A study was conducted to examine ; first, the cardiac response caused by various breath holding maneuvers, body water immersion and underwater swimming (US) ; second, the reproducibility of cardiac response in us; and third, the blood component variations caused by us. Water temperature used was 30°C. Fourteen healthy adults of both gender participated in this study. The results were as follows:
1. Those with stronger bradycardial response to apneic facial immersion (AFI) were subject to induced cardiac arrhythmias during or after us. And those with cardiac arrhythmias caused by AFI were inclined to produce a similar response even when their whole body was immersed as well as during us. Thus the test usingAFI proved to be valuable.
2. Heart rate of almost all subjects repeatedly showed a convex pattern, and their response to cardiac arrhythmias during and after us corresponded fairly accurately. Therefore it is presumed that cardiac function under the influence of US could be reproduced to some extent.
3. During static maneuvers, mainly bradycardiac arrhythmias were detected, including 2°AV block Wenckebach type in case of head out water immersion. On the other hand, brady, tachy and a combination of both were detected under us. From these findings and considering that the subjects with cardiac arrhythmias showed significant and specific variation of blood electrolyte and lactate, it was believed that various factors, including non-reciprocal increase of autonomic activities, the variations of blood component and so forth, simultaneously and interactively caused the cardiac arrhythmias during US.

This study examined the effects of gender and age difference on the electrocardiographic response to apneic facial immersion (AFT) . Twenty males (aged 27.2±3.8 yrs) and 16 females (aged 25.1±3.7 yrs) served on the study of gender while 94 males and females (aged 13-67 yrs) served on the study of age.
There was a significant difference between males and females in heart rate response in a few time series stages after AFT of 15°C and 30°C water temperature, however, then was no significant gender difference during each AFI in the bradycardiac response, incident rates and kinds of arrhythmias, latency of arrhythmias during AFT (LADA) and relative latency (RL) .
For the age study significant quadraticcorrelations were found between the bradycardiac response during each AFT and age in spite of a large individual difference. The incident rates of arrhythmias were reduced significantly with age. Also, incidental arrhythmias of the younger group were partially different from those of the young group, suggesting the characteristic difference by growth and development. The incidental manner of arrhythmias after AFT of the middle and elder group (aged 40.67 yrs) was suggestive of a part of their agerelated feature. Although LADA was significantly shorter in the younger group than in the young group, there was no significant difference in RL between both groups.
From these results, it was suggested that although gender need not be considered very carefully, age should be, for the method and criterion of AFI test.