|MadSci Network: Medicine|
Dear Rhonda, many thanks for your question regarding the carotid pulse. Indeed, if you feel a carotid pulse, you should do it on one side only. There are two reasons to be careful. The first reason goes – basically – for all people, the other one is important if you feel the pulse in people (usually the elderly) who might have arteriosclerosis of the carotid arteries. Reason no. 1: The main carotid artery branches into two large arteries just below the place where the jawbone joins the rest of the skull (the external and internal carotid artery; the former is feeding the face and other outlying portions of the skull, while the internal artery is entirely reserved for feeding the brain). At this point, there is a widening of the artery, the so-called carotid bulb (bulb is from Latin „bulbus“, meaning onion). This bulb contains a nervous organ, the glomus caroticum (carotid „clew“ or carotid body – a fuzzy patch of nerve tissue inside the artery wall). This organ is a kind of sensor, measuring, among other things, oxygen content of the blood and blood pressure. Now if you put pressure on these organs on both sides, they will report a much, much elevated blood pressure to the brain, and the brain will act accordingly: Namely by slowing down the heartbeat and open up peripheral blood vessels to lower blood pressure – and since the blood pressure is in reality not elevated but normal, you will get a severe lowering of blood pressure. Perhaps, if the reaction is vigorous, there might even be a cardiac arrest for a few seconds. And, oops, there goes your victim fainting and falling to the ground. Unpleasant. Although the reaction can occur in anybody, elderly people are especially at risk – Tight collars or neckties have been known to cause this kind of fainting („syncope“ in the medical language) in sensitive people, and in these even exerting pressure on only one of the two sinus can cause a severe reaction – the condition is called hypersensitive carotid sinus or carotid sinus syndrome. By the way, rubbing one (one! carefully!) of the carotid sinus can cause a beneficial reaction, too: In people with certain disturbances of the heart rhythm where the heart beats very fast, carotid sinus massage can stop the arrhythmia entirely. I did this once in my hospital’s emergency room, and, wow, it saved my day: There was this patient sweating and puffing, having an absolutely racing heartbeat. I touched him once by the neck, and – bang – there he was in a normal rhythm, breathing easily, suddenly feeling perfectly well. He looked as if I had worked some magic touch on him, when it was really just a bit of physiology... But sorry for bragging – here’s your reason No. 2: You probably know that arteriosclerosis of the neck arteries can cause strokes, by narrowing the arteries and thus cutting off blood supply to the brain. Now the good thing about the brain’s blood supply is that it is very flexible: There is one (smaller) artery getting to the brain through the spinal column, and there are the two larger internal carotid arteries (plus a very small amount of blood bridging over from the external). They all meet at the base of the brain in a kind of roundabout, the circle of Willis. This roundabout makes sure that even if the blood flow one or two of the arteries is cut off, the third one can usually (but barely) do the job. So in a young and healthy person, even cutting off the flow from both carotid arteries will not always result in a stroke or brain damage (DO! NOT! TRY! THIS!). But imagine someone with a reduced blood supply to the brain, i.e. an elderly person with arteriosclerosis: Even exerting mild pressure to the carotid (when feeling the pulse with both hands) might shut off the little blood supply there is and your victim might suffer a transient paralysis in the limb, unpleasant tickling or numbness, impaired vision or speech disturbances – and if it is a really bad day, even a permanent stroke (rare, but again you do not want to try!). In this second case, you can even do damage with only one hand – probably not by just feeling a pulse, but by carotid sinus massage – especially if you massage the „better“ of the two carotid arteries. If the other one happens to be completely obstructed by arteriosclerosis, supplies can run very low very fast. This occasionally in clinical practice: Carotid massage can be applied to test for the presence of the hypersensitive carotid sinus syndrome (see reason no. 1): If someone’s blood pressure goes down heavily upon massage, that might explain why this someone has been having a lot of falls recently . And there is a study showing that transient disturbances of the brain aren’t all that rare after this kind of maneuver. So, to summarize – you will probably not hurt yourself or your schoolmates by just feeling a pulse on both sides, but you will have a lot fewer nasty surprises if you do it on one side only. And with elderly, frail people, take special care (as always!). By the way, in most people it is possible to feel the pulse by a very light touch to the neck, if you know where to put your hands. With this kind of approach, you will not hurt anybody, ever. So I hope this helps – Yours truly Jens Peter Bork References: A description of carotid sinus massage: http://www.chclibrary.org/micromed/00041610.html A short, technical description of carotid sinus syndrome: http://www.5mcc.com/Assets/SUMMARY/TP0163.html A study showing that carotid sinus massage is useful for detecting people with hypersensitive carotid sinus: http://ageing.oupjournals.org/cgi/content/abstract/32/6/666 The study showing that neurological damage can occur after carotid sinus massage: http://ageing.oupjournals.org/cgi/content/abstract/29/5/413 A nice depiction of the circle of Willis, plus an article about what happens in a stroke: http://www.umm.edu/patiented/articles/what_a_stroke_000045_1.htm And finally, a picture about the reflexes that steer the reaction of the carotid sinus plus a picture of the sinus itself: http://cmbi.bjmu.edu.cn/hyper-book/ch02/ch02-8.htm
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