 Difference between Neurally Mediated Hypotension and Orthostatic Hypotension   What's the difference between orthostatic hypotension (OH) and Neurally mediated hypotension (NMH)? There are several differences even though in both conditions the blood pressure drops. There are different causes and symptoms between the two conditions. With OH the person's blood pressure drops for a few seconds (maybe up to 15-30 sec) when the person gets up suddenly. The vision may get black and the person feels faint and may momentarily pass out. The body does increase the blood pressure after the initial drop & the person goes on about their business. There is usually no lingering effects. With NMH for an unknown reason when the person has been standing for an extended period of time the brain sends a message to the heart to drop the blood pressure (there is no abnormalties in the heart or brain). The person may feel weak, tired, faint, dizziness, nauseated and afterwards may feel weak, acky and tired. The symptoms may last from a few hours up to a couple of days. This drop in blood pressure can occur while standing for extended periods of time, while doing yard work (mowing yard, spreading a lot of pine needles) on a hot day, taking a long steamy shower or sitting in a sauna. OH is discovered by taking the blood pressure in a lying position then in a standing position. NMH is detected by taking the tilt table test. Both conditions can be helped by increasing fluid intake and maybe increase salt intake (a little, if you rarely use salt and don't have high blood pressure). Also symptoms of both condition as with many conditions have a waxing & weaning variance (they come & go). If symptoms are severe or bothersome you can talk to your doctor about medications. Generally these conditions are beneign but can be debilitating in severe cases.  Neurally Mediated Hypotension Information on NMH including causes, symptoms, treatment, how NMH relates to CFS. Homeostatic control of blood pressure and heart rate requires frequent and rapid cardiovascular adjustments as an individual changes from supine to sitting and standing positions throughout the day. When these adjustments are not accomplished, orthostatic hypotension occurs. Some patients with severe orthostatic hypotension are severely incapacitated, and their families assume a significant burden in their care. The diagnosis of orthostatic hypotension requires the occurrence of a sustained postural decrease in blood pressure that may be accompanied by symptoms of cerebral hypoperfusion. While the degree of hypotension required to produce symptoms varies, a decrease of 20 mm Hg or more in systolic blood pressure is one commonly used diagnostic criterion. If blood pressure is assessed for less than two minutes following a postural change, the degree of hypotension may be overstated. This is particularly true in elderly patients because blunted baroreceptor reflexes are common in otherwise normal older individuals. In one study, 17 percent of normal elderly patients exhibited a fall in systolic blood pressure of more than 20 mm Hg after they had been standing for two minutes. Blood pressure criteria are more sensitive than symptoms in detecting orthostatic hypotension. However, treatment usually is not required in the absence of symptoms. Symptoms of cerebral hypoperfusion include dimming or loss of vision, lightheadedness, dizziness, diaphoresis, diminished hearing, pallor, nausea and weakness. Severe orthostatic decreases in cerebral perfusion can cause syncope. Classification and Clinical Features The causes of orthostatic hypotension can be divided into neurogenic and nonneurogenic categories. Frequent causes of nonneurogenic orthostatic hypotension are listed in Table 1. These nonneurogenic causes lead to orthostatic hypotension because of cardiac pump failure, reduced intravascular volume or venous pooling. In addition, many medications can cause or exacerbate orthostatic hypotension. Since the nonneurogenic causes of orthostatic hypotension are so common, they should be systematically reviewed in any patient who is experiencing postural decreases in blood pressure with symptoms of hypoperfusion. As a general rule, the postural drop in blood pressure with nonneurogenic etiologies is accompanied by a compensatory increase in heart rate (often exceeding 15 to 30 beats per minute). This increase in heart rate does not occur in patients with neurogenic causes of orthostatic hypotension. Among the neurogenic etiologies for orthostatic hypotension are a number of uncommon but well-described causes of primary autonomic system failure. However, secondary failure of the autonomic system due to disease (e.g., stroke, diabetes) of the central or peripheral nervous system is a much more common cause of neurogenic orthostatic hypotension (Table 2). Neurogenic Causes of Orthostatic Hypotension Primary automatic system failure Multisystem atrophy (Shy-Drager syndrome) Pure autonomic failure Subacute dysautonomia Secondary autonomic system failure Brain and brainstem Tumor Stroke Multiple sclerosis Spinal cord Transverse myelitis Syringomyleia Tumor Tabes dorsalis Peripheral nervous system Diabetes mellitus Guillain-Barre syndrome Alcoholic polyneuropathy Human immunodeficiency virus infection Amyloidosis Porphyria The neurogenic causes of orthostatic hypotension include primary disorders such as pure autonomic failure and multiple system atrophy. Pure autonomic failure is a syndrome that includes orthostatic hypotension, impotence, abnormal sweating and urinary incontinence. Somatic neurologic manifestations are absent. This disorder, which occurs most commonly in middle-aged and elderly men and women, results in the loss of postganglionic sympathetic neurons and is characterized by low levels of plasma norepinephrine when the affected patient is supine. However, it can be misleading to base the diagnosis on a single evaluation. A patient with apparent pure autonomic failure at one point may eventually develop other neurologic symptoms suggestive of multiple system atrophy. Patients with orthostatic hypotension accompanied by parkinsonian features, cerebellar dysfunction or pyramidal signs are likely to have multiple system atrophy.6 In most cases, death due to progressive neurologic deterioration occurs within seven to 10 years after the onset of symptoms. The supine plasma norepinephrine level is normal or elevated in patients with multiple system atrophy. The pathologic examination reveals a loss of neurons in many nuclei of the central nervous system. Patients with this syndrome often do not respond to treatment with antiparkinsonian medications. Sudden-onset dysautonomia or dysautonomia evolving over weeks may occur alone or in conjunction with orthostatic hypotension accompanied by mild sensory or motor findings. Some of these patients have Guillain-Barré syndrome with autonomic dysfunction as the predominant clinical abnormality. Secondary failure of the autonomic nervous system (due to a systemic disease resulting in lesions of the central or peripheral nervous system) is a more common cause of neurogenic orthostatic hypotension. The lesions can occur in the brain, brainstem, spinal cord or peripheral nervous system. On neurologic examination or imaging studies, central nervous system lesions associated with orthostatic hypotension are usually accompanied by focal abnormalities. Diabetes mellitus, Guillain-Barré syndrome and alcoholic polyneuropathy are the most common peripheral nervous system disorders leading to orthostatic hypotension. Autonomic neuropathy may be the first sign of peripheral nervous system disease in diabetic patients, but autonomic involvement is usually accompanied by the typical distal, symmetric polyneuropathy. Symptomatic orthostatic hypotension develops as a result of inadequate peripheral vasoconstriction. The orthostatic hypotension becomes apparent with standing, with arising in the morning after sleep or with the splanchnic pooling of blood following a meal. Postprandial hypotension is common in patients with severe diabetes mellitus, but it also occurs in otherwise normal elderly persons. Supine hypertension can coexist with orthostatic hypotension in patients with autonomic dysfunction. In the Guillain-Barré syndrome, afferent and efferent sympathetic fibers are damaged by the inflammatory demyelination that is characteristic of the disease. The loss of normal sympathetic efferents to arterioles results in both hypotension and the development of denervation supersensitivity. This adrenergic supersensitivity can cause marked hypertension in response to low doses of sympathomimetic agents (such as over-the-counter cold preparations) or in response to endogenous catecholamine release. The net result can be a marked fluctuation between severe hypertension and hypotension over brief periods of time. Up to 2 percent of patients with Guillain-Barré syndrome have fatal cardiovascular collapse due to refractory hypotension or cardiac arrhythmias.8 The severity of autonomic involvement is not clearly related to the severity of neurologic weakness. Because of this predisposition to dramatic blood pressure fluctuation, episodes of hypotension in patients with Guillain-Barré syndrome are best treated initially with fluids rather than vasopressors. Orthostatic hypotension due to autonomic failure occurs in patients with a history of chronic alcohol abuse, but only in association with signs of severe peripheral neuropathy (i.e., absent ankle reflexes and diminished sensation in the calves or thighs and hands). The contribution of autonomic involvement to the high mortality rates associated with alcoholism is unknown. Patient Evaluation The initial step in the evaluation of patients with orthostatic hypotension is the exclusion of treatable causes (Table 3). The history should include a review of medications that accentuate the risk of hypotension. Although the removal of a medication that may be responsible for the patient's orthostatic hypotension is a rational initial therapeutic step, follow-up may reveal a persistent underlying autonomic disturbance that was accentuated by the use of the medication. A complete review of the patient's medical history may reveal other possible causes of symptoms. The possible relationship between orthostatic hypotension, alcohol use, exercise, meals, or straining should be explored as well. TABLE 3 Initial Steps in the Evaluation of Neurogenic Orthostatic Hypotension Review coexisting medical disorders. Determine the relationship oforthostatic hypotension to meals, exercise, straining or Valsalva maneuvers, and standing up after getting out of bed in the morning. Record supine and standing blood pressure and pulse after two to three minutes. Perform a complete neurologic examination The physical examination should include measurement of supine and standing pulse and blood pressure, with an interval of two to three minutes between measurements in each position. A neurogenic cause of orthostatic hypotension is suggested if, after standing for two to three minutes, the patient exhibits a decrease in systolic blood pressure (especially a decrease of more than 20 mm Hg) and orthostatic symptoms without an increase in pulse rate. However, orthostatic decreases in blood pressure may occur occasionally in otherwise normal patients over 70 years of age. The neurologic evaluation should include a mental status examination to exclude neurodegenerative disorders, a cranial nerve assessment (evaluating, for example, downgaze, which is impaired in progressive supranuclear palsy), a motor examination to look for parkinsonian features such as tremor, rigidity and bradykinesia, and a sensory evaluation to identify polyneuropathies. If the diagnosis remains uncertain, follow-up neurologic evaluations over time may reveal additional neurologic findings that can lead to the appropriate diagnosis. Diagnostic Tests Autonomic function testing is useful when the history and the findings on physical examination are inconclusive. This type of testing may also be useful for investigating the extent of autonomic involvement or for monitoring autonomic function over time. The autonomic function tests are noninvasive and are relatively easy to administer in a specialized testing laboratory where data are collected under controlled circumstances. These tests provide quantitative information about autonomic function. Tilt-table testing is helpful in evaluating patients with syncope of unknown cause. This topic was discussed in detail in an earlier issue of American Family Physician. The two most commonly used studies in patients with orthostatic hypotension unaccompanied by syncope are the Valsalva response and heart rate variation with deep breathing (sinus arrhythmia). The results of these tests must be compared with the findings in age-matched control subjects. The Valsalva response assesses the functional integrity of the baroreceptor reflex15 (Figure 1). The patient exerts a constant expiratory pressure (Valsalva maneuver) for 15 seconds while blood pressure and heart rate changes are recorded. The response begins with a decline in the blood pressure due to reduced stroke volume and venous return. This is followed by a progressive rise in blood pressure (due to peripheral vasoconstriction); on release of the forced expiration, the blood pressure overshoots the baseline blood pressure and this results in a compensatory bradycardia (see arrows in Figure 1). The lack of a progressive rise in the blood pressure and the absence of an overshooting of the baseline blood pressure provide evidence for an abnormal efferent branch of the baroreceptor reflex arc. In contrast, the Valsalva ratio (i.e., the maximum tachycardia in phase II divided by the minimum bradycardia in phase IV during the Valsalva response) measures the function of both the afferent and efferent arms of the baroreceptor reflex arc. The normal sinus arrhythmia that occurs with deep breathing is a function of parasympathetic (vagal) efferent input to the heart and is the focus of heart rate variation testing. The test results can be influenced by the patient's position (supine or sitting), the rate and depth of the patient's respirations, the patient's age and medications. The test results are compared with the results of tests performed under the same conditions in normal age-matched control subjects. Normal sinus arrhythmia with deep breathing produces tachycardia during inspiration and bradycardia during expiration. In normal individuals, this difference in heart rate exceeds nine beats per minute. Other autonomic function tests are occasionally used to assess sympathetic nervous system abnormalities.12 For example, the quantitative sudomotor axon reflex test can assess regional sweat production quantitatively, while the cold pressor test can be used to localize a sympathetic lesion in the afferent or efferent limb of the baroreceptor reflex arc. Low supine plasma norepinephrine levels or a subnormal rise in the norepinephrine level on standing serve as biochemical markers of peripheral autonomic failure. Treatment A systematic evaluation to detect and treat nonneurogenic causes of orthostatic hypotension (especially medication side effects) is the first treatment step. In contrast, orthostatic hypotension due to neurogenic causes is usually not amenable to correction of the underlying cause. The treatment of orthostatic hypotension should be directed at alleviating the effect of symptoms on the patient's activities of daily living, rather than achieving arbitrary blood pressure goals. Treatment can often be individualized to address circumstances that are exacerbating orthostatic hypotension (Table 4). For example, vasodilatation can be minimized by avoiding alcohol ingestion and exposure to hot weather.19 Orthostatic hypotension following meals can be reduced by eating multiple small meals over the course of the day. Activities can be scheduled to avoid the early morning period when orthostatic hypotension is usually more severe. Sleeping in a head-up tilt position (30 degree tilt) minimizes nocturnal diuresis with resultant morning hypovolemia and orthostatic hypotension. Before a patient with orthostatic hypotension is given any new medication, the benefits of the drug should be carefully weighed against the possible impact of an exaggerated hypertensive response (in the setting of denervation supersensitivity). However, drug therapy is usually necessary in patients with significant disability due to neurogenic orthostatic hypotension. A stepwise approach to treatment usually begins with liberal salt intake in the patient who can tolerate increased intravascular volume. Fludrocortisone (Florinef), a potent mineralocorticoid, promotes renal sodium reabsorption and increases the sensitivity of arterioles to norepinephrine. The initial dose is 0.1 mg taken orally once or twice daily. Dosage increases can be made every one to two weeks. Hypokalemia, peripheral edema, weight gain, headache and supine hypertension are common side effects with chronic fludrocortisone therapy. Midodrine (ProAmatine) is an alpha1 agonist that was recently approved for use in the United States. The initial dose of 2.5 mg per day is increased daily to a maximum of 30 mg per day divided into two or three doses. Side effects include supine hypertension and piloerection. Over-the-counter sympathomimetics such as ephedrine, phenylephrine and phenylpropanolamine are also used to treat orthostatic hypotension. However, patients being treated with these agents must be monitored carefully to avoid unintended hypertensive responses. Erythropoietin, 25 to 75 U per kg administered subcutaneously three times a week, has been used to treat orthostatic hypotension in a subgroup of patients with anemia and autonomic dysfunction. The end point of treatment is a normal hematocrit. The blood pressure usually rises by about 10 mm Hg. Some patients require simultaneous iron replacement therapy as the hematocrit rises. The evening administration of intranasal desmopressin (DDAVP) minimizes nocturnal diuresis and may improve early morning hypotension in some patients. Caffeine and indomethacin (Indocin) are used to ameliorate postprandial hypotension. In one study, two cups of coffee with a meal were found to reduce postprandial hypotension by up to 50 percent. Treatment of Orthostatic Hypotension Avoidance of prolonged standing Slow, careful changes in position, especially on arising in the morning Avoidance of alcohol Avoidance of hot environments and hot showers or baths Multiple small meals Avoidance of rigorous exercise Sleeping with lead-up tilt Scheduling of activities in the afternoon Increased salt and fluid intake Pharmacologic treatments Removal of medications that exacerbate hypotension, when possible Fludrocortisone (Florinef) Sympathetic antagonists such as midodrine (ProAmatine) and over-the-counter sympathomimetics Erythropoietin  
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