The air hunger response of four elite breath-hold divers

Normal subjects terminate breath-holds due to intolerable ‘air hunger’. We hypothesize that competitive breath-hold divers might have increased tolerance of air hunger. We tested the air hunger (AH) response of four divers who could hold their breath for 6–9 min. Tidal volume and respiratory rate were controlled by mechanical ventilation (ventilation ≈0.16 L min−1 kg−1). AH was induced by raising PCO2PCO2 and rated using a visual analog scale whose maximum was defined as intolerable. SpO2 was maintained at >97%. Three divers reported the same uncomfortable urge to breathe as normal subjects; the slopes of their responses were within normal range. Both resting CO2 and AH threshold were shifted to higher CO2 in some divers. Diver 3 was unique amongst neurologically intact subjects we have studied: he denied feeling an urge to breathe, and denied discomfort. We conclude that elite divers’ strategies to tolerate intense air hunger are a minor factor in their ability to tolerate long breath-holds.