Overview
This lecture explains the pressure, volume, heart sounds, and EKG changes during the cardiac cycle, focusing on the left side of the heart.
The Cardiac Cycle Pressure Graph
- The graph illustrates pressure changes in the left atrium, left ventricle, and aorta over time.
- Left ventricular pressure rises sharply during systole, exceeding aortic pressure to open semilunar valves.
- Atrial contraction causes a small bump in atrial pressure, pushing blood into the ventricle.
- AV valves close when ventricular pressure exceeds atrial pressure, causing the first heart sound ("lub").
- Semilunar valves close when aortic pressure exceeds ventricular pressure, causing the second heart sound ("dub").
- The dicrotic notch is a small dip in aortic pressure as blood rebounds against closed semilunar valves.
Phases of the Cardiac Cycle
- Isovolumetric contraction: all valves closed, ventricular pressure rises but no blood flows.
- Ejection phase: ventricular pressure exceeds aortic pressure, semilunar valves open, and blood is ejected.
- Isovolumetric relaxation: all valves closed, ventricular pressure falls until it equals atrial pressure.
- AV valves open once ventricular pressure drops below atrial pressure, allowing passive filling.
Heart Sounds and Valve Status
- "Lub" (S1): closure of AV (atrioventricular) valves at the start of ventricular systole.
- "Dub" (S2): closure of semilunar valves at the start of ventricular diastole.
- Dicrotic notch occurs just after semilunar valve closure in the aortic pressure curve.
Volume and EKG Relationships
- Ventricular volume decreases as pressure rises and blood is ejected.
- The QRS complex on the EKG represents ventricular depolarization, leading to contraction and decreasing volume.
- Volume is lowest in the ventricle after blood ejection when pressure is highest.
Key Terms & Definitions
- Atrial Systole — contraction of the atrium, pushing blood into the ventricle.
- Ventricular Systole — contraction of the ventricle, ejecting blood into the aorta.
- AV Valves — atrioventricular valves separate atria from ventricles; close for the "lub" sound.
- Semilunar Valves — valves at the base of the aorta and pulmonary trunk; close for the "dub" sound.
- Isovolumetric Phase — period when all heart valves are closed and volume in the ventricles stays the same.
- Dicrotic Notch — small dip in aortic pressure due to the rebound of blood against the closed semilunar valves.
- QRS Complex — part of the EKG representing ventricular depolarization.
Action Items / Next Steps
- Practice interpreting pressure, volume, and EKG graphs for the cardiac cycle.
- Review the phases and corresponding valve events in the cardiac cycle.
- Prepare for the next topic on cardio dynamics.