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In most cases, vagal tone is not measured directly. Instead the processes affected by the vagus nerve – specifically heart rate and heart rate variability – are measured and used as a surrogate for vagal tone. Increased vagal tone (and thus vagal action) is generally associated with a lower heart rate and increased heart rate variability.
Episodes of vasovagal syncope are typically recurrent and usually occur when the predisposed person is exposed to a specific trigger. Before losing consciousness, the individual frequently experiences early signs or symptoms such as lightheadedness, nausea, the feeling of being extremely hot or cold (accompanied by sweating), ringing in the ears, an uncomfortable feeling in the heart, fuzzy ...
Low blood pressure occurs due to decreased systemic vascular resistance resulting from loss of sympathetic tone, which in turn causes blood pooling within the extremities rather than being available to circulate throughout the body. The slowed heart rate results from a vagal response unopposed by a sympathetic nervous system (SNS) response. [2]
More specifically, aerobic exercise leads to improvements in vagal tone (the nerve that regulates blood pressure and more), as well as lower heart rates, lower blood pressure and better control of ...
This reduces sympathetic tone to vascular smooth muscle. [9] This reduces heart rate and vascular resistance. [9] Digoxin increases vagal tone from the vasomotor centre, which decreases pulse. [7] G-series nerve agents have their most potent effect in the vasomotor center. [10]
Baroreflex activation is distinct from vagal stimulation. [8] [9] Electrical stimulation of the external surfaces of the carotid sinus activates baroreceptors believed to be in the adventitia of the artery. This stimulates an afferent limb which activates central nervous system pathways that in turn exert two different but synergistic autonomic ...
The vagus nerve plays a crucial role in heart rate regulation by modulating the response of sinoatrial node; vagal tone can be quantified by investigating heart rate modulation induced by vagal tone changes. As a general consideration, increased vagal tone (and thus vagal action) is associated with a diminished and more variable heart rate.
Topical atropine is used as a cycloplegic, to temporarily paralyze the accommodation reflex, and as a mydriatic, to dilate the pupils. [15] Atropine degrades slowly, typically wearing off in 7 to 14 days, so it is generally used as a therapeutic mydriatic, whereas tropicamide (a shorter-acting cholinergic antagonist) or phenylephrine (an α-adrenergic agonist) is preferred as an aid to ...