Arterial Blood Flow Measurements
Making measurements of arterial blood flow is one of the ways in which the fitness of elite athletes can be assessed. This is usually conducted by using a high precision ultrasound transducer, which can measure the diameter of an athlete's blood vessels and can show the amount of blood being pumped by the heart around the body.
The short film which follows below, shows the technique of Flow Mediated Dilation (FMD) which we can use to examine how blood vessels work, how healthy they are and how they respond to exercise.
The technique uses ultrasound technology (similar to that used to scan babies during pregnancy) to get a picture of the walls and inside of the major blood vessel in the arm (the brachial artery). On the left of the diagram below, diagram A, you can see the structure of an artery. The endothelium, which lines the inner wall of the blood vessel, acts as a layer that separates the blood from the muscular wall (the smooth muscle).
However, we know that this layer of endothelium, which is only one cell thick, is far more specialised than just a barrier. Indeed it releases many compounds that can diffuse into the smooth muscle causing it to relax or contract. When it relaxes the blood vessel gets wider (a larger diameter) causing a greater flow of blood and when it contracts the blood vessel gets narrower, causing less blood flow.
One of the most important compounds released from the endothelium is a molecule called nitric oxide (NO), which goes into the smooth muscle and relaxes it, therefore allowing more blood flow. You can see this happening on the right side of the diagram, diagram B.
What the video shows is the measurement of the diameter of the brachial artery at rest. A cuff is then placed on the forearm and inflated to stop all blood flow into the arm for 5 minutes. When the cuff is deflated, blood flows rapidly in and causes the release of nitric oxide (NO) from the endothelium, which increases the diameter of the blood vessel. We can measure the change in blood vessel diameter from rest to immediately after cuff deflation and calculate this as a percentage change and this is called the FMD. The greater this percentage increase after cuff deflation the more healthy the vessel (and the individual) and the greater the capacity for blood flow.
So now we know a little about why we are interested in measuring the diameter of the brachial artery, let's now watch the video to see one of these tests being carried out.
So the next task we would like you to perform is to try and answer the question of whether fitness increases the ability of the blood vessel to relax more after the above test.
So, we have given you 12 sets of blood vessel scans from 12 different people. Each set has 2 pictures. In each case, the top image is the person’s blood vessel diameter at rest and the bottom image is their blood vessel diameter after cuff deflation.
What we'd like you to do, either using a ruler on the screen or by downloading the images from here, is to measure the size of the artery diameter at rest and then after cuff deflation, between the yellow lines marking the boundary of the artery in each case. In order to do this accurately (to get an accurate measure of the exact diameter of the blood vessel) you will have to calibrate your measures with a scale that is equal to 1cm at the side of the scan. To help you do this correctly, download and save the following PowerPoint presentation to your PC. It only contains two slides but they are animated, so run it as a proper presentation to get its full impact by using the 'Page Down' button on your keyboard. Because of its size, the presentation may take a few seconds to download.
The other data we have supplied you with is the corresponding VO2 Max scores for all 12 people, in the table below. Remember that these scores give us our best estimate of an individual's fitness.
Test Subject | Age | Height (cm) | Weight (kg) | VO2 Max (ml/kg/min) |
Subject A | 24 | 180 | 66 | 55.63 |
Subject B | 23 | 172 | 73 | 45.58 |
Subject C | 20 | 174 | 78 | 48.90 |
Subject D | 25 | 182 | 74 | 42.40 |
Subject E | 28 | 173 | 65 | 38.02 |
Subject F | 25 | 183 | 76 | 43.48 |
Subject G | 41 | 182 | 72 | 58.31 |
Subject H | 22 | 182 | 76 | 49.12 |
Subject I | 35 | 180 | 85 | 39.89 |
Subject J | 37 | 181 | 82 | 38.07 |
Subject K | 24 | 178 | 78 | 42.82 |
Subject L | 32 | 181 | 81 | 43.32 |
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| | | Subject A | Subject B | 
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| Subject C | Subject D | 
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| Subject E | Subject F | 
|  | Subject G | Subject H | 
|  | Subject I | Subject J | 
|  | Subject K | Subject L |  | 
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| | | Now, having made a few arterial measurements on real subjects, we would like you to think about the results you have obtained and you should be able to draw some conclusions from that data. To help us bring all those conclusions together, we would like you to answer a few short questions using the Blood Flow Quiz on the next page. | |
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