODUCTION: In order to define accurately the relationship between EEG components (spindles, delta and theta frequencies) and the occurrence of interictal epileptiform discharges (IED) during sleep in partial epilepsy, a correlation study between spike overnight distribution and EEG spectral power time series was performed. METHODS: Eighteen patients (mean age: 24.7+/-5.5 years) affected by partial epilepsy underwent continuous EEG-polysomnography. The temporal series of Slow Wave Activity (SWA), Sigma Activity (SA) and Theta Band (TB), derived from spectral analysis, were obtained from a spike-free and pathologic alteration-free derivation, contralateral to the most active lead, where the IED count was performed. Relationships between SA, SWA and TB and time series of IED were tested by means of correlation techniques after data normalization. RESULTS: Our results revealed a significantly higher correlation between IED and SWA in 12 subjects; a significantly higher correlation between IED and SA in three subjects and a significant correlation with TB in three cases. CONCLUSIONS: Data suggest that in most adult patients with partial epilepsy IED production during sleep is facilitated by the action of synchronizing mechanisms which are active during NREM sleep and lead to the appearance of EEG delta waves. Nevertheless evidence is given of two smaller groups of patients. In one of them IED are more sensitive to the promoting action of the spindle generating mechanism, active during stage 2 of NREM sleep. In the other one the promoting action of TB, characterizing EEG during stage 1 and REM sleep, is evident.

Morning increase of whole blood viscosity in obstructive sleep apnea syndrome.

OBJECTIVE: Patients affected by obstructive sleep apnea syndrome (OSAS) have an increased risk of cardiovascular diseases such as stroke and myocardial infarction. The pathophysiological mechanisms leading to increased vascular risk are still matter of debate. A relative morning hyperviscosity could be one of the leading mechanisms of cardiovascular morbidity which is actually known to be especially high in the morning hours. METHODS: Whole blood viscosity (WBV) at seven shear rates, ranging from 0.47 to 118 sec(-1), haematocrit (Hct), and plasma fibrinogen (F) concentration, were measured on venous blood samples in 12 patients with OSAS and in 8 healthy controls at 8-9 p.m. and at 7-8 a.m. the morning after. WBV values were normalized on Hct by the computation of the standardised normal deviate z on the normal database of the laboratory. RESULTS: No changes were observed in controls. Hct, F and normalized WBV (independently from Hct changes) significantly increased in the morning hours in OSAS patients. CONCLUSIONS: Viscosity of whole blood increases in the morning in OSAS patients but not in healthy controls. This condition may be related to the increased susceptibility to cerebral ischemia in patients affected by OSAS, particularly evident in the early morning.

Spindles-inducing mechanism modulates sleep activation of interictal epileptiform discharges in the Landau-Kleffner syndrome.

PURPOSE: Landau-Kleffner syndrome (LKS) is characterized by a marked increase of interictal epileptiform discharges (IEDs) during sleep. During nonrapid eye movement (NREM) sleep, neuronal membrane potential oscillations lead to the appearance of spindles and delta waves in the surface EEG and might develop into paroxysmal synchronization. Spectral analysis allows the quantitative description of the dynamics of delta (slow-wave activity, SWA, 0.5-4.5 Hz) and sigma activity (SA, 12.0-16.0 Hz) and can be used to assess the relation between SA, SWA, and IEDs during sleep. METHODS: We performed six overnight continuous EEG-polysomnographic studies in three patients with LKS. The temporal series of SWA and SA were obtained from a spike-free derivation lead. The IEDs count was performed on the most active lead. Relations between sigma and SWA and time series of IEDs were tested by means of correlation techniques after data normalization. RESULTS: Our results revealed a significantly higher correlation between IEDs and SA with respect to SWA in all the subjects, in total sleep time. The same analysis limited to NREM sleep highlights the better correlation between SA and IEDs. CONCLUSIONS: Our data suggest that neural mechanisms involved in the generation of sleep spindles facilitate IEDs production in LKS.

[Sleepiness and road accidents among policemen on shif-work on Italian highways: study of the national highway network in the period of 1993-1997]. / Sonnolenza ed incidenti stradali nei turnisti della polizia stradale Italiana: uno studio sulla rete autostradale nazionale nel quinquennio 1993-1997.

Sleep disorders and daytime sleepiness are the most frequent disturbances reported by shift-workers. Sleepiness and fatigue can increase the risk of human errors and accidents especially during night work. In order to evaluate the time distribution and the possible role of sleepiness on road accidents in policemen on shift-work on highway patrols over 24 hours, we analyzed 1218 car accidents that occurred on the Italian highway network in the period 1993-1997. Accidents occurring during day shifts were significantly correlated with traffic density while accidents occurring during night shifts were not. During the 19:00-01:00 h shift the number of accidents showed a progressively increasing trend with two significant peaks around 23:00 and 01:00 h. Accidents occurring during the 01:00-07:00 h shift did not show significant trends. Information about sleep habits before starting night shifts were obtained by means of telephone interviews. While 85% of the subjects usually took a nap (30-90 min) before the 01:00-07:00 h shift only 15% took a short nap (< 30 minutes) before the 19:00-01:00 h shift. The data can be interpreted as a balance between circadian factors, homeostasis and fatigue related influences and spontaneously adopted counteracting strategies to increase the level of vigilance during night work hours. While a long nap seems to reduce the risk of accidents during the 01:00-07:00 h shift, policemen seem to underestimate the risk of sleepiness during the shift 19:00-01:00 h shift.

Correlation dimension of EEG slow-wave activity during sleep in narcoleptic patients under bed rest conditions.

The calculation of the correlation dimension (D2) was applied to the study of the profiles of EEG slow-wave activity in nine narcoleptic subjects and nine sex- and age-matched control subjects who, following a baseline night recording, were maintained on 16 h of diurnal sleep deprivation and, thereafter, submitted to a 32-h bed rest protocol. The reversibility test allowed us to reject the null hypothesis that the time series considered in our study were generated by a static transformation of a linear Gaussian random process. Similarly, all profiles showed a positive largest Lyapunov exponent. Finally, the computation of D2 showed an average value of 5.27 (0.68 S.D.) in normal controls and 4.05 (1.49 S.D.) in narcoleptic patients (p = 0.067). Four of the narcoleptic patients showed values of D2 lower than 4, this was never observed in the normal controls (p = 0.0294). This study indicates that the mechanism of sleep-wake regulation in narcolepsy shows a somewhat lower degree of complexity as compared to normal controls. In particular, these data seem to confirm the already suggested different and simpler coupling between the homeostatic process of sleep regulation and the circadian and ultradian drives to sleep that occurs in bed rest condition in this disease.

A method for the automatic detection of arousals during sleep.

A method for the automatic detection of arousals in digital polysomnographic recordings is described. The computer program analyzed two EEG and one EMG derivations marking variable length segments as arousals. The processing of EEG data started from the wavelet transform, which characterizes the signal in the time-frequency domain, and resulted in a set of indices used to discriminate possible arousal segments. Transient increases in muscle activity were also identified, while a multichannel and context sensitive analysis allowed arousal detection. Out of 11 overnight recordings, 3 were used as the training set and 8 as the program testing set. In the first stage of the study two EEG experts inspected the tracings independently to score arousals. They then reviewed all recordings and jointly examined each event for validation, both those scored by themselves and those scored by the computer. A reference set of definite arousals (1125 in the testing set) and a number of uncertain events (266) were thus obtained. The sensitivity of the automatic system (88.1%) was higher than that of the human experts (72.4 and 78.4%) while the selectivity was lower (74.5% for the automatic system, 83.0 and 82.0% for the experts). This suggested that automatic detection, followed by an expert's validation, may render the analysis of arousals more widely feasible as well as support the study of arousal features.