title: Cardiovascular responses to dry resting apnoeas in elite divers while breathing pure oxygen.
abstract: OBJECTIVE
  We hypothesized that the third dynamic phase (ϕ3) of the cardiovascular response to apnoea requires attainment of the physiological breaking point, so that the duration of the second steady phase (ϕ2) of the classical cardiovascular response to apnoea, though appearing in both air and oxygen, is longer in oxygen.
  
  
  METHODS
  Nineteen divers performed maximal apnoeas in air and oxygen. We measured beat-by-beat arterial pressure, heart rate (fH), stroke volume (SV), cardiac output (Q˙).
  
  
  RESULTS
  The fH, SV and Q˙ changes during apnoea followed the same patterns in oxygen as in air. Duration of steady ϕ2 was 105 ± 37 and 185 ± 36 s, in air and oxygen (p<0.05), respectively. At end of apnoea, arterial oxygen saturation was 1.00 ± 0.00 in oxygen and 0.75 ± 0.10 in air.
  
  
  CONCLUSIONS
  The results support the tested hypothesis. Lack of hypoxaemia during oxygen apnoeas suggests that, if chemoreflexes determine ϕ3, the increase in CO2 stores might play a central role in eliciting their activation.
authors.affiliation: Dipartimento di Scienze Cliniche e Sperimentali, Università di Brescia, Italy; Dipartimento di Specialità Medico-Chirurgiche, Scienze Radiologiche e Sanità Pubblica, Università di Brescia, Italy. Electronic address: nazzarenofagoni@gmail.com.
authors.forename: Nazzareno
authors.initials: N
authors.lastname: Fagoni
authors.affiliation: Dipartimento di Scienze Cliniche e Sperimentali, Università di Brescia, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Sivieri
authors.affiliation: Dipartimento di Scienze Mediche e Biologiche, Università di Udine, Italy.
authors.forename: Guglielmo
authors.initials: G
authors.lastname: Antonutto
authors.affiliation: Département des Neurosciences Fondamentales, Université de Genève, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Moia
authors.affiliation: Dipartimento di Scienze Cliniche e Sperimentali, Università di Brescia, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Taboni
authors.affiliation: Département des Neurosciences Fondamentales, Université de Genève, Switzerland.
authors.forename: Aurélién
authors.initials: A
authors.lastname: Bringard
authors.affiliation: Dipartimento di Scienze Cliniche e Sperimentali, Università di Brescia, Italy; Département des Neurosciences Fondamentales, Université de Genève, Switzerland.
authors.forename: Guido
authors.initials: G
authors.lastname: Ferretti
mesh_terms: D000328:Adult; D000388:Air; D001049:Apnea / Q000503:physiopathology*; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000502:physiology*; D001795:Blood Pressure Determination; D002302:Cardiac Output / Q000502:physiology*; D004242:Diving / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D010100:Oxygen / Q000008:administration & dosage* / Q000097:blood; D012119:Respiration
chemical_list: D010100:Oxygen
keywords: Arterial blood pressure; Baroreflexes; Cardiac output; Dry static apnoea; Heart rate; Oxygen apnoea