Autonomic Receptor Function and Dysfunction
Diagnostic Applications
- The European Society of Cardiology recommends autonomic function testing, including the Valsalva maneuver and deep-breathing test, to characterize cardiovascular sympathetic and parasympathetic autonomic function 1, 2, 3
- The Valsalva maneuver demonstrates autonomic control of cardiovascular function, with sympathetic outflow to blood vessels increasing and parasympathetic outflow to the heart decreasing during phase II 1, 2
- Heart rate variability during deep breathing is modulated by cardiac parasympathetic (vagal) outflow and is blunted or abolished in patients with cardiovascular autonomic failure 2
Autonomic Receptor Dysfunction
- The European Society of Cardiology defines classical orthostatic hypotension as a sustained reduction in systolic blood pressure of ≥20 mmHg or diastolic blood pressure of ≥10 mmHg within 3 minutes of standing 4
- Delayed orthostatic hypotension occurs beyond 3 minutes of standing, and orthostatic hypotension can result from impaired sympathetic vasoconstriction due to autonomic failure 4
- Postural Orthostatic Tachycardia Syndrome (POTS) is characterized by an excessive increase in heart rate upon standing without orthostatic hypotension, and laboratory evaluation should include thyroid function tests, complete blood count, basic metabolic panel, and cardiac biomarkers to rule out secondary causes 4, 5
Autonomic Receptors in Gastrointestinal Function
- The American Gastroenterological Association notes that parasympathetic stimulation via muscarinic receptors generally increases GI motility, while sympathetic stimulation via alpha adrenergic receptors generally decreases GI motility 7
- GLP-1 receptors on the myenteric plexus activate nitrergic and cyclic adenosine monophosphate pathways to inhibit vagal activity on the gut, leading to reduced gastric contractions and delayed emptying 7
- Autonomic innervation regulates gastric acid secretion, with increased fasting and postprandial gastric volumes observed with vagal stimulation, and parasympathetic stimulation increases secretion from digestive glands 7