Exam 1: 21 Jan 25 Understanding CO and the CV System Mechanically Flashcards
What is the Reynolds number?
A hypothetical number that is completely unitless
What does a Reynolds number greater than 2000 indicate?
Turbulent flow
What is turbulent flow characterized by?
Blood moving in all different directions, mass amounts of energy wasted, and risk for clotting
What can cause hardened arteries or plaque deposits?
Turbulent flow associated with narrowing of blood vessels
What is the equation for Reynolds number?
RE = (V x D x P) ÷ h
What does ‘V’ represent in the Reynolds number equation?
Velocity
What does ‘D’ represent in the Reynolds number equation?
Diameter
What does ‘P’ represent in the Reynolds number equation?
Density
What does ‘h’ represent in the Reynolds number equation?
Viscosity
Which blood vessels are most prone to turbulent flow?
Large arteries close to the heart, such as the Aorta
True or False: The venous side of circulation typically experiences turbulent flow.
False
How does the pressure change in the arterial system compared to the venous system when volume changes?
Pressure changes a lot in the arterial system when volume changes a little, indicating low compliance
What happens to pressure in the veins when volume is added or removed?
Pressure only changes a little, indicating high compliance
What effect does removing sympathetic stimulation have on arteries and veins?
Pressure in both decreases, but it decreases faster in arteries
What is the primary method for measuring blood flow?
Using flow meters, such as electromagnetic or ultrasonic flow meters
What does the pressure-volume loop analyze?
The different pressures and volumes in the chambers of the heart during the cardiac cycle
What is the end systolic volume (ESV) in a healthy heart after filling?
50 mls
What is the primary mode of filling in the heart?
Passive filling
What is the role of atrial contraction in ventricular filling?
Provides a small additional volume of blood to the ventricle right before contraction
Fill in the blank: The atrial contribution to filling becomes very important in cases of _______.
[heart pathology]
What happens to the atria in healthy individuals during the pumping and filling process?
The atria aren’t necessary; passive filling can occur via pulmonary veins.
Healthy individuals can achieve ventricular filling without atrial contraction.
What is the atrial kick and its significance in heart failure?
In heart failure, the atrial contraction may contribute about 25% or more to ventricular volume.
Healthy individuals do not rely on atrial contraction for ventricular filling.
What is diastole?
Diastole is the phase of filling in the cardiac cycle.
It begins when the ventricles are relaxed and blood fills the chambers.
What occurs at the end of diastole in the cardiac cycle?
The ventricle starts to contract.
This transition marks the end of phase one.
Describe phase two of the cardiac cycle.
In phase two, the heart contracts, increasing left ventricular pressure, forcing the mitral valve to close.
Both the aortic and mitral valves should be closed during this phase.
What is isovolumetric contraction?
It is the phase where the ventricles contract with both valves closed, resulting in no change in volume.
This phase is represented by a vertical line on the pressure-volume graph.
What defines the period of ejection in the cardiac cycle?
It occurs when left ventricular pressure exceeds aortic pressure, opening the aortic valve.
This happens during phase three.
How is stroke volume calculated?
Stroke volume is the difference between left ventricular end diastolic volume and left ventricular end systolic volume.
Example: 120 mL (EDV) - 50 mL (ESV) = 70 mL (SV).
What starts phase four of the cardiac cycle?
Phase four begins when the aortic valve closes and the mitral valve remains closed.
This phase is known as isovolumetric relaxation.
When does diastole officially start?
Diastole starts when the aortic valve closes, marking the end of phase three.
It continues until the start of phase two.
What is the role of pressure during the filling phase?
Ventricular pressure is very low during filling, increasing significantly during ejection.
Atrial contraction causes a slight increase in pressure during this phase.
What is the relationship between electrical events and pressure changes in the heart?
Electrical events, like depolarization, occur before changes in ventricular pressure.
This delay is due to the time it takes for calcium to bind and generate force.
How does the pressure-volume loop relate to the strength of the heart’s contraction?
The position of the pressure-volume loop indicates the contractile state of the heart.
Stronger contractions generate higher pressures, shifting the loop’s position.
What happens to left ventricular volume during phases 1 and 3?
Volume increases during phase 1 (filling) and decreases during phase 3 (ejection).
The volume change is significant in assessing cardiac function.
In what part of phase one does rapid filling occur?
Rapid filling occurs in the first third of phase one when the mitral valve opens.
Blood from the left atrium floods into the ventricle quickly.
What occurs when the mitral valve opens?
Blood floods into the ventricle very quickly
This represents the phase of rapid filling during the cardiac cycle.
What are the three parts of Phase 1 filling?
- Rapid filling
- Middle third (not much happening)
- End of phase with a little extra volume from the atria
How does a stenotic mitral valve affect ventricular filling?
Filling occurs slower due to impedance from the left atria to the left ventricle.
What happens to cardiac output during tachycardia with a bad mitral valve?
Cardiac output becomes a problem due to insufficient filling time.
What is the volume in the ventricle right before the aortic valve opens?
120 cc’s
What happens to ventricular volume during systole?
Volume decreases from 120 cc’s to about 50 cc’s, ejecting 70 cc’s.
True or False: Ejection stops at the peak of aortic pressure.
False
What is isovolumetric contraction?
Pressure increases without volume change, occurring during Phase II.
What correlates with the first heart sound?
AV valves closing
What correlates with the second heart sound?
Aortic valve closing
What is the expected pressure in the atria during contraction?
Atrial pressure increases.
Fill in the blank: The mitral valve is also known as the _______.
bicuspid valve
What is depicted in a Carl J. Wiggers diagram?
Various cardiac variables plotted over time.
What happens at a right atrial pressure of zero?
Normal cardiac output is about 5L/min.
What must happen for cardiac output to be sustained?
Blood must return to the heart.
What is the relationship between right atrial pressure and venous return?
Elevated right atrial pressure indicates elevated venous return.
What is the primary determinant of whether the heart can maintain cardiac output?
The health and efficiency of the heart’s pumping ability.
What is the normal venous return rate to the heart?
5 L/min
What happens to venous return if right atrial pressure is higher than zero?
Lower venous return
What is the relationship between venous return and cardiac output?
Cardiac output depends on venous return
What defines the flow in the cardiovascular system?
Delta P (pressure difference)
At what right atrial pressure does normal venous return occur?
Zero mmHg
What effect does a lower than normal right atrial pressure have on venous return?
Increases venous return
What is the mean systemic filling pressure (PSF) in mmHg?
7 mmHg
What happens to venous return if the right atrial pressure is significantly lower than normal?
Veins may collapse, limiting augmentation of venous return
What is the typical maximum venous return rate under normal conditions?
About 6 L/min
How does resistance to venous return affect blood flow back to the heart?
Higher resistance impedes venous return
What two factors primarily affect systemic filling pressure?
- Blood volume
- Venous tone
What happens to the venous return curve when mean systemic filling pressure is increased?
The curve shifts to the right without changing slope
What is the expected venous return at a filling pressure of 14 mmHg and right atrial pressure of 0 mmHg?
10 L/min
What effect does increased sympathetic nervous system activity have on systemic filling pressure?
Increases systemic filling pressure
True or False: Increased right atrial pressure typically leads to increased central venous pressure (CVP).
True
What happens to venous return if systemic filling pressure is reduced to 3.5 mmHg?
Expected venous return decreases to 2.5 L/min
What role do thoracic pressures play in venous return?
Elevated intra-thoracic pressures can cause veins to collapse
Fill in the blank: The average pressure of the cardiovascular system is the _______.
Mean systemic filling pressure (PSF)
What is the significance of the delta P in the context of the cardiovascular system?
It determines the pressure difference for filling the heart
What is the effect of increased venous tone on systemic filling pressure?
Increases systemic filling pressure
How does the compliance of veins affect mean systemic filling pressure?
Veins can hold more volume at lower pressure
What happens if the pressure in the thorax is not compensated for the internal pressure of the veins?
The chest veins may collapse before delivering blood to the heart.
How does the thorax influence the heart?
Both sides of the heart are influenced by thoracic conditions, affecting blood flow from the right to the left heart.
What can mechanical ventilation do to venous return?
Mechanical ventilation can make it harder or easier for blood to return to the heart.
What is the expected cardiac output with a right atrial pressure of zero in a healthy heart?
Approximately five liters per minute.
What happens to cardiac output with increased right atrial pressure in a healthy heart?
Cardiac output increases significantly until it tops out at about 13 liters per minute.
What is the Frank-Starling mechanism?
It refers to the alignment of cross bridges in ventricular muscle fibers that improves contractility with increased filling pressures.
What is direct atrial stretch?
A phenomenon where increased atrial stretch leads to a slight increase in heart rate and contractility.
What is the Bainbridge reflex?
A reflex that increases heart rate to accommodate higher filling pressures, requiring nervous system involvement.
What are the two key outputs of the Bainbridge reflex?
- Increase in sympathetic output
- Decrease in parasympathetic output
What happens to cardiac output in a heart with maximum sympathetic stimulation?
Cardiac output can plateau around 23 to 25 liters per minute in healthy individuals and up to 40 L/min in elite athletes.
What effect does a strong heart contraction have on right atrial pressure?
It can lower the right atrial pressure compared to normal levels.
How does a heart in failure affect right atrial pressure and filling pressures?
In heart failure, right atrial pressure increases, requiring higher filling pressures to maintain cardiac output.
What is the relationship between cardiac output and venous return?
Cardiac output must equal venous return.
What happens to the cardiac output if filling pressure is increased significantly?
The venous return curve shifts right, potentially increasing cardiac output to 13 liters per minute.
What is the impact of stimulating the heart strongly without changing circulatory conditions?
Cardiac output increases only slightly, perhaps to about six liters per minute.
Fill in the blank: The heart’s pumping effectiveness can be improved by _______.
[maximal sympathetic stimulation]
True or False: The Bainbridge reflex requires special neural input to function.
False
What two changes can significantly increase cardiac output?
- Strongly stimulating the heart
- Increasing the filling pressure
What happens if blood return to the heart is not improved?
Cardiac output change is limited
True or False: Stimulating the heart alone will lead to a significant increase in cardiac output.
False
What is required to achieve maximal cardiac output?
Coordination of both heart stimulation and improved blood return
Fill in the blank: If blood is returned to the heart better, cardiac output _______.
picks up a lot
What role does the contractile state of the heart play in increasing cardiac output?
Not significantly affected if blood return is improved
What advantage is gained by allowing more blood to return to the heart?
The heart acts as a stronger pump
