Sensors: Loggers: ECG Any 12 bit EASYSENSE Science in Sport Logging time: 10 seconds 204a ECG demonstration (Graph) Read Regular medical check ups are essential part of the life of a professional sports person. Early diagnosis of a condition can be important in redefining a training programme or deciding if medical / physiotherapy intervention is required. Increasingly you hear of medical tests being used to work out the potential for an individual, in these cases the tests are tailored to the sport and hopefully indicate the likelihood of future success. An ECG is simple non invasive test that can be conducted to reveal any underlying heart problems. On its own it may not provide any useful information. When ECG data is connected with other medical reports it can provide a good picture of condition, and room for improvement. An ECG (electrocardiogram) measures the electrical output of cardiac muscle during a heart beat cycle. Heart muscle has a very small potential difference (voltage) across its cell membranes. The cells of the heart can depolarize spontaneously, as the cells depolarize they contract. The group of cells in the heart that depolarize the fastest from an area called the pacemaker or sinoatrial node. The pacemaker is located in the right atrium. The atria and the ventricles are isolated from each other electrically. A depolarization of atrial cells does not directly affect the cells in the ventricles. A group of cells in the right atria, called the atrioventricular or AV node, conduct the electrical signals from an atrial depolarisation down a bundle of conducting fibers, called the Bundle of His, to the ventricles. This process creates a short time delay between the atria contracting and the ventricles contracting. Because the cells of cardiac muscle are closely interconnected, the wave of depolarization, contraction and repolarization spreads rapidly across all of the heart. The changes in the polarity of the heart cells can be measured, amplified, and plotted against time. The ECG is the graphical representation of the measured electrical currents, and indirectly of the muscle contraction. The Electrocardiogram A typical ECG shows a pulse caused by the depolarization of the atria, this is called the P wave and it lasts about 0.04 seconds. This wave is associated with the contraction of the atria. There is a short delay after the P wave while the AV node depolarizes and sends a signal along the Bundle of His to the Purkinje fibres in the ventricles. After the AV node depolarizes there is a sharp downward pulse called the Q wave. This is followed rapidly by an upward pulse of the line called the R wave. The R wave is followed by a strong downward pulse of the line called the S wave. These three waves together are called the QRS complex and they form the central portion of the ECG. This complex is caused by the depolarization of the ventricles and is associated with the contraction of the ventricles. 204a - 1
The recovery of the cardiac cells back to their resting polarity takes place with the movement of ions across the cell membranes. The movement of these ions generates a final wave called the T wave and indicates repolarization of the ventricles. The sequence from P wave to T wave represents one heart beat/cycle. The number of beats in a minute is called the heart rate and is typically 70-80 beats per minute at rest. The exact value will depend on the age, gender and fitness of the individual. R ECG / EKG uv QRS complex P wave T wave Q S P-R interval...120-200 milliseconds (0.12 to 0.20 seconds) QRS interval...under 100 milliseconds (under 0.10 seconds) Typical recording of 4 heartbeats using a Smart Q ECG Q-T interval...under 380 milliseconds (under 0.38 seconds) This sensor is NOT intended or suitable for medical diagnosis. Any results or patterns that differ from a published norm should not be seen as an indication of a medical condition. What you need 1. An EASYSENSE logger (12 bit). 2. A Smart Q ECG sensor. 3. Electrode patches (minimum of 3 per individual being tested). 4. Ethanol / Methylated spirit. 5. Paper towels. What you need to do 1. Use three electrode patches per subject. 2. Because the electrical signal produced by the heart is so small, it is very important that the electrodes make good contact with the skin. Rub the areas of skin where the patches will be 204a - 2
attached with a paper towel soaked in a strong alcohol or light abrasive material to remove dead skin and oils. 3. Peel three electrode patches from the backing paper. Place one electrode on the right wrist. The second electrode on the right elbow / upper arm, and the third electrode on the left elbow / upper arm. (This is one of several possible arrangements for ECG electrodes on the body) 4. Connect the crocodile clips on the sensor to the tabs on the edges of the electrode patches (position the tabs so the cables don t peel the patch away from the skin). The black reference lead must go to the right wrist electrode patch. Green clip Red clip Electrode patch Black clip EKG Sensor The green negative lead goes to the right elbow electrode patch. The red positive lead goes to the left elbow electrode patch. 5. This arrangement described is the most appropriate for use the classroom; it may not produce traces of the quality seen in the media / medical environment. Collecting the resting ECG 1. Connect the ECG sensor to input 1 of the logger. 2. From the EasySense software s Home screen select Open Setup (or File, Open Setup). Open the file Data Harvest Investigations (Edition 2) \ Setup file \ V2 \ 204a ECG graph. 3. The individual having their ECG taken should relax and stop moving. 4. Click on Start to begin recording data. The person whose ECG is being measured should remain calm and relaxed during the course of the recording. Encourage the person to breath normally. 5. Data recording stops automatically at 5 seconds, there will be brief pause as the data is retrieved and displayed. 6. If the ECG looks like the sample trace shown above, label and save the data. If the base line of the trace is not stable it is possible the recording was taken before the ECG sensor had stabilized. Wait for a few seconds and take a second reading. 7. If the trace shows a flat line, it is likely that one or more of the electrodes / crocodile connector is not making good contact. Smooth the electrodes against the skin and reconnect the crocodile clips. Take another reading. 204a - 3
Problems with recording? Check the connectors are on the correct electrodes. Check the electrode patches are not being pulled away from the skin by the weight of the crocodile clips. Make sure the test subject is not moving, especially the limbs the electrodes are connected to. All muscle movement generates electrical energy, which will swamp the delicate signal from the heart. Check you are using the correct recording times; the heart beat is of a very small duration. If the recording speed is set to low or too high the electrical event of the heart beat can be missed. Analysing the data 1. Use Zoom to draw a rectangle around a region of the data that includes four or five complete heart cycles. The graph will rescale to show the region you selected. 2. Use Values find the peak of a P wave. Record the time indicated in the lower panel. 3. Move the line to the point that corresponds to the peak of the Q wave. Record the time. 4. Move the line to the point that corresponds to the peak of the R wave. Record the time. 5. Calculate the P-R interval and record the time. 6. Move the values line to the point that corresponds to the peak of the S wave. Record the time. 7. Calculate the Q-R-S interval and record the time. 8. Move the values to the point that corresponds to the peak of the T wave. Record the time. 9. Calculate the overall Q-T interval and record the time. Results table: Interval Analysis Item Time (s) P wave begins Q wave begins R wave begins S wave begins T wave begins Item Time (s) Typical Time P-R interval QRS interval Q-T interval 0.12 to 0.20 sec under 0.10 sec under 0.38 sec 204a - 4
Questions? 1. Compare your values for the P-R, Q-R-S, and Q-T intervals to the ones given earlier. What could explain the differences? 2. How does the heart rate measured by the ECG compare to your heart rate measured with the Heart Rate Sensor or by the direct measurement of the pulse at the wrist or neck? What could explain the difference? Extension work Use the same individual and get them to do some light exercise for 3 to 5 minutes and then record the ECG. Compare the traces. (Leave the patches on the individual but remove the leads, walking around a room for several minutes will be enough to show a difference). Drink a caffeine containing drink and record the ECG at 5 minute intervals to see if the caffeine has any effect over heart rate. Take a resting ECG and then show the subject a short clip of an action scene from a film / TV programme to see how the heart rate has responded. 204a - 5