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Mechanical Engineering

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Dec 6, 2023

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1 Name: ____________________ Date: _____________ Lab Time: ____________ LAB 1: RESTING HEART RATE/BLOOD PRESSURE Purpose The purpose of this lab experience is to develop your knowledge in measuring a) resting heart rates (HR) by palpitation and b) resting blood pressures (BP) by auscultation. Heart Rate Heart rate is a common method of tracking intensity during exercise, but can be a useful measure at rest. Normal resting HR is represented in beats per minute (bpm) and is often described as between 60-100 bpm. Resting heart rate values below 60 bpm are labeled bradycardia, and above 100 bpm are labeled tachycardia. Blood Pressure Millions of Americans are hypertensive or have high blood pressure. Primary hypertension means that the cause of hypertension is not known; secondary hypertension means that it is caused by known endocrine or structural disorders. Thus, the primary clinical purpose of measuring blood pressure is to determine the potential risk of cardiovascular disease; if the pressure is high, then appropriate medications or lifestyle changes are recommended. Periodic monitoring of the blood pressure is done in order to check the efficacy of such recommendations. Another purpose of measuring resting blood pressure is to establish a baseline by which to compare the effect of exercise on blood pressure. Thus, the effects of different types, intensities, or durations of exercise may be compared by noting their effects upon the baseline value. For example, blood pressure comparisons may be made between (1) static versus dynamic exercise, (2) different intensities of muscle actions (e.g., 30 % vs. 80 % maximal forces), and (3) short versus long durations of exercise. Blood pressure is primarily dependent upon the volume of blood and the resistance of the blood vessels. The blood pressure commonly measured is that of the arteries. And may be defined for laboratory purposes as the force of blood distending the arterial walls. Typically, the brachial artery is sampled because of convenience and its position at heart level ( figure 1 ). Figure 1. The determination of blood pressure in the typical laboratory setting is based upon the sounds made by the vibrations from the vascular walls. These sounds are referred to as Korotkoff sounds ( figure 2 ). When there is no blood flow (i.e., a tourniquet is applied), there will be no vibrations and thus no sound. Paradoxically, when there is completely nonobstructed flow of the blood, there is also no vibration and thus no sound; this is due to the streamlined flow of the blood. When blood flow is restricted by the application of a tourniquet or by any kind of pressure, and then gradually released, a bolus of blood escapes at the peak point of blood pressure coinciding with left ventricular contraction ( systole ). This bolus of blood causes vascular vibrations that result in a faint sound ( phase 1 ); this is systolic pressure.

2 As the restriction or pressure continues to be released, more blood escapes, causing even greater vibration and louder sounds. Phases 2 and 3 are not commonly used in recording blood pressures. More blood escapes as the cuff pressure continues to decrease. However, after phase 3, as the blood flow becomes more streamlined due to less compression, there is a reduction of vibrations, causing a muffling sound (phase 4). The fourth phase is sometimes difficult to distinguish. When blood flow is completely streamlined (laminar flow), there is a disappearance of sound and denotes diastolic pressure or phase 5 , which reflects the lowest pressure that exists in the arteries. Figure 2. Pulse Pressure and Mean Arterial Pressure In addition to systolic and diastolic pressure, mean arterial pressure (MAP) is also frequently described. MAP is based upon the actual pressure that the arteries would sustain if blood flow was constant and not pulsating. Resting MAP is estimated using the equation below, accounting for the time of systole and diastole. Diastole represents 2/3 of the cardiac cycle, whereas systole is 1/3. For example, a person with a systolic blood pressure of 120 mmHg and a diastolic blood pressure of 80 mmHg would have a MAP of 93 mmHg. Assume: SBP is 120 mmHg and DBP is 80 mmHg MAP (mmHg) = 2/3 DBP + 1/3 SBP MAP (mmHg) = 2/3(80) + 1/3(120) = 53 + 40 = 93 mmHg After measuring blood pressure, values can be compared and categorized using the following guidelines: Blood Pressure Ranges (American Heart Association) Category Systolic (mmHg) and/or Diastolic (mmHg) Normal < 120 and < 80 Elevated 120 -129 and < 80 Hypertension Stage 1 130 - 139 or 80 - 89 Hypertension Stage 2 > 140 or > 90 Hypertensive Crisis > 180 and/or > 120

3 Methods Following the steps below, the lab will be completed in two parts. Part 1 is taking HR and recording resting values on DATASHEET 1 . Part 2 is taking BP and recording resting values on DATASHEET 2 . Following completion of the lab, the REPORT page should be filled out and any questions answered. Heart Rate 1. Ask participant to quietly rest for 3 minutes a. Sitting, standing, or laying down does not substantially influence resting heart rate as long as no change in position occurs during the 3 minutes 2. Find a pulse a. Wrists b. Side of your neck 3. For measurements at the wrist, palpate the anterior-lateral surface of your wrist (thumb side). 4. Use the tips of your first two fingers ( not your thumb ) and press over the radial artery. a. Hint: just medial to your styloid process 5. Once pulse is found, use a stopwatch and count for the corresponding beats and multiply by the factor to find your beats per minute. 6. Record data on DATASHEET 1 . 7. Factors influencing this measure include air temperature (heat increases), emotions (e.g., stress increases), and medications (e.g., beta-blockers, caffeine, thyroid drugs). Blood Pressure 1. The participant should sit comfortably in a chair with a backrest for at least 5 min. The arm bared is at heart level and resting on the armrest of a chair or on a table. Make sure to tell the participant to uncross their legs. a. Consider factors such as avoiding caffeine, smoking, or exercise for a minimum of 30 minutes before measures. 2. Make sure the blood pressure cuff is fully deflated before using. 3. Palpate and locate the brachial artery using two fingers ( not your thumb ). 4. Position the supported arm with palm facing up and press bell/diaphragm of stethoscope into the antecubital space. The gauge should be clearly visible to the technician. 5. For persons with suspected small or large arm circumferences, measure the circumference of the participant’s upper arm. a. The appropriate cuff size is selected based on the arm circumference (cuff circles 75- 100% of the arm) 6. Snugly place the blood pressure cuff so that the lower edge is approximately 2.5 cm (1 in.) above the antecubital space. Appropriate cuff tightness should be checked. 7. The center of the bladder should be over the brachial artery. a. Some cuffs have a mark to line up with the brachial artery. To assure alignment, it may be helpful to palpate the brachial artery along the medial side of the antecubital space. 8. Check air-release screw to confirm it is locked, test it a few times to make sure you can release it with appropriate control. 9. The bulb should be held with the air-release screw comfortably between the thumb and index finger, with the bulb resting in the palm of the hand. 10. After turning the air-release screw clockwise, quickly inflate the cuff to any of the three following levels: a. 180 mm Hg b. 20 mm Hg above expected or known SP c. 20 mm Hg to 30 mm Hg above the disappearance of the palpated radial pulse17

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4 11. Turn the air-release screw counterclockwise so that the cuff pressure decreases at a rate of about 2-3 mm Hg per second. 12. Listen carefully and mentally note the first Korotkoff sound of two consecutive beats—systolic pressure (first phase)—then fourth phase (muffling)—then fifth phase (disappearance)—at the nearest 2 mm mark on the manometer, respectively. a. NOTE: there are no odd numbers in these readings. Example: it can’t be 119, it is either 118 or 120 mm Hg 13. Continue listening for 10 mm Hg to 20 mm Hg below the last sound heard to confirm disappearance. 14. Rapidly and fully deflate the cuff and record the values in even numbers onto DATASHEET 2 . 15. Repeat the measurements after 1-2 minutes and then average the readings unless they differ by more than 5 mmHg.

5 DATASHEET 1 Participant 1 Initials: _______ Age: _______ Sex: ______ Height: _______ Weight: _______ Any factors that may be influencing these numbers: ________________________________ Time (seconds) Pulse Count HR (bpm) Pulse Count HR (bpm) 10 15 30 60 Participant 2 Initials: _______ Age: _______ Sex: ______ Height: _______ Weight: _______ Any factors that may be influencing these numbers: ________________________________ Time (seconds) Pulse Count HR (bpm) Pulse Count HR (bpm) 10 15 30 60 Participant 3 Initials: _______ Age: _______ Sex: ______ Height: _______ Weight: _______ Any factors that may be influencing these numbers: ________________________________ Time (seconds) Pulse Count HR (bpm) Pulse Count HR (bpm) 10 15 30 60

6 DATASHEET 2 Participant 1 Initials: _______ Age: _______ Sex: ______ Height: _______ Weight: _______ Any factors that may be influencing these numbers: ________________________________ Systolic/Phase 1 (mmHg) Diastolic/Phase 5 (mmHg) Trial 1 Trial 2 Average MAP = 2/3 DBP + 1/3 SBP = 2/3 (_______) + 1/3(_______) = _________ mmHg Participant 2 Initials: _______ Age: _______ Sex: ______ Height: _______ Weight: _______ Any factors that may be influencing these numbers: ________________________________ Systolic/Phase 1 (mmHg) Diastolic/Phase 5 (mmHg) Trial 1 Trial 2 Average MAP = 2/3 DBP + 1/3 SBP = 2/3 (_______) + 1/3(_______) = _________ mmHg Participant 3 Initials: _______ Age: _______ Sex: ______ Height: _______ Weight: _______ Any factors that may be influencing these numbers: ________________________________ Systolic/Phase 1 (mmHg) Diastolic/Phase 5 (mmHg) Trial 1 Trial 2 Average MAP = 2/3 DBP + 1/3 SBP = 2/3 (_______) + 1/3(_______) = _________ mmHg

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7 REPORT QUESTIONS Answer the questions on this page (you can use the back of this page if you need additional space). Please answer each part of each question in order. 1. Which time period of counting the pulse rate at rest should provide the most accurate results? Provide support for your answer. 2. Is your resting HR normal, bradycardic, or tachycardic? Do you think that your measured resting heart rate was accurate? What, if any, factors may have influenced the readings today? 3. How does your resting blood pressure, as measured in lab today, compare to the blood pressure guidelines and categories? Do you think that your measured resting blood pressure was accurate? Name at least 2 possible sources of error that could have influenced the accuracy of your results. 4. Evaluate your own blood pressure findings. What influences might affect your values, and what changes (if any) would you recommend to change any value (be thorough).