[The function of the heart changes in implementation of the diving reactions in humans]

The changes of chronotropic function of the heart and of the myocardium in the implementation of the diving response in humans were studied by the electrocardiographic method. The study involved 80 students aged 18-20 years. Diving simulation was performed by immersing the face in cold water during breath-hold exhale. When the water temperature was 12.3 +/- 2.3 degrees C, average duration of apnea was 31 +/- 11 s. The oxygen content in the exhaled air after apnea was 98.8 +/- 8.7 mm Hg, carbon dioxide--49.1 +/- 3.5 mm Hg. It was observed slowing of the heart rate, mainly due to the increasing of diastole in 41 of the 80 surveyed during simulating diving. But it also can be observed symptoms of conduction deterioration: atrioventricular block type I (22% of reactive type and 29% of the highly reactive type subjects), and exceeds standards QTc-interval prolongation (at 7.5% of the subjects). These responses are adaptive in nature and disappear in the recovery process. But the fact abnormalities of conduction in the myocardium must be considered when using the diving reflex in medical practice, as may be due to a predisposition to a certain pathology of the cardiovascular system.