Systemic and regional hemodynamic and (de)oxygenation responses across repeated breath-holds.

Introduction: Regional cerebral and peripheral tissue (de)oxygenation responses to breath-holding (apnea) have predominantly been examined during isolated attempts. How these responses evolve across repeated efforts remains unclear, as previous studies either averaged data across bouts or focused solely on the final repetition. Accordingly, this study mapped the (de)oxygenation dynamics across successive breath-holds. Methods: Fifteen non-divers performed three repeated maximal static breath-holds, separated by two-minute rest-intervals. Systemic cardiovascular variables, gas exchange, and cerebral frontal-cortex and forearm-muscle (de)oxygenation were assessed. Results: At each breath-hold onset, a transient fall in cerebral oxygenated hemoglobin (cO₂Hb) and arterial pressure occurred, coinciding with tachycardia. A cardiovascular steady state followed which persisted until the onset of involuntary breathing movements (IBMs). At IBM onset, cO₂Hb increased only during the first attempt (Δ8±5μM,p<0.001), with smaller changes in subsequent breath-holds (apnea-2,Δ3±6μM;apnea-3,Δ3±5μM,p≤0.014). Cerebral deoxygenated hemoglobin (cHHb) increased progressively across breath-holds (apnea-1,Δ3±4μM;apnea-2,Δ5±4μM;apnea-3,Δ7±5μM,p≤0.001), whereas arterial pressure increases were of similar magnitude (p≥0.064). Forearm (de)oxygenation profiles were comparable across attempts (p≥0.085). In 9 subjects, a triphasic peripheral response emerged: initial rapid decline in O₂Hb and rise in HHb at breath-holding onset, a transient intermediate-plateau, and further divergence near IBM onset. Breath-holds were terminated at successively lower cO₂Hb, cerebral tissue oxygen index, and end-tidal oxygen, and higher cHHb (p≤0.034), but similar end-tidal carbon dioxide levels (p>0.912). Conclusion: The magnitude and timing of regional (de)oxygenation responses vary greatly over repeated breath-holds. Cerebral oxygenation showed a pronounced increase during the first attempt, but progressively smaller changes across subsequent bouts. In contrast, peripheral tissue oxygenation, demonstrated a time-dependent decline across successive attempts.