CARDIOVASCULAR AND HEMATOLOGICAL RESPONSES TO A DRY DYNAMIC APNEA IN BREATH HOLD DIVERS.

ABSTRACT

The mammalian dive reflex, characterized by bradycardia and peripheral vasoconstriction, occurs in all mammals, including humans, in response to apnea. However, the dive reflex to a single, maximal, dry, dynamic apnea (DYN), and how it compares to a time-matched exercise control trial (EX) or dry static apnea (SA), has not been studied. We examined the hypotheses that, compared to EX and SA, the magnitude of the (a) cardiovascular response and (b) hematological response to DYN would be greater. Cardiovascular parameters (heart rate [HR], systolic [SBP], diastolic [DBP], and mean arterial [MAP] blood pressure) were continuously collected in twenty-three (F=6) moderate and elite freedivers, first during a maximal DYN, then during a time-matched SA and EX on a swimming ergometer in randomized order. Venous blood draws were made prior to and following each trial. The change in calculated oxygen saturation (DYN-17±13%, EX-2±1%, ΔSA-2±1%;P<0.05, all comparisons) was greater during DYN compared to EX and SA. During DYN, ΔSBP (DYN104±31mmHg, EX38±23mmHg, SA20±11mmHg), ΔDBP (DYN45±12mmHg, EX14±10mmHg, SA15±8mmHg) and ΔMAP (DYN65±17mmHg EX22±13mmHg, SA16±9mmHg) were increased compared to EX and SA, while ΔHR was greater during EX (DYN-24±23bpm, EX33±13bpm, SA-1±10bpm) than either DYN or SA (P<0.0001, all comparisons). Females had greater pressor response to EX (ΔSBP59±30mmHg, ΔDBP24±14mmHg, ΔMAP35±8mmHg) than males (ΔSBP31±15mmHg, ΔDBP11±6mmHg, ΔMAP18±8mmHg; P<0.01, all comparisons). Together, these data indicate that DYN elicits a distinct, exaggerated cardiovascular response compared to EX or SA alone.