Cardiovascular | Cardiac Cycle: Digital Version

Introduction to the Cardiac Cycle

In this section, the speaker introduces the topic of the cardiac cycle and encourages viewers to follow along with a provided picture.

The Cardiac Cycle Phases

• The speaker explains that they will go through each phase of the cardiac cycle.

• The first phase is mid to late ventricular diastole, which indicates that the heart is relaxing and filling with blood from the superior vena cava, inferior vena cava, coronary sinus, and pulmonary veins.

• Blood flows from the atria into the ventricles through open valves (tricuspid valve and mitral valve), aided by gravity.

• After passive filling, when 70-80% of blood has flowed down into the ventricles, atrial contraction occurs. This increases pressure in the atria and overcomes ventricular pressure.

Valve Opening and Blood Flow

• As atrial pressure becomes greater than ventricular pressure, both AV valves (mitral valve and tricuspid valve) open further.

• Due to relaxed myocardium and loose papillary muscles, these valves are naturally open during relaxation. This allows blood to flow passively into the ventricles.

• Approximately 70-80% of blood flows passively from atria to ventricles through open valves before atrial contraction.

Pressure Differences in Atria and Ventricles

• Atrial contraction leads to increased pressure inside the atria compared to ventricles due to Boyle's law.

• Atrial pressure becomes greater than ventricular pressure, causing the mitral and tricuspid valves to open fully.

• Ventricles receive blood from atria while in relaxation, resulting in low ventricular pressure (close to zero).

Pressure Differences in Arteries

• The pulmonary trunk pressure is greater than right ventricular pressure, while aortic pressure is greater than left ventricular pressure.

• Valves (pulmonary semilunar valve and aortic semilunar valve) allow blood flow out of the ventricles into the arteries in one direction only.

The transcript provided does not cover the entire cardiac cycle.

New Section

This section discusses the importance of open sound valves and the absence of sound in a healthy state. It also explains the relationship between atrial contraction, depolarization, and the P wave on an EKG.

Sound Valves and Atrial Contraction

• The absence of sound indicates a healthy state.

• If there is sound, it may indicate pathology.

• Atrial contraction occurs after depolarization, which is represented by the P wave on an EKG.

• The P wave usually appears towards the end of ventricular diastole.

New Section

This section explains isovolumetric contraction during ventricular contraction and its significance in terms of blood flow.

Isovolumetric Contraction

• Isovolumetric contraction refers to ventricular contraction with no blood entering or leaving the ventricles.

• During this phase, pressure inside the ventricles increases as myocytes depolarize.

• The right ventricle's pressure may increase to 4 mmHg, while the left ventricle's pressure may rise to 25 mmHg.

• As a result, the pressure in both ventricles becomes greater than that in their respective atria.

• The tricuspid and mitral valves close due to increasing pressure, allowing for one-way flow from atria to ventricles only.

New Section

This section discusses how increasing ventricular pressure leads to valve closure and introduces heart sounds.

Valve Closure

• Increasing ventricular pressure causes closure of tricuspid and mitral valves (also known as AV valves).

• The closure of these valves produces a heart sound called S1 or "lub."

• S1 is a normal heart sound associated with valve closure during ventricular contraction.

New Section

This section explains the relationship between ventricular pressure and arterial pressure, leading to valve opening or closure.

Ventricular Pressure and Arterial Pressure

• Ventricles contract and attempt to pump blood out.

• For blood to be pumped out, ventricular pressure must be greater than arterial pressure.

• The aortic pressure is around 80 mmHg during diastole, while the pulmonary trunk pressure is approximately 10 mmHg.

• If ventricular pressure is less than arterial pressure, the aortic and pulmonic valves remain closed.

New Section

This section discusses depolarization of the ventricles and its representation on an EKG as the QRS complex.

Depolarization of Ventricles

• Ventricles depolarize during mid to late ventricular systole.

• Depolarization is represented by the QRS complex on an EKG.

• This phase corresponds to continued ventricular contraction with increasing but still insufficient pressure to overcome arterial pressure.

New Section

This section explains the ongoing contraction of the ventricles during mid to late ventricular systole.

Continued Ventricular Contraction

• The ventricles continue contracting during mid to late ventricular systole.

• The right ventricle's pressure may reach 25 mmHg, while the left ventricle's pressure can rise up to 120 mmHg.

• Comparatively, aortic pressure is around 80 mmHg, and pulmonary trunk pressure is approximately 10 mmHg.

Ventricular Pressure and Valve Closure

In this section, the focus is on the relationship between ventricular pressure and valve closure.

Ventricular Pressure Greater than Atrial Pressure

• The ventricular pressure is greater than the atrial pressure.

• As a result, both the mitral valve and tricuspid valve should be closed during this phase.

Sound Production during Isovolumetric Contraction

• The snapping shut of the mitral valve and tricuspid valve during isovolumetric contraction causes a sound.

• This sound indicates that these valves are closed.

• During mid to late ventricular systole, there should be no sound if everything is normal.

Ventricular Pressure Greater than Arterial Pressure

• The ventricular pressure (25 mmHg) is greater than the arterial pressure (10 mmHg).

• This pressure gradient allows blood to flow out of the ventricles and into the arteries.

Semilunar Valve Opening

• The aortic valve and pulmonic valve open when the ventricular pressure exceeds arterial pressure.

• There should be no sound during this phase if everything is normal.

Isovolumetric Relaxation

This section discusses isovolumetric relaxation, where there is no change in volume while the heart is in relaxation.

Volume Unchanged during Relaxation

• During isovolumetric relaxation, there is no change in volume in the ventricles.

• No blood enters or leaves the ventricles during this phase.

Trending Back towards Zero Pressure

• As relaxation progresses, ventricular pressure starts trending back towards zero.

• Although not yet at zero, at this point, ventricular pressure remains greater than atrial pressure.

Mitral and Tricuspid Valve Closure

• Since ventricular pressure is still greater than atrial pressure, the mitral and tricuspid valves remain closed.

• There should be no sound during this phase if everything is normal.

Ventricles Compared to Aorta

This section focuses on the comparison between ventricular pressure and aortic pressure.

Aortic Filling with Blood

• The aorta starts filling with blood during this period.

• As the ventricles contract and pump blood into the aorta, its pressure increases.

Ventricular Pressure Drops below Arterial Pressure

• As ventricular pressure drops below arterial pressure (80 mmHg), the semilunar valves start closing.

• These valves only allow one-way blood flow out of the ventricles and into the arteries.

Second Heart Sound (S2)

• When the aortic valve and pulmonic valve snap shut, it produces a sound known as S2 or "dub."

• S2 is a normal heart sound, but any other sounds may indicate pathology.

Conclusion

The transcript provides an overview of ventricular pressure changes, valve closure, and sound production during different phases of cardiac contraction and relaxation. It emphasizes the relationship between pressures in the heart chambers and how it affects valve function. Understanding these concepts helps in identifying normal heart sounds and potential pathologies.

New Section Cardiac Cycle Overview

This section provides an overview of the cardiac cycle and its importance in understanding the functioning of the heart.

Understanding the Cardiac Cycle

• The cardiac cycle is a series of events that occur during one heartbeat.

• It involves both mechanical and electrical processes.

• The cycle consists of two main phases: diastole and systole.

• Diastole is the relaxation phase, where the heart chambers fill with blood.

• Systole is the contraction phase, where blood is pumped out of the heart.

Key Points about the Cardiac Cycle

• The cardiac cycle video provides a clear explanation of how the heart functions.

• It aims to help viewers understand and clarify any confusion they may have had about this topic.

• Viewers are encouraged to like, comment, and subscribe to support the creators' work.

• Links to social media platforms and donation pages are provided for further engagement.

Conclusion

The cardiac cycle video offers valuable insights into understanding how the heart works. By explaining key concepts such as diastole and systole, it helps viewers grasp the mechanics behind each heartbeat. Engaging with the creators through likes, comments, subscriptions, or donations can support their efforts in producing high-quality educational content.