🫀 [#3] CICLO CARDÍACO: DIAGRAMA PRESSÃO-VOLUME OU VOLUME-PRESSÃO | MK Fisiologia

Summary

In this video, Miriam Curauch explains the cardiac cycle using the pressure-volume diagram to illustrate the heart's performance during a beat. She walks through each phase of the cycle—ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation—highlighting how pressure and volume in the left ventricle change. The video also explores how to calculate important cardiac metrics like stroke volume and ejection fraction, as well as the factors affecting heart function. By understanding the pressure-volume loop, viewers gain insight into how variations in pressure affect cardiac efficiency.

Takeaways

• 😀 The video explains the concept of the cardiac cycle, focusing on the pressure-volume diagram or the volume-pressure diagram.
• 😀 The diagram visually represents the variations in pressure and volume in the left ventricle during a cardiac cycle.
• 😀 The pressure-volume diagram shows a loop or loop-shaped curve, representing the relationship between pressure and volume during the cardiac cycle.
• 😀 The four main phases of the cardiac cycle are: ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation.
• 😀 The diagram starts with the opening of the mitral valve, marking the beginning of the ventricular filling phase.
• 😀 During the isovolumetric contraction phase, the pressure increases without a change in ventricular volume as all valves are closed.
• 😀 The ventricular ejection phase starts when the aortic valve opens, leading to a rapid decrease in ventricular volume as blood is ejected.
• 😀 The isovolumetric relaxation phase occurs after the aortic valve closes, during which the ventricle relaxes without a change in blood volume.
• 😀 The video explains how the pressure-volume diagram can be used to calculate key heart performance metrics like stroke volume and ejection fraction.
• 😀 The stroke volume is calculated as the difference between the end-diastolic volume (EDV) and end-systolic volume (ESV).
• 😀 The video discusses how the pressure-volume loop can change based on different experimental pressure curves, affecting heart performance.

Q & A

What is the pressure-volume diagram (P-V diagram) used for in the context of cardiac physiology?

The pressure-volume (P-V) diagram is used to visualize the variations in pressure and volume within the left ventricle during the cardiac cycle. It helps understand how the heart functions as a pump, showing the different phases of ventricular contraction and relaxation.

How is the pressure-volume diagram created?

The pressure-volume diagram is created by plotting the pressure (on the Y-axis) and the volume (on the X-axis) of the left ventricle at various points throughout the cardiac cycle. These points are obtained by measuring the pressure and volume at different stages of the cycle.

What is the significance of the loop formed in the pressure-volume diagram?

The loop formed in the P-V diagram represents the changes in pressure and volume in the left ventricle during the cardiac cycle. This loop helps in understanding the mechanical events of the heart, such as filling, contraction, ejection, and relaxation.

What is the first phase of the cardiac cycle shown in the P-V diagram?

The first phase of the cardiac cycle shown in the P-V diagram is the 'ventricular filling' phase, which begins when the mitral valve opens, allowing blood to flow from the atrium into the ventricle. This phase is characterized by an increase in the volume of the left ventricle.

What happens at point B in the pressure-volume diagram?

At point B, the mitral valve closes, marking the end of the ventricular filling phase and the beginning of the isovolumetric contraction phase. During this phase, the pressure in the ventricle increases without a change in volume, as all the heart valves are closed.

What occurs at point C in the P-V diagram?

At point C, the aortic valve opens, initiating the ventricular ejection phase. During this phase, the pressure in the ventricle increases rapidly while the volume decreases as blood is ejected into the aorta.

What is the role of the aortic valve closure in the pressure-volume diagram?

The closure of the aortic valve, represented by point D in the P-V diagram, marks the end of the ventricular ejection phase and the start of the isovolumetric relaxation phase. After the aortic valve closes, the ventricular muscle relaxes, and the pressure begins to decrease.

What is the difference between isovolumetric contraction and isovolumetric relaxation?

Isovolumetric contraction occurs when the ventricle contracts with all valves closed, causing an increase in pressure without a change in volume. Isovolumetric relaxation, on the other hand, occurs when the ventricle relaxes with all valves closed, causing a decrease in pressure while the volume remains constant.

How can the stroke volume be calculated using the pressure-volume diagram?

The stroke volume can be calculated by subtracting the end-systolic volume (the volume of blood left in the ventricle after ejection) from the end-diastolic volume (the volume of blood in the ventricle at the end of filling). This difference represents the volume of blood ejected by the ventricle during each heartbeat.

What factors influence the performance of the heart as a pump according to the pressure-volume diagram?

The performance of the heart as a pump can be influenced by factors such as the end-diastolic volume, end-systolic volume, and the ventricular pressure curves (diastolic and systolic). Changes in these parameters affect the heart's ability to pump blood effectively, altering stroke volume and ejection fraction.