Cardiovascular changes during maximal breath-holding in elite divers.

During maximal breath-holding six healthy elite breath-hold divers, after an initial "easy-going" phase in which cardiovascular changes resembled the so-called "diving response", exhibited a sudden and severe rise in blood pressure during the "struggle" phase of the maneuver. These changes may represent the first tangible expression of a defense reaction, which overrides the classic diving reflex, aiming to reduce the hypoxic damage and to break the apnea before the loss of consciousness.