title: Static apnea effect on heart rate and its variability in elite breath-hold divers.
abstract: BACKGROUND
  The diving response includes cardiovascular adjustments known to decrease oxygen uptake and thus prolong apnea duration. As this diving response is in part characterized by a pronounced decrease in heart rate (HR), it is thought to be vagally mediated.
  
  
  METHODS
  In five professional breath-hold divers (BHDs) and five less-trained controls (CTL), we investigated whether the diving response is in fact associated with an increase in the root mean square successive difference of the R-R intervals (RMSSD), a time-domain heart rate variability (HRV) index. HR behavior and arterial oxygen saturation (SaO2) were continuously recorded during one maximal apnea. Short-term changes in SaO2, HR, and RMSSD were calculated over the complete apnea duration.
  
  
  RESULTS
  BHDs presented bi-phasic HR kinetics, with two HR decreases (32 +/- 17% and 20 +/- 10% of initial HR). The second HR decrease, which was concomitant to the pronounced SaO2 decrease, was also simultaneous to a marked increase in RMSSD. CTL showed only one HR decrease (50 +/- 10% of initial HR), which appeared before the concomitant SaO2 and RMSSD changes. When all subject data were combined, arterial desaturation was positively correlated with total apnea time (r = 0.87, P < 0.01).
  
  
  CONCLUSIONS
  This study indicates that baroreflex stimulation and hypoxia may be involved in the bi-phasic HR response of BHDs and thus in their longer apnea duration.
authors.affiliation: Centre d'Etudes des Transformations des Activités Physiques et Sportives, Equipe d'Accueil, Faculté des Sciences du Sport et de l'Education Physique de Rouen, Université de Rouen, France. frederic.lemaitre@univ-rouen.fr
authors.forename: Frédéric
authors.initials: F
authors.lastname: Lemaître
authors.forename: Martin
authors.initials: M
authors.lastname: Buchheit
authors.forename: Fabrice
authors.initials: F
authors.lastname: Joulia
authors.forename: Pierre
authors.initials: P
authors.lastname: Fontanari
authors.forename: Claire
authors.initials: C
authors.lastname: Tourny-Chollet
mesh_terms: D000328:Adult; D001049:Apnea / Q000503:physiopathology*; D004242:Diving / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000097:blood
chemical_list: D010100:Oxygen