title: A beat-by-beat analysis of cardiovascular responses to dry resting and exercise apnoeas in elite divers.
abstract: OBJECTIVE
  Cardiovascular responses during resting apnoea include three phases: (1) a dynamic phase of rapid changes, lasting at most 30 s; (2) a subsequent steady phase; and (3) a further dynamic phase, with a continuous decrease in heart rate (HR) and an increase in blood pressure. The interpretation was that the end of the steady phase corresponds to the physiological apnoea breaking point. This being so, during exercise apnoeas, the steady phase would be shorter, and the rate of cardiovascular changes in the subsequent unsteady phase would be faster than at rest.
  
  
  METHODS
  To test these hypotheses, we measured beat-by-beat systolic (SBP), diastolic, and mean blood pressures (MBP), HR, and stroke volume (SV) in six divers during dry resting (duration 239.4 ± 51.6 s) and exercise (30 W on cycle ergometer, duration 88.2 ± 20.9 s) maximal apnoeas, and we computed cardiac output ([Formula: see text]) and total peripheral resistance (TPR).
  
  
  RESULTS
  Compared to control, at the beginning of resting (R1) and exercising (E1) apnoeas, SBP and MBP decreased and HR increased. SV and [Formula: see text] fell, so that TPR remained unchanged. At rest, HR, SV, [Formula: see text], and SBP were stable during the subsequent phase; this steady phase was missing in exercise apnoeas. Subsequently, at rest (R3) and at exercise (E2), HR decreased and SBP increased continuously. SV returned to control values. Since [Formula: see text] remained unchanged, TPR grew.
  
  
  CONCLUSIONS
  The lack of steady phase during exercise apnoeas suggests that the conditions determining R3 were already attained at the end of E1. This being so, E2 would correspond to R3.
authors.affiliation: Dipartimento di Scienze Cliniche E Sperimentali, Università di Brescia, Brescia, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Sivieri
authors.forename: Nazzareno
authors.initials: N
authors.lastname: Fagoni
authors.forename: Aurélien
authors.initials: A
authors.lastname: Bringard
authors.forename: Michela
authors.initials: M
authors.lastname: Capogrosso
authors.forename: Renza
authors.initials: R
authors.lastname: Perini
authors.forename: Guido
authors.initials: G
authors.lastname: Ferretti
mesh_terms: D000328:Adult; D056352:Athletes; D001794:Blood Pressure; D062485:Breath Holding; D004242:Diving / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D008297:Male