Seasonal observations on the cardiac rhythm during diving in the Korean ama.

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Abstract
Ecg were obtained from 5 ama in the summer (water temperature of 27[degree] C) and the winter (water temperature of 10[degree] C) during each of the following apneic maneuvers; breath holding (BH) in air, BH in water, surface swim with head submerged underwater, and diving to a depth of 5 m. Although a sinus bradycardia was noted in all cases, the extent of this bradycardia was least during BH in air and was greatest during BH in water as well as during surface swim. Moreover, the bradycardia during diving was less severe than during BH in water. Quantitatively, the extent of bradycardia during each apneic maneuver was approximately 20% greater in the winter than in the summer. Cardiac arrhythmias were uniformly noted in all apneic maneuvers, the incidence being approximately 43% in the summer and 72% in the winter. Of various arrhythmias, abnormal P wave and nodal rhythm were most frequently observed, although idioventricular rhythm, premature atrial beats, and premature ventricular beats were occasionally seen. On the basis of these findings, it is concluded that the diving bradycardia is mainly attributable to both breath holding and water submergence and the cardiac arrhythmia during diving to breath holding alone, and also that cold stimulus plays a valuable role in potentiating the development of both bradycardia and arrhythmia during diving.

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