Oxygen - Enhanced Breath - Hold Diving , Phase I : Hyperventilation and Carbon Dioxide Elimination Neal W . Pollock

Hyperventilation (HV) is commonly used to extend breath-hold time by eliminating carbon dioxide to delay the hypercapnic stimulus to end breath-hold. The chief hazard is that loss of consciousness may result from hypoxia before the hypercapnic drive initiates a breathing cycle. The purpose of this study is to evaluate the efficacy of oxygen inspiration to improve the safety of breath-holding techniques. Phase I evaluates the effect of different HV rates on end-tidal carbon dioxide concentration (Petcog) and whole body elimination of carbon dioxide. Eleven healthy, fit individuals (10 male, one female) completed three rounds of 60 s of HV at the following rates: 10, 15, 20, 25, 30 and 35 breaths min". Individual performance was not difficult to regulate and stable from trial to trial. The metabolic cost of HV was higher than expected, with mean "bonus elimination" of carbon dioxide between 200-1000 mL. End-HV, PetCO, was negatively correlated with HV rate (~-0.688; pa.05) while end-HV sum of symptom scores was positively correlated (~0.314; pq.05). Based on the Phase I experience, the HV rate of 20 breaths nun"' is accepted as optimal for 60 s of HV in terms of subjective comfort, ensuring that end-HV PetCO, remains above the 20 torr (2.67 kPa) safe lower limit, and for ease of pacing.