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.
Highlights
Physiological or pathological stimulation of the trigeminal nerve can trigger sudden cardiovascular disturbances with the characteristic features of a nervous reflex [1]
Cardiovascular Autonomic Regulation in Trigeminal Reflexes or its nuclear sensitive complex triggered a reflex that induced cardiovascular symptoms including a sharp reduction of heart rate, hypotension, apnea, and gastric hypermotility [6, 7]
The trigeminal reflexes can be triggered by stimuli sensed by thermoreceptors in the facial skin [13], nasal mucosa [14], and eyeball [4, 15]
Summary
Physiological or pathological stimulation of the trigeminal nerve can trigger sudden cardiovascular disturbances with the characteristic features of a nervous reflex [1]. Schaller and colleagues [10, 11] first published the occurrence of a central reflex in humans during cerebellopontine angle and brainstem surgeries and merged these peripheral and central responses into a single autonomic reflex, which is generally accepted as the trigeminocardiac reflex These reflexes represent somato-autonomic responses where the trigeminal nerve is the afferent pathway, the vagus and sympathetic nerves are the efferent pathways, and numerous brainstem nuclei serve as integration centers [12]. The trigeminal reflexes can be triggered by stimuli sensed by thermoreceptors in the facial skin (diving reflex) [13], nasal mucosa (nasopharyngeal reflex) [14], and eyeball (oculocardiac reflex) [4, 15] They can be activated by direct stimulation of some trigeminal branches and the trigeminal nuclear complex of the brainstem (trigeminocardiac reflex) [16]
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