The Diving Reflex: from Fundamental Reseach to Medical Practice
Authors: Baranova Tatiana , Podyacheva Ekaterina , Zemlyanukhina Tatiana , Mitrofanova Alla 
Published: April 2020

Knowing natural mechanisms of protection against extreme environmental factors is the key to the human organism control. For example, in secondary aquatic Amniotes, the most important universal form of adaptation to diving is the diving reflex (DR), which is accompanied by reflexes of apnea, bradycardia, peripheral vasoconstriction and selective redistribution of blood flow. The blood supply is stopped to the organs that can withstand temporary hypoxia and redistributed to the organs, which are most vulnerable to a lack of oxygen, such as the brain and heart.

DR allows the organism to consume less oxygen in the process of diving. These reactions are qualitatively similar between species and DR elicited in diving mammals is quite similar to that of humans.

The human DR can be triggered by simulating diving, i.e. by immersion the face in water and holding the breath. Then, signals from cold and tactile sensors of the facial skin, baro‐ and chemoreceptors in the circulatory system, and mechanoreceptors in the respiratory system come to the n. vagus nucleus and then, via cholinergic fibers, to the heart sinoatrial node, thus causing bradycardia. Long‐term conative apnea makes adrenergic effects on the heart increase. The total effect on the heart sinoatrial node from n. vagus and sympathetic postganglionic neurons depends also on background state of the sinoatrial node cells; this state is in turn dependent on various neuropeptides released by cardiomyocytes and endothelial tissue in the blood vessels.

During diving, the peripheral vessels are constricted by signals coming from the medulla oblongata's vasomotor center through adrenergic sympathetic fibers to the muscular walls of the vessels.

Besides that, the reflexes under consideration are modulated by the epinephrine and norepinephrine level in the blood, hormones of the renin‐angiotensin and kinin‐bradykinin systems, and level of enzymes disintegrating those hormones.

The diving simulation model provides two channels to influence the cardiovascular system: the strong cholinergic effect on the heart's sinoatrial node and the adrenergic effect on the peripheral vessels. Modulating the input from receptive fields with consideration of the object's individual sensitivity makes it possible to influence the heart's function and vascular tone by intentionally varying peripheral blood circulation and the blood supply to the heart and brain.

Our study is based upon a multi‐year study of diving mammals and the human DR. More than 2000 persons were examined. Criteria for evaluating the human diving reaction were developed and formalized and diving reaction manifestations were categorized. Our primary objective today is find out why the vascular system and myocard show different sensibility to the adrenergic and cholinergic effects of the diving reflex. Attaining this objective would make it possible to apply DR phenomena in medical practice more successfully, to understand the cause’s human organism's different sensibility to β‐adrenergic blocking agents and cholinergic agents and to be capable of predicting predisposition to arterial hypertension.