Lecture 5 - Jan 30 Flashcards
What does the right vagus nerve typically handle in the heart?
SA node
What does the left vagus nerve typically handle in the heart?
AV node
How does sympathetic innervation compare to vagus nerve innervation in the heart?
Sympathetic innervation is widespread and covers more ventricular muscle.
What happens to heart rate if vagus nerve input is removed?
Heart rate increases significantly.
What is the typical heart rate at rest when sympathetic activity is removed?
About 60 beats per minute.
What is the innermost layer surrounding the heart called?
Serous pericardium
What is the function of the visceral layer of the serous pericardium?
Covers the outside of the heart and reduces friction.
What is the fibrous pericardium?
A thicker, less compliant layer surrounding the heart.
What are the two layers of the serous pericardium?
- Visceral layer
- Parietal layer
How do electrical signals move through the heart muscle?
Via gap junctions and electrical current through ions.
Which ion is most important for conducting action potentials in the heart?
Sodium
What is the orientation of muscle fibers in the ventricles?
Two thick muscle layers oriented at perpendicular angles.
What are the parts of the heart valves called?
Cusps or leaflets
How are the cusps of the AV valves attached to the ventricles?
Via chordae tendinae.
What role do papillary muscles play in heart valve function?
They reinforce AV valves to prevent backflow during ejection.
What is a normal ejection fraction (EF) for the heart?
58%
What distinguishes the bicuspid valve from the tricuspid valve?
Bicuspid has two cusps; tricuspid has three cusps.
What causes aortic stenosis?
Gum up of the aortic valve leading to difficulty in coronary perfusion.
What are the three cusps of the aortic valve?
- Left cusp
- Right cusp
- Posterior cusp
What is the function of the cardiac cartilaginous rings?
They insulate electrical activity between the atria and ventricles.
True or False: The anterior cusp of the pulmonary artery is located on the posterior side.
False
Fill in the blank: The left cusp of the pulmonary artery is located on the ______ side.
right
What happens to the heart if papillary muscles are damaged?
It can lead to valve problems.
What is the normal volume ejected from the ventricle during contraction?
70 mL
What happens when heart valves do not close properly?
Leaky valves can cause chambers to fill from multiple sources.
What separates the atria from the ventricles in the heart?
A layer of insulation made out of cartilage
This insulation acts as an electrical insulator to keep the electrical activity of the atria separate from that of the ventricles.
What is the purpose of the small opening in the cartilaginous ring of the heart?
It allows the AV node to fire an action potential into the lower portions of the heart
This small opening is crucial for the normal electrical conduction between the atria and ventricles.
What are the three cusps of the right ventricle?
- Anterior Cusp
- Posterior Cusp
- Septal Cusp
These cusps are connected to the right ventricular wall by papillary muscles.
What are the two main cusps of the left AV valve?
- Anterior Cusp
- Posterior Cusp
There is also a smaller commissural cusp that is part of the posterior cusp.
What is the first main split point off of the left coronary artery?
Left Anterior Descending artery (LAD)
The LAD runs down the front middle of the heart.
What is the second main split point off of the left coronary artery?
Circumflex artery
The circumflex artery wraps around the back of the heart.
What is the posterior descending artery (PDA) commonly a branch of?
Right coronary artery (RCA)
In some individuals, the PDA may branch from the left coronary artery.
What is the continuous part of the coronary venous circulation that empties into the right atrium?
Coronary sinus
The coronary sinus collects deoxygenated blood from the coronary veins.
How much coronary blood flow is typically needed per minute for each 100 grams of heart muscle?
70 mL
The average heart requires about 225 mL of blood per minute to meet its metabolic needs.
When does the coronary blood flow increase?
When the ventricles are filling
This is due to lower pressures in the wall of the heart during diastole.
What happens to coronary perfusion during systole?
It decreases
High internal pressures during systole restrict blood flow.
What type of blood vessels are embedded in the walls of the heart?
Endocardial or sub-endocardial blood vessels
These vessels are deeper compared to the superficial epicardial vessels.
Which coronary artery typically provides blood flow to the high-pressure side of the heart?
Left coronary artery
Conversely, the right coronary artery generally supplies the lower pressure areas.
What causes negative coronary blood flow in the left coronary artery?
Retrograde coronary perfusion during early systole
This occurs when the high-pressure contraction of the heart squeezes blood back into the coronary arteries.
What drives coronary blood flow?
Delta P (pressure gradient)
Aortic pressure serves as the source pressure to drive coronary circulation.
Fill in the blank: The average heart needs about ______ mL of good blood per minute.
225 mL
This amount is necessary to satisfy the metabolic requirements of the heart.
What drives coronary blood flow?
Aortic pressure
Aortic pressure is the pressure available to drive coronary blood flow
What happens when aortic pressure is high?
More perfusion occurs
High aortic pressure allows for better blood flow to the coronary arteries
What is the equation for delta P in coronary blood flow?
Delta P = aortic pressure - wall pressure
What occurs when driving pressure is higher than wall pressure?
Blood flow occurs
What is the consequence of wall pressure being higher than aortic pressure?
Reverse coronary blood flow can occur
What does the Wigger’s diagram illustrate in terms of delta P?
Delta P is the difference between aortic pressure and ventricular pressure
During which phase is coronary perfusion most significant?
Diastole
How does increased heart rate affect coronary perfusion?
Reduces time for diastolic filling and perfusion
What happens to ventricular filling during diastole?
Most filling occurs at the beginning and end of diastole
What effect does a high heart rate have on a healthy heart?
It typically does not cause concern as middle diastole filling is minimal
What is the primary concern when increasing heart rate in someone with coronary disease?
Reduced time for coronary perfusion
What is aortic stenosis?
Obstruction of blood flow from the left ventricle
What happens to left ventricular pressure during aortic stenosis?
It must exceed aortic pressure to eject blood
What is the impact of high wall pressures during aortic stenosis?
Increased difficulty in perfusing the left ventricle
What happens to pulse pressure in aortic stenosis?
Pulse pressure narrows
What is mitral stenosis?
A filling problem due to a stenotic bicuspid valve
How does mitral stenosis affect left ventricular pressure?
Left ventricular pressure becomes elevated after compensation
What occurs during aortic regurgitation?
Blood leaks back into the ventricle, lowering diastolic blood pressure
What is the effect of mitral insufficiency?
Blood is ejected into both the aorta and atria
What is the A wave in the CVP waveform?
A small increase in pressures due to atrial contraction
What causes the C wave in the CVP waveform?
AV valves bulging back during the beginning of systole
What is the V wave in the CVP waveform?
Pressure increase due to blood filling the atria
True or False: Increased heart rate is always a concern for healthy hearts.
False
Fill in the blank: The difference between aortic pressure and ventricular pressure is called _______.
[delta P]
What does the C Wave represent in the CVP waveform?
The C Wave is a function of the AV valves bulging back during ventricular contraction.
It occurs even in healthy individuals, resulting in a backward bulge of the valves.
What causes the V Wave in the CVP waveform?
The V Wave results from atrial filling while the AV valves are closed.
Blood returning from circulation increases atrial pressure until the AV valves open.
What is the X Descent in the CVP waveform?
The X Descent occurs after the C Wave when the atria are emptying and atrial pressure decreases.
It follows the phase when the AV valves stop bulging backwards.
What does the Y Descent represent in the CVP waveform?
The Y Descent occurs after the V Wave when the AV valves open, allowing rapid filling of the ventricle.
This results in a decrease in atrial pressure.
What is systemic vascular resistance (SVR) compared to pulmonary vascular resistance (PVR)?
SVR is several times higher than PVR due to higher systemic pressures.
Normal clinical numbers for SVR fall between 800-1600, while PVR is between 40-180.
What formula is used to calculate systemic vascular resistance (SVR)?
SVR = (MAP - CVP) / Cardiac Output.
MAP is mean arterial pressure and CVP is central venous pressure.
What is the normal range for mean pulmonary arterial pressure?
Normal mean pulmonary arterial pressure is about 16 mmHg.
This pressure is used to estimate pulmonary vascular resistance.
How is pulmonary vascular resistance (PVR) calculated?
PVR = (Mean Pulmonary Arterial Pressure - Left Atrial Pressure) / Cardiac Output.
The left atrial pressure is often estimated using pulmonary arterial wedge pressure.
What are peripheral resistance units (PRU) and how are they calculated?
PRU = ΔP / Flow.
Normal PRU for systemic circulation is 1, and it can be converted to CGS units.
What happens to cardiac output during a normal breathing cycle?
Cardiac output can initially drop due to reduced venous return when thoracic pressure decreases.
Increased negative pressure in the thorax pulls blood into the chest but not directly into the heart.
True or False: During inspiration, CVP increases due to higher venous pressure.
False
CVP drops during inspiration as thoracic pressure becomes more negative.
What is the effect of negative thoracic pressure on the veins during inspiration?
Negative thoracic pressure reduces internal pressures in the veins, facilitating venous return to the heart.
This process can cause a delay in filling the heart.
Fill in the blank: The normal range for systemic vascular resistance (SVR) is ______.
800-1600.
This range is based on typical clinical measurements.
What happens to pressure in veins during inspiration?
Drops
This drop in pressure occurs because the chest fills with blood, affecting thin-walled veins.
How does the right atrium compare in wall thickness to veins?
Thicker
The thicker walls of the right atrium reduce the likelihood of being pulled apart compared to thin-walled veins.
What is the initial effect of inspiration on cardiac output?
Drops briefly
Initially, cardiac output may drop due to decreased preload.
How does pulmonary circulation respond during inspiration?
Becomes compliant
The thin-walled nature of pulmonary arteries and veins allows them to respond to thoracic pressure changes.
What happens to preload for the left side of the heart during inspiration?
Decreases significantly
The reduction in thoracic pressure leads to decreased preload for the left heart.
What does the term ‘afterload’ refer to in cardiac physiology?
The pressure the heart must work against to eject blood
Afterload is influenced by systemic vascular resistance and arterial pressure.
Does afterload for the right heart change during inspiration?
Decreases
Lower pulmonary arterial pressure during inspiration reduces afterload for the right heart.
How does left heart afterload change during inspiration?
Remains unchanged
The aorta’s thick walls prevent significant changes in afterload due to thoracic pressure.
What is the overall cardiac output change for the right heart during early inspiration?
Probably drops a little
There is some debate that it could increase slightly due to reduced afterload.
What is the effect of decreased preload on left ventricular cardiac output during inspiration?
Substantially reduced
The left ventricle pumps against normal afterload but with decreased preload.
True or False: The pulmonary venous pressure increases during inspiration.
False
Pulmonary venous pressure decreases due to the drop in thoracic pressure.
What happens to pulmonary arterial pressures during inspiration?
Drop
This drop is due to the negative thoracic pressure affecting the pulmonary arteries.
What occurs within the first heartbeat of normal inspiration?
Transient changes in cardiac output
These changes illustrate the complexities of cardiac output during respiration.
On inspiration, what happens to the CVP (central venous pressure)?
Decreases
This reduction in CVP reflects the decreased preload for the right heart.
Fill in the blank: During early inspiration, preload for the left side of the heart _______.
Drops
This drop significantly reduces cardiac output from the left ventricle.
What is a key factor influencing cardiac output during the respiratory cycle?
Preload and afterload changes
The balance between these factors is crucial for understanding cardiac performance.
What is the relationship between thoracic pressure and cardiac output during inspiration?
Negative thoracic pressure reduces preload
This leads to various changes in cardiac output dynamics.
