Can the mammalian dive response override posttraumatic stress disorder?

Abstract

Posttraumatic stress disorder (PTSD) is a burdensome condition that has been made worse by the Covid-19 pandemic and that can lead to suicide, especially among childhood trauma victims, rape victims, military service members, and law enforcement. Physiological responses characterized by PTSD are thought to be evolutionary mechanisms that function to promote survival by heightening the stress response in an anticipatory fashion, allowing the organism to react quickly to recurring stressors or threats, even when stressors or threats are not present in the immediate environment. Frequent and sudden activation of the stress response can be uncomfortable and deleterious to health. The mammalian dive response (MDR) is another evolutionary adaptation that functions to promote survival by conserving oxygen when submerged underwater, and like the stress response, it disrupts the homeostatic environment. However, the physiological reactions induced by the MDR are mostly mediated parasympathetically and promote dramatic slowing of the heart rate, while the fight or flight response has opposite physiological effects. Frequent activation of the MDR and its parasympathetic components, such as bradycardia and vagus nerve stimulation, might inhibit sympathetic nervous system (SNS) factors involved with stress and may condition lasting beneficial changings of parasympathetic physiology that protect against the deleterious SNS mechanisms involved in prolonged stress and PTSD.