Antagonistic and Synergistic Activation of Cardiovascular Vagal and Sympathetic Motor Outflows in Trigeminal Reflexes

Abstract

The trigeminal nerve and heart are strongly related through somato-autonomic nervous reflexes that induce rapid changes in cardiovascular function. Several trigeminal reflexes have been described, but the diving and trigeminocardiac reflexes are the most studied. The heart is a target organ dually innervated by the sympathetic and parasympathetic systems. Thus, how cardiac function is regulated during the trigeminal reflexes is the result of the combination of an increased parasympathetic response and increased, decreased, or unaltered sympathetic activity. Various hemodynamic changes occur as a consequence of these alterations in autonomic tone. Often in the oxygen-conserving physiological reflexes such as the diving reflex, sympathetic/parasympathetic co-activation reduces the heart rate and either maintains or increases blood pressure. Conversely, in the trigeminocardiac reflex, bradycardia and hypotension due to parasympathetic activation and sympathetic inactivation tend to be observed. These sudden cardiac innervation disturbances may promote the generation of arrhythmias or myocardial ischemia during surgeries in the trigeminal territory. However, the function and mechanisms involved in the trigeminal reflexes remain to be fully elucidated. The current review provides a brief update and analysis of the features of these reflexes, with special focus on how the autonomic nervous system interacts with cardiovascular function.

Diving in the Arctic: Cold Water Immersion’s Effects on Heart Rate Variability in Navy Divers

“…The significant increase in mean heart rate at the beginning of the dives suggests that there actually was a strong activation of the SNS. This is in line with most earlier observations of the diving reflex and sensation of cold also causing an SNS activation (Boussuges et al, 2007;Buchholz et al, 2017). After the first SNS response, the mean heart rate and LF/LH ratio suggested that SNS activity actually decreased over time.…”

“…Physical stress at the beginning of a cold-water dive, together with the diving reflex and cold stress-induced SNS activation, leads to a quick concurrent increase in both PNS and SNS activity. This, in turn, is a known risk factor for arrhythmia and sudden death (Buchholz et al, 2017;Kane and Davis, 2018).…”

Autonomic responses to tooth clenching in migraineurs—augmented trigeminocardiac reflex?

“…Migraine and MTC duration were the main modifiers of this increase. The observed changes in vagal activity likely occurred due to trigeminocardiac reflex (TCR), induced by irritation of the trigeminal‐innervated structures and well known as an inducer of bradycardia and hypotension . According to Lapi et al, TCR may influence the regulation of the cerebral blood flow.…”

“…According to Lapi et al, TCR may influence the regulation of the cerebral blood flow. However, the effect of this reflex is a result of increased vagal activation combined with the state of sympathetic activity . Thus, impaired autonomic regulation in migraineurs may influence the responses to masticatory irritation, too.…”

Neuromodulation as a new avenue for resuscitation in hemorrhagic shock

“…Trigeminal afferent fibers carry sensory information from the face and project to a range of targets within the brain via the central nervous system (CNS) (Mercante et al 2017). This then spreads "down" to the autonomic nervous system (ANS), with the potential to modulate the nervous, cardiovascular, and respiratory systems (Buchholz et al 2017). The ANS is pivotal in regulating the functions of our internal organs and maintaining vital signs and homeostasis (McCorry 2007), and major autonomic instability is a common feature in extreme situations such as hemorrhagic shock (Cooke et al 2008;Li et al 2019).…”