Lemons2lemonade Posted June 10, 2012 Report Share Posted June 10, 2012 A review of postural orthostatictachycardia syndromeSheila Carew, Margaret O. Connor, John Cooke, Richard Conway, Christine Sheehy,Aine Costelloe, and Declan Lyons*Blood Pressure Unit, Mid Western Regional Hospital, Limerick, IrelandReceived 4 July 2008; accepted 4 November 2008IntroductionPostural orthostatic tachycardia syndrome (POTS) is defined as asustained heart rate increase of 30 bpm or increase of heartrate to 120 bpm within the first 10 min of orthostasis associatedwith symptoms of orthostatic intolerance1–3 and without significantorthostatic hypotension (OH).Patients with POTS are predominately female (4:1) and relativelyyoung,4,5 but can range in age from 15 to 50 years.6 Differences inmuscle sympathetic nerve discharge characteristics, in the settingof sympathetic fibre loss associated with POTS, may contributeto the predisposition to and greater prevalence of POTS infemale individuals.7There are no accurate epidemiological studies, but it is estimatedthat in the USA alone, there are millions of people affectedby POTS.8PathophysiologyNormal physiology of standingWhen supine, up to 30% of the blood volume is in the thorax.During orthostasis, 300–800 mL of blood is gravitated downwardsfrom the thorax into the abdomen and lower extremities. Most ofthis pooling into lower limb veins occurs within 10 s. This causes adecrease in venous return to the right side of the heart witha subsequent reduction in the stroke volume and cardiac output.Arterial baroreceptors (carotid sinuses and the aortic arch) andcardiopulmonary mechanoreceptors (heart and lung) detect areduction in pulse pressure and stroke volume. Compensatoryreflexes lead to increased sympathetic nervous system output(peripheral arteriolar vasoconstriction) and reduced parasympatheticnervous system output (reduced vagal tone to the heartwith cardio-acceleration). After orthostasis in normal subjects,there is a 10–15 bpm increase in heart rate, systolic bloodpressure remains stable, and diastolic blood pressure usuallyincreases (10 mmHg).9Postural orthostatic tachycardiasyndromePostural orthostatic tachycardia syndrome is a clinical manifestationof multiple underlying mechanisms. It can be divided into anumber of overlapping pathophysiological models as follows.NeuropathicThis is thought to be associated with partial dysautonomia. Theevidence in support of this is as follows:† Distal anhidrosis of the legs is commonly found on thermoregulatorysweat testing and quantitative sudomotor axon reflextesting (up to 50% of POTS patients).4,10† Ganglionic acetylcholine receptor antibody is positive inbetween 10 and 15% of the cases.4,11† There is a blunted increase in post-ganglionic sympathetic nervedischarge (muscle sympathetic nerve activity).12 This peripheralabnormality might reflect partial dysautonomia. Astronautsreturning from prolonged exposure to microgravity oftendisplay a form of orthostatic intolerance with features similarto POTS.13 This is felt to be due to abnormal muscle sympatheticnerve activity.14† It is shown that leg arteriolar vasoconstriction is impaired.Therefore, increased arterial inflow can enhance venous fillingand cause venous pooling, despite the fact that venous capacitanceis normal. Quote Link to comment Share on other sites More sharing options...
Chaos Posted June 10, 2012 Report Share Posted June 10, 2012 Lemons..would it be possible to perhaps post the link to this? For some reason I can't view it. It's coming thru in programming language. Quote Link to comment Share on other sites More sharing options...
Mytwogirlsrox Posted June 10, 2012 Report Share Posted June 10, 2012 Interesting that POTs is defined as a sustained increased HR of 30 bpm or greater that 120 bpm. Seems like isn't always the diagnostic criteria. Some studies just say an increase of 30bpm or greater than 120.... Interesting Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.