Cardiac Cycle Overview

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Questions and Answers

Which wave in the atrial pressure tracing is associated with atrial contraction?

C wave

Y wave

A wave (correct)

X wave

What is the main effect of negative inotropic agents on muscle contraction?

Enhance force of contraction

Reduce the force of contraction (correct)

Have no effect on muscle contraction

Increase sarcomere shortening

Which event is linked to the X descent in the atrial pressure tracing?

Atrial contraction

Passive filling of the atria

Bulging of the tricuspid valve

Atrial relaxation (correct)

In isovolumetric contraction, what characteristic is observed?

Volume remains constant while pressure changes Signup and view all the answers

What does the V wave in the atrial pressure tracing represent?

Passive filling of the atria Signup and view all the answers

What primarily determines the stroke volume during the cardiac cycle?

Contractility, preload, and afterload Signup and view all the answers

Which statement about isovolumetric phases of the cardiac cycle is correct?

Both atrioventricular and semilunar valves are closed during isovolumetric contraction. Signup and view all the answers

How does increased sympathetic nervous system stimulation affect cardiac contraction?

It enhances inotropy and increases the force of contraction. Signup and view all the answers

What is the physiological basis of how preload influences stroke volume?

Increased preload optimizes overlap between actin and myosin filaments. Signup and view all the answers

Which factor is a primary determinant of afterload?

Systemic vascular resistance and arterial pressure Signup and view all the answers

What role does the phonocardiogram play in cardiac physiology?

It captures the sounds associated with heart valves closing. Signup and view all the answers

In the context of the cardiac cycle, what does the end-systolic volume indicate?

The volume of blood remaining in the ventricles after contraction Signup and view all the answers

Which of the following factors is NOT considered a positive inotropic agent?

Atenolol Signup and view all the answers

What occurs to stroke volume when afterload increases?

Stroke volume decreases and ejection fraction decreases. Signup and view all the answers

In the pressure-volume loop, what does a more vertical ESPVR line indicate?

Higher inotropic state. Signup and view all the answers

What primarily determines afterload in the context of cardiac physiology?

Tension needed to open the aortic valve. Signup and view all the answers

Which of the following factors affects the total cardiac workload based on the pressure-volume loop?

Area within the pressure-volume loop. Signup and view all the answers

What is the normal pulmonary artery pressure?

25/7 mm Hg Signup and view all the answers

How does increasing afterload affect myocardial oxygen demand compared to increasing inotropy?

Increases more than with inotropy changes. Signup and view all the answers

Which of the following correctly defines stroke volume?

The volume of blood ejected during each heartbeat Signup and view all the answers

What is the relationship described by Laplace’s law concerning wall tension?

Wall tension increases as wall thickness decreases. Signup and view all the answers

Which aspect of the heart's workload is considered the minority when comparing pressure-volume work and kinetic energy?

Kinetic energy related to ejecting blood. Signup and view all the answers

What does ejection fraction (EF) represent?

The proportion of end-diastolic volume ejected during each heartbeat Signup and view all the answers

Which parameter is NOT a factor that impacts stroke volume?

Heart rate Signup and view all the answers

What does the distance between line AD and CB represent in the context of stroke volume?

The stroke volume itself. Signup and view all the answers

What does end diastolic volume (EDV) directly correspond to in the heart's functioning?

Preload Signup and view all the answers

What is the significance of ejection fraction in heart function assessment?

It is often measured as an estimate of heart function in heart failure. Signup and view all the answers

Which parameter is NOT typically measured in a ventricular pressure-volume loop?

Blood oxygen saturation Signup and view all the answers

Which phase of the pressure-volume loop corresponds to the phase where contraction occurs without a change in volume?

From B to C Signup and view all the answers

What happens during the transition from point D to A in the pressure-volume loop?

The ventricle relaxes but does not yet fill. Signup and view all the answers

What does increased afterload typically result from?

Aortic stenosis and elevated blood pressure. Signup and view all the answers

Study Notes

Cardiac Cycle:

The force of contraction in a cardiomyocyte is influenced by the amount of calcium available to bind to troponin (inotropy) and preload (optimal actin and myosin overlap during diastole).
Increased inotropy can be stimulated by the sympathetic nervous system, increased heart rate, thyroid hormone, and cortisol.
Preload is determined by the extent of ventricular filling.
The Wiggers diagram is a graphical representation of the cardiac cycle, including ventricular pressures, an electrocardiogram (ECG), ventricular volume, and phonocardiogram.
The Wiggers diagram shows the key landmarks of the cardiac cycle: the a, c, and v waves and x and y descents of the atrial pressure tracing.
The Wiggers diagram also displays the isovolumetric contraction and relaxation phases of the ventricular cycle, and the changes in ventricular volume during systole and diastole.
The a wave corresponds to atrial contraction, the c wave to the bulging of the tricuspid valve, the x descent to atrial relaxation, the v wave to passive filling of the atria, and the y descent to the emptying of the atria into the ventricles.
The right ventricle pumps the same amount of blood per minute as the left ventricle, although it develops lower pressures due to its thinner walls and its connection to the pulmonary circulation.
The pressure-volume loop is used to assess the workload of the ventricle, contractility, and compliance of the heart.
The area within the pressure-volume loop represents the total workload of the ventricle.
The slope of the end-systolic pressure-volume relationship (ESPVR) reflects the inotropic state of the ventricle.
Increased afterload reduces stroke volume and ejection fraction, and increases myocardial oxygen demand.
The Ventricular Pressure-Volume Loop is a visual representation of the cardiac cycle, tracking pressure and volume changes in the ventricle throughout systole and diastole.
Key points of this loop include:
- Point A: End of diastole, ventricle at low volume, beginning of filling.
- Point B: End of filling, ventricle at maximum volume (EDV).
- Point C: Beginning of isovolumetric contraction.
- Point D: Beginning of ejection, ventricle at maximum pressure.
- Point A: End of ejection, ventricle at lowest volume (ESV) and beginning of relaxation.
The length of the loop reflects stroke volume, which is influenced by preload, afterload, and contractility.
Preload is represented by point B (EDV) on the Pressure-Volume Loop.
Afterload is represented by the purple line, indicating the pressure that the heart must overcome to eject blood.
Higher afterload leads to more vertical purple line, indicating a more difficult workloadfor the heart.
Inotropy (contractility) is represented by the tangent line at point D (ESPVR).
A steeper tangent line indicates higher inotropic state.
Negative inotropic agents reduce the force of contraction, leading to reduced sarcomere shortening.

Cardiac Calculations and Parameters:

End diastolic volume (EDV) is the volume in the ventricle at the end of diastole.
End systolic volume (ESV) is the volume in the ventricle at the end of systole.
Stroke volume (SV) is the volume of blood ejected with each heartbeat (SV = EDV - ESV).
Cardiac Output (CO) is the volume of blood ejected per minute (CO = SV x HR).
Ejection fraction (EF) is the proportion of EDV that is ejected during systole (EF = SV/EDV = (EDV - ESV)/EDV).
EDV corresponds to preload. Increasing preload can increase contractility.
Stroke volume is impacted by preload, contractility (inotropy), and afterload.
Afterload is the pressure that the ventricle must overcome to eject blood.
Ejection fraction is a common measure of heart function.

Key Facts & Figures:

Normal pulmonary artery pressure is ~ 25/7 mm Hg.
Normal atrial pressures are slightly lower in the right atrium than the left atrium.
The pressure-volume curve displays systolic and diastolic blood pressure, EDV, ESV, stroke volume, contractility, afterload, and preload.
The majority of work performed by the ventricle is pressure-volume work.
Cardiac workload primarily stems from pressure-volume work, with minimal kinetic energy involved in ejecting blood.
Hypertension increases myocardial oxygen demand.
Cardiac output is a key factor in delivering oxygen and nutrients to tissues.
Wall tension can be calculated using Laplace’s law: Wall stress (σ) = (Pressure x Radius) / Wall thickness.
Cardiac output is influenced by both heart rate and stroke volume.

Heart Failure:

Hearts that work excessively under strain endure molecular and histological changes.
Compensation mechanisms in heart failure often compromise the force of contraction.
Ejection fraction is an important indicator of heart function in heart failure.

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Description

Explore the key concepts of the cardiac cycle, including inotropy, preload, and the graphical representation through the Wiggers diagram. Understand how these factors influence heart function, including the role of calcium and the phases of ventricular contraction and relaxation. This quiz will test your knowledge of these fundamental cardiovascular principles.