Aula: Fisiologia Cardíaca - Ciclo Cardíaco | Fisiologia Cardiovascular Humana #1

Summary

This video delves into the cardiac cycle, explaining how blood flows through the heart during the phases of contraction (systole) and relaxation (diastole). It highlights the processes of ejection, filling, and the pressure-volume changes that occur, alongside key measurements such as stroke volume, ejection fraction, and cardiac output. The importance of heart sounds, especially in pathological conditions, is discussed, and the role of the electrocardiogram (ECG) in monitoring the heart’s electrical activity is also touched upon. The video offers a comprehensive overview of heart physiology, crucial for understanding cardiovascular health.

Takeaways

• 😀 The cardiac cycle consists of multiple phases, including rapid filling, slow filling, and atrial contraction.
• 😀 The ejection fraction of a healthy adult is typically around 60%, which is the percentage of blood ejected from the ventricles during systole.
• 😀 The end-diastolic volume (EDV) represents the total blood volume in the ventricles at the end of diastole, while the end-systolic volume (ESV) represents the remaining blood volume after systole.
• 😀 Stroke volume is the amount of blood ejected by the heart with each contraction, and it is a key measure of cardiac function.
• 😀 Cardiac output (CO) is the amount of blood pumped by the heart per minute and is calculated as stroke volume multiplied by heart rate.
• 😀 For a healthy adult weighing around 70 kg, cardiac output is typically around 5 liters per minute, calculated from a stroke volume of approximately 70 ml and a heart rate of 70 beats per minute.
• 😀 The phases of ventricular filling include the rapid filling phase (which accounts for 70% of ventricular filling), the slow filling phase (10%), and the atrial contraction phase (20%).
• 😀 The phases of systole and diastole include contraction and relaxation of the ventricles, where pressure changes drive the movement of blood.
• 😀 The concept of 'ventricular relaxation' (isovolumetric relaxation) occurs after systole when the ventricles relax but the volume remains constant, and pressure falls.
• 😀 The electrocardiogram (ECG) waveform has distinct phases: P wave (atrial depolarization), QRS complex (ventricular depolarization), and T wave (ventricular repolarization), each corresponding to key events in the cardiac cycle.

Q & A

What is the cardiac cycle?

The cardiac cycle is the sequence of events that occurs during one complete heartbeat. It involves the contraction (systole) and relaxation (diastole) of the heart chambers, leading to the ejection and filling of blood.

What happens during the systolic phase of the cardiac cycle?

During systole, the ventricles contract, increasing the pressure inside them and pushing blood into the arteries. This phase is responsible for the ejection of blood from the heart.

What is the diastolic phase and why is it important?

The diastolic phase is when the heart relaxes after contraction, allowing the ventricles to refill with blood. This phase is crucial for maintaining proper blood volume and pressure for the next cycle.

What is meant by the 'ejection fraction'?

Ejection fraction refers to the percentage of blood that is ejected from the ventricles during systole. A normal ejection fraction is typically around 60%, meaning 60% of the blood in the ventricles is pumped out.

How is 'cardiac output' calculated?

Cardiac output is the amount of blood the heart pumps per minute. It is calculated by multiplying the heart rate (beats per minute) by stroke volume (the volume of blood ejected with each beat).

What is the 'stroke volume' in the context of the cardiac cycle?

Stroke volume is the volume of blood that is ejected from the ventricles during each heartbeat. It is an important determinant of cardiac output.

What is the role of the heart's 'muscle' in blood circulation?

The heart's muscle, including the smooth muscle in the arteries, plays a critical role in contracting and maintaining blood pressure during the cardiac cycle. This ensures efficient blood flow through the circulatory system.

What does the term 'volume end-systolic' refer to?

The 'volume end-systolic' refers to the amount of blood remaining in the ventricles after the heart has completed systole, i.e., the end of the contraction phase. It typically remains around 50 ml in a healthy adult.

What are the phases of ventricular filling?

The phases of ventricular filling include rapid filling (about 70% of the blood volume), slow filling (around 10%), and atrial contraction (about 20%), which together ensure the ventricles are fully filled before the next contraction.

What is the relationship between the ECG waves and the cardiac cycle?

The ECG provides a graphical representation of the electrical activity of the heart. The P-wave corresponds to atrial depolarization, the QRS complex to ventricular depolarization, and the T-wave to ventricular repolarization, each aligning with specific events in the cardiac cycle.