Baroreflex

from Wikipedia, the free encyclopedia

The baroreflex or baroreceptor reflex is a homeostatic mechanism that maintains blood pressure . It is based on a negative feedback loop, in which an increased blood pressure reflexively lowers the heart rate and thus the blood pressure; conversely, a low blood pressure suppresses the baroreflex, causing the heart rate and thus the blood pressure to rise again.

This system is based on specialized neurons , so-called baroreceptors , in the aortic arch and the carotid sinus to measure changes in blood pressure and report them to the brainstem . Other changes in blood pressure are mediated by the autonomic nervous system . The atrial natriuretic peptide is part of a parallel negative feedback loop as an antagonist to the renin-angiotensin system .

anatomy

Baroreceptors are found in the auricle and vena cava , but the most sensitive baroreceptors are found in the carotid sinus and aortic arch . The baroreceptors in the carotid sinus are innervated by the glossopharyngeal nerve; the baroreceptors in the aortic arch from the vagus nerve . The activity of the baroreceptors is transmitted via these nerves to the nucleus tractus solitarii (NTS) of the brain stem.

The NTS sends excitatory glutamatergic fibers to the caudal ventrolateral medulla (CVLM) and activates it. The activated CVLM then sends inhibitory GABAergic fibers to the rostral ventral medulla (RVLM) and inhibits it. The RVLM is the primary nucleus for controlling the sympathetic nervous system; it sends excitatory fibers to the preganglionic neurons of the intermediolateral nuclei of the spinal cord. As a result, the baroreceptors activate the NTS at high blood pressure, which activates the CVLM, which in turn inhibits the RVLM and thus inhibits the sympathetic nervous system, which leads to a lowering of the blood pressure. Conversely, a low blood pressure leads to an increase in the tone of the sympathetic nervous system through less inhibition of the RVLM.

The NTS also sends excitatory fibers to the nucleus ambiguus , which regulates the parasympathetic nervous system, thus further reducing the effects of the sympathetic nervous system when blood pressure is elevated.

It has been found that electrical stimulation of the Baroreflex, using a device similar to a pacemaker, lowers blood pressure in patients with resistant hypertension.

Effect on heart rate variability

The baroreflex is part of the low-frequency component of heart rate variability , at around 0.1 Hz.

Baroreflex activation therapy for the treatment of refractory hypertension

Baroreflex activation is different from vagal stimulation. It works through an afferent limb which has the dual effect of stimulating vagal outflow and dampening global sympathetic outflow.

Seven clinical studies have shown that stimulating the baroreceptors with a pacemaker-like device lowers blood pressure in people with treatment-resistant hypertension.

The observed decrease in systolic blood pressure at the longest available follow-up is 36 mmHg (359 patients). In the first 6 months, the average drop in blood pressure was 21 mmHg (307 patients). For patients in Europe, Baroreflex activation therapy devices have received the CE mark for the treatment of resistant hypertension.

Baroreflex activation therapy for the treatment of heart failure

The lowering of the sympathetic nervous activity through the Baroreflex activation therapy indicates a potential in the treatment of chronic heart failure, since in this condition intensive sympathetic activation often takes place and patients with such sympathetic activation have a significantly increased risk of serious arrhythmias and exhibit death.

One study has already shown that Baroreflex Activation Therapy improves functional status, quality of life, exercise capacity and the N-terminal natriuretic peptide.

The randomized, controlled BeAT-HF study is currently being conducted in the US and Europe to investigate the effects on symptoms, exercise tolerance, blood markers, morbidity and mortality of heart failure.

literature

  • Berne, Robert M., Levy, Matthew N .: Cardiovascular Physiology . Mosby, Philadelphia, PA 2001, ISBN 0-323-01127-6 .
  • Boron, Walter F., Boulpaep, Emile L .: Medical Physiology: A Cellular and Molecular Approach . Elsevier / Saunders, Philadelphia, PA 2005, ISBN 1-4160-2328-3 .

Individual evidence

  1. ^ M Wallbach, MJ Koziolek: Baroreceptors in the carotid and hypertension-systematic review and meta-analysis of the effects of baroreflex activation therapy on blood pressure. . In: Nephrology, dialysis, transplantation: official publication of the European Dialysis and Transplant Association - European Renal Association . November 9, 2017. doi : 10.1093 / ndt / gfx279 . PMID 29136223 .
  2. ↑ IJ Scheffers, AA Kroon, J Schmidli, J Jordan, JJ Tordoir, MG Mohaupt, FC Luft, H Haller, J Menne, S Engeli, J Ceral, S Eckert, A Erglis, K Narkiewicz, T Philipp, PW de Leeuw: Novel baroreflex activation therapy in resistant hypertension: results of a European multi-center feasibility study. . In: Journal of the American College of Cardiology . 56, No. 15, October 5, 2010, pp. 1254-8. doi : 10.1016 / j.jacc.2010.03.089 . PMID 20883933 .
  3. ↑ WT Abraham, MR Zile, FA Weaver, C Butter, A Ducharme, M Halbach, D Klug, EG Lovett, J Müller-Ehmsen, JE Schafer, M Senni, V Swarup, R Wachter, WC Little: Baroreflex Activation Therapy for the Treatment of Heart Failure With a Reduced Ejection Fraction. . In: JACC. Heart failure . 3, No. 6, June 2015, pp. 487-496. doi : 10.1016 / j.jchf.2015.02.006 . PMID 25982108 .
  4. ↑ Barostim Therapy for Heart Failure: BEAT-HF . Retrieved April 19, 2018.