title: Dawn simulation light: a potential cardiac events protector.
abstract: OBJECTIVE
  Major cardiovascular events frequently increase in the morning due to abrupt changes in the sympatho-vagal cardiac control during the transition from sleep to wakefulness. These neural changes are translated into stepwise increases in cardiac functions, resulting in a potential cardiovascular stress. Here, we explored whether light can "optimize" heart rate and its neural control, by actively promoting a less steep transition from sleep to wakefulness, thus minimizing morning cardiovascular vulnerability.
  
  
  METHODS
  Seventeen healthy young men were awakened 2-hours before their habitual wake-time. In a counterbalanced within-subject design, we applied a control condition (darkness during sleep and dim light during wakefulness) or dawn-simulation-light (DSL) starting 30-minutes before and ending 30-minutes after scheduled wake-up time.
  
  
  RESULTS
  Our data reveal a significantly gradient reduction in heart rate during the transition from sleep to wakefulness, when applying DSL as compared to a control condition. Likewise, cardiac sympatho-vagal control smoothly increased throughout the 30-min sleep episode preceding scheduled wake-up under DSL and remained stable for the first 30-min of wakefulness. Interestingly, these effects were mostly driven by changes in the parasympathetic cardiac control.
  
  
  CONCLUSIONS
  Our data demonstrate for the first time that a non-invasive strategy, as light exposure surrounding the wake-up process, can significantly reduce the deleterious sleep-to-wake evoked cardiac modulation in healthy young men awakened under conditions of increased sleep pressure. A translational approach of this light exposure, which closely resembles natural lighting conditions in the morning, may therefore act as a potential protector for cardiac vulnerability in the critical morning hours.
authors: Centre for Chronobiology, Psychiatric Hospital of the University of Basel, Basel, Switzerland. Electronic address: antoine.viola@upkbs.ch.
authors: Antoine U
authors: AU
authors: Viola
authors: Centre for Chronobiology, Psychiatric Hospital of the University of Basel, Basel, Switzerland.
authors: Virginie
authors: V
authors: Gabel
authors: Cyclotron Research Centre, University of Liège, Liège, Belgium.
authors: Sarah L
authors: SL
authors: Chellappa
authors: Centre for Chronobiology, Psychiatric Hospital of the University of Basel, Basel, Switzerland.
authors: Christina
authors: C
authors: Schmidt
authors: IT VitaLight I&D PC Drachten, Philips Consumer Lifestyle, Drachten, The Netherlands.
authors: Vanja
authors: V
authors: Hommes
authors: Department of Biomedical and Clinical Sciences, Division of Medicine and Pathophysiology, L. Sacco Hospital, University of Milan, Milan, Italy.
authors: Eleonora
authors: E
authors: Tobaldini
authors: Department of Biomedical and Clinical Sciences, Division of Medicine and Pathophysiology, L. Sacco Hospital, University of Milan, Milan, Italy.
authors: Nicola
authors: N
authors: Montano
authors: Centre for Chronobiology, Psychiatric Hospital of the University of Basel, Basel, Switzerland.
authors: Christian
authors: C
authors: Cajochen
mesh_terms: D000328:Adult; D001143:Arousal / Q000502:physiology / Q000528:radiation effects*; D004562:Electrocardiography; D006339:Heart Rate / Q000502:physiology / Q000528:radiation effects*; D006801:Humans; D006854:Hydrocortisone / Q000032:analysis; D008027:Light; D008297:Male; D012463:Saliva / Q000737:chemistry; D055815:Young Adult
chemical_list: D006854:Hydrocortisone
keywords: Cardiac control; Circadian functions; Heart rate; Heart rate variability; Light