Cardiac Cycle (Pressure-Graph Visually Explained) | Heart Physiology

Cardiomyocyte QUIZ:    • Cardiac Cycle QUIZ  

Content:
0:00 Introduction
0:46 What is Cardiac Cycle?
01:47 5 Phases of Cardiac Cycle
03:33 Bottle Cap Phenomenon
04:59 Pressure-Time Graph
05:29 Atrial Systole
07:05 Isovolumetric Contraction
08:28 Ejection
11:45 Isovolumetric Relaxation
13:05 Passive Filling
14:14 Active Filling
14:48 Valves
15:16 Phonocardiogram
18:20 Ventricular Volumes
22:08 Next video
22:46 QUIZ

Welcome to Taim Talks Cardio

🫀 Join me:    / @taimtalksmed  
📷 Follow my IG:   / taimtalksmed  

Complete Cheat Code for Heart Physiology series:
1st Video: Types of cardiac muscle, action potentials of pacemaker cells and contractile myocardium, and general properties of cardiomyocytes.
2nd Video: Detailed exploration of the cardiac cycle, including phase-by-phase events, valve operations, and pressure differences.
3rd Video: Cardiac output.
4th Video: Regulation of heartbeat

The cardiac cycle refers to the series of mechanical events occurring within one heartbeat. It includes the phases of contraction (systole) and relaxation (diastole) of the heart muscle.

Phases of the Cardiac Cycle
Five phases:
Atrial Systole: Both atria contract, pushing blood into the ventricles. This phase lasts about 0.1 seconds.
Isovolumetric Contraction: The ventricles contract with no blood flow out as all valves are closed, lasting about 0.04 seconds.
Ventricular Ejection: Ventricles push blood into the pulmonary trunk and aorta, lasting about 0.26 seconds. Together with isovolumetric contraction, ventricular contraction lasts about 0.3 seconds.
Isovolumetric Relaxation: All chambers relax, with no blood flow into the ventricles but passive blood flow into the atria, lasting about 0.08 seconds.
Passive Filling: AV valves open, allowing blood to flow passively into the ventricles without atrial contraction, lasting about 0.32 seconds.

Valve Operations and Pressure Differences
Bottle Cap Phenomenon:
The video explains how pressure differences control valve operations during each phase. Using a simple analogy with a bottle and a cap, it demonstrates how pressure inside the bottle (heart chambers) relative to the outside (other chambers) determines whether the cap (valve) opens or closes.

Pressure Curve and Graphical Representation
Vertical Axis: Blood pressure in mmHg.
Horizontal Axis: Time in seconds.
Red: Left ventricular pressure.
Blue: Left atrial pressure.
Yellow: Aortic pressure.

Atrial Systole
During atrial systole, atrial pressure is higher than ventricular pressure, keeping AV valves open and semilunar valves closed, pushing blood into the ventricles.

Isovolumetric Contraction
In this phase, ventricular pressure rises sharply without blood movement, as both AV and semilunar valves remain closed.

Ventricular Ejection
Here, the ventricles contract, pushing blood into the great arteries. The atrial pressure dynamics are also explained, emphasizing the role of the AV plane in venous return.

Isovolumetric Relaxation
During this phase, the ventricles relax, and pressures fall. Both AV and semilunar valves remain closed initially. Brief rise in aortic pressure due to blood flow back into the semilunar valve pockets before decreasing as blood continues to the periphery.

Passive Filling
In this final phase, atrial pressure exceeds ventricular pressure, opening the AV valves and allowing blood to flow passively into the ventricles.

Heart Sounds
First Heart Sound (S1): Heard at the beginning of ventricular systole due to AV valve closure, blood vibrations, and semilunar valve opening.
Second Heart Sound (S2): Heard at the beginning of diastole due to semilunar valve closure.
Third Heart Sound (S3): Recorded at the beginning of the filling phase due to blood flowing into the ventricles.
Fourth Heart Sound (S4): Recorded during atrial systole due to strong atrial contraction.

Ventricular Volumes
End Diastolic Volume (EDV): Maximum blood volume in the ventricles at the end of diastole (110-150 ml).
Stroke Volume (SV): Blood volume ejected during one cycle (60-100 ml).
Reserve Volume: Additional volume ejected during strong contractions (20-40 ml).
Residual Volume: Volume never ejected from ventricles.
Reserve and residual volumes form the End Systolic Volume (ESV).
Ejection Fraction (EF), the percentage of EDV ejected, normally 50-70%. Heart failure affects EF, reducing it below 50%.

#cardiacphysiology #heartfunction #cardiaccycle #ecg #medicaleducation #usmlepreparation
#nursingeducation #premed #heartanatomy

Sources:
University lectures and notes
Barrett, K. E., Barman, S. M., Boitano, S., & Brooks, H. L. (2016). Ganong's review of medical physiology (25th ed.). McGraw-Hill Education.
Hall, J. E. (2016). Guyton and Hall textbook of medical physiology (13th ed.). Elsevier.
Mohrman, D. E., & Heller, L. J. (2014). Cardiovascular physiology (11th ed.). McGraw-Hill Education.
Biorender