Modified Ventilatory Response Characteristics to Exercise in Breath-Hold Divers

Specific adjustments to repeated extreme apnea are not fully known and understood. While a blunted ventilatory chemosensitivity to CO2 is described for elite breath-hold divers (BHDs) at rest, it is unclear whether specific adaptations affect their response to dynamic exercise. Eight elite BHDs with a previously validated decrease in CO2 chemosensitivity, 8 scuba divers (SCDs), and 8 matched control subjects were included in a study where markers of ventilatory response, Fowler's dead space, partial pressure of carbon dioxide (pCO(2)), and blood lactate concentrations during cycle exercise were measured. Maximal power output did not differ between the groups, but lactate threshold (theta L) appeared at a significantly lowered respiratory compensation point (RCP) and at a higher VO2 for the BHDs. End-tidal (p(et)CO(2)) and estimated arterial pCO(2) (p(a)CO(2)) were significantly higher in BHDs at theta L, the RCP, and maximum exhaustion. BHDs showed a significantly (P < .01) slower breathing pattern in relation to a given tidal volume at a specific work rate. In summary, BHDs presented signs of a metabolic shift from aerobic to anaerobic energy supply, decreased chemosensitivity during exercise, and a distinct ventilatory-response pattern during cycle exercise that differs from SCDs and controls.