D313 Laboratory Report

D313 Laboratory Report

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Western Governors University

D313 Anatomy and Physiology II with Lab

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LABORATORY REPORT

Activity: Effect of Exercise on Cardiac Output
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Predictions

1. Will heart rate (HR) change during exercise?
   It is predicted that heart rate will increase during exercise to meet the higher oxygen demands of the body.

2. What happens to stroke volume (SV) during exercise?
   Stroke volume is expected to increase during exercise, as the heart pumps more blood per beat.

3. How will cardiac output (CO) be affected during exercise?
   Cardiac output is predicted to increase during exercise, reflecting the combined effect of increased heart rate and stroke volume.

Materials and Methods

Variables and Measurements

• Dependent Variables: End-Diastolic Volume (EDV), End-Systolic Volume (ESV), and cardiac cycle length.

• Independent Variable: Level of physical activity, categorized as resting or exercising.

• Controlled Variables: Age, weight, height, gender, and general health of subjects to ensure consistency.

Instrumentation

• What instrument was used to measure cardiac volumes?
  An echocardiograph was utilized to assess cardiac volumes in this experiment.

• Does the echocardiograph use X-rays? Explain.
  No, the echocardiograph operates using high-frequency sound waves (ultrasound) to create detailed images of the heart, avoiding the use of X-rays, which are ionizing radiation.

Results

Table 1: Cardiac Cycle Length, EDV, and ESV During Rest and Exercise

Analysis of Cardiac Cycle Length, EDV, and ESV

1. What is the average resting cardiac cycle length?
   The average cardiac cycle length at rest is approximately 814 milliseconds.

2. How does the cardiac cycle length change during exercise?
   The average cardiac cycle length decreases to about 420 milliseconds during exercise, reflecting a faster heart rate.

3. What is the average EDV at rest and during exercise?
   The average EDV remains constant at 141 mL both at rest and during exercise, indicating no significant change.

4. How does the ESV change with exercise?
   ESV decreases substantially during exercise, from an average of 69 mL at rest to 32 mL, suggesting more efficient ventricular emptying.

Table 2: Heart Rate, Stroke Volume, and Cardiac Output at Rest and During Exercise

Analysis of Heart Rate, Stroke Volume, and Cardiac Output

1. What was the average resting heart rate?
   The average resting heart rate was 74 beats per minute.

2. How did heart rate change during exercise?
   The heart rate increased significantly during exercise to an average of 143 beats per minute.

3. What was the stroke volume at rest and during exercise?
   Stroke volume rose from an average of 73 mL at rest to 109 mL during exercise.

4. How did cardiac output respond to exercise?
   Cardiac output increased nearly threefold from 5.3 L/min at rest to 15.6 L/min during exercise, meeting the increased oxygen demands of active muscles.

Discussion

What caused the increase in heart rate with exercise?

The heart rate rises during exercise because muscles require more oxygen to sustain activity. The cardiovascular system responds by increasing heart rate, thereby pumping blood more rapidly to deliver oxygen-rich blood to tissues efficiently.

How do venous return and heart rate influence exercise EDV?

During exercise, venous return (the flow of blood back to the heart) increases due to muscular activity and vascular adjustments. Although the heart rate increases, reducing filling time, the enhanced venous return compensates by maintaining or even increasing end-diastolic volume (EDV), enabling the heart to fill adequately and pump more blood per beat.

Why does ESV decrease during exercise?

Exercise lowers the end-systolic volume because the heart contracts more forcefully, ejecting a larger proportion of blood from the ventricles. This reduction in residual volume facilitates increased stroke volume and cardiac output.

Why does stroke volume increase with exercise?

Stroke volume increases because the heart’s enhanced contractility during exercise allows it to eject more blood with each beat. This effect results from improved ventricular filling (due to increased venous return) and more forceful ventricular contractions.

What is the significance of the increase in cardiac output during exercise?

The increase in cardiac output is crucial as it supports the heightened metabolic demands of the body during physical activity. More blood — and therefore oxygen and nutrients — is delivered to active tissues, enhancing performance and endurance.

Were the initial predictions supported by the experiment?

Yes, the predictions were confirmed by the data: heart rate increased (from 74 to 143 bpm), stroke volume increased (from 73 to 109 mL), and cardiac output rose significantly (from 5.3 to 15.6 L/min) during exercise, validating the hypotheses.

Application

1. What is the average stroke volume of the right ventricle at rest and after exercise?
   The stroke volume of the right ventricle averages 73 mL at rest and increases to 109 mL after exercise, mirroring the left ventricle’s output to maintain balanced circulation.

2. If the left ventricle’s stroke volume exceeds that of the right ventricle for one beat, how is this discrepancy corrected?
   In a healthy heart, the stroke volumes of the ventricles are nearly equal to maintain efficient circulation. If the left ventricle ejects more blood than the right, the heart compensates on the next beat by adjusting ventricular filling volumes, ensuring blood volume equilibrium and preventing congestion or depletion in either pulmonary or systemic circuits.

3. Why do elite athletes often have lower resting heart rates but greater cardiac output during exercise?
   Elite athletes typically have a thicker, stronger myocardium that enables a higher stroke volume at rest. This efficiency allows their hearts to pump more blood per beat, reducing the need for a high resting heart rate. During exercise, their hearts can further increase stroke volume and cardiac output effectively, supporting superior athletic performance.

References

• Guyton, A. C., & Hall, J. E. (2021). Textbook of Medical Physiology (14th ed.). Elsevier.

• McArdle, W. D., Katch, F. I., & Katch, V. L. (2015). Exercise Physiology: Nutrition, Energy, and Human Performance (8th ed.). Wolters Kluwer.

• Marieb, E. N., & Hoehn, K. (2018). Human Anatomy & Physiology (11th ed.). Pearson.

D313 Laboratory Report

• Echocardiography. (2021). In American Heart Association. Retrieved from https://www.heart.org/en/health-topics/heart-attack/diagnosing-heart-attack/echocardiogram