A deep transfer learning approach for sleep stage classification and sleep apnea detection using wrist-worn consumer sleep technologies

Obstructive sleep apnea (OSA) is a common, underdiagnosed sleep-related breathing disorder with serious health implications Objective - We propose a deep transfer learning approach for sleep stage classification and sleep apnea (SA) detection using wrist-worn consumer sleep technologies (CST). Methods - Our model is based on a deep convolutional neural network (DNN) utilizing accelerometers and photo-plethysmography signals from nocturnal recordings. The DNN was trained and tested on internal datasets that include raw data from clinical and wrist-worn devices; external validation was performed on a hold-out test dataset containing raw data from a wrist-worn CST. Results - Training on clinical data improves performance significantly, and feature enrichment through a sleep stage stream gives only minor improvements. Raw data input outperforms feature-based input in CST datasets. The system generalizes well but performs slightly worse on wearable device data compared to clinical data. However, it excels in detecting events during REM sleep and is associated with arousal and oxygen desaturation. We found; cases that were significantly underestimated were characterized by fewer of such event associations. Conclusion - This study showcases the potential of using CSTs as alternate screening solution for undiagnosed cases of OSA. Significance - This work is significant for its development of a deep transfer learning approach using wrist-worn consumer sleep technologies, offering comprehensive validation for data utilization, and learning techniques, ultimately improving sleep apnea detection across diverse devices.

Validation of the newly developed Sleep Screening Questionnaire Children and Adolescents (SSQ-CA) with objective sleep measures

OBJECTIVES

Objectively validated pediatric sleep questionnaires covering a broader age range and different sleep disturbances are lacking, therefore we developed the Sleep Screening Questionnaire Children and Adolescents (SSQ-CA) and compared it with objective sleep parameters.

METHODS

This child-reported questionnaire was developed by a multidisciplinary panel and face validated. In a cross-sectional prospective design, participants aged 6-17, answered the questionnaire twice with 21-28 days in between, wore actigraphy (AG) and kept a sleep diary for seven nights and home-polysomnography (PSG) for one of these nights. Exploratory factor analyses (EFA), reliability and validity assessments were performed.

RESULTS

Of the 139 participants, 128 (F:47.7%, AG: n = 128, PSG: n = 59), were included in the analyses. Mean age: 11.3 years (SD: 2.9). EFA revealed 11 factors and 40 items loading above r = 0.4. Subscale internal consistency: 0.54-0.92. Subscale test-retest reliability: r = 0.71-0.87. Total sleep time (TST) from SSQ-CA on weekdays correlated with PSG (r = 0.48, p = 0.001) and with AG (r = 0.75, p < 0.001). The subscale total score for "Sleep duration and latency" correlated with TST from AG (r = -0.19, p = 0.03) and sleep latency (r = 0.31, p < 0.001), but not for PSG variables. The subscale "Awakenings" showed no correlation with objective measures whereas "Circadian rhythm" correlated to AG-derived mid-sleep time (r = 0.34, p < 0.001).

CONCLUSIONS

The SSQ-CA shows adequate reliability for the 6-17-year-olds and acceptable criterion validity for two subscales. It appears to be a useful tool for screening for sleep disturbances in combination with objective tools as the subjective and objective parameters seem to uncover different aspects of sleep.

The effect of group-based cognitive behavioural therapy for insomnia in patients with rheumatoid arthritis: a randomized controlled trial

OBJECTIVES

The primary objective was to compare the effect of cognitive behavioural therapy for insomnia (CBT-I) to usual care on sleep efficiency, measured by polysomnography (PSG) immediately after the intervention at week 7. Secondary objectives included comparing the longer-term effect on sleep- and RA-related outcomes at week 26.

METHODS

In a randomized controlled trial using a parallel group design, the experimental intervention was 6 weeks' nurse-led group-based CBT-I; the comparator was usual care. Analyses were based on the intention-to-treat (ITT) principle; missing data were statistically modelled using repeated-measures linear mixed effects models adjusted for the level at baseline.

RESULTS

The ITT population consisted of 62 patients (89% women), with an average age of 58 years and an average sleep efficiency of 83.1%. At primary end point, sleep efficiency was 88.7% in the CBT-I group, compared with 83.7% in the control group (difference: 5.03 [95% CI -0.37, 10.43]; P = 0.068) measured by PSG at week 7. Key secondary outcomes measured with PSG had not improved at week 26. However, for all the patient-reported key secondary sleep- and RA-related outcomes, there were statistically highly significant differences between CBT-I and usual care (P < 0.0001), e.g. insomnia (Insomnia Severity Index: -9.85 [95% CI -11.77, -7.92]) and the RA impact of disease (RAID: -1.36 [95% CI -1.92, -0.80]) at week 26.

CONCLUSION

Nurse-led group-based CBT-I did not lead to an effect on sleep efficiency objectively measured with PSG. However, CBT-I showed improvement on all patient-reported key secondary sleep- and RA-related outcomes measured at week 26.

TRIAL REGISTRATION

ClinicalTrials.gov, https://clinicaltrials.gov, NCT03766100.

Impact of Nonpharmacologic Interventions Targeting Sleep Disturbances or Disorders in Patients With Inflammatory Arthritis: A Systematic Review and Meta-Analysis of Randomized Trials

OBJECTIVE

Patients with inflammatory arthritis have a high risk of sleep disturbances and disorders. The objective was to evaluate the evidence of nonpharmacologic interventions targeting sleep disturbances or disorders in patients with inflammatory arthritis.

METHODS

A systematic search was undertaken from inception to September 8, 2020. We included randomized trials concerning nonpharmacologic interventions applied in adults with inflammatory arthritis and concomitant sleep disturbances or disorders. The primary outcome was the sleep domain, while secondary outcomes were core outcome domains for inflammatory arthritis trials and harms. The Cochrane Risk of Bias tool was applied, and the overall quality of the evidence was assessed using Grading of Recommendations Assessment, Development and Evaluation criteria. Effect sizes for continuous outcomes were based on the standardized mean difference, combined using random-effects meta-analysis.

RESULTS

Six trials (308 patients) were included in the quantitative synthesis; 3 of these reported improvement in sleep in favor of the nonpharmacologic interventions. The meta-analysis of the sleep domains indicated a large clinical effect of -0.80 (95% confidence interval -1.33, -0.28) in favor of nonpharmacologic interventions targeting sleep disturbances or disorders. The estimate was rated down twice for risk of bias and unexplained inconsistency; this risk was assessed as corresponding to low-quality evidence. None of the secondary core outcomes used in contemporary inflammatory arthritis trials indicated a clinical benefit in favor of nonpharmacologic interventions targeting sleep.

CONCLUSION

Nonpharmacologic interventions targeting sleep disturbances/disorders in patients with inflammatory arthritis indicated a promising effect on sleep outcomes, but not yet with convincing evidence.

White matter microstructure and sleep-wake disturbances in individuals at ultra-high risk of psychosis

Aim

White matter changes in individuals at ultra-high risk for psychosis (UHR) may be involved in the transition to psychosis. Sleep-wake disturbances commonly precede the first psychotic episode and predict development of psychosis. We examined associations between white matter microstructure and sleep-wake disturbances in UHR individuals compared to healthy controls (HC), as well as explored the confounding effect of medication, substance use, and level of psychopathology.

Methods

Sixty-four UHR individuals and 35 HC underwent clinical interviews and diffusion weighted imaging. Group differences on global and callosal mean fractional anisotropy (FA) was tested using general linear modeling. Sleep-wake disturbances were evaluated using the subjective measures disturbed sleep index (DSI) and disturbed awakening index (AWI) from the Karolinska Sleep Questionnaire, supported by objective sleep measures from one-night actigraphy. The primary analyses comprised partial correlation analyses between global FA/callosal FA and sleep-wake measures. Secondary analyses investigated multivariate patterns of covariance between measures of sleep-wake disturbances and FA in 48 white matter regions of interest using partial least square correlations.

Results

Ultra-high risk for psychosis individuals displayed lower global FA (F = 14.56, p < 0.001) and lower callosal FA (F = 11.34, p = 0.001) compared to HC. Subjective sleep-wake disturbances were significantly higher among the UHR individuals (DSI: F = 27.59, p < 0.001, AWI: F = 36.42, p < 0.001). Lower callosal FA was correlated with increased wake after sleep onset (r = -0.34, p = 0.011) and increased sleep fragmentation index (r = -0.31, p = 0.019) in UHR individuals. Multivariate analyses identified a pattern of covariance in regional FA which were associated with DSI and AWI in UHR individuals (p = 0.028), but not in HC. Substance use, sleep medication and antipsychotic medication did not significantly confound these associations. The association with objective sleep-wake measures was sustained when controlling for level of depressive and UHR symptoms, but symptom level confounded the covariation between FA and subjective sleep-wake measures in the multivariate analyses.

Conclusion

Compromised callosal microstructure in UHR individuals was related to objectively observed disruptions in sleep-wake functioning. Lower FA in ventrally located regions was associated with subjectively measured sleep-wake disturbances and was partly explained by psychopathology. These findings call for further investigation of sleep disturbances as a potential treatment target.

A flexible deep learning architecture for temporal sleep stage classification using accelerometry and photoplethysmography

Wrist-worn consumer sleep technologies (CST) that contain accelerometers (ACC) and photoplethysmography (PPG) are increasingly common and hold great potential to function as out-of-clinic (OOC) sleep monitoring systems. However, very few validation studies exist because raw data from CSTs are rarely made accessible for external use. We present a deep neural network (DNN) with a strong temporal core, inspired by U-Net, that can process multivariate time series inputs with different dimensionality to predict sleep stages (wake, light-, deep-, and REM sleep) using ACC and PPG signals from nocturnal recordings. The DNN was trained and tested on 3 internal datasets, comprising raw data both from clinical and wrist-worn devices from 301 recordings (PSG-PPG: 266, Wrist-worn PPG: 35). External validation was performed on a hold-out test dataset containing 35 recordings comprising only raw data from a wrist-worn CST. An accuracy = 0.71±0.09, 0.76±0.07, 0.73±0.06, and κ = 0.58±0.13, 0.64±0.09, 0.59±0.09 was achieved on the internal test sets. Our experiments show that spectral preprocessing yields superior performance when compared to surrogate-, feature-, raw data-based preparation. Combining both modalities produce the overall best performance, although PPG proved to be the most impactful and was the only modality capable of detecting REM sleep well. Including ACC improved model precision to wake and sleep metric estimation. Increasing input segment size improved performance consistently; the best performance was achieved using 1024 epochs (∼8.5 hrs.). An accuracy = 0.69±0.13 and κ = 0.58±0.18 was achieved on the hold-out test dataset, proving the generalizability and robustness of our approach to raw data collected with a wrist-worn CST.

Brain tumours result in sleep disorders in children and adolescents

BACKGROUND AND OBJECTIVES

Sleep disturbances are frequently reported in children with brain tumours. The objective of our cross-sectional study was to systematically examine sleep in these children. We hypothesised that children with tumours involving the sleep-wake-regulatory areas have an altered sleep-wake-regulation.

METHODS

Sixty-one patients aged 0-18 years and with a diagnosis of a primary brain or cervical medullary tumour were included. They were categorised based upon tumour location into two groups - those affecting the sleep-wake regulatory regions, i.e. brain stem, basal forebrain, hypothalamus, thalamus, and posterior fossa compressing the brain stem and those that did not. Sleep history, questionnaire surveys, polysomnography, and multiple sleep latency test were used, as indicated clinically. Surveys included Pediatric Daytime Sleepiness Scale, Children's Sleep Habits Questionnaire, Strengths and Difficulties Questionnaire, and Pediatric Quality of Life Inventory, Multidimensional Fatigue Scale and Generic Core Scale.

RESULTS

Patients with tumours involving the sleep-wake regulatory areas were sleepier/more fatigued (p = 0.03). Sleep apnoea was observed in 86% of all the patients and comorbid narcolepsy in 8%, without group differences (p ≥ 0.12). Patients with tumours involving the sleep-wake-regulatory areas had more emotional problems (p = 0.04), were more affected by mental health problems (p < 0.001), and had poorer quality of life (p ≤ 0.03).

CONCLUSIONS

Many children with brain tumours suffer from disturbed sleep, poor mental health, and low quality of life. We recommend that systematic sleep evaluation is included in their routine care along with psychological and social support.

Effect of a dynamic lighting intervention on circadian rest-activity disturbances in cognitively impaired, older adults living in a nursing home: A proof-of-concept study

Development of non-pharmacological interventions to improve disrupted rest-activity patterns and disturbed behavior in people with dementia is an important research goal. Here we report a proof-of-concept study which evaluates the effect and applicability of a dynamic light intervention to improve rest-activity patterns in cognitively impaired, institutionalized, older adults. The study was a randomized, open-label, proof-of-concept trial of limited sample size conducted at a nursing home for older adults in a non-metropolitan area in Denmark. Participants were 24 older nursing home residents with cognitive deficiencies. Equipment for delivery of a specialized dynamic light intervention was installed in the private apartments (within the nursing home) of the residents in the experimental group (N = 12). Study duration was four weeks. The control group (N = 12) was exposed to conventional lighting. We measured activity and rest using actigraphy, functional disability, behavioral disturbances, and time in bed We performed regression analyses to examine differences between the intervention groups. Participants in the experimental group partially improved on one of three diurnal rhythm variables, but otherwise no differences were observed between the two intervention groups. The improvement was found for the intradaily variability during the first part of the intervention period indicating a more stable and less fragmented 24-h rest-activity rhythm. However, availability of staff assistance in response to impaired physical mobility of the residents seemed to be a stronger determinant of activity level and pattern. The examined intervention showed promising results but did not consistently alter circadian rest-activity patterns in older nursing home residents given the current sample size. Future studies in the field need to consider real-life applicability of the experimental intervention and the interaction and importance of other important zeitgebers than light.

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Circadian rest-activity disturbances are frequent in nursing home residents.

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Dynamic lighting might stabilize certain aspects of circadian disruption.

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Future interventions should include zeitgebers other than light.

Pre-treatment of blood samples reveal normal blood hypocretin/orexin signal in narcolepsy type 1

The hypocretin/orexin system regulates arousal through central nervous system mechanisms and plays an important role in sleep, wakefulness and energy homeostasis. It is unclear whether hypocretin peptides are also present in blood due to difficulties in measuring reliable and reproducible levels of the peptides in blood samples. Lack of hypocretin signalling causes the sleep disorder narcolepsy type 1, and low concentration of cerebrospinal fluid hypocretin-1/orexin-A peptide is a hallmark of the disease. This measurement has high diagnostic value, but performing a lumbar puncture is not without discomfort and possible complications for the patient. A blood-based test to assess hypocretin-1 deficiency would therefore be of obvious benefit. We here demonstrate that heating plasma or serum samples to 65°C for 30 min at pH 8 significantly increases hypocretin-1 immunoreactivity enabling stable and reproducible measurement of hypocretin-1 in blood samples. Specificity of the signal was verified by high-performance liquid chromatography and by measuring blood samples from mice lacking hypocretin. Unspecific background signal in the assay was high. Using our method, we show that hypocretin-1 immunoreactivity in blood samples from narcolepsy type 1 patients does not differ from the levels detected in control samples. The data presented here suggest that hypocretin-1 is present in the blood stream in the low picograms per millilitres range and that peripheral hypocretin-1 concentrations are unchanged in narcolepsy type 1.

Large genome-wide association study identifies three novel risk variants for restless legs syndrome

Restless legs syndrome (RLS) is a common neurological sensorimotor disorder often described as an unpleasant sensation associated with an urge to move the legs. Here we report findings from a meta-analysis of genome-wide association studies of RLS including 480,982 Caucasians (cases = 10,257) and a follow up sample of 24,977 (cases = 6,651). We confirm 19 of the 20 previously reported RLS sequence variants at 19 loci and report three novel RLS associations; rs112716420-G (OR = 1.25, P = 1.5 × 10-18), rs10068599-T (OR = 1.09, P = 6.9 × 10-10) and rs10769894-A (OR = 0.90, P = 9.4 × 10-14). At four of the 22 RLS loci, cis-eQTL analysis indicates a causal impact on gene expression. Through polygenic risk score for RLS we extended prior epidemiological findings implicating obesity, smoking and high alcohol intake as risk factors for RLS. To improve our understanding, with the purpose of seeking better treatments, more genetics studies yielding deeper insights into the disease biology are needed.

Cognitive behavioural therapy for insomnia in patients with rheumatoid arthritis: protocol for the randomised, single-blinded, parallel-group Sleep-RA trial

BACKGROUND

More than half of patients with rheumatoid arthritis complain of insomnia, which is predominantly treated with hypnotic drugs. However, cognitive behavioural therapy for insomnia is recommended as the first-line treatment in international guidelines on sleep. Patients with rheumatoid arthritis suffer from debilitating symptoms, such as fatigue and pain, which can also be linked to sleep disturbance. It remains to be determined whether cognitive behavioural therapy for insomnia can be effective in patients with rheumatoid arthritis. The aim of the Sleep-RA trial is to investigate the efficacy of cognitive behavioural therapy for insomnia on sleep and disease-related symptoms in patients with rheumatoid arthritis. The primary objective is to compare the effect of cognitive behavioural therapy for insomnia relative to usual care on changes in sleep efficiency from baseline to week 7 in patients with rheumatoid arthritis. The key secondary objectives are to compare the effect of cognitive behavioural therapy for insomnia relative to usual care on changes in sleep onset latency, wake after sleep onset, total sleep time, insomnia, sleep quality, fatigue, impact of rheumatoid arthritis and depressive symptoms from baseline to week 26 in patients with rheumatoid arthritis.

METHODS

The Sleep-RA trial is a randomised controlled trial with a two-group parallel design. Sixty patients with rheumatoid arthritis, insomnia and low-to-moderate disease activity will be allocated 1:1 to treatment with cognitive behavioural therapy for insomnia or usual care. Patients in the intervention group will receive nurse-led, group-based cognitive behavioural therapy for insomnia once a week for 6 weeks. Outcome assessments will be carried out at baseline, after treatment (week 7) and at follow-up (week 26).

DISCUSSION

Data on treatment of insomnia in patients with rheumatoid arthritis are sparse. The Sleep-RA trial is the first randomised controlled trial to investigate the efficacy of cognitive behavioural therapy for insomnia in patients with rheumatoid arthritis. Because symptoms of rheumatoid arthritis and insomnia have many similarities, we also find it relevant to investigate the secondary effects of cognitive behavioural therapy for insomnia on fatigue, impact of rheumatoid arthritis, depressive symptoms, pain, functional status, health-related quality of life and disease activity. If we find cognitive behavioural therapy for insomnia to be effective in patients with rheumatoid arthritis this will add weight to the argument that evidence-based non-pharmacological treatment for insomnia in rheumatological outpatient clinics is eligible in accordance with the existing international guidelines on sleep.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT03766100. Registered on 30 November 2018.

A Blind Source-Based Method for Automated Artifact-Correction in Standard Sleep EEG

Electroencephalogram (EEG) is a common tool in sleep medicine, but it is often compromised by non-neural artifacts. Excluding visually identified artifacts is time-consuming and removes relevant EEG information. Blind source separation (BSS) techniques, on the other hand, are capable of separating "brain" from "artifact source components". Existing algorithms for automated component labeling require either a priori morphological information or adaptation to individual recordings. We present a method for the automated identification of artifact components based on their autocorrelation and spectral properties. It requires no tuning for individual recordings. The method was tested on 100 one-minute EEG segments during rapid eye movement sleep. EEG source components were estimated by second order blind source identification and, as reference, manually labeled as "brain" or "artifact component". The algorithm identified electro-cardiogram components by autocorrelation peaks between 0.5-1.5 seconds and -oculogram components by linear discriminant analysis of spectral band-power. Using 5-fold cross-validation, we observed 97% accuracy (95% sensitivity, 98% specificity), as well as minimized correlation of artifacts and the EEG. The approach has demonstrated its potential as promising tool for a broad range of sleep medical applications.

Automatic, electrocardiographic-based detection of autonomic arousals and their association with cortical arousals, leg movements, and respiratory events in sleep

Study Objectives

The current definition of sleep arousals neglects to address the diversity of arousals and their systemic cohesion. Autonomic arousals (AA) are autonomic activations often associated with cortical arousals (CA), but they may also occur in relation to a respiratory event, a leg movement event or spontaneously, without any other physiological associations. AA should be acknowledged as essential events to understand and explore the systemic implications of arousals.

Methods

We developed an automatic AA detection algorithm based on intelligent feature selection and advanced machine learning using the electrocardiogram. The model was trained and tested with respect to CA systematically scored in 258 (181 training size/77 test size) polysomnographic recordings from the Wisconsin Sleep Cohort.

Results

A precision value of 0.72 and a sensitivity of 0.63 were achieved when evaluated with respect to CA. Further analysis indicated that 81% of the non-CA-associated AAs were associated with leg movement (38%) or respiratory (43%) events.

Conclusions

The presented algorithm shows good performance when considering that more than 80% of the false positives (FP) found by the detection algorithm appeared in relation to either leg movement or respiratory events. This indicates that most FP constitute autonomic activations that are indistinguishable from those with cortical cohesion. The proposed algorithm provides an automatic system trained in a clinical environment, which can be utilized to analyze the systemic and clinical impacts of arousals.

Cerebral blood flow, oxygen metabolism, and lactate during hypoxia in patients with obstructive sleep apnea

Study Objectives

Obstructive sleep apnea (OSA) is associated with increased risk of stroke but the underlying mechanism is poorly understood. We suspect that the normal cerebrovascular response to hypoxia is disturbed in patients with OSA.

Methods

Global cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), and lactate concentration during hypoxia were measured in patients with OSA and matched controls. Twenty-eight patients (82.1% males, mean age 52.3 ± 10.0 years) with moderate-to-severe OSA assessed by partial polysomnography were examined and compared with 19 controls (73.7% males, mean age 51.8 ± 10.1 years). Patients and controls underwent magnetic resonance imaging (MRI) during 35 min of normoxia followed by 35 min inhaling hypoxic air (10%-12% O2). After 3 months of continuous positive airway pressure (CPAP) treatment, 22 patients were rescanned.

Results

During hypoxia, CBF significantly increased with decreasing arterial blood oxygen concentration (4.53 mL (blood)/100 g/min per -1 mmol(O2)/L, p < 0.001) in the control group, but was unchanged (0.89 mL (blood)/100 g/min per -1 mmol(O2)/L, p = 0.289) in the patient group before CPAP treatment. The CBF response to hypoxia was significantly weaker in patients than in controls (p = 0.003). After 3 months of CPAP treatment the CBF response normalized, showing a significant increase during hypoxia (5.15 mL (blood)/100 g/min per -1 mmol(O2)/L, p < 0.001). There was no difference in CMRO2 or cerebral lactate concentration between patients and controls, and no effect of CPAP treatment.

Conclusions

Patients with OSA exhibit reduced CBF in response to hypoxia. CPAP treatment normalized these patterns.

Neuroimaging markers of global cognition in early Alzheimer's disease: A magnetic resonance imaging-electroencephalography study

INTRODUCTION

Magnetic resonance imaging (MRI) and electroencephalography (EEG) are a promising means to an objectified assessment of cognitive impairment in Alzheimer's disease (AD). Individually, however, these modalities tend to lack precision in both AD diagnosis and AD staging. A joint MRI-EEG approach that combines structural with functional information has the potential to overcome these limitations.

MATERIALS AND METHODS

This cross-sectional study systematically investigated the link between MRI and EEG markers and the global cognitive status in early AD. We hypothesized that the joint modalities would identify cognitive deficits with higher accuracy than the individual modalities. In a cohort of 111 AD patients, we combined MRI measures of cortical thickness and regional brain volume with EEG measures of rhythmic activity, information processing and functional coupling in a generalized multiple regression model. Machine learning classification was used to evaluate the markers' utility in accurately separating the subjects according to their cognitive score.

RESULTS

We found that joint measures of temporal volume, cortical thickness, and EEG slowing were well associated with the cognitive status and explained 38.2% of ifs variation. The inclusion of the covariates age, sex, and education considerably improved the model. The joint markers separated the subjects with an accuracy of 84.7%, which was considerably higher than by using individual modalities.

CONCLUSIONS

These results suggest that including joint MRI-EEG markers may be beneficial in the diagnostic workup, thus allowing for adequate treatment. Further studies in larger populations, with a longitudinal design and validated against functional-metabolic imaging are warranted to confirm the results.

The Effects of Naturalistic Light on Diurnal Plasma Melatonin and Serum Cortisol Levels in Stroke Patients during Admission for Rehabilitation: A Randomized Controlled Trial

Background: Stroke patients admitted for rehabilitation often lack sufficient daytime blue light exposure due to the absence of natural light and are often exposed to light at unnatural time points. We hypothesized that artificial light imitating daylight, termed naturalistic light, would stabilize the circadian rhythm of plasma melatonin and serum cortisol levels among long-term hospitalized stroke patients. Methods: A quasi-randomized controlled trial. Stroke patients in need of rehabilitation were randomized between May 1, 2014, and June 1, 2015 to either a rehabilitation unit equipped entirely with always on naturalistic lighting (IU), or to a rehabilitation unit with standard indoor lighting (CU). At both inclusion and discharge after a hospital stay of at least 2 weeks, plasma melatonin and serum cortisol levels were measured every 4 hours over a 24-hour period. Circadian rhythm was estimated using cosinor analysis, and variance between time-points. Results: A total of 43 were able to participate in the blood collection. Normal diurnal rhythm of melatonin was disrupted at both inclusion and discharge. In the IU group, melatonin plasma levels were increased at discharge compared to inclusion (n = 23; median diff, 2.9; IQR: -1.0 to 9.9, p = 0.030) and rhythmicity evolved (n = 23; p = 0.007). In the CU group, melatonin plasma levels were similar between discharge and inclusion and no rhythmicity evolved. Overall, both patient groups showed normal cortisol diurnal rhythms at both inclusion and discharge. Conclusions: This study is the first to demonstrate elevated melatonin plasma levels and evolved rhythmicity due to stimulation with naturalistic light.

A flexible method for the automated offline-detection of artifacts in multi-channel electroencephalogram recordings

Electroencephalogram (EEG) signal quality is often compromised by artifacts that corrupt quantitative EEG measurements used in clinical applications and EEG-related studies. Techniques such as filtering, regression analysis and blind source separation are often used to remove these artifacts. However, these preprocessing steps do not allow for complete artifact correction. We propose a method for the automated offline-detection of remaining artifacts after preprocessing in multi-channel EEG recordings. In contrast to existing methods it requires neither adaptive parameters varying between recordings nor a topography template. It is suited for short EEG segments and is flexible with regard to target applications. The algorithm was developed and tested on 60 clinical EEG samples of 20 seconds each that were recorded both in resting state and during cognitive activation to gain a realistic artifact set. Five EEG features were used to quantify temporal and spatial signal variations. Two distance measures for the single-channel and multi-channel variations of these features were defined. The global thresholds were determined by three-fold cross-validation and Youden's J statistic in conjunction with receiver operating characteristics (ROC curves). We observed high sensitivity of 95.5%±4.8 and specificity of 88.8%±2.1. The method has thus shown great potential and is promising as a possible tool for both EEG-based clinical applications and EEG-related research.

Restless legs syndrome is associated with major comorbidities in a population of Danish blood donors

BACKGROUND

Restless Legs Syndrome (RLS) is characterized by uncomfortable nocturnal sensations in the legs making sedentary activities and sleep difficult, and is thus linked with psychosocial distress. Due to the symptomatology and neurobiology of RLS (disrupting brain iron and dopamine) it is likely that RLS associates with poorer health-related quality of life (HRQL) and depressive disorder. The objective of this study was to investigate the RLS-HRQL and the RLS-depressive disorder links in a generally healthy population that is not biased by medications.

METHODS

Complete data, including the Cambridge-Hopkins RLS questionnaire, the 12-item short-form standardized health survey (SF-12), the Major Depression Inventory (MDI), body mass index, smoking status, alcohol consumption, and education were available for 24,707 participants enrolled in the Danish Blood Donor Study from May 1, 2015 to February 1, 2017. Information on quality of sleep was available for all RLS cases. T-tests and multivariable logistic regression models were applied to examine the associations of RLS and MDI scores, and the physical and mental component scores (PCS and MCS) of SF-12, respectively. Analyses were conducted separately for men and women.

RESULTS

RLS associated with poorer MCS and poorer PCS. Moreover, Participants with RLS were more likely to classify with depressive disorder. Poor quality of sleep was associated with depressive disorder and poorer MCS among RLS cases, and with poorer PCS in female RLS cases.

CONCLUSION

Thus, we demonstrated that RLS is associated with a significantly lower HRQL and a higher prevalence of depressive disorder among otherwise healthy individuals.

Decrease in scale invariance of activity fluctuations with aging and in patients with suprasellar tumors

Motor activity in healthy young humans displays intrinsic fluctuations that are scale-invariant over a wide range of time scales (from minutes to hours). Human postmortem and animal lesion studies showed that the intact function of the suprachiasmatic nucleus (SCN) is required to maintain such scale-invariant patterns. We therefore hypothesized that scale invariance is degraded in patients treated for suprasellar tumors that compress the SCN. To test the hypothesis, we investigated 68 patients with nonfunctioning pituitary macroadenoma and 22 patients with craniopharyngioma, as well as 72 age-matched healthy controls (age range 21.0–70.6 years). Spontaneous wrist locomotor activity was measured for 7 days with actigraphy, and detrended fluctuation analysis was applied to assess correlations over a range of time scales from minutes to 24 h. For all the subjects, complex scale-invariant correlations were only present for time scales smaller than 1.5 h, and became more random at time scales 1.5–10 h. Patients with suprasellar tumors showed a larger decrease in correlations at 1.5–10 h as compared to healthy controls. Within healthy subject, gender and age >33 year were associated with attenuated scale invariance. Conversely, activity patterns at time scales between 10 and 24 h were significantly more regular than all other time scales, and this was mostly associated with age.

In conclusion, scale invariance is degraded in healthy subjects at the ages of >33 year as characterized by attenuation of correlations at time scales 1.5–10 h. In addition, scale invariance was more degraded in patients with suprasellar tumors as compared to healthy subjects.

A Noise-Assisted Data Analysis Method for Automatic EOG-Based Sleep Stage Classification Using Ensemble Learning

Reducing the number of recording modalities for sleep staging research can benefit both researchers and patients, under the condition that they provide as accurate results as conventional systems. This paper investigates the possibility of exploiting the multisource nature of the electrooculography (EOG) signals by presenting a method for automatic sleep staging using the complete ensemble empirical mode decomposition with adaptive noise algorithm, and a random forest classifier. It achieves a high overall accuracy of 82% and a Cohen's kappa of 0.74 indicating substantial agreement between automatic and manual scoring.

A Sleep Position Trainer for positional sleep apnea: a randomized, controlled trial

We tested the effect of the Sleep Position Trainer, a vibrational device, for positional sleep apnea in an open, randomized controlled trial with 101 patients, where 52 patients were allocated to Sleep Position Trainer and 49 patients to a non-treatment control group for 2 months (Part 1). All patients were then followed as a cohort for a period of 6 months with use of the Sleep Position Trainer (Part 2). The participants were assessed with polygraphy at entry, and after 2 and 6 months. The mean apnea-hypopnea index supine was 35 per h (SD, 18) in the Sleep Position Trainer group and 38 per h (SD, 15) in the control group at entry. In a per protocol analysis, the mean total apnea-hypopnea index at entry and after 2 months in the Sleep Position Trainer group was 18 per h (SD, 10) and 10 per h (SD, 9; P < 0.001) versus 20 per h (SD, 9) and 18 per h (SD, 10; NS) in the control group. The mean supine sleep time decreased from 47% (SD, 22) to 17% (SD, 18; P < 0.001) in the Sleep Position Trainer group after 2 months. In the control group, the mean supine sleep time was 48% (SD, 20) at entry and 39% (SD, 21; NS) after 2 months. The positive effect of Sleep Position Trainer was maintained in all patients treated with Sleep Position Trainer after 6 months. Daytime sleepiness improved after 6 months. Compliance with the Sleep Position Trainer device during the first 2 months, defined as use of Sleep Position Trainer >4 h per night for all weekdays, was 75.5% (SD 21.2). The discontinuation rate was 28.8 and 49.4% after 2 and 6 months, respectively.

Normal Morning Melanin-Concentrating Hormone Levels and No Association with Rapid Eye Movement or Non-Rapid Eye Movement Sleep Parameters in Narcolepsy Type 1 and Type 2

STUDY OBJECTIVES

Other than hypocretin-1 (HCRT-1) deficiency in narcolepsy type 1 (NT1), the neurochemical imbalance of NT1 and narcolepsy type 2 (NT2) with normal HCRT-1 levels is largely unknown. The neuropeptide melanin-concentrating hormone (MCH) is mainly secreted during sleep and is involved in rapid eye movement (REM) and non-rapid eye movement (NREM) sleep regulation. Hypocretin neurons reciprocally interact with MCH neurons. We hypothesized that altered MCH secretion contributes to the symptoms and sleep abnormalities of narcolepsy and that this is reflected in morning cerebrospinal fluid (CSF) MCH levels, in contrast to previously reported normal evening/afternoon levels.

METHODS

Lumbar CSF and plasma were collected from 07:00 to 10:00 from 57 patients with narcolepsy (subtypes: 47 NT1; 10 NT2) diagnosed according to International Classification of Sleep Disorders, Third Edition (ICSD-3) and 20 healthy controls. HCRT-1 and MCH levels were quantified by radioimmunoassay and correlated with clinical symptoms, polysomnography (PSG), and Multiple Sleep Latency Test (MSLT) parameters.

RESULTS

CSF and plasma MCH levels were not significantly different between narcolepsy patients regardless of ICSD-3 subtype, HCRT-1 levels, or compared to controls. CSF MCH and HCRT-1 levels were not significantly correlated. Multivariate regression models of CSF MCH levels, age, sex, and body mass index predicting clinical, PSG, and MSLT parameters did not reveal any significant associations to CSF MCH levels.

CONCLUSIONS

Our study shows that MCH levels in CSF collected in the morning are normal in narcolepsy and not associated with the clinical symptoms, REM sleep abnormalities, nor number of muscle movements during REM or NREM sleep of the patients. We conclude that morning lumbar CSF MCH measurement is not an informative diagnostic marker for narcolepsy.

Narcolepsy

Narcolepsy is a chronic sleep disorder that has a typical onset in adolescence and is characterized by excessive daytime sleepiness, which can have severe consequences for the patient. Problems faced by patients with narcolepsy include social stigma associated with this disease, difficulties in obtaining an education and keeping a job, a reduced quality of life and socioeconomic consequences. Two subtypes of narcolepsy have been described (narcolepsy type 1 and narcolepsy type 2), both of which have similar clinical profiles, except for the presence of cataplexy, which occurs only in patients with narcolepsy type 1. The pathogenesis of narcolepsy type 1 is hypothesized to be the autoimmune destruction of the hypocretin-producing neurons in the hypothalamus; this hypothesis is supported by immune-related genetic and environmental factors associated with the disease. However, direct evidence in support of the autoimmune hypothesis is currently unavailable. Diagnosis of narcolepsy encompasses clinical, electrophysiological and biological evaluations, but simpler and faster procedures are needed. Several medications are available for the symptomatic treatment of narcolepsy, all of which have quite good efficacy and safety profiles. However, to date, no treatment hinders or slows disease development. Improved diagnostic tools and increased understanding of the pathogenesis of narcolepsy type 1 are needed and might lead to therapeutic or even preventative interventions.

Sleep spindle alterations in patients with Parkinson's disease

The aim of this study was to identify changes of sleep spindles (SS) in the EEG of patients with Parkinson's disease (PD). Five sleep experts manually identified SS at a central scalp location (C3-A2) in 15 PD and 15 age- and sex-matched control subjects. Each SS was given a confidence score, and by using a group consensus rule, 901 SS were identified and characterized by their (1) duration, (2) oscillation frequency, (3) maximum peak-to-peak amplitude, (4) percent-to-peak amplitude, and (5) density. Between-group comparisons were made for all SS characteristics computed, and significant changes for PD patients vs. control subjects were found for duration, oscillation frequency, maximum peak-to-peak amplitude and density. Specifically, SS density was lower, duration was longer, oscillation frequency slower and maximum peak-to-peak amplitude higher in patients vs. controls. We also computed inter-expert reliability in SS scoring and found a significantly lower reliability in scoring definite SS in patients when compared to controls. How neurodegeneration in PD could influence SS characteristics is discussed. We also note that the SS morphological changes observed here may affect automatic detection of SS in patients with PD or other neurodegenerative disorders (NDDs).

Sleep in cluster headache - beyond a temporal rapid eye movement relationship?

BACKGROUND AND PURPOSE

Cluster headache (CH) is a primary headache disorder characterized by severe attacks of unilateral pain following a chronobiological pattern. There is a close connection with sleep as most attacks occur during sleep. Hypothalamic involvement and a particular association with rapid eye movement (REM) sleep have been suggested. Sleep in a large, well-characterized population of CH patients was investigated.

METHODS

Polysomnography (PSG) was performed on two nights in 40 CH patients during active bout and one night in 25 age, sex and body mass index matched controls in hospital. Macrostructure and other features of sleep were analyzed and related to phenotype. Clinical headache characterization was obtained by semi-structured interview.

RESULTS

Ninety-nine nights of PSG were analyzed. Findings included a reduced percentage of REM sleep (17.3% vs. 23.0%, P = 0.0037), longer REM latency (2.0 vs. 1.2 h, P = 0.0012) and fewer arousals (7.34 vs. 14.1, P = 0.003) in CH patients. There was no difference in prevalence of sleep apnea between patients (38%) and matched controls (32%, P = 0.64) although the apnea index in patients was numerically higher (mean apnea-hypopnea index 10.75 vs. 4.93). No temporal association between nocturnal attacks (n = 45) and particular sleep stages was observed.

CONCLUSIONS

To date, this is the largest study of sleep in CH. It is demonstrated that REM sleep is affected which is in line with our current understanding of CH and hypothalamic involvement in the regulation of this sleep stage. Further, fewer arousals were found in CH patients but no association between apnea events or specific sleep stages. The findings support a central role of the hypothalamus and arousal systems in CH.

Prepulse inhibition is associated with attention, processing speed, and 123I-FP-CIT SPECT in Parkinson's disease

BACKGROUND

Prepulse inhibition is a measure of sensorimotor gating, which reflects the ability to filter or 'gate' irrelevant information. Prepulse inhibition is dramatically altered in basal ganglia disorders associated with dysfunction in the midbrain dopaminergic system, and corresponding cognitive information processing deficits such as slowed processing speed. Parkinson's disease is characterised by the degeneration of the midbrain dopaminergic system and is associated with cognitive dysfunction, including slowed information processing. Although sensorimotor processes in Parkinson's disease have been extensively studied in relation to motor function, less is known about the potential role of sensorimotor processes in cognitive function.

OBJECTIVE

We investigated the relationship between prepulse inhibition, cognition and nigrostriatal dysfunction, as measured with 123I-FP-CIT-SPECT scanning, in patients with Parkinson's disease.

METHODS

38 Parkinson patients were assessed with prepulse inhibition, neuropsychological tests, and neurological investigation. A subset of these patients underwent 123I-FP-CIT-SPECT scanning.

RESULTS

Patients with a higher level of prepulse inhibition performed better on cognitive measures tapping attention and processing speed than patients with a lower level of prepulse inhibition. Furthermore, there were significant correlations between prepulse inhibition and 123I-FP-CIT uptake in the striatum.

CONCLUSIONS

Our results suggest that the level of prepulse inhibition is related to the efficiency of information processing in Parkinson's disease, and to the density of dopamine transporters in the striatum.

Validation of the ICSD-2 criteria for CSF hypocretin-1 measurements in the diagnosis of narcolepsy in the Danish population

STUDY OBJECTIVES

The International Classification of Sleep Disorders (ICSD-2) criteria for low CSF hypocretin-1 levels (CSF hcrt-1) still need validation as a diagnostic tool for narcolepsy in different populations because inter-assay variability and different definitions of hypocretin deficiency complicate direct comparisons of study results.

DESIGN AND PARTICIPANTS

Interviews, polysomnography, multiple sleep latency test, HLA-typing, and CSF hcrt-1 measurements in Danish patients with narcolepsy with cataplexy (NC) and narcolepsy without cataplexy (NwC), CSF hcrt-1 measurements in other hypersomnias, neurological and normal controls. Comparisons of hypocretin deficiency and frequency of HLA-DQB1*0602-positivity in the Danish and eligible NC and NwC populations (included via MEDLINE search), by (re)calculation of study results using the ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean).

MEASUREMENTS AND RESULTS

In Danes, low CSF hcrt-1 was present in 40/46 NC, 3/14 NwC and 0/106 controls (P < 0.0001). Thirty-nine of 41 NC and 4/13 NwC patients were HLA-DQB1*0602-positive (P < 0.01). Hypocretin-deficient NC patients had higher frequency of cataplexy, shorter mean sleep latency, more sleep onset REM periods (P < 0.05) and more awakenings (NS) than did NC patients with normal CSF hcrt-1. Across populations, low CSF hcrt-1 and HLA-DQB1*0602-positivity characterized the majority of NC (80% to 100%, P = 0.53; 80% to 100%, P = 0.11) but a minority of NwC patients (11% to 29%, P = 0.75; 29% to 89%, P = 0.043).

CONCLUSION

The study provides evidence that hypocretin deficiency causes a more severe NC phenotype. The ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean) is valid for diagnosing NC, but not NwC. HLA-typing should precede CSF hcrt-1 measurements because hypocretin deficiency is rare in HLA-DQB1*0602-negative patients.

Normal levels of cerebrospinal fluid hypocretin-1 and daytime sleepiness during attacks of relapsing-remitting multiple sclerosis and monosymptomatic optic neuritis

There is emerging evidence that multiple sclerosis (MS), the hypothalamic sleep-wake regulating neuropeptide hypocretin-1 (hcrt-1) and the sleep disorder narcolepsy may be connected. Thus, the major pathophysiological component of narcolepsy is lack of hcrt-1. Dysfunction of the hypocretin system has been reported in MS case reports with attacks of hypothalamic lesions, undetectable cerebrospinal fluid (CSF) hcrt-1 and hypersomnia, but not found during remission in small samples. Finally, daytime sleepiness, the major symptom of narcolepsy, is reported in several MS populations, and there are case reports of co-existent narcolepsy and MS. However, it is unknown whether hcrt-1 and daytime sleepiness generally change during MS attacks. We therefore analyzed whether daytime sleepiness (using the Epworth Sleepiness Scale (ESS)) and CSF hcrt-1 levels differed between MS attack and remission, in 48 consecutively referred patients with relapsing–remitting MS (RRMS) or monosymptomatic optic neuritis (MON). Twenty-seven patients were in attack and 21 in remission. ESS was normal both during attacks (5.4 ± 3.0) and remission (5.8 ± 2.6), and mean CSF hcrt-1 was normal (456 ± 41 pg/ml). No statistically significant differences were found between attack and remission. MRI scans revealed no hypothalamic lesions. The results show that the hypocretin system is intact and sleepiness is not typical in RRMS and MON without hypothalamic lesions on MRI.

[Whiplash injury syndrome. A prospective study of 39 patients with whiplash injury]

The acute symptoms after whiplash trauma can be explained by the neck sprain, but the pathogenesis of the "late whiplash syndrome" and the reasons why only some people have persistent symptoms more than six months are still unknown. Thirty-four consecutive cases of piskesmaeld injury were examined clinically three times; respectively within 14 days, after one month and finally seven months post-injury. In addition, MRI of the brain and the cervical spine, neuropsychological tests and motor evoked potentials (MEP) were done one month post-injury and repeated after six months, if abnormalities were found. We found the total recovery rate (asymptomatic patients) was 29% after seven months. All MEP examinations were normal. The correlation between MRI and the clinical findings was poor. Cognitive dysfunction as a symptom of brain injury was not found. Stress at the same time as the accident predicted more symptoms at follow-up. We conclude that long-lasting distress and poor outcome were more related to the occurrence of stressful life events than to clinical and paraclinical findings.

[Cognitive symptoms in persons with snoring and sleep apnea. An epidemiologic study of 1.504 women and men aged 30-60 years. The Dan-MONICA II study]

The objective of the study was to evaluate the relation between every-night (habitual) snoring, sleep apnoea and cognitive complaints (concentration and memory complaints) in an adult population-based sample. In the DAN-MONICA (MONItoring trends in CArdiovascular iseases) 1504 males and females aged 30, 40, 50 and 60 years were classified according to their snoring habits. Nocturnal respiration was measured in 748 participants. The following measures were regarded as potential confounders: age, gender, unintended sleepiness, insomnia, depression, hypnotic use, alcohol consumption by questionnaire, body mass index (BMI) and blood pressure. Concentration and memory problems were both related to depression, insomnia and unintended sleepiness. Snoring and sleep apnoea (defined as a respiratory distress index-RDI > or = 5) were associated with concentration problems and unintended sleepiness. The odds ratios (95% confidence intervals) between snoring, concentration and memory problems, calculated by logistic regression analysis after adjustments for the above confounders, were 1.90 (1.23-2.91, p < 0.01) and 1.38 (0.97-1.99, NS). For those with sleep apnoea, the odds ratios were 3.53 (1.42-8.73. p < 0.001) and 1.51 (0.81-2.14, NS) for concentration and memory problems, respectively. The main conclusion drawn from this study is that cognitive complaints show a high correlation to mood, insomnia and hypersomnia. Habitual snoring and sleep apnoea show a correlation to concentration problems, but not to memory problems. This suggests that part of the association between snoring, sleep apnoea and cognitive dysfunction is related to the presence of sleep disturbances and daytime sleepiness.

[Muscle biopsies in patients with fibromyalgia. A study based on light and electron microscopy]

The value of muscle biopsy in fibromyalgia is still questioned. In this study we obtained 49 quadriceps biopsies from 20 patients and compared them blindly to 15 biopsies from five normal controls. Using light microscopy, histochemical and immunoenzymatic methods we found no definite evidence of muscle disease. Nevertheless, we subjected biopsies from nine of the patients and five other controls for further ultrastructural evaluations and demonstrated pathologic findings e.g. empty sleeves of basement membrane, many lipofuscin bodies and other degenerative changes. We conclude that ultrastructural evaluation cannot yet be used for diagnostic purposes, but the negative findings at light microscopy, including histochemical and immunoenzymatic techniques, might be of importance in evaluating difficult cases.

[Preoperative EEG in medically intractable epilepsy]

The aim of the preoperative neurophysiological investigations is to identify the primary epileptogenic focus and its relation to functional cortical areas. The investigations include interictal and ictal extracranial (scalp) electroencephalography (EEG) and invasive methods (depth, subdural, foramen ovale electrodes and peroperative electrocorticography). If an epileptic focus is located in the anterior part of the temporal lobe by the use of scalp EEG, this is normally regarded as sufficient for an anterior lobectomy. However, because of poor spatial resolution by scalp EEG, it is difficult to separate mesial from lateral foci, identify the exact extent of posterior temporal or extra-temporal foci, identify the primary focus in patients with bilateral abnormalities and identify cases with minor scalp EEG-changes. As invasive EEG shows higher spatial resolution and gives an opportunity to evaluate functional areas, invasive EEG has significant advantages in these patients. Use of invasive EEG bears a slightly increased risk and discomfort to the patient, but is necessary in the presurgical evaluation of some patients suffering from medically intractable epilepsy.

[Cardiovascular risk factors in snorers. The Copenhagen Male Study]

Former studies on the association between snoring and cardiovascular disease (CVD) have only partly taken established CVD risk factors into consideration. In the Copenhagen Male Study, 3323 men aged 54-74 years were classified according to self-reported snoring habits. Eleven CVD risk factors were examined. The prevalence of snoring decreased with age, with a 50% higher frequency of snorers in the youngest quintile than in the oldest, p < 0.00001. Snoring, age adjusted, was positively associated with tobacco smoking, p < 0.001, alcohol consumption p < 0.0001, body mass index (BMI), p < 0.0001, serum triglyceride level, p < 0.01, systolic blood pressure, p < 0.05 and diastolic blood pressure, p = 0.07. Snorers were less physically active in leisure time than others, p < 0.01. The association between self-reported snoring and blood pressure disappeared when other factors, including BMI, were taken into consideration. No significant associations were found between snoring and social class, snoring and low or high density lipoprotein, nor between snoring and hypertension. We conclude that snoring is associated with major cardiovascular risk factors. Accordingly, it is evident that in studies on snoring and cardiovascular disease, proper controlling for the influence of potential confounders is a sine qua non.

White lead exposure among Danish police officers employed in fingerprint detection

White lead exposure among Danish police officers employed in fingerprint detection. Scand j work environ health 9 (1983) 511-513. White lead is often used by police officers employed in fingerprint detection (dactylography). On the basis of a case of mild lead intoxication in a police officer all 22 exposed police officers at the Bureau of Dactylographic Identification in Copenhagen were examined. All went through a clinical examination and blood lead determination. None of the participants showed any sign of lead intoxication. The median blood lead concentration was 0.97 mumol/l (10th-90th percentiles 0.72-1.44 mumol/l), a value definitely higher than the average of the general population matched for age and sex. A correlation between the weekly white lead exposure and blood lead concentration (r = 0.87, p less than 0.0001) was found among the participants.