In vivo recordings from the human vagus nerve using ultrasound‐guided microneurography

Abstract

Key points The vagus nerve is the largest cranial nerve and innervates many structures in the neck, thorax and abdomen. Although single‐unit recordings from the vagus nerve have been performed in experimental animals for several decades, no recordings have ever been made from the human vagus nerve. The vagus nerve is routinely stimulated clinically, yet we know little of its physiology in humans. We describe the methodology and provide preliminary results of the first intraneural single‐unit recordings from the cervical vagus in awake humans, using tungsten microelectrodes inserted into the nerve through ultrasound guidance. Abstract Intraneural microelectrodes have been used extensively to record from single somatosensory axons supplying muscle, tendons, joints and skin, as well as to record from postganglionic sympathetic axons supplying muscle and skin, in accessible peripheral nerves in awake humans. However, the vagus nerve has never been targeted, probably because of its close proximity to the carotid artery and jugular vein in the neck. Here, we report the first unitary recordings from the human cervical vagus nerve, obtained using ultrasound‐guided insertion of tungsten microelectrodes into fascicles of the nerve. We identified tonically‐active neurones in which firing rates were inversely related to heart rate (and directly related to the cardiac interval), which we classified as putative preganglionic parasympathetic axons directed to the sinoatrial node of the heart. We also recorded from tonically‐active presumed sensory axons from the airways and presumed motor axons to the larynx. This new methodology opens exciting new opportunities for studying the physiology of the human vagus nerve in health and disease.

How far have we reached? Perhaps not enough, new avenues are about to be travelled

“…Ottaviani et al . (2020) also recorded what was classified as the cardioinhibitory motor axon (once the Hz range matched that found in animal studies), which showed an inverse relationship with heart rate.…”

“…In a breakthrough study reported in The Journal of Physiology , Ottaviani et al . (2020) successfully recorded vagus nerve activity in awake humans using an ultrasound‐guided microneurography approach. For the first time in humans, a tungsten microelectrode was inserted into the vagus nerve in the neck, enabling direct measurement of vagal axon activity.…”

What happens in vagus, no longer stays in vagus

“…Furthermore, another consideration requiring investigation is the classification of firing patterns and rates in the human vagus nerve. Unlike recordings of muscle sympathetic nerve activity (MSNA), which have been well characterized in humans, there are no prior data, beyond those of the study by Ottaviani et al (2020), providing insight into the typical behaviour of the vagus nerve in humans. This consideration will require further investigation to allow for better repeatability and standardization of vagal recordings.…”

“…Future studies could isolate and characterize the different neurons responsible for either decreasing heart rate or the force of contraction in healthy and diseased populations. The results of the study by Ottaviani et al (2020) also offer the possibility to record the heterogenous populations of baroreceptive and chemoreceptive vagal afferents located throughout the atria, ventricular, coronary and pulmonary vasculature. For example, the application of lower body positive pressure, a stimulus that results in multi-unit MSNA sympathoinhibition, was found to activate a subpopulation of MSNA single units, comprising a response that was accentuated in patients with heart failure with reduced ejection fraction (Millar et al 2015).…”

Vagus nerve recordings: new opportunities to investigate autonomic function in humans

“…In the current issue of The Journal of Physiology, Ottaviani et al (2020) report a case series of the first intraneural recordings from the cervical vagus nerve in humans using the microneurography technique.…”