‘Autonomic conflict’: a different way to die during cold water immersion?

Abstract

Cold water submersion can induce a high incidence of cardiac arrhythmias in healthy volunteers. Submersion and the release of breath holding can activate two powerful and antagonistic responses: the 'cold shock response' and the 'diving response' . The former involves the activation of a sympathetically driven tachycardia while the latter promotes a parasympathetically mediated bradycardia. We propose that the strong and simultaneous activation of the two limbs of the autonomic nervous system ('autonomic conflict') may account for these arrhythmias and may, in some vulnerable individuals, be responsible for deaths that have previously wrongly been ascribed to drowning or hypothermia. In this review, we consider the evidence supporting this claim and also hypothesise that other environmental triggers may induce autonomic conflict and this may be more widely responsible for sudden death in individuals with other predisposing conditions.

Exercise at depth alters bradycardia and incidence of cardiac anomalies in deep-diving marine mammals

“…3a). Similar to humans [24][25][26] , these irregular IBI patterns were associated with independent ectopic heart beats that were most evident during periods of constant elevated SF (Fig. 3b).…”

“…In submerged humans 24,30 , as for Weddell seals (Fig. 3a), cardiac arrhythmias often occur in association with alternating short periods of tachycardia and bradycardia correlated with exercise.…”

“…3a), cardiac arrhythmias often occur in association with alternating short periods of tachycardia and bradycardia correlated with exercise. Based on this, it is not surprising that the swimming segment of cold water triathlons accounts for over 90% of race day deaths in human athletes 31 with cardiac malfunction cited as an underlying contributing factor 24 .…”

“…Regardless of the underlying mechanisms, normal cardiac rhythms can be disrupted when cardiac-stimulating and cardiac-suppressing neural signals switch quickly 24 . In human breath-hold divers, when exercise is superimposed on the diving response, sympathetic neural activation dictates cardiac variability and the ultimate level of bradycardia that is achieved 25,26 .…”

Deleterious Effects of Cold Air Inhalation on Coronary Physiological Indices in Patients With Obstructive Coronary Artery Disease

“…This resulted in an additional pressure load on the ventricle, increasing relative ejection time and impairing ventricular relaxation 31. Ventricular relaxation may also be further impaired by relative autonomic conflict caused by parasympathetic activation of facial trigeminal receptors during cold air inhalation32: this would dampen ß‐adrenoceptor‐mediated protein kinase A activation mentioned in the paragraph above. Furthermore, we observed a significantly exaggerated reduction in the diastolic time fraction during exercise with cold air.…”