Effects of repeated apneas on apneic time and diving response in non-divers.

Human breath-hold divers usually perform a series of dives with short intervals. Repeated apneas prolong apneic time, and an accentuated diving response has been suggested to be the cause. The aim of this study was to investigate the effect of repeated apneas on apneic time and diving response in humans. Forty-one subjects performed a series of five apneas with face immersion in water of 10 degrees C, separated by 2-min intervals. Apneas were performed at rest and to individual maximal duration. Heart rate, mean arterial pressure, skin capillary blood flow, and respiratory movements were recorded. Thirty-eight of the subjects were used for analysis of cardiovascular parameters, and in 23 subjects the physiologic breaking point could be detected by the involuntary breathing movements. Heart rate reduction and blood pressure increase were most prominent during the first apneic face immersion, whereas skin capillary blood flow reduction was most intense in the second apneic face immersion. Blood pressure and skin capillary blood flow during recovery from apneic episodes also changed throughout the series. Repetition increased apneic time by 55% and postponed the occurrence of involuntary breathing movements by 27% in subjects passing the physiologic breaking point. We conclude that both physiologic factors, associated with the accumulation of CO2, and psychologic factors, related to the capacity to withstand the respiratory drive, contribute to the prolongation of apneic time whereas an increased diving response does not contribute.