D313 Laboratory Report

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 expected that heart rate will increase during physical activity. This physiological response is due to the elevated demand for oxygen and nutrients by active muscles. Consequently, the cardiovascular system responds by accelerating heart rate to enhance oxygen delivery throughout the body, supporting sustained muscle work.

What happens to stroke volume (SV) during exercise?

Stroke volume is anticipated to increase during exercise. This increase occurs because the heart contracts more forcefully, expelling a greater volume of blood with each beat. The enhanced stroke volume improves the efficiency of blood circulation, supplying working muscles with the oxygen they require.

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

Cardiac output, defined as the product of heart rate and stroke volume, is expected to rise significantly during exercise. This elevation reflects the body’s adaptation to increased metabolic demands, ensuring adequate oxygen and nutrient delivery to tissues engaged in physical exertion.

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, general health status	Maintained constant to reduce bias and ensure reliability.

Instrumentation

What instrument was used to measure cardiac volumes?

An echocardiograph was utilized to assess cardiac volumes. This non-invasive device employs high-frequency sound waves to create real-time images of the heart, allowing measurement of chamber size and ventricular function.

Does the echocardiograph use X-rays? Explain.

No, the echocardiograph operates using ultrasound technology, which involves high-frequency sound waves rather than ionizing radiation like X-rays. This makes echocardiography a safer diagnostic method, avoiding exposure to harmful radiation.

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 was approximately 814 milliseconds, corresponding to a resting heart rate of about 74 beats per minute.
How does the cardiac cycle length change during exercise?
During exercise, the cardiac cycle length decreased substantially to around 420 milliseconds, reflecting a marked increase in heart rate and faster cardiac rhythm to meet heightened circulatory demands.
What is the average EDV at rest and during exercise?
The end-diastolic volume remained fairly constant at 141 mL in both resting and exercising states, indicating consistent ventricular filling despite shorter diastolic periods during exercise.
How does the ESV change with exercise?
End-systolic volume decreased significantly from 69 mL at rest to 32 mL during exercise, indicating enhanced ventricular contraction and more effective 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 normative adult values.
How did heart rate change during exercise?
Heart rate almost doubled during exercise, rising to an average of 143 beats per minute to meet the increased oxygen demands.
What was the stroke volume at rest and during exercise?
Stroke volume increased from 73 mL at rest to 109 mL during exercise, reflecting improved ventricular contractility and enhanced venous return.
How did cardiac output respond to exercise?
Cardiac output surged from 5.3 L/min at rest to 15.6 L/min during exercise, nearly tripling to satisfy the metabolic needs of working muscles.

Discussion

What caused the increase in heart rate with exercise?

The elevation in heart rate during exercise results from sympathetic nervous system activation, which releases catecholamines such as epinephrine and norepinephrine. These hormones stimulate the heart to beat faster, increasing oxygen delivery to active muscles.

How do venous return and heart rate influence exercise EDV?

Venous return increases during exercise due to the skeletal muscle pump and enhanced respiratory activity, which push more blood toward the heart. Although a higher heart rate reduces ventricular filling time, the increased venous return compensates by maintaining or slightly increasing the end-diastolic volume (EDV).

Why does ESV decrease during exercise?

End-systolic volume decreases because of stronger ventricular contractions, driven by increased sympathetic stimulation and greater calcium availability in cardiac muscle cells. This allows more complete emptying of the ventricles during systole.

Why does stroke volume increase with exercise?

Stroke volume increases due to a combination of enhanced venous return, increased myocardial contractility, and reduced peripheral vascular resistance. These factors enable the heart to fill more effectively and eject blood more forcefully.

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

Increased cardiac output is crucial for delivering oxygen and nutrients to meet the metabolic demands of exercising muscles and for removing metabolic waste products. This adaptation supports prolonged physical activity and delays fatigue.

Were the initial predictions supported by the experiment?

Yes, the initial predictions were confirmed. Heart rate, stroke volume, and cardiac output all showed marked increases during exercise, consistent with the physiological expectations.

Application

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

The average stroke volume of the right ventricle closely matches that of the left ventricle, measuring approximately 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 imbalance is corrected through the Frank-Starling mechanism, whereby increased ventricular filling pressure in subsequent cycles equalizes output between ventricles, preventing congestion or inadequate perfusion.

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

Elite athletes develop hypertrophied cardiac muscles that allow for a larger stroke volume at rest, reducing the need for a high resting heart rate. During intense exercise, their hearts can further increase stroke volume, resulting in superior cardiac output and enhanced endurance.

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.

D313 Laboratory Report

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

D313 Laboratory Report Echocardiography. (2021). In American Heart Association. Retrieved from https://www.heart.org/en/health-topics/heart-attack/diagnosing-heart-attack/echocardiogram