Lecture 2 - Jan 21 Flashcards
What is the Reynolds number?
A hypothetical number that is unitless.
What indicates turbulent flow in relation to Reynolds number?
A Reynolds number greater than 2000.
What are the implications of turbulent flow?
Wasted energy and risk for clotting.
What factors increase the risk of turbulent flow?
- Elevated velocity
- Wide diameter
- Higher density
- Viscosity
Which blood vessels are most prone to turbulent flow?
Large arteries close to the heart, such as the aorta.
How does blood viscosity differ from density?
Viscosity refers to thickness, while density is mass per volume.
What is the compliance difference between the arterial and venous systems?
Arterial system has low compliance; venous system holds larger volume with little pressure change.
What happens to pressure when sympathetic stimulation is removed?
Pressure in arteries decreases faster than in veins.
What measurement tools can be used to assess blood flow?
- Flow meters
- Electromagnetic probes
- Ultrasonic flow meters
- Lasers
What does the pressure-volume loop represent?
Different pressures and volumes in the heart chambers during the cardiac cycle.
What occurs during Phase 1 of the cardiac cycle?
Filling phase where the ventricle fills primarily passively.
What is preload and what influences it?
Preload is the initial stretching of the cardiac muscle, influenced by venous return, heart rate, arterial elastance, and myocardial contractility.
What is the role of atrial contraction in ventricular filling?
Atrial contraction provides a small additional volume to the ventricle.
What defines the end of diastole?
When the ventricle starts to contract.
What happens during Phase 2 of the cardiac cycle?
Isovolumetric contraction where pressure increases without a change in volume.
What is stroke volume and how is it calculated?
The difference between end-diastolic volume and end-systolic volume.
What causes the aortic valve to close?
When ventricular pressure is lower than aortic pressure.
What occurs during Phase 4 of the cardiac cycle?
Isovolumetric relaxation where ventricular pressure decreases until the mitral valve opens.
What is the significance of the pressure volume curve?
It reflects the contractile state of the heart and the pressures generated.
What does a high contractile state indicate about the pressure volume loop?
It may be positioned differently on the graph, indicating higher internal and external pressures.
What electrical events precede changes in pressures during the cardiac cycle?
The QRS complex precedes the increase in ventricular pressure.
What defines diastole in the context of the cardiac cycle?
Diastole starts when the aortic valve closes.
What is the starting point of diastole?
Diastole starts when the aortic valve closes.
When does systole officially start?
Systole starts officially at the end of phase one.
What occurs during phase 1 of the cardiac cycle?
Low pressures during filling, high pressures during ejection.
What is the end diastolic volume (EDV) in a healthy heart?
120 cc’s.
What is the end systolic volume (ESV) in a healthy heart?
50 cc’s.
What is the stroke volume (SV) expected during phase 1?
70 cc’s.
True or False: There are no volume changes during phase II or IV.
True.
What is the key characteristic of phase II in the cardiac cycle?
Isovolumetric contraction with no volume change.
What happens to ventricular volume during ejection?
Decreases from 120 cc’s to 50 cc’s.
What is the effect of a stenotic mitral valve on filling?
Filling may not happen as fast.
What happens to atrial pressure during atrial contraction?
Atrial pressure increases.
How does the heart maintain its cardiac output during exercise?
By changing its output rapidly, potentially increasing to 5L/min or more.
What is the normal right atrial pressure for the right side of the heart?
Zero mmHg.
What happens to venous return at a right atrial pressure of zero?
Venous return is about 5L/min.
Fill in the blank: At the end of diastole, the ventricles are filled to _______ cc’s.
[EDV] 120 cc’s.
What is the relationship between right atrial pressure and venous return?
Higher right atrial pressure leads to lower venous return.
What occurs during the plateau phase of the cardiac cycle?
Venous return starts to pick up.
What is the significance of the tricuspid valve’s location?
It serves as the isogravimetric point for zeroing out pressure transducers.
What is the purpose of plotting atrial pressure against cardiac output?
To assess the relationship between atrial pressure and cardiac output.
What happens to atrial pressure when the mitral valve closes?
Atrial pressure increases as blood returns without a place to go.
What does the first heart sound correlate with?
AV valves closing.
What does the second heart sound correlate with?
Aortic valve closing.
What does a larger delta P represent in the circulatory system?
The difference between the average pressure of the circulatory system and the pressure at the end of the circulatory system
It helps quantify the pressure gradient driving venous return.
What is the normal right atrial pressure, and how does a negative right atrial pressure affect venous return?
Normal right atrial pressure is 0 mmHg; a negative right atrial pressure augments venous return
This occurs because lower pressure allows veins to fill more effectively.
What is the plateau phase in venous return?
A phase where venous return reaches a maximum of about 6 liters per minute
This occurs when atrial pressure is very low and further increases in venous return are limited.
What happens to large veins when the right atrial pressure is significantly lower than normal?
The large veins can collapse, preventing further augmentation of venous return
This is similar to the behavior of jugular veins under negative pressure.
Define Mean Systemic Filling Pressure (PSF).
The average pressure of the cardiovascular system, typically around 7 mmHg
It represents the pressure that helps fill the heart when the heart is paused.
What is the effect of stopping the heart on the systemic filling pressure?
The pressures in the system will equilibrate, stabilizing at mean systemic filling pressure
This reflects the balance of blood volume in arteries and veins.
What is the typical delta P available to fill the right side of the heart?
Typically 7 mmHg
This is the difference between average systemic pressure and right atrial pressure.
What factors can increase systemic filling pressure?
- Elevations in resistance
- Contraction of systemic veins
The sympathetic nervous system plays a key role in venous contraction.
What does resistance to venous return describe?
How easy it is for blood to return to the heart
Lower resistance indicates easier venous return, affecting cardiac output.
What is the relationship between resistance to venous return and cardiac output?
Lower resistance correlates with higher venous return and likely higher cardiac output
Changes in resistance alter the slope of venous return curves.
What happens to the venous return curve when mean systemic filling pressure is increased?
The curve shifts to the right without changing its slope
This indicates a greater volume of blood returning to the heart at higher filling pressures.
What happens to venous return if systemic filling pressure is reduced?
Venous return and cardiac output will decrease
This is illustrated by a lower X-intercept on the venous return curve.
What two main factors affect systemic filling pressure?
- Blood volume
- Venous tone
Changes in venous tone can significantly influence central venous pressure (CVP).
How can elevated intra-thoracic pressures affect venous return?
They can cause veins to collapse, hindering blood return to the heart
This is particularly relevant in mechanical ventilation scenarios.
What is the expected cardiac output with a normal right atrial pressure?
Approximately 5 liters per minute
This assumes a normally stimulated, healthy heart.
What effect does increasing right atrial pressure have on cardiac output?
Increased right atrial pressure usually leads to enhanced cardiac output
This effect is capped at about 13 liters per minute under normal conditions.
What happens to cardiac output when right atrial pressure reaches about 4 mmHg?
Cardiac output tops out at about 13 liters per minute
This indicates a plateau phase in the relationship between atrial pressure and output.
What is the maximum cardiac output observed at a right atrial pressure of about 4 mmHg?
13 liters per minute
This represents a plateau phase where cardiac output is capped unless further stimulation occurs.
What happens to cardiac output with maximum sympathetic stimulation?
Cardiac output increases, but still follows the basic profile of higher right atrial pressure leading to higher output
This indicates that sympathetic stimulation enhances cardiac output further.
What is the Frank Starling mechanism?
The alignment of cross bridges of ventricular muscle fibers that improves contractility
This mechanism is crucial for effective heart function.
What is the effect of direct atrial stretch on heart rate?
Increases heart rate by about 10 to 15% of normal
This occurs without requiring neural input.
What is the Bainbridge reflex?
A reflex that increases heart rate to accommodate higher filling pressure
The Bainbridge reflex can increase heart rate by about 40 to 50%.
What are the two mechanisms by which heart rate increases due to atrial stretch?
- Direct atrial stretch
- Bainbridge reflex
Bainbridge reflex relies on neural circuitry, unlike direct atrial stretch.
What happens to right atrial pressure when the heart is hyper effective?
Right atrial pressure may reduce, aiding in higher cardiac output
This can happen if the heart generates a vacuum effect.
What occurs when the heart is inhibited?
Right atrial pressure increases due to reduced pumping effectiveness
This results in a buildup of pressure in the filling portions of the heart.
How does congestive heart failure affect cardiac output and filling pressures?
Filling pressures must be increased to maintain cardiac output necessary for survival
High central venous pressures (CVPs) are common in heart failure patients.
What are the two components that determine actual cardiac output?
- Conditions of the circulatory system
- Conditions of the heart
These components must be plotted together to find the average system state.
What happens to cardiac output when both filling pressure and heart stimulation are increased?
Cardiac output increases significantly
This shows the importance of coordination between heart strength and venous return.
True or False: Cardiac output can increase significantly by stimulating the heart alone without adjusting venous return.
False
Cardiac output is limited without changes in venous return.
Fill in the blank: The heart rate picks up via _______ and Bainbridge reflex.
direct atrial stretch
What is the expected cardiac output for a healthy individual when stimulated strongly?
Increases slightly, possibly above 5 liters per minute
Without changes in circulation, the increase remains minimal.
What is the relationship between cardiac output and venous return?
Cardiac output must equal venous return
This principle is essential for understanding circulatory system function.
What is indicated by a right atrial pressure of zero in a normal system?
Both venous return and cardiac output are typically around 5 liters per minute
This represents a baseline for normal heart function.
