DIVING RESPONSE AND APNEIC TIME IN HUMANS

The aim of this study was to compare apneic time with the human diving response, defined as heart rate (HR) reduction and reduced skin blood flow, in groups with varying degrees of breath-hold diving experience . Apneic time and HR reduction at apneas in air and apneas with face i mmersion in cold water were thus recorded in nine groups. Skin capilla ry blood flow was recorded in six of the groups. AU subjects received the same information on maximizing apneic duration, and no information about their progress during the apneas. The longest apneas and the mo st pronounced cardiovascular adjustments were found in the young, trai ned divers. It was found that apneic time was significantly correlated to HR reduction among the nine groups (r = 0.94, P < 0.001), and to s kin capillary blood flow reduction among the six groups where the para meter was measured (r = 0.82, P < 0.05). The correlation between HR re duction and skin capillary blood flow reduction was also significant ( r = 0.85, P < 0.05). When the difference in HR reduction and apneic ti me between apneas in air and apneas with face immersion were compared in the nine groups, it was found that all groups reacted with a more p ronounced HR reduction during apneas with face immersion. AU groups wi thout prior breath-hold diving experience were found to perform shorte r apneas with face immersion than apneas in air, or apneas of the same duration in both conditions, which has been reported in other studies . However, in all groups with diving experience, the apneic time was p rolonged during apneas with face immersion. The results of this study suggest an oxygen-conserving effect of the diving response in trained apneic divers.