Lab answers

Cardiac output (CO) is the amount of blood pumped by the heart in one minute and is dependent on SV and HR.

CO (L/min) = SV x HR

As the need for oxygen and nutrients increases with exercise, so does CO to maintain oxidative production of ATP. This is achieved through the changes in HR and SV. CO increases as much as 5-fold when going from rest to maximal exercise. Aerobic training can increase maximal CO, which increases the capacity for exercise by delivering more oxygenated blood to the working muscles.

Blood pressure (BP) is defined as the pressure exerted by the blood against the walls of the blood vessels. Since the heart is a pulsatile pump contracting during systole and relaxing during diastole, blood pressure in the arteries is constantly changing. It oscillates between a relatively higher pressure, the systolic blood pressure (SBP), which occurs during the systolic phase of the cardiac cycle, and a lower pressure, called diastolic blood pressure (DBP), that occurs during the diastolic phase. Resting systolic and diastolic blood pressures are measured in units of millimeters of mercury (mmHg) and normally range from about 90-119 and 60-79 mmHg, respectively.

Mean blood pressure or mean arterial pressure (MAP) is the average pressure exerted by the blood against the arterial walls over the duration of the cardiac cycle, and as such, represents the true driving pressure of the circulatory system. It is directly measured through arterial catheterization, but can be estimated from DBP and SBP as follows:

Many different factors can influence resting and exercise blood pressure. In general, these influences can be grouped into physiologic/internal and environmental/external factors. Age, gender, cardiac output, total peripheral resistance, the condition or elasticity of the blood vessels, and blood viscosity are physiologic/internal factors that can affect blood pressure. In addition, an increase in blood volume as a result of fluid retention by the kidneys can cause blood pressure to increase. Some environmental/external factors which affect blood pressure are body position, exercise, temperature, altitude, emotions, food, and drugs. Thus, when measuring blood pressure, especially when evaluating an individual for suspected hypertension, care should be taken to standardize the environmental conditions under which blood pressure is measured.

American Heart Association, 2017

Resting heart rate and blood pressure measurement

Heart rate can be measured by different methods including electrocardiogram (ECG), telemetry (heart rate monitors), auscultation (stethoscope), and palpation. Feeling a pulse with the fingers is termed palpation. The pulse is generated by the pulsatile pumping of blood in the arteries. Four common sites are brachial, carotid, radial, and temporal arteries, but the pulse is most commonly palpated over the radial or carotid arteries in adults. The Timed Heart Rate Method requires counting the number of pulses in a specific amount of time. Usually pulse counts are taken for 6, 10, 15, or 30 seconds. The pulse is then multiplied by 10, 6, 4, or 2 respectively. Begin counting with zero (0, 1, 2, 3, . . .).

In the laboratory setting, blood pressure is determined indirectly by listening to the Korotkoff sounds, which are sounds made from vibrations along the vascular walls. The cuff of a sphygmomanometer is inflated around a limb (usually the upper arm) until the pressure in the cuff exceeds that expected for the SBP. At this cuff pressure, the underlying artery is collapsed, preventing blood flow. A stethoscope is then positioned on the skin just above the artery, but distal to the cuff. If the arm is used, the stethoscope is placed over the brachial artery in the antecubital space at the elbow. As the cuff is slowly deflated by opening its valve and the pressure drop is read off the manometer, a point will be reached at which the SBP will exceed the pressure exerted by the cuff, blood will be forced through the compressed artery for a brief moment, and then the artery will snap closed as the arterial pressure falls during diastole. This brief opening and closing of the artery, along with the turbulent blood flow through the compressed artery, produces sounds that can be heard through the stethoscope. As the pressure continues to fall in the cuff, the sounds marking the closure of the artery change in pitch and intensity, marking the different phases of blood pressure. Eventually, as the cuff pressure falls still further, the sound disappears, altogether. The blood pressure phases and sounds described by Nicolai Korotkoff are shown in Table 3.2.

For adults, the first Korotkoff sound marks SBP. As the volume of blood passing through the constricted artery increases with the continued release of cuff pressure, the sounds become progressively louder through phases II to III. The sounds then become suddenly muffled in phase IV as arterial constriction is reduced still further and diastolic pressure is approached. Finally, the Korotkoff sounds disappear in phase V, which is usually taken as the diastolic blood pressure.

Procedures

Resting Heart Rate

1. Rest in a seated position for about 5 minutes.

2. Use a 15 second count and multiply by 4 to determine your resting HR. Record in Data Table 6.0 (Stage 1 – Pre).

Resting Blood Pressure

1. Subject should be seated with their left arm resting on the armrest of a chair or table. The upper arm should be at the approximate level of the left atrium, the midpoint of the sternum.

2. Position cuff so that the lower edge is approximately one inch (2-3 cm) above the antecubital space.

3. Use the automatic blood pressure cuff to measure resting systolic and diastolic blood pressure and record in Data Table 6.0 (Stage 1 – Pre).

Heart rate and blood pressure measurement during exercise

Procedures

Exercise Heart Rate

1. Place heart rate monitor chest strap on your skin, just below the sternum. Strap should be tight enough so that electrodes are touching the skin and so the strap does not move. You can wet the electrodes with water to get a good connection between your chest and transmitter.

2. Adjust bike to a comfortable position (adjust seat height to approximately hip level, adjust handlebar height to approximately seat level, spin the pedals for a few revolutions to check position, adjust position as necessary for comfort).

3. Pedal at a frequency of 80 revolutions per minute (rpm).

4. Press the Stages button on the bike console to get to the Warm-Up screen. You must be in the Warm-Up screen to pair the heart rate monitor.

5. Once heart rate is detected on the screen, find an easy resistance (RPE = 1) on the bike (adjust by turning the blue knob to the left to make it easier and to the right to make it harder), and then press the Stages button.

6. Stage 2: 3 minutes. maintain power at an RPE = 1, cadence 80 rpm. Record Watts, HR, SBP, & DBP at the end of the 3-minute stage. Press the stages button.

7. Stage 3: 3 minutes, increase resistance using the blue knob to maintain power at an RPE = 2-3, cadence 80 rpm. Record Watts, HR, SBP, & DBP at the end of the 3-minute stage. Press the stages button.

8. Stage 4: 3 minutes, increase resistance using the blue knob to maintain power at an RPE = 4-5, cadence 80 rpm. Record Watts, HR, SBP, & DBP at the end of the 3-minute stage. Press the stages button.

9. Stage 5: 3 minutes, increase resistance using the blue knob to maintain power at an RPE = 6-7, cadence 80 rpm. Record Watts, HR, SBP, & DBP at the end of the 3-minute stage. Press the stages button.

10. Stage 6: 3 minutes, increase resistance using the blue knob to maintain power at an RPE = 8-9, cadence 80 rpm. Record Watts, HR, SBP, & DBP at the end of the 3-minute stage. Take the resistance all the way off and press the stages button.

11. Stage 7: 5 minutes recovery. Record Watts, HR, SBP, & DBP at the end of the 3-minute stage.

12. HR and BP measurements will be taken 30 seconds before the end of each stage, or earlier if need be to ensure that the blood pressure measurement can be completed before the load is increased for the next stage. Record the BP and HR values on Data Table 6.0 for the appropriate stage.

13. Normally, systolic blood pressure rises with workload due to increased cardiac output. Values exceeding 200 mm Hg are not uncommon. However, if SBP exceeds 250 mm Hg, the test should be terminated. The DBP normally stays the same or decreases slightly during moderate dynamic exercise. If DBP exceeds 115 mm Hg, exercise should be terminated.

Lab Questions

1. Use the provided Excel spreadsheet to calculate the following variables for each stage for each subject:

a. Stroke volume mL/beat (SV = 101 + (0.50 x SBP) - (1.09 x DBP) - (0.61 x Age)

b. Cardiac output L/min (CO = HR x SV) *Don’t forget to divide by 1000 to get L/min*

c. Mean arterial pressure (MAP = DBP + [0.333 x (SBP – DBP)])

d. Means and standard deviations for each stage:

i. Watts

ii. Heart rate

iii. Stroke volume

iv. Cardiac output

v. Systolic blood pressure

vi. Diastolic blood pressure

vii. Mean arterial pressure

e. Percent change in the following variables comparing rest (Variable 1) to Stage 6 of exercise (Variable 2) (Percent change = ((Variable 2 – Variable 1) / Variable 1)*100):

i. Heart rate

ii. Stroke volume

iii. Cardiac output

iv. Mean arterial pressure

f. Create a separate line graph for each of the following variables with Stage number (Stages 1-7) as the x-axis and the variable as the y-axis (use the mean for each variable):

i. Heart rate

ii. Stroke volume

iii. Cardiac output

iv. Mean arterial pressure

2. According to Table 6.0, classify your resting (Stage 1 – Pre-exercise) blood pressure.

3. Describe the relationship between exercise intensity and heart rate, stroke volume, cardiac output, and mean arterial pressure. How and why do each change with changing exercise intensity?

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