M Kerkhofs

Centre Hospitalier Universitaire de Charleroi, Charleroi, Walloon Region, Belgium

Are you M Kerkhofs?

Claim your profile

Publications (113)362.06 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The aim of this pilot study was to explore the risk of metabolic abnormalities in steel workers employed in different shift-work rotations. Male workers in a steel factory [16 employed in a fast clockwise rotation (CW), 18 in slow counterclockwise rotation (CC), 9 day workers (DW); mean age 43.3 ± SD 6.8 years] with at least 5 years experience in their current work schedule participated. All workers provided fasting blood samples between 06:00 and 08:00 h for plasma glucose, insulin, apo-lipoproteins A and B (ApoA, ApoB), high- and low-density lipoproteins (HDL and LDL), total cholesterol (tCH), triglycerides (TG), minimally oxidized (mox) LDL, C-reactive protein (CRP), interleukin-8 (IL-8) and serum 25-hydroxyvitamin D (25(OH)D). HOMA index (homeostatic model assessment) was calculated to evaluate insulin resistance, beta cell function and risk of diabetes. Information on demographics, health, stimulants, sleep, social and work life, chronotype (phase of entrainment) and social jetlag (difference between mid-sleep on workdays and free days) as a surrogate for circadian disruption was collected by questionnaire. Neither chronotype nor social jetlag was associated with any of the metabolic risk blood markers. There were no significant differences in 25(OH)D, ApoA, ApoB, CRP, HDL, IL-8, insulin, LDL, mox-LDL, mox-LDL/ApoB ratio, tCH and TG levels between the three work groups. Although we did observe absolute differences in some of these markers, the small sample size of our study population might prevent these differences being statistically significant. Fasting glucose and HOMA index were significantly lower in CW compared to DW and CC, indicating lower metabolic risk. Reasons for the lower fasting glucose and HOMA index in CW workers remains to be clarified. Future studies of workers in different shift rotations are warranted to understand better the differential effects of shift-work on individual workers and their health indices.
    Chronobiology International 09/2014; Sep 4:1-7.. · 4.35 Impact Factor
  • Médecine du Sommeil 01/2014; 11(1):21.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Intermittent hypoxia (hypoxia-reoxygenation) is often associated with cardiovascular morbidity and mortality. We describe a new device which can be used to submit cohorts of mice to controlled and standardised hypoxia-normoxia cycles at an individual level. Mice were placed in individual compartments to which similar gas flow parameters were provided using an open loop strategy. Evaluations made using computational fluid dynamics were confirmed by studying changes in haemoglobin oxygen saturation in vivo. We also modified the parameters of the system and demonstrated its ability to generate different severities of cyclic hypoxemia very precisely, even with very high frequency cycles of hypoxia-reoxygenation. The importance of the parameters on reoxygenation was shown. This device will allow investigators to assess the effects of hypoxia–reoxygenation on different pathological conditions, such as obstructive sleep apnoea or chronic obstructive pulmonary disease.
    PLoS ONE 04/2013; 8(4):e59973. · 3.53 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: OBJECTIVE: Dehydroepiandrosterone (DHEA) administration is widely evocated as a "fountain of youth", but previous studies have provided inconsistent results. We aimed to investigate in healthy postmenopausal women the effects of a 3-wk oral DHEA administration on individual steroid levels, multiple 24-h hormonal profiles and sleep architecture. DESIGN: Seven healthy non-obese postmenopausal women, off hormone replacement therapy for ≥2 months, were investigated in a randomized, cross-over, double-blind, placebo-controlled study. For 3 wk, subjects took daily at 2300 h a capsule of either 50 mg DHEA or placebo. Sleep was polygraphically recorded during the last two nights, blood samples were drawn at 15-min intervals during the last 24 h. RESULTS: Under DHEA, testosterone and estradiol levels were increased in all individuals. Individual increments were highly variable, not related to each other, and were not related to placebo values. However, the testosterone to estradiol ratio was markedly increased under DHEA. DHEA administration had little, if any, effect on thyroid function, GH secretion, prolactin, ACTH and cortisol profiles. DHEA effects on sleep appeared to be mediated by its conversion to androgens and estrogens: sleep quality was enhanced by increments in testosterone and dampened by increments in estradiol levels. CONCLUSION: Since DHEA-induced elevations in testosterone and estradiol levels varied widely between individuals and were largely unpredictable, DHEA administration might not be the most appropriate approach to compensate for the reduction observed in androgen and estrogen production in postmenopausal women. DHEA supplementation may result either in sleep stimulation or inhibition, depending on the ratio between DHEA-induced increments in testosterone vs. estradiol. © 2013 Blackwell Publishing Ltd.
    Clinical Endocrinology 03/2013; · 3.40 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: OBJECTIVE: The aim of this study was to identify atherosclerotic risk using pulse wave velocity (PWV) in steel workers employed in different shift-work rotations, and to elucidate its relationship to social jetlag and shift schedule details. PARTICIPANTS: Male workers in a steel factory (n=77, 32 fast clockwise (CW), 30 slow counterclockwise (CC), 15 day workers (DW); mean age 42 ± SD 7.6 yrs) with at least 5 years of experience in their current work schedule participated. METHODS: All workers completed questionnaires on demographics, health, psychotropic agents, sleep, social and work life, social jetlag (difference between mid-sleep time on workdays and days off used as a marker of circadian disruption) and chronotype (mid-sleep time on free days corrected for sleep deficit on workdays). In 63 workers we measured PWV, blood pressure (BP), heart rate (HR) between 08:00 and 12:30 h in controlled posture conditions (no caffeine/smoking/exercise). RESULTS: There was no significant difference in PWV (covariates: age, BP) between the different shift-rotations (CW, CC and DW). In all workers combined, HR and social jetlag were significantly positively correlated. Demographic variables did not differ between shift-workers and day workers; shift-workers (CW, CC) reported significantly more stomach upsets, digestion problems, weight fluctuations, and social jetlag. The CW and CC workers did not differ in ratings of how shift-work affected sleep, social and work life. CONCLUSIONS: PWV was not different between the two shift-rotations. This pilot study shows first evidence that HR is related to social jetlag, and therefore warrants more studies in different shift schedules.
    Work 01/2013; · 0.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 1Charite´ University Hospitals, Berlin, DE, 2CBMT, Charleroi, BE, 3ArcelorMittal Industeel Belgium, Charleroi, BE, 4University of Surrey, Guildford, UK, 5Free University of Brussels, Charleroi, BE, 6University of Basel, Basel, CH Objective: Pulse wave velocity (PWV; a marker for atherosclerotic risk), glucose, insulin and social jetlag (difference between mid-sleep time on workdays and days off used as a marker of circadian disruption) were measured in rotating shift-workers (fast clockwise (CW), slow counterclockwise (CC)), and day workers (DW), to test for differential effects in different shift rotations. Methods: Seventy-seven male steel workers (42 ± 7.6 years, mean ± SD) completed questionnaires on demographics, health, stimulants, sleep, social and work life, social jetlag and chronotype (mid-sleep time on free days corrected for sleep deficit on workdays). We measured PWV, blood pressure (BP) and heart rate (HR) between 08:00 and 12:30 h in controlled posture conditions (no caffeine/smoking/exercise) in 63 workers, of which 37 provided fasting blood samples (06:00–08:00 h) for assessment of plasma glucose and insulin. Results: Age, body mass index (BMI), waist-hip-ratio (WHR), BP, HR, smoking, coffee consumption and chronotype did not differ between shift-workers and day workers. Shift-workers (CW, CC) reported significantly more stomach upsets (+44.8%, P = 0.021), digestion problems (+42.3%, P = 0.017), weight fluctuations (+38%, P = 0.008) and social jetlag (P = 0.001). The CW and CC workers did not differ in ratings of how shift-work affected sleep, social and work life. There was no significant difference in PWV (covariates: age, BP) between the three groups. In all workers combined, HR and social jetlag were significantly positively correlated (r = 0.309, P = 0.021, adjusted for age). Glucose was significantly higher in DW (6.1 ± 0.4 mM, mean ± SEM) compared to CW (4.7 ± 0.3 mM) (P = 0.022, covariates: age, BMI, WHR). There was no difference in insulin levels between the three groups. Conclusions: Although PWV was not different between the two shift-rotations this pilot study shows first evidence of HR being associated with social jetlag. The observed differences between different shift rotations and day workers warrant further studies of this type. Supported by the DFG (German Research Foundation) and the 6th Framework Project EUCLOCK (018471).
    21st Congress of the European Sleep Research Society; 09/2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Previous studies have shown increased sleepiness and mood changes in shiftworkers, which may be due to sleep deprivation or circadian disruption. Few studies, however, have compared responses of experienced shiftworkers and non-shiftworkers to sleep deprivation in an identical laboratory setting. The aim of this laboratory study, therefore, was to compare long-term shiftworkers and non-shiftworkers and to investigate the effects of one night of total sleep deprivation (30.5 h of continuous wakefulness) and recovery sleep on psychomotor vigilance, self-rated alertness, and mood. Eleven experienced male shiftworkers (shiftwork ≥5 yrs) were matched with 14 non-shiftworkers for age (mean ± SD: 35.7 ± 7.2 and 32.5 ± 6.2 yrs, respectively) and body mass index (BMI) (28.7 ± 3.8 and 26.6 ± 3.4 kg/m(2), respectively). After keeping a 7-d self-selected sleep/wake cycle (7.5/8 h nocturnal sleep), both groups entered a laboratory session consisting of a night of adaptation sleep and a baseline sleep (each 7.5/8 h), a sleep deprivation night, and recovery sleep (4-h nap plus 7.5/8 h nighttime sleep). Subjective alertness and mood were assessed with the Karolinska Sleepiness Scale (KSS) and 9-digit rating scales, and vigilance was measured by the visual psychomotor vigilance test (PVT). A mixed-model regression analysis was carried out on data collected every hour during the sleep deprivation night and on all days (except for the adaptation day), at .25, 4.25, 5.25, 11.5, 12.5, and 13.5 h after habitual wake-up time. Despite similar circadian phase (melatonin onset), demographics, food intake, body posture, and environmental light, shiftworkers felt significantly more alert, more cheerful, more elated, and calmer than non-shiftworkers throughout the laboratory study. In addition, shiftworkers showed a faster median reaction time (RT) compared to non-shiftworkers, although four other PVT parameters did not differ between the groups. As expected, both groups showed a decrease in subjective alertness and PVT performance during and following the sleep deprivation night. Subjective sleepiness and most aspects of PVT performance returned to baseline levels after a nap and recovery sleep. The mechanisms underlying the observed differences between shiftworkers and non-shiftworkers require further study, but may be related to the absence of shiftwork the week prior to and during the laboratory study as well as selection into and out of shiftwork.
    Chronobiology International 06/2012; 29(5):537-48. · 4.35 Impact Factor
  • Médecine du Sommeil 04/2012; 9(2):45–46.
  • Source
    Myriam Kerkhofs, Karim Zouaoui Boudjeltia
    Sleep 01/2012; 35(7):895-6. · 5.10 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In addition to its effects on cognitive function, compelling evidence links sleep loss to alterations in the neuroendocrine, immune and inflammatory systems with potential negative public-health ramifications. The evidence to suggest that shorter sleep is associated with detrimental health outcomes comes from both epidemiological and experimental sleep deprivation studies. This review will focus on the post-sleep deprivation and recovery changes in immune and inflammatory functions in well-controlled sleep restriction laboratory studies. The data obtained indicate non-specific activation of leukocyte populations and a state of low-level systemic inflammation after sleep loss. Furthermore, one night of recovery sleep does not allow full recovery of a number of these systemic immune and inflammatory markers. We will speculate on the mechanism(s) that link(s) sleep loss to these responses and to the progression of cardiovascular disease. The immune and inflammatory responses to chronic sleep restriction suggest that chronic exposure to reduced sleep (<6 h/day) and insufficient time for recovery sleep could have gradual deleterious effects, over years, on cardiovascular pathogenesis with a heightened risk in women and in night and shift workers. Finally, we will examine countermeasures, e.g., napping or sleep extension, which could improve the recovery processes, in terms of alertness and immune and inflammatory parameters, after sleep restriction.
    Sleep Medicine Reviews 08/2011; 16(2):137-49. · 8.68 Impact Factor
  • Source
    S Devuyst, T Dutoit, P Stenuit, M Kerkhofs
    [Show abstract] [Hide abstract]
    ABSTRACT: Since the 1970s, various automatic sleep spindles procedures have been implemented and presented in the literature. Unfortunately, their results are not easily comparable because the databases, the assessment methods and the terminologies employed are often radically different. In this study, we propose a systematic assessment method for any automatic sleep spindles detection algorithm. We apply this assessment method to our own automatic detection process in order to illustrate and legitimate its use. We obtain a global sensitivity of 70.20%, for a false positive proportion (relative to the total number of visually scored sleep spindles) of only 26.44% (False positive rate = 1.38% and specificity = 98.62%).
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 08/2011; 2011:1713-6.
  • [Show abstract] [Hide abstract]
    ABSTRACT: A number of neuroactive progesterone metabolites produce sedative-like effects. However, the effects of progesterone administration on sleep are not well characterized. To investigate the effects of a 3-wk progesterone administration on sleep architecture and multiple hormonal profiles. Eight healthy postmenopausal women, 48-74 yr old, without sleep complaints or vasomotor symptoms. None was on hormone replacement therapy. They did not take any medication for ≥ 2 months. Randomized, double-blind, placebo-controlled study. For 3 wk, subjects took daily at 2300 h a capsule of either 300 mg of progesterone or placebo. Sleep was polygraphically recorded during the last two nights, and blood samples were obtained at 15-min intervals for 24 h. During the first night (no blood sampling), sleep was similar in both conditions. Under placebo, blood sampling procedure was associated with marked sleep disturbances, which were considerably reduced under progesterone treatment: mean duration of wake after sleep onset was 53% lower, slow-wave sleep duration almost 50% higher, and total slow-wave activity (reflecting duration and intensity of deep sleep) almost 45% higher under progesterone than under placebo (P ≤ 0.05). Nocturnal GH secretion was increased, and evening and nocturnal TSH levels were decreased under progesterone (P ≤ 0.05). Progesterone had no effect on undisturbed sleep but restored normal sleep when sleep was disturbed (while currently available hypnotics tend to inhibit deep sleep), acting as a "physiologic" regulator rather than as a hypnotic drug. Use of progesterone might provide novel therapeutic strategies for the treatment of sleep disturbances, in particular in aging where sleep is fragmented and of lower quality.
    The Journal of Clinical Endocrinology and Metabolism 02/2011; 96(4):E614-23. · 6.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Understanding the interactions between sleep and the immune system may offer insight into why short sleep duration has been linked to negative health outcomes. We, therefore, investigated the effects of napping and extended recovery sleep after sleep restriction on the immune and inflammatory systems and sleepiness. After a baseline night, healthy young men slept for a 2-h night followed by either a standard 8-h recovery night (n=12), a 30-min nap (at 1 p.m.) in addition to an 8-h recovery night (n=10), or a 10-h extended recovery night (n=9). A control group slept 3 consecutive 8-h nights (n=9). Subjects underwent continuous electroencephalogram polysomnography and blood was sampled every day at 7 a.m. Leukocytes, inflammatory and atherogenesis biomarkers (high-sensitivity C-reactive protein, interleukin-8, myeloperoxidase, fibrinogen and apolipoproteins ApoB/ApoA), sleep patterns and sleepiness were investigated. All parameters remained unchanged in the control group. After sleep restriction, leukocyte and - among leukocyte subsets - neutrophil counts were increased, an effect that persisted after the 8-h recovery sleep, but, in subjects who had a nap or a 10-h recovery sleep, these values returned nearly to baseline. Inflammatory and atherogenesis biomarkers were unchanged except for higher myeloperoxidase levels after sleep restriction. The increased sleepiness after sleep restriction was reversed better in the nap and extended sleep recovery conditions. Saliva cortisol decreased immediately after the nap. Our results indicate that additional recovery sleep after sleep restriction provided by a midday nap prior to recovery sleep or a sleep extended night can improve alertness and return leukocyte counts to baseline values.
    Brain Behavior and Immunity 01/2011; 25(1):16-24. · 5.61 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Many studies have evaluated the ways in which sleep disturbances may influence inflammation and the possible links of this effect to cardiovascular risk. Our objective was to investigate the effects of chronic sleep restriction and recovery on several blood cardiovascular biomarkers. Nine healthy male non-smokers, aged 22-29 years, were admitted to the Sleep Laboratory for 11 days and nights under continuous electroencephalogram polysomnography. The study consisted of three baseline nights of 8 hours sleep (from 11 pm to 7 am), five sleep-restricted nights, during which sleep was allowed only between 1 am and 6 am, and three recovery nights of 8 hours sleep (11 pm to 7 am). Myeloperoxidase-modified low-density lipoprotein levels increased during the sleep-restricted period indicating an oxidative stress. A significant increase in the quantity of slow-wave sleep was measured during the first recovery night. After this first recovery night, insulin-like growth factor-1 levels increased and myeloperoxidase concentration peaked. We observed for the first time that sleep restriction and the recovery process are associated with differential changes in blood biomarkers of cardiovascular disease.
    PLoS ONE 01/2011; 6(11):e28230. · 3.53 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Neuropeptide Y (NPY), a 36-amino-acid peptide from the pancreatic polypeptide family, is one of the more abundant peptides in the central nervous system. It acts as a neurohormone and as a neuromodulator. NPY is widely distributed in the brain, particularly the hypothalamus, the amygdala, the locus coeruleus and the cerebral cortex. At least six NPY receptors subtypes have been identified. NPY is involved in the regulation of several physiological functions such as food intake, hormonal release, circadian rhythms, cardiovascular disease, thermoregulation, stress response, anxiety and sleep. Sleep promoting effects of NPY as well as wakefulness effects of NPY were found in animals, depending on the site of injection as well as on the functional state of the structure. In humans, NPY was found to have hypnotic properties, possibly acting as a physiological antagonist of corticotropin-releasing hormone (CRH). In conclusion, NPY participates in sleep regulation in humans, particularly in the timing of sleep onset and may as such play a role in the integration of sleep regulation, food intake and metabolism.
    Sleep Medicine Reviews 06/2010; 14(3):161-5. · 8.68 Impact Factor
  • Source
    S Devuyst, T Dutoit, P Stenuit, M Kerkhofs
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present an automatic method for K-complexes detection based on features extraction and the use of fuzzy thresholds. The validity of our process was examined on the basis of two visual K-complexes scorings performed on 5 excerpts of 30 minutes. Results were investigated through all different sleep stages. The algorithm provides global true positive rates of 61.72% and 60.94%, respectively with scorer 1 and scorer 2. The false positive proportions (compared to the total number of visually scored K-complexes) are of 19.62% and 181.25%, while the false positive rates estimated on a one 1 second resolution are only of 0.53% and 1.53%. These results suggest that our approach is completely suitable since its performances are similar to those of the human scorers.
    Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2010; 2010:4658-61.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Our 24 h society promotes wakefulness to the detriment of sleep. Many people reduce their sleep time voluntary or by obligation. The effects of sleep restriction on performances and on vigilance are becoming to be recognized. However, the effects of chronic sleep loss on health and disease, particularly cardiovascular disease, are less documented. Several studies have evidenced a relation between a reduction of sleep duration and cardiovascular pathology. The mechanisms involved in these associations are not elucidated at the present time. We are using the sleep restriction model in order to evaluate the relationships between sleep reduction and the inflammatory processes involved in cardiovascular diseases. Our data show that a sleep restriction, even moderated, is able to influence cardiovascular risk factors in otherwise healthy subjects.
    Médecine du Sommeil. 01/2009; 6(3).
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report about a young woman suffering from chronic fatigue. The polysomnography reveals central sleep apnea syndrome. Magnetic resonance imaging of the brain and the cervical spine shows a Chiari type I malformation associated with syringomyela. Suboccipital decompression resulted in a complete resolution of fatigue and apnea.
    Médecine du Sommeil 01/2009; 6(3):109-112.
  • M. Kerkhofs
    Médecine du Sommeil. 01/2009; 6(3).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In this paper, we present a series of algorithms for dealing with artifacts in electroencephalograms (EEG), electrooculograms (EOG) and electromyograms (EMG). The aim is to apply artifact correction whenever possible in order to lose a minimum of data, and to identify the remaining artifacts so as not take them into account during the sleep stage classification. Nine procedures were implemented to minimize cardiac interference and slow ondulations, and to detect muscle artifacts, failing electrode, 50/60Hz main interference, saturations, highlights abrupt transitions, EOG interferences and artifacts in EOG. Detection methods were developed in the time domain as well as in the frequency domain, using adjustable parameters. A database of 20 excerpts of polysomnographic sleep recordings scored in artifacts by an expert was available for developing (excerpts 1 to 10) and testing (excerpts 11 to 20) the automatic artifact detection algorithms. We obtained a global agreement rate of 96.06%, with sensitivity and specificity of 83.67% and 96.47% respectively.
    12/2008: pages 146-150;

Publication Stats

2k Citations
362.06 Total Impact Points

Institutions

  • 2004–2012
    • Centre Hospitalier Universitaire de Charleroi
      Charleroi, Walloon Region, Belgium
  • 1988–2012
    • Université Libre de Bruxelles
      • • Laboratory of Experimental Medicine (LME)
      • • Laboratory of Experimental Medicine (LABOMEDEX)
      • • Department of Psychiatry
      • • Endocrinology Unit
      • • Department of Chest Medicine
      Bruxelles, Brussels Capital Region, Belgium
  • 2010–2011
    • Université de Mons
      Mons, Walloon Region, Belgium
  • 1984–2008
    • Free University of Brussels
      • • Department of Intensive Care Medicine
      • • Department of Psychiatry
      Bruxelles, Brussels Capital Region, Belgium
  • 1993–2007
    • University Hospital Brussels
      • Department of Psychiatry
      Bruxelles, Brussels Capital Region, Belgium
  • 1998–2002
    • University-Hospital Brugmann UVC
      Bruxelles, Brussels Capital Region, Belgium
  • 1991
    • University of Chicago
      • Department of Medicine
      Chicago, IL, United States