title: Associations of baroreflex sensitivity, heart rate variability, and initial orthostatic hypotension with prenatal and recent postnatal methylmercury exposure in the Seychelles Child Development Study at age 19 years.
abstract: BACKGROUND
  A few studies have suggested an association between prenatal exposure to methylmercury and decreased heart rate variability (HRV) related to autonomic heart function, but no study has examined this association using baroreflex sensitivity (BRS). In this study we assessed the distribution of BRS and immediate orthostatic hypotension (IOH) in young Seychellois adults and their associations with exposure to prenatal and recent postnatal methylmercury.
  
  
  METHODS
  Subjects in the Seychelles Child Development Study (SCDS) main cohort were evaluated at age 19 years. Non-invasive beat-to-beat blood pressure (BP) monitoring (Finapres, Ohmeda) was performed at rest and during active standing in 95 consecutive subjects. Recent postnatal mercury exposure was measured in subjects' hair at the age of 19 years and prenatal exposure in maternal hair grown during pregnancy. BRS was estimated by sequence analysis to identify spontaneous ascending and descending BP ramps. HRV was estimated by the following markers: PNN50 (relative numbers of normal-to-normal intervals which are shorter by more than 50 ms than the immediately following normal-to-normal intervals); rMSSD (root mean of the squared sum of successive interval differences); LF/HF (low frequency/high frequency component ratio); ratio of the mean expiratory/inspiratory RR intervals (EI ratio); and the ratio between the longest RR interval 30 s after active standing and the shortest RR interval at 15 s (Max30/Min15). IOH was estimated by the deepest BP fall within the first 15 s after active standing up.
  
  
  RESULTS
  Prenatal MeHg exposures were similar in boys and girls (6.7±4.3, 6.7±3.8 ng/g) but recent postnatal mercury levels were higher in males than females (11.2±5.8 vs 7.9±4.3 ng/g, p=0.003). Markers of autonomic heart rate control were within the normal range (BRS: 24.8±7 ms/mm Hg, PNN50: 24.9±6.8%, rMSSD: 68±22, LF/HF: 0.61±0.28) in both sexes. After standing, 51.4% of subjects had a transient systolic BP drop>40 mm Hg, but only 5.3% reported dizziness or had syncope. Prenatal and recent postnatal MeHg levels, overall, were not associated with BRS, E/I ratio, PNN50, rMSSD, LF/HF ratio, Max30/Min15 ratio, and IOH.
  
  
  CONCLUSIONS
  This study provides no support for the hypothesis that prenatal or recent postnatal MeHg exposure from fish consumption is associated with impaired autonomic heart rate control.
authors: Service d'Angiologie, Hôpital Cantonal, Fribourg 1700, Switzerland. daniel.periard@h-fr.ch.
authors: Daniel
authors: D
authors: Périard
authors: Service d'Angiologie, Hôpital Cantonal, Fribourg 1700, Switzerland. beqirajbujar@gmail.com.
authors: Bujar
authors: B
authors: Beqiraj
authors: Service d'Angiologie, Hôpital Cantonal, Fribourg 1700, Switzerland. daniel.hayoz@h-fr.ch.
authors: Daniel
authors: D
authors: Hayoz
authors: Section of Non Communicable Diseases, Ministry of Health, Victoria, Seychelles. barathi.viswanathan@health.gov.sc.
authors: Bharathi
authors: B
authors: Viswanathan
authors: Department of Biostatistics, University of Rochester, Rochester, NY 14642, USA. katie_evans@urmc.rochester.edu.
authors: Katie
authors: K
authors: Evans
authors: Department of Biostatistics, University of Rochester, Rochester, NY 14642, USA. sally_thurston@urmc.rochester.edu.
authors: Sally W
authors: SW
authors: Thurston
authors: Department of Pediatrics, University of Rochester, Rochester, NY 14642, USA. philip_davidson@urmc.rochester.edu.
authors: Philip W
authors: PW
authors: Davidson
authors: Department of Pediatrics, University of Rochester, Rochester, NY 14642, USA. gary_myers@urmc.rochester.edu.|Institute of Social and Preventive Medicine, Lausanne University Hospital, CHUV, Lausanne 1010, Switzerland. gary_myers@urmc.rochester.edu.
authors: Gary J
authors: GJ
authors: Myers
authors: Section of Non Communicable Diseases, Ministry of Health, Victoria, Seychelles. pascal.bovet@chuv.ch.|Institute of Social and Preventive Medicine, Lausanne University Hospital, CHUV, Lausanne 1010, Switzerland. pascal.bovet@chuv.ch.
authors: Pascal
authors: P
authors: Bovet
mesh_terms: D017704:Baroreflex / Q000187:drug effects*; D004781:Environmental Exposure / Q000009:adverse effects*; D004785:Environmental Pollutants / Q000633:toxicity*; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007024:Hypotension, Orthostatic / Q000139:chemically induced*; D008297:Male; D008767:Methylmercury Compounds / Q000633:toxicity*; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced*; D012750:Seychelles; D055815:Young Adult
chemical_list: D004785:Environmental Pollutants; D008767:Methylmercury Compounds