D313 Laboratory Report

Grace J.
November 12, 2025November 12, 2025
BSN, D313, Western Governors University

Student Name

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 anticipated that the heart rate will increase during physical exertion. This physiological response occurs because the muscles demand more oxygen and nutrients to sustain activity, prompting the cardiovascular system to elevate heart rate for efficient oxygen delivery throughout the body.

What happens to stroke volume (SV) during exercise?

Stroke volume is expected to rise during exercise. This increase happens as the heart contracts more forcefully and ejects a larger volume of blood per beat, enhancing overall circulatory efficiency.

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

Cardiac output, which is the product of heart rate and stroke volume, is predicted to increase substantially during exercise. This rise reflects the body’s adaptive mechanism to satisfy the heightened metabolic and oxygen demands of working muscles.

Materials and Methods

Variables and Measurements

Variable Type	Variables	Description
Dependent Variables	End-Diastolic Volume (EDV), End-Systolic Volume (ESV), Cardiac Cycle Length	Quantitative indicators of cardiac function.
Independent Variable	Level of Physical Activity	Classified as “Resting” or “Exercising.”
Controlled Variables	Age, gender, body weight, height, and general health status	Maintained constant to ensure reliability and minimize bias.

Instrumentation

What instrument was used to measure cardiac volumes?
An echocardiograph was employed to evaluate cardiac volumes. This non-invasive imaging tool measures chamber dimensions and ventricular performance by using sound waves.

Does the echocardiograph use X-rays? Explain.
No. The echocardiograph operates through ultrasound technology, which uses high-frequency sound waves to generate real-time images of the heart. Unlike X-rays, it does not involve ionizing radiation, making it a safer diagnostic method.

Results

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?

At rest, the average cardiac cycle length measured approximately 814 milliseconds, corresponding to a heart rate near 74 beats per minute.

How does the cardiac cycle length change during exercise?

During exercise, the cycle shortened significantly to about 420 milliseconds, indicating a higher heart rate and faster cardiac rhythm to support greater circulatory demand.

What is the average EDV at rest and during exercise?

The end-diastolic volume (EDV) remained relatively stable at 141 mL across both conditions, suggesting the heart maintained consistent ventricular filling despite reduced diastolic duration.

How does the ESV change with exercise?

The end-systolic volume (ESV) decreased notably from 69 mL at rest to 32 mL during exercise, reflecting more efficient ventricular contraction and 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 mean resting heart rate was 74 beats per minute (bpm), consistent with typical adult resting values.

How did heart rate change during exercise?

During exercise, heart rate rose dramatically to an average of 143 bpm, almost doubling from the resting level to accommodate increased oxygen transport needs.

What was the stroke volume at rest and during exercise?

Stroke volume increased from 73 mL at rest to 109 mL during exercise, demonstrating enhanced cardiac efficiency through improved ventricular contractility and venous return.

How did cardiac output respond to exercise?

Cardiac output expanded from 5.3 L/min at rest to 15.6 L/min during exercise, nearly a threefold increase. This change underscores the cardiovascular system’s capacity to meet elevated metabolic demands.

Discussion

What caused the increase in heart rate with exercise?

Exercise stimulates the sympathetic nervous system, which releases catecholamines (epinephrine and norepinephrine). These hormones accelerate heart rate to enhance oxygen delivery to active muscles, supporting sustained physical effort.

How do venous return and heart rate influence exercise EDV?

Venous return increases during exercise as skeletal muscles compress veins and respiratory activity promotes blood flow toward the heart. Although the elevated heart rate shortens filling time, this augmented venous return preserves or slightly raises end-diastolic volume (EDV).

Why does ESV decrease during exercise?

A decrease in end-systolic volume (ESV) results from stronger ventricular contractions driven by increased sympathetic activity and calcium ion availability. This efficient ejection allows the heart to pump a larger proportion of its contents per beat.

Why does stroke volume increase with exercise?

Stroke volume rises due to a combination of enhanced venous return, improved myocardial contractility, and reduced peripheral resistance. Together, these factors enable the ventricles to fill more effectively and eject blood more forcefully.

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

The elevation in cardiac output ensures that oxygen and nutrients are adequately supplied to tissues while metabolic waste products are efficiently removed. This adaptation is vital for maintaining endurance and delaying fatigue during physical exertion.

Were the initial predictions supported by the experiment?

Yes, the predictions were validated. Heart rate, stroke volume, and cardiac output all showed substantial increases during exercise. Specifically, heart rate rose from 74 to 143 bpm, stroke volume from 73 to 109 mL, and cardiac output from 5.3 to 15.6 L/min.

Application

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

The right ventricle’s average stroke volume aligns closely with that of the left ventricle, measuring approximately 73 mL at rest and 109 mL during exercise. This equilibrium maintains consistent 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 transient imbalance is self-corrected through the Frank-Starling mechanism, wherein increased ventricular filling pressure in subsequent cycles restores equilibrium between the left and right ventricles, preventing congestion or inadequate perfusion.

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

Elite athletes possess hypertrophied cardiac muscles that allow greater stroke volume at rest, thereby reducing the necessity for a high heart rate. During intense activity, their powerful ventricles can further elevate stroke volume, yielding superior cardiac output and enhanced performance efficiency.

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.