Increased ventilatory response to carbon dioxide after dive training.

Area of Science:

• Physiology
• Environmental Medicine
• Diving Science

Background:

• Divers exhibit a reduced ventilatory response to elevated carbon dioxide (CO₂) levels compared to non-divers.
• Hypoventilation and subsequent CO₂ retention during diving pose significant risks.
• The origin of altered CO₂ response in divers (inherited vs. acquired) remains unclear.

Purpose of the Study:

• To determine if a military rebreather diving training program influences the ventilatory response to CO₂.
• To investigate potential adaptations in respiratory control following dive training.

Main Methods:

• Novice rebreather divers and controls (Amphibious Rangers) underwent CO₂ rebreathing tests at baseline, after water exercise, and after dive training.
• Tests involved rebreathing 100% oxygen with increasing inspiratory CO₂ (iCO₂) until symptom limitation or a target end-tidal CO₂ of 8.0 kPa.
• Cognitive distraction (memory game) was employed to minimize conscious control of breathing; data analyzed using t-tests.

Main Results:

• Divers showed a significant increase in Minute Ventilation (V'E) at all iCO₂ levels post-dive training compared to baseline and water exercise.
• The change in Hypercapnic Ventilatory Response (HCVR) before and after dive training did not reach statistical significance.
• At baseline, controls exhibited a trend towards higher V'E than divers at elevated iCO₂ levels.

Conclusions:

• Military rebreather diving programs may be associated with an enhanced ventilatory response to CO₂.
• This suggests that dive training could induce physiological adaptations in respiratory control.
• Further research is needed to fully elucidate the mechanisms and implications of these changes for diver safety.