Lecture 10: Cardiac Cycles and Sounds Flashcards
What comes first electrical event or mechanical event?
Electrical (depolarization/repolarization)
What officially begins the cardiac cycle and what does this represent?
P wave. Atrial depolarization by SA node
How is the atrium depolarized?
SA node sends electrical impulse to AV node, depolarizing the cells of the atrium so it can contract
What is the PR interval, what does it represent and why is this important physiologically?
Delay of AP in the AV node. Ventricle basically waits for the atrium to finish it’s thing before doing anything so ventricular and atrial contraction don’t occur at the same time
How is the ventricle depolarized? What direction does this happen and why?
- AV Node is helped by bundles and Purkinje fibers to send impulses throughout the thick ventricle.
- Apex up. Efficient for ejecting blood from ventricle to vessel (ventricle has to squeeze the blood upwards)
What does the QRS complex represent?
Ventricular depolarization
What does the time delay between the QRS (depolarization) and the increase in ventricular pressure (contraction) represent?
Time lag between electrical and mechanical event
What does T wave represent?
Ventricular repolarization, this will be followed by ventricle relaxation
What does the X and Y axes of an ECG represent?
X: time (P wave to P wave)
Y: depends, can represent volume or pressure in the atrium, ventricle or aorta
What is the maximum time between 1 P-wave and the next?
1 second (=60 BPM, lowest normal HR)
What needs to happen to pass the blood from one chamber to another?
Pressure from the previous chamber needs to exceed the pressure of the next chamber (e.g atrium to ventricle, ventricle to vessel)
Draw the graph for left ventricular volume during one cardiac cycle. Label the significant events during this curve
Ok
Draw the graph of the pressure curves for the atrial, ventricular and aortic pressure during one cardiac cycle. Label the significant events during this curve.
Ok
What curve for pressure has the highest span? Why is that?
Ventricular pressure curve. V pressure needs to be lower than A pressure to get blood, and needs to be higher than aortic pressure to release blood. So it fluctuates a lot.
What is necessary to open the valves?
What is necessary to close the valves?
Pressure in the previous chamber overcomes the diastolic pressure of the next vessel/chamber allowing blood to pass to the next destination
Pressure in the next chamber overcomes the pressure from the previous chamber/
What is the dicrotic notch and what causes it?
Small spike in aortic pressure at the end of systole.
Caused by closing of the aortic valve which pushes some blood to the aorta
Draw the curve of the jugular venous pressure during one cardiac cycle. Label the significant events during this curve.
Ok
What is the a wave? What is the c wave? What is the V wave? What is x descent? What is y descent?
atrial contraction tricuspid valve closure venous filling atrial relaxation (interrupted by c wave) atrial emptying
What does atrial systole mean?
A pressure > V pressure. Blood moves from A to V.
Is aortic pressure higher or lower than A and V pressure?
Higher, because the the higher pressure is needed to eject the blood to the system
What are the normal aortic and pulmonary arterial pressures?
Aortic: 120/70
Pulmonary A: 25/15
What causes heart sounds?
Draw the locations of the 4 heart sounds on the Wiggers diagram
Blood hits some part of the heart and causes audible vibrations
Ok
What causes the 1st heart sound?
bicuspid valves close and blood hits the closed valve
What causes the second sound?
aortic valves close and blood loses its forward momentum and backflows from the vessel and hits the closed valve behind it
What causes the 3rd sound? Can you hear this in adults?
Blood rapidly fills the ventricles
Not always
What causes the 4th sound? Can you hear this in adults?
Last bit of blood is passed from A to V
What causes a heart murmur?
Blood goes the wrong direction or its flow is obstructed
If you have a systolic murmur, what is going on if …
Wrong direction:
Obstruction of flow:
Bicuspid valve is defective and causes blood to go back to left atrium
Aorta or pulmonary artery stenosis (blood stuck in ventricle)
If you have a diastolic murmur, what is going on if…
Wrong direction:
Obstruction of flow:
Semilunar valves are defective so blood returns to the ventricle
Blood cannot get into the ventricles because of stenosis
