Increased ventilatory response to carbon dioxide after dive training

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.

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.

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.

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