Orthostatic Hypotension: causes, mechanisms, and influencing factors

1. Orthostatic Hypotension:causes, mechanisms, and influencing factors Christopher J Mathias, DPhil, FRCP Neurology 1995; 45:S6-S11 medslides.com

2. Control of Blood Pressure • autonomic nervous system • heart’s resistance and capacitance • intravascular volume • hormones • renin-angiotensin-aldosterone system • aldosterone • local endothelin or nitric acid Neurology 1995; 45:S6-S11 medslides.com

3. 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; 46:1470 medslides.com

4. 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; 45:S6-S11 medslides.com

5. 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; 46:1470 medslides.com

6. Autonomic Nervous SystemNeurogenic causes of orthostatic hypotension • Primary autonomic failure • Secondary autonomic failure Neurology 1995; 45:S6-S11 medslides.com

7. 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; 45:S6-S11 medslides.com

8. Secondary autonomic failure • central • spinal • peripheral • miscellaneous • drugs • neurally mediated syncope Neurology 1995; 45:S6-S11 medslides.com

9. Secondary autonomic failure1. central • brain tumors, especially of the 3rd ventricle or posterior fossa • multiple sclerosis • syringobulbia • age-related Neurology 1995; 45:S6-S11 medslides.com

10. Secondary autonomic failure2. spinal • spinal transverse myelitis • transverse myelitis • syringomyelia • spinal tumor Neurology 1995; 45:S6-S11 medslides.com

11. 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; 45:S6-S11 medslides.com

12. Secondary autonomic failure4. miscellaneous • autoimmune and collagen disorders • renal failure • neoplasia • human immunodeficiency virus infection Neurology 1995; 45:S6-S11 medslides.com

13. Secondary autonomic failure5. drugs • centrally acting • clonidine, methyldopa, reserpine, barbiturates, anesthetics • peripherally acting • guanethidine, bethanadine • phenoxybenzamine, prazosin • propranolol, timolol Neurology 1995; 45:S6-S11 medslides.com

14. Secondary autonomic failure6. neurally mediated syncope • vasovagal syncope • carotid sinus hypersensitivity • micturition syncope • glossopharyngeal neuralgia and syncope Neurology 1995; 45:S6-S11 medslides.com

15. 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; 45:S6-S11 medslides.com

16. 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; 45:S6-S11 medslides.com

17. Rise in plasma norepinephrine after 10 min Head-up tilt to 450 Multiple system atrophy Noradrenaline (pg/mL) Pure autonomic failure Dopamine ß-OHdeficiency medslides.com

18. 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; 45:S6-S11 medslides.com

19. 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; 45:S6-S11 medslides.com

20. Nonneurogenic Hypotension2. vasodilatation • drugs-nitrates • alcohol • heat, pyrexia • hyperbradykinism • systemic mastocytosis • extensive varicose veins Neurology 1995; 45:S6-S11 medslides.com

21. 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, Addison’s, diabetes insipidus, diuretics Neurology 1995; 45:S6-S11 medslides.com

22. Nonneurogenic Hypotension3. miscellaneous • Sepsis • Endotoxic shock Neurology 1995; 45:S6-S11 medslides.com

23. 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; 45:S6-S11 medslides.com

24. 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; 69:359-361 medslides.com