Voluntary breath-holding (BH) elicits several hemodynamic changes, but little is known about maximal static immersed-body BH. We hypothesized that the diving reflex would be strengthened with body immersion and would spare more oxygen than maximal dry static BH, resulting in a longer BH duration. Eleven trained breath-hold divers (BHDs) performed a maximal dry-body BH and a maximal immersed-body BH. Cardiac output (CO), stroke volume (SV), heart rate (HR), left ventricular end-diastolic volume (LVEDV), contractility index (CTI), and ventricular ejection time (VET) were continuously recorded by bio-impedancemetry (PhysioFlow PF-05). Arterial oxygen saturation (SaO(2)) was assessed with a finger probe oximeter. In both conditions, BHDs presented a bi-phasic kinetic for CO and a tri-phasic kinetic for SV and HR. In the first phase of immersed-body BH and dry-body BH, results (mean +/- A SD) expressed as percentage changes from starting values showed decreased CO (55.9 +/- A 10.4 vs. 39.3 +/- A 16.8 %, respectively; p < 0.01 between conditions), due to drops in both SV (24.9 +/- A 16.2 vs. 9.0 +/- A 8.5 %, respectively; p < 0.05 between conditions) and HR (39.7 +/- A 16.7 vs. 33.6 +/- A 17.0 %, respectively; p < 0.01 between conditions). The second phase was marked by an overall stabilization of hemodynamic variables. In the third one, CO kept stabilizing due to increased SV (17.0 +/- A 20.2 vs. 10.9 +/- A 13.8 %, respectively; p < 0.05 between conditions) associated with a second HR drop (14.0 +/- A 10.0 vs. 12.7 +/- A 8.9 %, respectively; p < 0.01 between conditions). This study highlights similar time-course patterns for cardiodynamic variables during dry-body and immersed-body BH, although the phenomenon was more pronounced in the latter condition.
