title: Cardiac repolarization and autonomic regulation during short-term cold exposure in hypertensive men: an experimental study.
abstract: OBJECTIVE
  The aim of our study was to assess the effect of short-term cold exposure, typical in subarctic climate, on cardiac electrical function among untreated middle-aged hypertensive men.
  
  
  METHODS
  We conducted a population-based recruitment of 51 hypertensive men and a control group of 32 men without hypertension (age 55-65 years) who underwent whole-body cold exposure (15 min exposure to temperature -10°C, wind 3 m/s, winter clothes). Conduction times and amplitudes, vectorcardiography, arrhythmias, and heart rate variability (autonomic nervous function) were assessed.
  
  
  RESULTS
  Short-term cold exposure increased T-peak to T-end interval from 67 to 72 ms (p<0.001) and 71 to 75 ms (p<0.001) and T-wave amplitude from 0.12 to 0.14 mV (p<0.001) and from 0.17 to 0.21 mV (p<0.001), while QTc interval was shortened from 408 to 398 ms (p<0.001) and from 410 to 401 ms (p<0.001) among hypertensive men and controls, respectively. Cold exposure increased both low (from 390 to 630 ms2 (p<0.001) and 380 to 700 ms2 (p<0.001), respectively) and high frequency heart rate variability (from 90 to 190 ms2 (p<0.001) and 150 to 300 ms2 (p<0.001), respectively), while low-to-high frequency-ratio was reduced. In addition, the frequency of ventricular ectopic beats increased slightly during cold exposure. The cold induced changes were similar between untreated hypertensive men and controls.
  
  
  CONCLUSIONS
  Short-term cold exposure with moderate facial and mild whole body cooling resulted in prolongation of T-peak to T-end interval and higher T-wave amplitude while QTc interval was shortened. These changes of ventricular repolarization may have resulted from altered cardiac autonomic regulation and were unaffected by untreated hypertension.
  
  
  BACKGROUND
  ClinicalTrials.gov NCT02007031.
authors.affiliation: Center for Environmental and Respiratory Health Research, University of Oulu, Oulu, Finland; Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland.
authors.forename: Heidi
authors.initials: H
authors.lastname: Hintsala
authors.affiliation: Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland; Institute of Clinical Medicine, Department of Internal Medicine, University of Oulu, Oulu, Finland.
authors.forename: Tuomas V
authors.initials: TV
authors.lastname: Kenttä
authors.affiliation: Department of Exercise and Medical Physiology, Verve Research, Oulu, Finland; Department of Applied Science, London South Bank University, London, England.
authors.forename: Mikko
authors.initials: M
authors.lastname: Tulppo
authors.affiliation: Department of Exercise and Medical Physiology, Verve Research, Oulu, Finland.
authors.forename: Antti
authors.initials: A
authors.lastname: Kiviniemi
authors.affiliation: Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland; Institute of Clinical Medicine, Department of Internal Medicine, University of Oulu, Oulu, Finland.
authors.forename: Heikki V
authors.initials: HV
authors.lastname: Huikuri
authors.affiliation: Institute of Health Sciences, University of Oulu, Oulu, Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Mäntysaari
authors.affiliation: Institute of Health Sciences, University of Oulu, Oulu, Finland; Unit of General Practice, Oulu University Hospital, Oulu, Finland.
authors.forename: Sirkka
authors.initials: S
authors.lastname: Keinänen-Kiukaannemi
authors.affiliation: Medical Informatics and Statistics Research Group, University of Oulu, Oulu, Finland.
authors.forename: Risto
authors.initials: R
authors.lastname: Bloigu
authors.affiliation: Institute of Biomedicine, Department of Physiology and Biocenter of Oulu, University of Oulu, Oulu, Finland; Department of Psychiatry, Kuopio University Hospital, Kuopio, Finland.
authors.forename: Karl-Heinz
authors.initials: KH
authors.lastname: Herzig
authors.affiliation: Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland; Institute of Health Sciences, University of Oulu, Oulu, Finland; Oulu City Hospital, Oulu, Finland.
authors.forename: Riitta
authors.initials: R
authors.lastname: Antikainen
authors.affiliation: Institute of Biomedicine, Department of Physiology and Biocenter of Oulu, University of Oulu, Oulu, Finland; Finnish Institute of Occupational Health, Oulu, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Rintamäki
authors.affiliation: Center for Environmental and Respiratory Health Research, University of Oulu, Oulu, Finland; Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland; Institute of Health Sciences, University of Oulu, Oulu, Finland; Department of Medicine, Oulu University Hospital, Oulu, Finland.
authors.forename: Jouni J K
authors.initials: JJ
authors.lastname: Jaakkola
authors.affiliation: Center for Environmental and Respiratory Health Research, University of Oulu, Oulu, Finland; Medical Research Center Oulu, Oulu University Hospital and University of Oulu, Oulu, Finland; Institute of Health Sciences, University of Oulu, Oulu, Finland.
authors.forename: Tiina M
authors.initials: TM
authors.lastname: Ikäheimo
mesh_terms: D000368:Aged; D003080:Cold Temperature; D022062:Electrophysiologic Techniques, Cardiac; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D006973:Hypertension / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D014672:Vectorcardiography