Dynamic cerebral autoregulation is acutely impaired during maximal apnoea in trained divers

Aims: To examine whether dynamic cerebral autoregulation is acutely impaired during maximal voluntary apnoea in trained divers. Methods: Mean arterial pressure (MAP), cerebral blood flow-velocity (CBFV) and end-tidal partial pressures of O₂ and CO₂ (PETO₂ and PETCO₂) were measured in eleven trained, male apnoea divers (28±2 yr; 182±2 cm, 76±7 kg) during maximal "dry" breath holding. Dynamic cerebral autoregulation was assessed by determining the strength of phase synchronisation between MAP and CBFV during maximal apnoea. Results: The strength of phase synchronisation between MAP and CBFV increased from rest until the end of maximal voluntary apnoea (P<0.05), suggesting that dynamic cerebral autoregulation had weakened by the apnoea breakpoint. The magnitude of impairment in dynamic cerebral autoregulation was strongly, and positively related to the rise in PETCO₂ observed during maximal breath holding (R² =0.67, P<0.05). Interestingly, the impairment in dynamic cerebral autoregulation was not related to the fall in PETO ₂ induced by apnoea (R² = 0.01, P= 0.75). Conclusions: This study is the first to report that dynamic cerebral autoregulation is acutely impaired in trained divers performing maximal voluntary apnoea. Furthermore, our data suggest that the impaired autoregulatory response is related to the change in PETCO₂, but not PETO₂, during maximal apnoea in trained divers.