Cardiac Output and Heart Rate Control

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Questions and Answers

What condition is commonly associated with a chronic increase in preload?

Arrhythmia

Myocardial infarction

Heart failure (correct)

Angina pectoris

Which of the following situations would result in high afterload?

Blood loss

Bradycardia

Aortic valve stenosis (correct)

Hyperventilation

Which method is NOT considered a direct method for measuring cardiac output?

Thermodilution method

Electromagnetic flow-meter devices

Hamilton dye dilution method

Indicator dilution technique (correct)

What is the formula for calculating cardiac output using the Hamilton dye dilution method?

COP = Q / (C x t) Signup and view all the answers

According to the Fick principle, the blood flow to an organ is equal to which of the following?

The total oxygen consumed divided by the arterial-venous difference Signup and view all the answers

What is the normal venous return in an adult male at rest?

5 L/min Signup and view all the answers

What is the main substance measured by the Fick principle when assessing lung blood flow?

Oxygen Signup and view all the answers

The pressure gradient in the circulatory system generally follows which pattern?

Arteries > capillaries > veins Signup and view all the answers

What is stroke volume defined as?

Volume of blood ejected by each ventricle with each beat Signup and view all the answers

Which factor does NOT directly affect end diastolic volume (EDV)?

Cardiac contraction strength Signup and view all the answers

What is the role of sympathetic stimulation on stroke volume?

Increases stroke volume Signup and view all the answers

How is the ejection fraction (EF) calculated?

SV / EDV x 100% Signup and view all the answers

What effect do thyroid hormones and catecholamines have on stroke volume?

They increase stroke volume Signup and view all the answers

According to the Frank-Starling Law, how does an increase in preload affect stroke volume?

It increases stroke volume Signup and view all the answers

What is considered a positive inotropic effect?

Increased contractility of the heart muscle Signup and view all the answers

Which statement about stroke volume and gender is accurate?

Stroke volume of males is greater than that of females Signup and view all the answers

What happens to stroke volume during sleep?

It decreases Signup and view all the answers

How do chemoreceptors affect stroke volume?

By increasing stroke volume Signup and view all the answers

What is the definition of cardiac output?

The volume of blood ejected by each ventricle per minute. Signup and view all the answers

What factors can normally affect cardiac output?

Age, gender, and physical activity Signup and view all the answers

Which of the following equations represents the control of cardiac output?

COP = HR x SV Signup and view all the answers

Which heart rate condition is characterized by a heart rate greater than 100 beats per minute?

Tachycardia Signup and view all the answers

How do neural factors generally influence heart rate?

Sympathetic nervous system increases HR, parasympathetic decreases HR Signup and view all the answers

What effect do hormones like thyroid hormones and catecholamines have on heart rate?

They increase the heart rate. Signup and view all the answers

In which situation would a very high heart rate negatively impact cardiac output?

When there is less time for the heart to fill, reducing stroke volume Signup and view all the answers

What is the normal range for heart rate in resting adults?

60-100 beats per minute Signup and view all the answers

Study Notes

Cardiac Output

Cardiac output (COP) is the volume of blood ejected by each ventricle per minute.
In a healthy young male at rest, COP equals 5 L/min.
Cardiac index is COP divided by surface area.
Normal cardiac index is 2.5 to 4 L/min/m².
COP is affected by age, gender, and physical activity.

Control of Cardiac Output

COP = Heart rate (HR) x Stroke volume (SV)
Changes in HR or SV affect COP.

Heart Rate

Average heart rate is 60-100 beats/minute.
Above 100 bpm is tachycardia.
Below 60 bpm is bradycardia.
Factors affecting HR are described as chronotropic effects.

Normal Heart Rate Variations

Age: HR decreases with age.
Gender: Females generally have a slightly higher HR than males.
Sleep: HR decreases during sleep.
Training: Athletes have a lower resting HR.
Neural Factors:
- Sympathetic increases HR.
- Parasympathetic decreases HR.
- Chemoreceptors increase HR.
- Baroreceptors decrease HR.
- Bainbridge effect increases HR.

Hormones and Physical Factors Affecting Heart Rate

Hormones (thyroid and catecholamines) increase HR.
Fever or high temperature increase HR.

Heart Rate and Cardiac Output

High heart rate = less time for cardiac filling = reduced stroke volume and COP.

Stroke Volume

Stroke volume (SV) is the volume of blood ejected by each ventricle in each beat.
SV = End diastolic volume (EDV) – End systolic volume (ESV).
Normal SV is approximately 70 mL.

Stroke Volume Variations

Age: SV increases with age.
Gender: Males generally have a higher SV than females.
Sleep: SV decreases during sleep.
Exercise: SV is higher in athletes.
Neural Factors:
- Sympathetic increases SV.
- Parasympathetic has no direct effect on SV.
- Chemoreceptors increase SV.
- Baroreceptors decrease SV.
Hormones and Physical Factors:
- Thyroid and catecholamines increase SV.
- Fever or high temperature increase SV.

Ejection Fraction (EF)

EF = SV/EDV x 100%
Normal EF is approximately 65%.
A sensitive indicator of myocardial contractility.
EF decreases in heart failure.

Preload

Preload is the tension in the ventricular muscle before contraction.
Preload equals end-diastolic volume (EDV).
Increased venous return results in increased preload.
Increased preload results in increased stroke volume.
Frank-Starling Law: As preload increases, the force of contraction increases.
Chronic high preload can lead to cardiac muscle dilatation and heart failure.

Afterload

Afterload is the resistance the ventricle must overcome to eject blood.
High afterload is associated with hypertension and aortic valve stenosis.

Measurement of Cardiac Output

Indirect methods: Indicator dilution technique, Fick principle, and thermodilution method.
Direct methods: Electromagnetic or ultrasonic flow-meter devices.
Hamilton dye dilution method: Dye injected into vein, arterial samples taken to measure dye concentration over time. COP calculated using dye dilution formulas.
Fick principle: Blood flow to an organ can be calculated by measuring consumption or addition of a substance by that organ (e.g. oxygen)
Cardiac output is measured using Fick's principle, where cardiac output is estimated by measuring the rate of oxygen consumption by the lungs and the differences in oxygen concentration between arterial and venous blood. Using the principle, the cardiac output (COP), can be calculated from the amount of oxygen consumed (or added) by the lungs in a given time. For example, if the lungs consume 250 ml of oxygen per minute, and the difference in oxygen concentration between arterial and venous blood is 50 ml/L, then the cardiac output is 250 ml/min / (50 ml/L) = 5 L/min, in a male adult at rest.

Venous Return

Venous return is the volume of blood returning to the heart per minute.
Normal venous return is 5 L/min.
Factors affecting venous return include:
- Pressure Gradient (arteries > capillaries > veins).
- Blood Volume (reduced by bleeding).
- Venomotor Tone (constriction increases return; dilation decreases return).
- Muscle Pump and Respiratory Pump.
- Gravity (standing decreases return).
- Valvular Lesions/Pericardial Effusion (decrease return).

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Description

This quiz covers the concepts of cardiac output (COP) and its control mechanisms, including heart rate and stroke volume. Understand how factors like age, gender, and physical activity influence COP and heart rate variations. Explore the physiological principles that govern these vital signs in human health.