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# Secondly, if feasible, modification of antihypertensive drugs should be considered. | # Secondly, if feasible, modification of antihypertensive drugs should be considered. | ||
Surgical or pharmacological destruction of (the oesophageal branches of) the vagus nerve has shown not to be successful. Based on predominantly positive therapeutic response in over a dozen cases, the treatment of choice of oesophageal syncope is insertion of a cardiac demand pacemaker (Basker & Cooper, 2000). Management of persisting neuralgia is symptomatic. | Surgical or pharmacological destruction of (the oesophageal branches of) the vagus nerve has shown not to be successful. Based on predominantly positive therapeutic response in over a dozen cases, the treatment of choice of oesophageal syncope is insertion of a cardiac demand pacemaker (Basker & Cooper, 2000). Management of persisting neuralgia is symptomatic. | ||
=Arterial system= | |||
The arterial system consists of three major groups of arteries. | |||
These are: | |||
*Elastic arteries | |||
*Muscular arteries | |||
*Arterioles | |||
== Elastic arteries == | |||
Elastic arteries are the '''aorta''' and the '''major branches of it''' close to the heart. The vessel walls contain the most elastin of all vessels and elastin is found in all the vessels layers. Elastic arteries also contain smooth muscle cells, but these are mostly inactive in vasoconstriction. By elastically dilating when [[Blood pressure|blood pressure]] increases (right after a heartbeat) and contracting when [[Blood pressure|pressure]] drops they maintain [[Blood flow|blood flow]] in between heartbeats. The elasticity also gives a more constant [[Blood pressure|BP]] throughout the rest of the vascular system. The diameter of elastic arteries ranges from ''2.5 to 1 cm''. | |||
== Muscular arteries == | |||
Muscular arteries have a diameter of 1 to 0.3 cm and derive from elastic arteries. Muscular arteries regulate the [[Blood flow|blood flow]] to specific organs. They are active during vasoconstriction and contain relatively the most smooth muscle cells in the tunica media. They contain less elastin than elastic arteries and are thus less distensible. | |||
== Arterioles == | |||
The smallest arteries are called arterioles. The tunica media of the arterioles mostly contain smooth muscle cells. Their diameter ranges from 0.3 cm to 10 µm, and the smallest arterioles lead into '''capillary beds'''. [[Blood flow]] into capillary beds is regulated by these arterioles. The arterioles change in diameter due to '''neural, hormonal and local chemical influences'''. These changes in diameter lead to the changes in [[Blood flow|blood flow]] in the capillary beds. When arterioles constrict, the capillary beds that lay behind the constricting arterioles is bypassed. When they dilate, [[Blood flow|blood flow]] in the capillary beds increases dramatically. | |||
== Capillaries == | |||
[[File:Capillary_Bed_aangepast.jpg|frame|Capillary bed]] | |||
Capillaries are no arteries. They are the smallest of all blood vessels and their function is to exchange materials with every cell in the body. The average capillary diameter is 8 to 10 µm, so that red blood cells can just pass through them. | |||
A capillary bed consists of a network of interweaving capillaries. These capillary beds connect arterioles, and venules, the smallest vessels of the [[Venous system|venous system]]. In most of the capillary beds, two types of vessels are found: | |||
*a vascular shunt | |||
*and true capillaries | |||
A '''vascular shunt''' connects connects an arteriole with a [[Venous system|venule]] directly. These vessels do not exchange materials with the surrounding fluid. True capillaries exchange materials. The arteriole that directly connects with the capillaries is called a terminal arteriole and this arteriole feeds directly into the metarteriole. This metarteriole feeds into the thoroughfare channel and then the [[Venous system|postcapillary venule]]. These vessels together make the vascular shunt. | |||
'''True capillaries''' normally branch off the metarteriole and empty in the [[Venous system|postcapillary venule]]. The root of the true capillaries is surrounded by smooth muscle cells. This is called a precapillary sphincter. It acts as a valve that regulates [[Blood flow|blood flow]] through the capillary bed. If the sphincters are contracted, the blood will pass through the vascular shunt, and no exchange of materials will take place. If the valves are relaxed, blood will flow through the capillaries and exchange with the surrounding cells occurs. | |||
=Postural Tachycardia Syndrome (POTS)= | |||
POTS is a hetergeneous group of disorders with similar cinlical manifestations. POTS is characterized by a combination of an abnormally high heart frequency (tachycardia) while standing (postural) and symptoms of palpitations, light-headedness, and other sensations that occur due to cerebral hypoperfusion (see [[Symptoms and signs of presyncope|symptoms and signs of presyncope]]) | |||
</div> | |||
An abnormal heart rate respons is defined as: | |||
* Sustained heart rate increment of > 30 bpm within 10 minutes of standing or head-up tilt | |||
* Patients aged 12-19 years require an increment of > 40 bpm | |||
* '''Or''' a heart rate that exceeds 120 bpm | |||
* The heart rate increment cannot be associated conditions as prolonged bed rest, or medications that diminish vascular or autonomic tone | |||
* Symptoms of cerebral hypoperfusion and autonomic overactivity | |||
==Pathophysiology== | |||
The etiology and pathophysiology of POTS are unknown, but are likely to be heterogeneous. The syndrome is associated with deconditioning, recent viral illness, chronic fatigue syndrome and a limited or restricted autonomic neuropathy. The differential diagnosis includes conditions that cause tachycardia, such as thyrotoxicosis, inappropriate sinus tachycardia and other cardiac rhythm abnormalities, pheochromocytoma, hypoadrenalism, anxiety, dehydration, and medications (e.g., vasodilators, diuretics, and b-agonists). Many patients report that their symptoms started after a febrile illness, pregnancy, surgery, trauma or sepsis. The present thought on the pathophysiology of POTS after such an event is that POTS is an autoimmune disorder. | |||
==Epidemiology== | |||
The prevalence of POTS is not known, but estimates suggest at least 500.000 people are affected by POTS in the United States alone<cite>Grubb</cite>. The syndrome is more common in women. | |||
==Clinical presentation== | |||
The orthostatic symptoms of POTS consists of light-headedness, visual blurring or tunnel vision, palpitations, tremulousness, and weakness (especially in the legs). Other symptoms include fatigue, exercise intolerance, hyperventilation, shortness of breath, anxiety, chest pain, nausea, acral coldness or pain, and concentration difficulaties and headaches. On clinical examination, in addition to the heart rate increment, pulse pressure may be reduced and acral coldness may be present. Continued standing may lead to venous prominence, cyanosis and foot swelling. A hyperadrenergic state is present in some patients who have a resting tachycardia, sweating, and tremulousness. | |||
==References== | |||
<biblio> | |||
#Grubb pmid=18506020 | |||
</biblio> | |||
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