Cardiac Cycle and Pressure-Volume Relationship

Pressure, Volume, Time Relation in the Heart

• The lecture details the pressure-volume-time relationship in the cardiac cycle.
• Learning objectives for Theme 15 include identifying phases of the cardiac cycle, explaining the atrial pressure curve, defining systolic, diastolic, and pulse pressure, and calculating ejection fraction.
• Objective 9 involves drawing and labeling a pressure curve for a complete cardiac cycle during contraction , defining the opening and closing of valves, and identifying the first and second heart sounds.

Cardiac Cycle Phases

• The cardiac cycle describes the events that start from one heartbeat's start to the next.
• The cardiac cycle involves phases like diastole and systole, including isovolumetric contraction, rapid ejection, slow ejection, isovolumetric relaxation, rapid/slow filling, and atrial systole.
• Ventricular diastole has two phases where both sets of chambers are relaxed, and ventricles filling passively(Late Diastole). Atrial contraction forces additional blood into the ventricles (Atrial Systole)
• The cardiac cycle demonstrates the changing pressure and volume during heart contractions.
• Isovolumetric contraction is the initial phase of ventricular contraction where the ventricles contract, increasing pressure but volume remains constant as the AV valves close.
• Rapid ejection is the subsequent phase marked by opening of the aortic valve, rapid filling of the aorta, pressure rise, and eventual volume reduction.
• Isovolumic relaxation is when the ventricular pressure drops below aortic pressure, the aortic valve closes, and all valves are closed as the ventricles repolarize.
• Rapid/slow filling occurs as the AV valves open and blood passively flows into relaxed ventricles.
• Atrial systole finishes filling the ventricles.

Cardiac Cycle Measurements

• End diastolic volume (EDV) is the heart volume at the end of ventricular diastole, typically 120-135mL.
• End systolic volume (ESV) is the heart volume at the end of ventricular systole, usually around 50 mL.
• Stroke volume (SV) is the volume ejected from the heart during a single contraction (EDV-ESV).

Ejection Fraction

• Ejection fraction (EF) is the percentage of the end-diastolic volume ejected.

Heart Sounds and Valves

• Heart valve closures produce characteristic sounds.
• The different phases of the cardiac cycle (contraction and relaxation, and the opening and closing of valves) generate the heart sounds (S1 and S2).

Atrial Pressure Curves

• "A wave" depicts atrial contraction during the late phase of ventricular diastole.
• "C wave" is due to AV valve backflow.
• "V wave" is caused by atrial filling while AV valves are closed.

Definitions of Pressure Measurements

• Systolic pressure - maximum pressure during ventricular contraction.
• Diastolic pressure - maximum pressure before ventricular contraction
• Pulse pressure - difference between systolic and diastolic pressures

Theme 18 and Work Loop

• Theme 18 is about work loop (pressure/volume relation) during a cardiac cycle, stroke volume vs. stroke work, and identifying stroke volume/ stroke work from a pressure-volume loop.

Figure Interpretation

• Figure A does NOT show ventricular systole.
• Figure B shows ventricular systole, where the ventricles are contracting to push blood out.

Discussion of Pages and their Information

• Note the diagrams and charts, linking terminology, functions, and physical heart parameters.

Explore the intricate relationship between pressure and volume during the cardiac cycle in this quiz. Understand the phases of the cardiac cycle, the significance of atrial pressure curves, and important metrics like systolic and diastolic pressures. This quiz also tests your ability to identify heart sounds and calculate ejection fractions.