Physics 2020: Group Quiz 1 Problem Group Name: Names: Group Assignment Part 1: Y
ID: 133019 • Letter: P
Question
Physics 2020: Group Quiz 1 Problem Group Name: Names: Group Assignment Part 1: You need to measure a patient's blood pressure using a mercury sphygmomanometer, but they have casts covering the entirety of both arms so you will not be able to wrap the inflatable cuff anywhere on their arms. Instead you will have to use a larger cuff that wraps around their upper leg so you can listen to their femoral artery. (i) Explain how this may affect your measurement. (ii) What will you do to ensure the accuracy of your measurement? Explain why your method will work.[Hint: Recall Occam's razor and keep your method as simple as necessary.Explanation / Answer
The femoral artery is a large blood vessel in the thigh and is the main arterial supply to the leg. It enters the thigh as the common femoral artery which is a continuation of the external iliac artery. Normally blood pressure is measured in the brachial artery which is a major blood vessel located in the upper arm and hand. The pulse of the brachial artery can be felt in the front side of the elbow. This is why blood pressure is measured in this area.
Normally, the blood pressure in the legs is 10% to 20% higher than the brachial artery pressure. In fact, if the blood pressure readings are lower in the legs as compared to that in the arms then it is a cause for concern and might indicate the beginning of peripheral vascular disease.
For measuring the blood pressure in the thigh, the cuff should be at least 25% wider than the average leg diameter. It should be long enough to encircle the limb.
The increase in diameter of the cuff will increase its surface area that is in contact with the limb. As it is, pressure and area are related inversely, that is, if the area increases, pressure decreases. Keeping this in mind, the diameter of the cuff is kept as the average diameter of the person's leg. The blood pressure reading obtained by this method will have little chances of error.