A dive into the physiological responses to maximal apneas, O2 and CO2 tables in apnea novices.

Purpose: Apnea duration is dependent on three factors: oxygen storage, oxygen consumption, hypoxia and hypercapnia tolerance. While current literature focuses on maximal apneas to improve apnea duration, apnea trained individuals use timed-repeated submaximal apneas, called "O₂ and CO₂ tables". These tables claim to accommodate the body to cope with hypoxia and hypercapnia, respectively. The aim of this study was twofold. First, to investigate the determinants of maximal apnea duration in apnea novices. Second, to compare physiologic responses to maximal apneas, O₂ and CO₂ tables.

Methods: After medical screening, lung function test and hemoglobin mass measurement, twenty-eight apnea novices performed three apnea protocols in random order: maximal apneas, O₂ table and CO₂ table. During apnea, peripheral oxygen saturation (SpO₂), heart rate (HR), muscle (mTOI) and cerebral (cTOI) tissue oxygenation index were measured continuously. End-tidal carbon dioxide (EtCO₂) was measured before and after apneas.

Results: Larger lung volumes, higher resting cTOI and lower resting EtCO₂ levels correlated with longer apnea durations. Maximal apneas induced greater decreases in SpO₂ (- 16%) and cTOI (- 13%) than O₂ (- 8%; - 8%) and CO₂ tables (- 6%; - 6%), whereas changes in EtCO₂, HR and mTOI did not differ between protocols.

Conclusion: These results suggest that, in apnea novices, O₂ and CO₂ tables did not induce a more profound hypoxia and hypercapnia, but a similar reduction in oxygen consumption than maximal apneas. Therefore, apnea novices should mainly focus on maximal apneas to improve hypoxia and hypercapnia tolerance. The use of specific lung training protocols can help to increase oxygen storage capacity.