This study tested whether hypercapnic ventilatory response (HCVR) is affected by experience in apnoea and
explored the possible underlying mechanisms of this phenomenon, with reference to maximum breath hold time (BHT).
Elite apnoea divers (EBH=11) and novice subjects (NBH=10) performed a HCVR test (BM), which was repeated by the
latter group on another day (PRE) after subjects executed five repeated maximum apnoeas. Subsequently, after a two
week period of daily apnoea training, NBH subjects repeated HCVR test (POST). Diaphragmatic activity was recorded to
determine apnoea easy going phase.
Baseline HCVR of EBH was not lower than that of NBH. After execution of five apnoeas, HCVR in EBH decreased
(P≤0.05) whereas it was not different among BM, PRE, and POST conditions in the NBH. Higher BHT and easy going
phase values ensued from apnoea maneuvers in EBH than in NBH (PRE and POST), and in NBH POST compared to PRE
condition (P≤0.05). HCVR was highly correlated (P≤0.05) with the cumulative easy going phase in EBH, PRE condition
but nothing-similar observed in NBH, neither in PRE nor in POST conditions.
These results indicate that at rest HCVR is not lower in experienced, than novice, skin divers; this response becomes dull
after five repeated maximum apnoeas only in EBH. In the NBH group, two weeks of apnoea training are not adequate to
affect HCVR despite an increase of BHT. It appears that after a repeated maximum apnoeas maneuver experienced skin
divers improve BHT by extending easy going phase whereas NBH by other means.