Moderators: I didn't know where to put this. Its not really first aid or emergency so...move at your discretion
To me, anyone with a basic grasp of physics or a general understanding of Newton's third law should be able to answer this question.
Ok...I just returned from taking my first nursing school test and I am livid (I am envisioning feeding a puppy chocolate and putting it in a microwave with a tin foil hat right now.....not really) because I know I missed a couple of questions but one in particular is driving me crazy.
Here is the gist of the question: An obese woman's blood pressure was taken using an adult sized cuff(too small). What will the outcome be?
I knew it was either going to be A. Falsely High
or B. Falsely Low
To begin, here is my understanding of how a Sphygmomanometer works. The cuff is wrapped around the arm about an inch above the brachial pulse. The cuff contains a bladder and when filled up with air the needle rises and occludes the artery. As the air is slowly released, the needle in the gauge decreases and the blood begins to flow back through the vessel. When listening with a stethoscope, the first sound you here is the blood coming back through and this is the measure of the maximum output pressure of the heart (systolic reading).
So, I remember reading the night before about how if the cuff is too loose it will yield a falsely high reading. The rationale being that you will need excessive pressure to occlude the artery.
This makes sense, right? If the cuff is loose, the bladder will have to fill with more air than usual to occlude the artery since it has all the extra room thus giving you a high reading. Easy stuff.
Remembering this, I thought to myself "Well, if a loose cuff yields a falsely high pressure than a tight cuff must yield a falsely low reading. If the cuff is tight, there is already an increased pressure on the artery to begin with, thus you will need less pressure (air) to occlude the artery giving you a False Low pressure." So I put B. Falsely Low.
It turns out I am wrong. The book states that a cuff that is too narrow will give you a Falsely High blood pressure stating you will need excessive pressure to occlude the artery.
So my question is is my brain not functioning properly or is there some kind of phenomenon that occurs with tight cuffs that I am not aware of? I mean, if the cuff is tight to begin with how in the name of all that is holy will you need excessive pressure to occlude the brachial artery?
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