ABSTRACT

Ekman L, Sjöblom C, Ekström M, Frånberg O. Increased ventilatory response to carbon dioxide after dive training. Undersea Hyperb Med. 2025 Fourth Quarter; 52(4):587-597.

Introduction: Divers are reported to have a lower ventilatory response to elevated levels of carbon dioxide (CO2) than non-divers. Hypoventilation with CO2 retention during diving is potentially dangerous. It is unknown if CO2 retention is largely inherited or develops during diving training. We aimed to investigate if a military dive training course would influence the ventilatory response to CO2.

Methods: Novice rebreather Divers with Amphibious Rangers as controls were tested at baseline, after
12 weeks of water exercise training, and after 15 weeks of diving: participants rebreathed in a Douglas bag filled with an initial 100% oxygen, resulting in increasing levels of inspiratory CO2 (iCO2). The test was performed until symptom-limitation or an expiratory CO2 of 8.0 kPa. To decrease conscious control of breathing, participants were distracted with a memory game during the test. Differences between groups and over time were analyzed using independent and paired t-tests.

Results: Ten Divers and six Amphibious Rangers completed baseline testing and eight Divers completed all tests. Divers had a statistically significant higher Minute Ventilation (V’E) after dive training, compared to after water exercise training and baseline, at all levels of iCO2. However, the change in Hypercapnic ventilatory response (HCVR) before and after dive training across pCO2 values 5.0-7.9, did not reach statistical significance. At baseline, Amphibious Rangers had a non-significant higher V’E compared to Divers at higher levels of iCO2.

Conclusion: A military rebreather diving program might be associated with increased ventilatory response to CO2.

Keywords: carbon dioxide retention; diving; rebreather-semi-closed circuit respiratory response