Phillip December 11, 2025 No Comments

D313 Laboratory Report

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Western Governors University

D313 Anatomy and Physiology II with Lab

Prof. Name

Date

Laboratory Report

Predictions

Will heart rate (HR) change during exercise?

It is expected that heart rate will rise substantially once physical activity begins. As exercise intensity increases, working skeletal muscles consume oxygen at a much higher rate. To meet this rising metabolic requirement, the cardiovascular system accelerates heart rate so that more oxygenated blood can circulate to active tissues. This response is a hallmark of the body’s acute adaptation to exercise and is primarily regulated by sympathetic neural activation.

What happens to stroke volume (SV) during exercise?

Stroke volume is projected to increase during exercise due to both enhanced ventricular filling and stronger myocardial contractility. As muscular contractions and respiratory movements augment venous return, the ventricles receive a greater volume of blood. Simultaneously, sympathetic stimulation boosts the force of contraction, allowing for a larger volume of blood to be ejected with each heartbeat.

How will cardiac output (CO) be affected during exercise?

Cardiac output, the product of heart rate and stroke volume, is anticipated to rise dramatically. This increase reflects the heart’s ability to scale its pumping capacity to match the heightened oxygen and nutrient requirements of exercising tissues. As both HR and SV rise, CO increases proportionally, often several-fold above resting levels.

Materials and Methods

Variables and Measurements

The variables used in this study are outlined below.

Table 1

Variables and Descriptions

Variable Type	Variables	Description
Dependent Variables	End-Diastolic Volume (EDV), End-Systolic Volume (ESV), Cardiac Cycle Length	Quantitative markers of ventricular filling, ejection, and timing.
Independent Variable	Level of Physical Activity	Categorized as “Resting” and “Exercising.”
Controlled Variables	Age, gender, height, weight, and baseline health status	Ensured uniformity across subjects to reduce confounding factors.

Instrumentation

What instrument was used to measure cardiac volumes?

Cardiac chamber volumes were assessed using echocardiography. This non-invasive imaging modality relies on ultrasound waves to visualize ventricular size, assess wall motion, and calculate both systolic and diastolic volumes with real-time accuracy.

Does the echocardiograph use X-rays? Explain.

No. An echocardiograph employs high-frequency sound waves rather than ionizing radiation. The ultrasound-based technology captures dynamic images as sound waves reflect off cardiac structures. Because it does not expose patients to radiation, echocardiography is considered a safe and repeatable diagnostic method for evaluating cardiac performance.

Results

Table 2

Cardiac Cycle Length, End-Diastolic Volume (EDV), and End-Systolic Volume (ESV) at Rest and During Exercise

Subject	Cardiac Cycle Length (msec) Resting	EDV (mL) Resting	ESV (mL) Resting	Cardiac Cycle Length (msec) Exercising	EDV (mL) Exercising	ESV (mL) 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 resting cardiac cycle length averaged 814 milliseconds, which corresponds to a heart rate of roughly 74 beats per minute. This duration reflects a typical resting interval for ventricular filling and ejection.

How does the cardiac cycle length change during exercise?

During exercise, the cardiac cycle shortened markedly to an average of 420 milliseconds. This reduction indicates a pronounced rise in heart rate, enabling more rapid circulation to support increased metabolic demands.

What is the average EDV at rest and during exercise?

EDV remained relatively stable at 141 mL for both resting and exercise conditions. Despite reduced filling time during exercise, enhanced venous return preserved diastolic volume, allowing the heart to maintain adequate preload.

How does the ESV change with exercise?

ESV declined from 69 mL at rest to 32 mL during exercise. This reduction demonstrates stronger ventricular contraction and improved ejection efficiency, both characteristic responses to sympathetic stimulation.

Table 3

Heart Rate (HR), Stroke Volume (SV), and Cardiac Output (CO) at Rest and During Exercise

Subject	HR (beats/min) Resting	SV (mL) Resting	CO (L/min) Resting	HR (beats/min) Exercising	SV (mL) Exercising	CO (L/min) 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 mean resting heart rate was 74 bpm, aligning with established norms for healthy adults in a relaxed physiological state.

How did heart rate change during exercise?

During physical exertion, the average heart rate rose to 143 bpm, almost doubling its resting value. This surge supports increased blood flow and oxygen transport to active musculature.

What was the stroke volume at rest and during exercise?

Stroke volume increased markedly from 73 mL at rest to 109 mL during exercise. This rise reflects the combined influence of heightened venous return, greater myocardial contractility, and more forceful ventricular ejection.

How did cardiac output respond to exercise?

Cardiac output expanded from 5.3 L/min to 15.6 L/min, representing nearly a threefold increase. This substantial escalation demonstrates the cardiovascular system’s capacity to support elevated physical activity levels.

Discussion

What caused the increase in heart rate with exercise?

The increase in heart rate is primarily attributable to activation of the sympathetic nervous system. As exercise begins, circulating catecholamines—specifically epinephrine and norepinephrine—bind to cardiac receptors, accelerating heart rate and strengthening contractility. This rapid modulation enables efficient delivery of oxygen and nutrients during physical exertion.

How do venous return and heart rate influence exercise EDV?

During exercise, venous return rises due to both muscle pump action and enhanced respiratory mechanics, which channel blood back toward the heart. Although increased heart rate shortens diastolic duration, the substantial rise in venous return compensates for shorter filling time, thereby sustaining or slightly increasing EDV.

Why does ESV decrease during exercise?

ESV decreases because the ventricles contract more forcefully under sympathetic influence. Elevated intracellular calcium levels improve myocardial contractile efficiency, enabling the heart to eject a larger proportion of blood with each beat. This enhanced ejection reduces the remaining volume inside the ventricle.

Why does stroke volume increase with exercise?

Stroke volume increases due to a combination of factors, including increased venous return, enhanced myocardial contractility, and reduced systemic vascular resistance. These physiological adaptations promote more effective ventricular filling and ejection, allowing the heart to supply greater blood volume per beat.

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

Greater cardiac output ensures that working tissues receive adequate oxygen while metabolic byproducts such as carbon dioxide and lactate are removed promptly. This enhanced circulatory capacity supports endurance, delays fatigue, and maintains homeostasis during prolonged or intensive activity.

Were the initial predictions supported by the experiment?

Yes. The data confirmed all initial predictions: heart rate, stroke volume, and cardiac output increased significantly during exercise. These findings align with well-established physiological principles of cardiovascular adaptation to physical stress.

Application

What is the average stroke volume of the right ventricle at rest and after exercise?

The right ventricle typically pumps a stroke volume comparable to that of the left ventricle. Based on the recorded values, its stroke volume is approximately 73 mL at rest and 109 mL during exercise, ensuring balanced output between 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 imbalance is corrected through the Frank-Starling mechanism. When one ventricle ejects slightly more blood than the other, the resulting shift in intraventricular pressure and volume causes the subsequent beat to restore equilibrium. This mechanism prevents accumulation of blood in either circulation and maintains consistent cardiac function.

Why do elite athletes often have lower resting heart rates but greater cardiac output during exercise?

Elite athletes display cardiac hypertrophy and superior ventricular compliance, enabling them to pump a larger stroke volume even at rest. Consequently, their resting heart rate remains low. During strenuous exercise, their well-conditioned myocardium can markedly elevate stroke volume, resulting in exceptionally high cardiac output and superior aerobic performance.

References

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.