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(Circulation. 2002;105:2518.)
© 2002 American Heart Association, Inc.
Clinical Investigation and Reports |
From the Autonomic Dysfunction Center, Vanderbilt University, Nashville, Tenn.
Correspondence to David Robertson, MD, Autonomic Dysfunction Center, AA3228 MCN, Vanderbilt University, Nashville, TN 37232-2195. E-mail david.robertson{at}mcmail.vanderbilt.edu
| Abstract |
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Methods and Results Impairment of the baroreflex may produce an unusually broad spectrum of clinical presentations; with acute baroreflex failure, a hypertensive crisis is the most common presentation. Over succeeding days to weeks, or in the absence of an acute event, volatile hypertension with periods of hypotension occurs and may continue for many years, usually with some attenuation of pressor surges and greater prominence of depressor valleys during long-term follow-up. With incomplete loss of baroreflex afferents, a mild syndrome of orthostatic tachycardia or orthostatic intolerance may appear. Finally, if the baroreflex failure occurs without concomitant destruction of the parasympathetic efferent vagal fibers, a resting state may lead to malignant vagotonia with severe bradycardia and hypotension and episodes of sinus arrest.
Conclusions Although baroreflex failure is not the most common cause of the above conditions, correct differentiation from other cardiovascular disorders is important, because therapy of baroreflex failure requires specific strategies, which may lead to successful control.
Key Words: baroreceptors hypertension tachycardia
| Introduction |
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| Physiology |
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Physiological transduction of stretch is common to many tissues and organs, mediating light touch, hearing, and distention at visceral sites. The carotid sinus itself contains a stretch receptor. It has been proposed that the DEG/ENaC family of cation channels, which are responsible for touch sensation in Caenorhabditis elegans, are components of the baroreceptor mechanosensor.9 The expression of the
subunit of ENaC in the fine baroreceptor nerve terminals innervating the aortic arch and carotid sinus is the first indication of the molecular identity of baroreceptor mechanotransduction. The role of this class of channels in baroreceptor function is supported by inhibition of baroreceptor activity with amiloride analogs, which are known to inhibit DEG/ENaC channels. Both ß and
subunits of DEG/ENaC have also been identified in mechanosensory structures in the rat footpad, which are believed to mediate light touch.10 The
subunit of ENaC is also present in osteoblasts, a cell type that responds to mechanical stimulation.11
| Problems Identifying Baroreflex Failure |
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Another problem in understanding baroreflex failure is the paucity of reported cases in the world literature. Until recently, there were not referral centers for autonomic disorders where groups of such patients could be studied in detail. Now that such facilities are available, we may expect more detailed elucidation of pathophysiology to emerge from future studies.
An additional level of complexity is the presence of both afferent and efferent nerve traffic in each of the cranial nerves involved in baroreflex function. The degree to which efferent nerves suffer collateral damage will no doubt have a significant impact on the clinical presentation of baroreflex lesions. This is particularly true when there is involvement of the vagus nerve.
Confusion also exists in the difference between baroreflex failure and autonomic failure. Some have used these terms interchangeably. But in reality, the cardiovascular manifestations of these two disorders are quite different (Table 1). The presentation of autonomic failure is dominated by orthostatic hypotension, whereas the presentation of acute baroreflex failure often resembles that of pheochromocytoma.
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Focus heretofore has been on completeness of interruption of afferent baroreflex nerves in the presence of baroreflex failure. However, clinical studies have provided evidence for asymmetry in central control of cardiovascular function.13,14 Over the last two decades, Jannetta and Gendell15 have described arterial loops impinging on cardiovascular nuclei in the left brain stem as being the cause of unexplained hypertension in some patients. Future studies of baroreflex failure need to address whether left-sided baroreflex input elicits a disproportionate effect on cardiovascular regulation.
| Causes of Baroreflex Failure |
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| Clinical Manifestations of Baroreflex Failure |
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Volatile Hypertension
This is the most commonly encountered presentation of baroreflex failure. It may develop insidiously after a substantial period of time during which baroreflex function gradually declines. Alternatively, hypertensive crisis may evolve over days and weeks into the more chronic volatile hypertension phase. This phase is usually more or less permanent, although the pressor surges moderate over time. These patients display an interrupted afferent baroreflex input from the carotid sinus to the nucleus tractus solitarii with accompanied interrupted efferent parasympathetic output to the heart and blood vessels (Figure 2).
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Abrupt sympathetic activation characterizes volatile hypertension. Thus, whereas baseline blood pressure may be normal to elevated, marked abrupt increases or surges of blood pressure lasting minutes to hours occur and are accompanied by tachycardia. These pressor surges are elicited by mental or physical stress,30 during which sympathetic outflow is increased,31 and are characterized by dizziness or lightheadedness, palpitations, and severe headaches.32 Profuse sweating often occurs. Tremulousness, anxiety, and irritability are typical of these episodes, although in some cases, the irritability may trigger the pressor surge rather than vice versa. Mild and transient elevations in plasma glucose have also occasionally been seen. Intraocular pressure may also increase in baroreflex failure.33 Plasma norepinephrine may increase to levels >1000 mg/mL, as encountered in pheochromocytoma.34,35 Values >2000 pg/mL are occasionally seen. Patients with volatile hypertension can have hypotensive valleys as well as pressor peaks, especially during periods of quiet, sedation, or sleep, when sympathetic outflow is diminished.36
With time, the pressor peaks may attenuate somewhat and the depressor valleys may become a greater problem for the patient, but these changes in the character of baroreflex failure are often played out over many years. Nevertheless, because of the complexity of treating these polar shifts in blood pressure, frequent follow-up of patients is important to make certain they are at an optimal regimen at all times.
Orthostatic Tachycardia
Orthostatic tachycardia, defined as an increase in heart rate by >30 bpm from the supine to upright position, is one of the most common findings among patients referred to tertiary centers with complaints of orthostatic intolerance. Most patients referred for orthostatic tachycardia have neuropathic postural tachycardia syndrome37 or some other cause for their symptoms rather than baroreflex failure. But this syndrome is also occasionally a presentation of clinical baroreflex impairment. In some cases, it may primarily reflect interruption of efferent right vagus nerve activity, leading to a loss of parasympathetic input to the sinus node, with a consequent increase in heart rate. In other cases, mild sympathetic activation may occur with stress and provoke tachycardia disproportionate to the increase in blood pressure. Occasionally, patients presenting with orthostatic tachycardia will ultimately progress to the volatile hypertension form of baroreflex failure. Other patients have remained stable for a prolonged period of time.
Malignant Vagotonia
Severe bradycardia and asystole attributable to increased parasympathetic tone are rarely encountered in baroreflex failure. More commonly, lesions lead to complete or near-complete destruction of afferent baroreflex input, producing denervation of the heart and cardiovascular system and tachycardia.
Nevertheless, patients with selective baroreflex failure (Jordan syndrome) possess interrupted afferent baroreflex input from the carotid sinus to the nucleus tractus solitarii with intact efferent sympathetic and parasympathetic output to the heart and blood vessels (Figure 3). They display malignant vagotonia with hypotension, bradycardia, and asystole.38 Along with the hypertensive episodes encountered in the other forms of baroreflex failure, patients with this form may have episodes of hypotension with a systolic pressure <50 mm Hg. Accompanying symptoms include fatigue and dizziness, with possible progression to frank syncope. The most severe episodes tend to occur during early morning sleep. Episodes have also occurred after intravenous nitroprusside, sublingual nitroglycerin, and the stress of neurosurgery. Also observed in these patients are periods of asystole during rest, lasting for 20 seconds or more, mandating the placement of a cardiac pacemaker.
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| Differential Diagnosis of Baroreflex Failure |
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Despite the long differential diagnosis, key features of the history and examination of the patient with baroreflex failure make it possible to make the diagnosis. The most important finding is excessive excursion of heart rate during normal daily activities (confirming autonomic control of heart rate), coupled with absent bradycardia in response to a pressor such as phenylephrine or absent tachycardia in response to a depressor such as nitroprusside. In practice, the history of prior trauma exposure is usually the most important consideration in suspecting the diagnosis of baroreflex failure.
| Therapy of Baroreflex Failure |
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The pharmacological treatment of choice for blood pressure surges is clonidine (Table 4). Clonidine acts centrally and peripherally to attenuate sympathetic activation and limit the extent to which pressor surges can occur. The
-adrenoreceptor blocker phenoxybenzamine has been relatively unsuccessful in reducing the frequency of pressor surges, although the magnitude of surges (but not tachycardia) is controlled.46 It may be that the sedative effects of the
2-adrenoreceptor agonists such as clonidine may assist the patients in preventing hypertensive episodes. In the case of clonidine, the inconvenience of frequent oral dosing can be avoided by using patch preparations. Most patients with baroreflex failure will require significant doses, whether oral or transdermal. To reduce the possibility of loss of a patch with consequent provocation of clonidine withdrawal, we sometimes use two No. 1 patches, one placed on Sunday and a second placed on Wednesday of each week, staggered this way to lessen the likelihood of inadvertent, complete discontinuation of clonidine.
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In patients who have been well controlled for months to years, it is sometimes possible to modify treatment regimens from
2-adrenoreceptor agonists to benzodiazepines, such as diazepam. Although relatively high doses of benzodiazepines are required, patients often tolerate this extremely well.
Finally, because of the excessive levels of plasma norepinephrine encountered in this patient population, agents that prevent release of norepinephrine may also be helpful. Guanadrel, which inhibits the release of norepinephrine from peripheral sympathetic nerve endings,47 is particularly effective. It has a short half-life and therefore is very useful in instituting therapy. It is excluded from the central nervous system so that no central side effects may occur. Because of a longer half-life, 5 days at its site of action, guanethidine may provide a more efficacious and easy coverage regimen for the long-term. Like guanadrel, guanethidine is excluded from the central nervous system, which limits its side effects. Occasionally, patients experience diarrhea on moderate to high doses of guanethidine.
In some patients, prevention of hypotension is also required. This is quite different, because the hypotensive episodes are usually short lived and most agents have a longer half-life than the usual duration of these spells. Fludrocortisone may still be the best way to treat this problem, because patients with baroreflex failure may have reduced plasma volume. Generally, low doses are sufficient. Fludrocortisone requires time for its full effect, thus its dosage should not be increased more frequently than at 2-week intervals. In highly exceptional cases, where excessive
2-agonist effect has been elicited, with consequent prolonged hypotension, administration of the
2-adrenoreceptor antagonist, yohimbine, at modest doses (1 to 5 mg) will usually lead to improvement.
Finally, if severe bradycardia (<40 bpm) is detected or if the patient has concomitant evidence of significant heart block, the placement of a pacemaker may be necessary. This may free the clinician to use a broader range of pharmacotherapy to manage the pressor and depressor manifestations of the disease.
In addition to issues of therapy, avoidance of agents that may be harmful in baroreflex failure is also an important part of management (Table 5). Because the pressor surges depend on high synaptic norepinephrine concentrations, anything that causes those concentrations to be higher is generally contraindicated. Because 80% to 90% of synaptic norepinephrine is removed by the norepinephrine transporter,48 blockade of this transporter by tricyclic antidepressants will potentiate the pressor effect of sympathetic activation. This may be particularly important in the heart, where up to 90% of norepinephrine removal is mediated by the norepinephrine transporter. Likewise, agents that reduce the breakdown of norepinephrine, such as monoamine oxidase inhibitors, should be avoided. Although not systematically studied, it would seem more appropriate to treat depression in patients with baroreflex failure with selective serotonin reuptake inhibitors than with tricyclic antidepressants or monoamine oxidase inhibitors. Other agents whose ultimate effect is to enhance norepinephrine availability, such as amphetamines and cocaine, should also be avoided. Although yohimbine has occasionally been used in situations where the effect of
2-agonists have led to excessive hypotension, in other circumstances it is likely to result in a profound pressor response and should therefore be avoided.
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| Conclusion |
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| Acknowledgments |
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| Footnotes |
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Received January 29, 2002; revision received March 20, 2002; accepted March 21, 2002.
| References |
|---|
2. Lampen H, Kezdi P, Koppermann E, et al. Experimenteller entzugelungshochdruck bei arterieller hypertonie. Z Kreislaufforschung. 1949; 38: 577592.
3. Kezdi P. Baroreceptors in normotension. Prog Brain Res. 1977; 47: 3542.[Medline] [Order article via Infotrieve]
4. Talman WT. Kynurenic acid microinjected into the nucleus tractus solitarius of rat blocks the arterial baroreflex but not responses to glutamate. Neurosci Lett. 1989; 102: 247252.[CrossRef][Medline] [Order article via Infotrieve]
5. Sved AF, Ito S, Madden CJ. Baroreflex dependent and independent roles of the caudal ventrolateral medulla in cardiovascular regulation. Brain Res Bull. 2000; 51: 12933.[CrossRef][Medline] [Order article via Infotrieve]
6.
Taylor DG, Gebber GL. Baroreceptor mechanisms controlling sympathetic nervous rhythms of central origin. Am J Physiol. 1975; 228: 10021013.
7. Chapleau MW, Abboud FM. Introduction.In: Chapleau MW, Abboud FM, eds. Neuro-Cardiovascular Regulation: From Molecules To Man. New York, NY: The New York Academy of Sciences; 2001: xiiixxii.
8.
Montano N, Cogliati C, da Silva VJ, et al. Effects of spinal section and of positive-feedback excitatory reflex on sympathetic and heart rate variability. Hypertension. 2000; 36: 10291034.
9. Drummond HA, Price MP, Welsh MJ, et al. A molecular component of the arterial baroreceptor mechanotransducer. Neuron. 1998; 21: 14351441.[CrossRef][Medline] [Order article via Infotrieve]
10.
Drummond HA, Abboud FM, Welsh MJ. Localization of ß and
subunits of ENaC in sensory nerve endings in the rat foot pad. Brain Res. 2000; 884: 112.[CrossRef][Medline]
[Order article via Infotrieve]
11.
Kizer N, Guo X, Hruska K. Reconstitution of stretch-activated cation channels by expression of the
-subunit of the epithelial sodium channel cloned from osteoblasts. Proc Natl Acad Sci U S A. 1997; 94: 10131018.
12.
Fagius J, Wallin BG, Sundlöf G, et al. Sympathetic outflow in man after anaesthesia of the glossopharyngeal and vagus nerves. Brain. 1985; 108: 423438.
13. Hilz MJ, Dütsch M, Perrine K, et al. Hemispheric influence on autonomic modulation and baroreflex sensitivity. Ann Neurol. 2001; 49: 575584.[CrossRef][Medline] [Order article via Infotrieve]
14.
Zamrini EY, Meador KJ, Loring DW, et al. Unilateral cerebral inactivation produces differential left/right heart rate responses. Neurology. 1990; 40: 14081411.
15. Jannetta PJ, Gendell HM. Clinical observations on etiology of essential hypertension. Surg Forum. 1979; 30: 431432.[Medline] [Order article via Infotrieve]
16.
Biller J, Feinberg WM, Castaldo JE, et al. Guidelines for carotid endarterectomy: a statement for healthcare professionals from a special writing group of the stroke council, American Heart Association. Stroke. 1998; 29: 554562.
17. Towne JB, Bernhard VM. The relationship of postoperative hypertension to complications following carotid endarterectomy. Surgery. 1980; 88: 575580.[Medline] [Order article via Infotrieve]
18. DeToma G, Nicolanti V, Plocco M, et al. Baroreflex failure syndrome after bilateral excision of carotid body tumors: an underestimated problem. J Vasc Surg. 2000; 31: 806810.[CrossRef][Medline] [Order article via Infotrieve]
19.
Phillips AM, Jardine DL, Parkin PJ, et al. Brain stem stroke causing baroreflex failure and paroxysmal hypertension. Stroke. 2000; 31: 19972001.
20. Jansen JC, Van den Berg R, Kuiper A, et al. Estimation of growth rate in patients with head and neck paragangliomas influences the treatment proposal. Cancer. 2000; 88: 28112816.[CrossRef][Medline] [Order article via Infotrieve]
21. Netterville JL, Reilly KM, Robertson D, et al. Carotid body tumors: a review of 30 patients with 46 tumors. Laryngoscope. 1995; 105: 115126.[Medline] [Order article via Infotrieve]
22. Milunsky J, DeStefano AL, Huang X, et al. Familial paragangliomas: linkage to chromosome 11q23 and clinical implications. Am J Med Genet. 1997; 72: 6670.[CrossRef][Medline] [Order article via Infotrieve]
23. Robertson RM. Baroreflex failure.In: Robertson D, Low PA, Polinsky RJ, eds. Primer on the Autonomic Nervous System. New York, NY: Academic Press; 1996: 197201.
24. Shapiro MH, Ruiz-Ramon P, Fainman C, et al. Light-headedness and defective cardiovascular reflexes after neck radiotherapy. Blood Press Monit. 1996; 1: 8185.[Medline] [Order article via Infotrieve]
25.
Biaggioni I, Whetsell WO, Jobe J, et al. Baroreflex failure in a patient with central-nervous-system lesions involving the nucleus-tractus-solitarii. Hypertension. 1994; 23: 491495.
26.
Tellioglu T, Oates JA, Biaggioni I. Munchausens syndrome presenting as baroreflex failure. N Engl J Med. 2000; 343: 581.
27. Hirschowitz BI, Groll A, Ceballos R. Hereditary nerve deafness in 3 sisters with absent gastric motility, small bowel diverticulitis and ulceration and progressive sensory neuropathy. Birth Defects Orig Art Ser. 1972; 8: 2741.
28.
Jordan J, Toka HR, Heusser K, et al. Severely impaired baroreflex-buffering in patients with monogenic hypertension and neurovascular contact. Circulation. 2000; 102: 26112618.
29.
Schuster H, Wienker TF, Toka HR, et al. Autosomal dominant hypertension and brachydactyly in a Turkish kindred resembles essential hypertension. Hypertension. 1996; 28: 10851092.
30. Kuchel O, Cusson JR, Larochelle P, et al. Posture- and emotion induced severe hypertensive paroxysms with baroreceptor dysfunction. J Hypertens. 1987; 5: 277283.[CrossRef][Medline] [Order article via Infotrieve]
31.
Bishop VS. Carotid baroreflex control of blood pressure and heart rate in men during dynamic exercise [editorial]. J Appl Physiol. 1994; 77: 491492.
32.
Aksamit TR, Floras JS, Victor RG, et al. Paroxysmal hypertension due to sinoaortic baroreceptor denervation in humans. Hypertension. 1987; 9: 309314.
33. Joos KM, Kakaria SK, Lai KS, et al. Intraocular pressure and baroreflex failure. Lancet. 1998; 351: 1704.
34. Floras JS, Aylward PE, Victor RG, et al. Epinephrine facilitates neurogenic vasoconstriction in humans. J Clin Invest. 1988; 81: 12651274.
35. Manger WM, Gifford RW. Catecholamine metabolism: biosynthesis, storage, release, and inactivation.In: Manger WM, Gifford RW, eds. Clinical and Experimental Pheochromocytoma. Cambridge, Mass: Blackwell Science; 1996: 831.
36.
Somers VK, Dyken ME, Mark AL, et al. Sympathetic-nerve activity during sleep in normal subjects. N Engl J Med. 1993; 328: 303307.
37.
Jacob G, Costa F, Shannon JR, et al. The neuropathic postural tachycardia syndrome. N Engl J Med. 2000; 343: 10081014.
38.
Jordan J, Shannon JR, Black BK, et al. Malignant vagotonia due to selective baroreflex failure. Hypertension. 1997; 30: 10721077.
39.
Hamada M, Shigematsu Y, Mukai M, et al. Blood pressure response to the valsalva maneuver in pheochromocytoma and pseudopheochromocytoma. Hypertension. 1995; 25: 266271.
40. Smit AJ, Wieling W, Karemaker JM. Clinical approach to cardiovascular reflex testing.In: Smit AJ, ed. Impaired Baroreflex Function: Diagnosis and Treatment of Orthostatic Hypotension. Amsterdam, The Netherlands: University of Amsterdam; 1998: 1729.
41.
Shannon JR, Jordan J, Diedrich A, et al. Sympathetically mediated hypertension in autonomic failure. Circulation. 2000; 101: 27102715.
42.
Jacob G, Shannon JR, Costa F, et al. Abnormal norepinephrine clearance and adrenergic receptor sensitivity in idiopathic orthostatic intolerance. Circulation. 1999; 99: 17061712.
43.
Stewart JM, Weldon A. Reflex vascular defects in the orthostatic tachycardia syndrome of adolescents. J Appl Physiol. 2001; 90: 20252032.
44. Robertson RM, Medina E, Shah N, et al. Neurally mediated syncope: pathophysiology and implications for treatment. Am J Med Sci. 1999; 317: 102109.[CrossRef][Medline] [Order article via Infotrieve]
45.
Sato T, Kawada T, Shishido T, et al. Novel therapeutic strategy against central baroreflex failure: a bionic baroreflex system. Circulation. 1999; 100: 299304.
46.
Robertson D, Hollister AS, Biaggioni I, et al. The diagnosis and treatment of baroreflex failure. N Engl J Med. 1993; 329: 14491455.
47. Hoffman BB, Carruthers SG. Cardiovascular disorders: hypertension.In: Carruthers SG, Hoffman BB, Melmon KL, et al, eds. Clinical Pharmacology. New York, NY: McGraw-Hill; 2000: 65234.
48.
Esler M, Jennings G, Lambert G, et al. Overflow of catecholamine neurotransmitters to the circulation: source, fate, functions. Physiol Rev. 1990; 70: 963985.
49. Reis DJ. The brain and hypertension: reflections on 35 years of inquiry into the neurobiology of the circulation. Circulation. 1984; 70 (suppl III): 3145.
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