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Western Governors University
D313 Anatomy and Physiology II with Lab
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Date
Will heart rate (HR) change during exercise?
It is expected that heart rate will rise when engaging in physical activity. This increase is a normal physiological response, as the muscles require a higher supply of oxygen and nutrients to sustain the exertion. Consequently, the cardiovascular system accelerates the heart rate to enhance oxygen delivery throughout the body efficiently.
What happens to stroke volume (SV) during exercise?
Stroke volume is predicted to increase during exercise. This occurs because the heart contracts more forcefully, ejecting a larger volume of blood with each beat, thereby improving the efficiency of blood circulation to meet increased metabolic demands.
How will cardiac output (CO) be affected during exercise?
Cardiac output, defined as the product of heart rate and stroke volume, is anticipated to significantly increase during physical exertion. This adjustment is essential to supply working muscles with adequate oxygen and nutrients by enhancing the overall blood flow.
Variables and Measurements
| Variable Type | Variables | Description |
|---|---|---|
| Dependent Variables | End-Diastolic Volume (EDV), End-Systolic Volume (ESV), Cardiac Cycle Length | Quantitative measures reflecting cardiac function. |
| Independent Variable | Level of Physical Activity | Classified as either “Resting” or “Exercising.” |
| Controlled Variables | Age, gender, body weight, height, general health status | Held constant to ensure accuracy and reduce bias. |
Instrumentation
What instrument was used to measure cardiac volumes?
An echocardiograph was used to assess cardiac volumes. This non-invasive imaging device employs ultrasound waves to visualize heart chambers and measure ventricular performance.
Does the echocardiograph use X-rays? Explain.
No, echocardiography utilizes ultrasound technology, which operates through high-frequency sound waves to produce real-time images of the heart. Unlike X-rays, it does not use ionizing radiation, making it a safer alternative for cardiac imaging.
Table 1: Cardiac Cycle Length, End-Diastolic Volume (EDV), and End-Systolic Volume (ESV) at Rest and During Exercise
| Subject | Cardiac Cycle Length (msec) | EDV (mL) | ESV (mL) | Cardiac Cycle Length (msec) | EDV (mL) | ESV (mL) |
|---|---|---|---|---|---|---|
| Resting | Exercising | |||||
| Subject 1 | 814 | 145 | 65 | 447 | 143 | 31 |
| Subject 2 | 820 | 140 | 74 | 398 | 140 | 31 |
| Subject 3 | 809 | 139 | 67 | 414 | 140 | 35 |
| Average | 814 | 141 | 69 | 420 | 141 | 32 |
Analysis of Cardiac Cycle Length, EDV, and ESV
What is the average resting cardiac cycle length?
The average cardiac cycle length during rest was approximately 814 milliseconds, corresponding to a heart rate of about 74 beats per minute.
How does the cardiac cycle length change during exercise?
During physical activity, the cardiac cycle length decreased significantly to about 420 milliseconds. This reduction indicates an accelerated heart rate and a faster cardiac rhythm to meet the increased circulatory demands.
What is the average EDV at rest and during exercise?
End-diastolic volume (EDV) remained fairly constant at approximately 141 mL in both resting and exercising states. This stability suggests that ventricular filling is maintained despite a shorter diastolic period during exercise.
How does the ESV change with exercise?
End-systolic volume (ESV) dropped substantially from an average of 69 mL at rest to 32 mL during exercise. This decrease reflects more efficient ventricular contraction and enhanced blood ejection.
Table 2: Heart Rate (HR), Stroke Volume (SV), and Cardiac Output (CO) at Rest and During Exercise
| Subject | HR (beats/min) | SV (mL) | CO (L/min) | HR (beats/min) | SV (mL) | CO (L/min) |
|---|---|---|---|---|---|---|
| Resting | Exercising | |||||
| Subject 1 | 74 | 80 | 5.9 | 134 | 112 | 15.0 |
| Subject 2 | 73 | 66 | 4.8 | 151 | 109 | 16.5 |
| Subject 3 | 74 | 72 | 5.3 | 145 | 105 | 15.2 |
| Average | 74 | 73 | 5.3 | 143 | 109 | 15.6 |
Analysis of Heart Rate, Stroke Volume, and Cardiac Output
What was the average resting heart rate?
The average resting heart rate was 74 beats per minute, consistent with normal adult resting values.
How did heart rate change during exercise?
Heart rate nearly doubled during exercise, increasing to an average of 143 beats per minute to meet heightened oxygen transport requirements.
What was the stroke volume at rest and during exercise?
Stroke volume increased from an average of 73 mL at rest to 109 mL during exercise, highlighting improved cardiac efficiency through stronger ventricular contractions and increased venous return.
How did cardiac output respond to exercise?
Cardiac output rose from 5.3 liters per minute at rest to 15.6 liters per minute during exercise—almost tripling to meet the elevated metabolic demands of working muscles.
What causes the increase in heart rate during exercise?
The rise in heart rate is driven by sympathetic nervous system activation, which releases catecholamines such as epinephrine and norepinephrine. These hormones accelerate heart rate to boost oxygen delivery to active muscles, facilitating sustained physical activity.
How do venous return and heart rate influence exercise EDV?
During exercise, venous return increases due to muscular contractions compressing veins and enhanced respiratory activity that pushes blood back to the heart. Although increased heart rate shortens the diastolic filling time, the augmented venous return compensates, maintaining or slightly increasing the end-diastolic volume.
Why does ESV decrease during exercise?
End-systolic volume falls because of more powerful ventricular contractions driven by sympathetic stimulation and increased calcium ion availability. This stronger contraction allows the heart to eject a greater proportion of blood per beat, improving overall efficiency.
Why does stroke volume increase with exercise?
Stroke volume rises due to several factors including increased venous return, enhanced myocardial contractility, and reduced peripheral resistance. These changes enable the ventricles to fill more completely and contract more forcefully, resulting in greater blood ejection.
What is the significance of the increase in cardiac output during exercise?
The increased cardiac output is essential for delivering adequate oxygen and nutrients to tissues and removing metabolic waste. This physiological adjustment supports sustained endurance and delays the onset of fatigue during prolonged physical exertion.
Were the initial predictions supported by the experiment?
Yes, the results confirmed the predictions. Heart rate increased from 74 to 143 bpm, stroke volume from 73 to 109 mL, and cardiac output nearly tripled from 5.3 to 15.6 L/min during exercise.
What is the average stroke volume of the right ventricle at rest and after exercise?
The right ventricle’s stroke volume averages similarly to the left ventricle, at around 73 mL at rest and 109 mL during exercise, maintaining balanced pulmonary and systemic circulation.
If the left ventricle’s stroke volume exceeds that of the right ventricle for one beat, how is this discrepancy corrected?
Any temporary difference is rectified by the Frank-Starling mechanism, where increased ventricular filling pressure in subsequent cardiac cycles restores balance between the ventricles, preventing blood accumulation or insufficient perfusion.
Why do elite athletes often have lower resting heart rates but greater cardiac output during exercise?
Elite athletes typically develop hypertrophied cardiac muscles, allowing higher stroke volumes even at rest, reducing the need for elevated heart rates. During intense exercise, their enhanced ventricular function supports even greater stroke volumes, leading to superior cardiac output and more efficient performance.
Guyton, A. C., & Hall, J. E. (2021). Textbook of Medical Physiology (14th ed.). Elsevier.
Marieb, E. N., & Hoehn, K. (2018). Human Anatomy & Physiology (11th ed.). Pearson.
McArdle, W. D., Katch, F. I., & Katch, V. L. (2015). Exercise Physiology: Nutrition, Energy, and Human Performance (8th ed.). Wolters Kluwer.
Echocardiography. (2021). In American Heart Association. Retrieved from https://www.heart.org/en/health-topics/heart-attack/diagnosing-heart-attack/echocardiogram
