Orthostatic Hypotension: causes, mechanisms, and influencing factors

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Orthostatic Hypotensioncauses, mechanisms, and
influencing factors

• Christopher J Mathias, DPhil, FRCP
• Neurology 1995 45S6-S11

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Control of Blood Pressure

• autonomic nervous system
• hearts resistance and capacitance
• intravascular volume
• hormones
• renin-angiotensin-aldosterone system
• aldosterone
• local endothelin or nitric acid

Neurology 1995 45S6-S11
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Orthostatic hypotensionconsensus definition (1)

• reduction of
• systolic BP of at least 20 mm Hg, or
• diastolic BP of at least 10 mm Hg
• within 3 minutes of standing (some may
• take more than 10 minutes)
• similar drop in blood pressure within 3 minutes
  in a head-up tilt table test at an angle of at
  least 60 degrees

1. Neurology 1996 461470
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Orthostatic hypotension

• when associated with relevant symptoms
  indicating impaired perfusion, a smaller drop in
  blood pressure may be equally important,
  especially for further investigation.

Neurology 1995 45S6-S11
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Orthostatic hypotensionsymptoms

• symptoms develop on assuming the erect posture
• lightheadedness, dizziness, blurred vision,
  weakness, fatigue, cognitive impairment, nausea,
  palpitations, tremulousness, headache, neck ache
• some patients may be asymptomatic

Neurology 1996 461470
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Autonomic Nervous SystemNeurogenic causes of
orthostatic hypotension

• Primary autonomic failure
• Secondary autonomic failure

Neurology 1995 45S6-S11
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Primary autonomic failure

• chronic
• pure autonomic failure
• Shy-Drager syndrome
• with parkinsonian features
• with cerebellar and pyramidal features
• with multiple system atrophy (combination)
• acute or subacute dysautonomias

Neurology 1995 45S6-S11
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Secondary autonomic failure

• central
• spinal
• peripheral
• miscellaneous
• drugs
• neurally mediated syncope

Neurology 1995 45S6-S11
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Secondary autonomic failure1. central

• brain tumors, especially of the 3rd ventricle or
  posterior fossa
• multiple sclerosis
• syringobulbia
• age-related

Neurology 1995 45S6-S11
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Secondary autonomic failure2. spinal

• spinal transverse myelitis
• transverse myelitis
• syringomyelia
• spinal tumor

Neurology 1995 45S6-S11
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Secondary autonomic failure3. peripheral

• afferent
• Guillain-Barre syndrome, Tabes dorsalis,
  Holmes-Adie syndrome
• efferent
• diabetes mellitus, amyloidsis, surgery,
  dopamine-b-hydroxylase deficiency
• afferent / efferent
• familial dysautonomia (Riley-Day synd)

Neurology 1995 45S6-S11
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Secondary autonomic failure4. miscellaneous

• autoimmune and collagen disorders
• renal failure
• neoplasia
• human immunodeficiency virus infection

Neurology 1995 45S6-S11
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Secondary autonomic failure5. drugs

• centrally acting
• clonidine, methyldopa, reserpine, barbiturates,
  anesthetics
• peripherally acting
• guanethidine, bethanadine
• phenoxybenzamine, prazosin
• propranolol, timolol

Neurology 1995 45S6-S11
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Secondary autonomic failure6. neurally mediated
syncope

• vasovagal syncope
• carotid sinus hypersensitivity
• micturition syncope
• glossopharyngeal neuralgia and syncope

Neurology 1995 45S6-S11
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Neurogenic orthostatic hypotensionpathophysiology

• major abnormality is the lack of neurally
  mediated vasoconstriction in large vascular beds
  (skeletal muscle and the splanchnic bed)
• gravitational pooling in the periphery with lack
  of compensatory change

Neurology 1995 45S6-S11
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Plasma norepinephrine level

• measure of sympathetic activity
• in neurogenic OH, the sympathetic nervous system
  is not activated, the rise in NE level is minimal
  or absent despite a marked fall in BP
• basal NE level cannot determine the site of lesion

Neurology 1995 45S6-S11
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Rise in plasma norepinephrine after 10 min
Head-up tilt to 450
Multiple system atrophy
Noradrenaline (pg/mL)
Pure autonomic failure
Dopamine ß-OHdeficiency
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Nonneurogenic causesof hypotension

• cardiac impairment
• myocardial impaired ventricular filling
• impaired output cardiac arrhythmia
• vasodilatation
• low intravascular volume
• blood / plasma loss fluid / electrolytes
• miscellaneous

Neurology 1995 45S6-S11
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Nonneurogenic Hypotension1. cardiac impairment

• myocardial
• myocarditis, myocardial infarction
• impaired ventricular filling
• atrial myxoma, constrictive pericarditis
• impaired output
• aortic stenosis, hypertrophic cardiomyopathy
• cardiac arrhythmia
• bradycardia, tachydysrhythmias

Neurology 1995 45S6-S11
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Nonneurogenic Hypotension2. vasodilatation

• drugs-nitrates
• alcohol
• heat, pyrexia
• hyperbradykinism
• systemic mastocytosis
• extensive varicose veins

Neurology 1995 45S6-S11
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Nonneurogenic Hypotension3. low intravascular
volume

• Blood / plasma loss
• hemorrhage, burns, hemodialysis
• Fluid / electrolyte
• inadequate intake (anorexia, vomiting)
• diarrhea (including ileostomy)
• renal/endocrine (salt losing nephropathy,
• Addisons, diabetes insipidus, diuretics

Neurology 1995 45S6-S11
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Nonneurogenic Hypotension3. miscellaneous

• Sepsis
• Endotoxic shock

Neurology 1995 45S6-S11
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Factors influencingpostural hypotension

• speed of positional change
• prolonged recumbency
• time of day (morning on rising)
• warm environment (hot weather, central heating,
  hot bath)

Neurology 1995 45S6-S11
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Factors influencingpostural hypotension

• food and alcohol (1)
• physical exertion (2)(bending forward, abdominal
  compression, leg crossing, squatting)
• increased intrathoracic pressure(micturition,
  cough, defication)

1. Mathias CJ, et al. 1992 Autonomic Failure 2.
Smith GDP, et al. 1993 BHJ 1993 69359-361