7. Cardiac System 4 Flashcards
What are hemodynamics?
What 2 functions does vascular system have?
Study of fluid mechanics of the blood
Vascular system serves for distribution of blood (pipeline) and exchange
Study graph on slide 14 oct 10
Study graph of pressures in different regions of heart (LV, aorta, arteries/arterioles, capillaries, veins & RA, RV, PA, PV & LA)
Slide 4 oct 10
Ok
What is pulmonary wedge pressure (PCW/PCWP)?
What does pulmonary edema have to do with this?
Used to estimate left atrial pressure (hard to measure LAP directly)
Pulmonary edema with elevation of PCW can suggest left ventricular dysfunction
Pulmonary edema with normal PCW could suggest respiratory diseases
Slides 5-11
What are the different waves of the right atrium/central venous pressure?
Graph and on slide 10 oct 10
A wave- atrial systole after rapid ventricular filling phase
C wave- started by closing of tricuspid valve while atria continues to fill
(Drop in atrial pressure after peak of c wave is due to rate of atrial relaxation is faster than rate of atrial filling)
V wave- atrial filling continues, tricuspid stays closed (rising phase is atrium stretching with filling, falling phase is tricuspid valve opening)
Slides 10-13 oct 10
How does velocity (1 of 6 factors) affect blood flow?
Cardiac output=venous return
Flow rate= velocity x cross sectional area
Velocity of flow within a single vessel is inversely proportional to cross sectional area (diameter)
Greater cross sectional area=lower velocity
Slides 16-18 oct 10
How does pressure (2 of 6 factors) affect blood flow?
Pressure=force per unit area
Rate of flow is proportional to pressure gradient (pressure drop) across vessel
Pressure gradient goes up, blood flow goes up
Important for heart to contract forcefully to generate a high enough pressure head to facilitate the movement of blood
How does viscosity (3 of 6 factors) affect blood flow?
Viscosity is the frictional property of molecules as they slide by one another
Blood flow is inversely proportional to viscosity
Viscosity goes up, blood flow goes down
How does resistance (4 of 6 factors) affect blood flow?
What are the proportionalities of blood flow to resistance to radius?
Hydraulic resistance is changes in pressure divided by flow rate
R= (Pf-Pi)/Q
Radius is dominant factor in determining resistance to flow
R α 1/r^4
Q α r^4
2x increase in radius (r)
16x decrease in resistance (R)
16x increase in flow (Q)
Slides 21-29 oct 10
How do you find resistance in capillaries arranges in series compared to in parallel?
Series:
Rt (series)= R + R = 2R
Parallel:
1/Rt (parallel)= 1/R + 1/R= 2/R
Rt (parallel) = R/2
Rt (series)»_space; Rt (parallel)
Slide 25 oct 10
How does flow pattern (5 of 6 factors) affect blood flow?
Use Reynolds number to predict flow
If Reynolds number less than 2000- laminar flow
If Reynolds number more than 3000- turbulent flow
For laminar- flow rate is linearly proportional to pressure drop
For turbulent- flow rate is proportional to
square root of pressure drop
Slides 30-33 oct 10
How does hematocrit of blood (6 of 6 factors) affect blood flow?
Hematocrit is ratio of volume of red blood cells to volume of whole blood
Viscosity of blood increases as hematocrit increases and it slows the flow rate
Slides 34-36 oct 10
What is blood pressure?
What are the 2 things that influence it?
Blood pressure is the force exerted by blood against a vessel wall
Influenced by;
1. Physiological- HR, SV, CO=HRxSV, peripheral resistance (systemic vascular resistance SVR which is diameter of small arteries and arterioles that contribute to majority of resistance to flow between artery and vein compartments)
- Physical- effective circulating blood volume (blood volume within the vasculature that can be utilized to perfuse the organ systems in body, not anatomical blood volume)
Elastic characteristics
What are the 4 components in blood pressure?
- Systolic pressure (SP)- upper limit of periodic oscillations of blood pressure initiated by ventricular systole (120mmHg)
- Diastolic pressure (DP)- it is minimum pressure within the arteries during ventricular diastole (80mmHg)
- Pulse pressure (PP)- difference between systolic and diastolic pressure
PP=SP-DP - Mean arterial pressure (mAP)- average pressure in arteries over time
mAP= DP + 1/3PP or 1/3SP + 2/3 DP
What are the 3 levels of control in the neural control (autonomic) of cardiovascular function?
1 of 2
- Higher centres such as cortex- (connected to hypothalamus and medulla) responsible for alternating cardiovascular function during emotional stress
- Hypothalamus- plays integrative role by modulating medullary neuronal activity
- Medulla of brainstem- afferent fibers from baroreceptors, chemoreceptors and stretch receptors enter medulla at nucleus tratus solitarius
Contains both parasympathetic and sympathetic centres
Slides 4-6 oct 15
What is the sensor for regulation of cardiovascular function;
Baroreceptors (high pressure sensors)
It’s 2 types?
1 of 3
Primary sensors for the detection of arterial blood pressure changes
They are stretch receptors
Regulates arterial blood pressure through negative feedback
They respond to stretching of vessel walls and increase firing rates
Carotid sinus receptors and aortic arch receptors (aortic arch higher threshold to fire and less sensitive)
Slides 13-14 oct 15
What is the sensor for regulation of cardiovascular function;
Baroreceptors (low pressure sensors)
It’s 2 types?
2 of 3
All located in proximities of heart (venoatrial junctions, low pressure chambers of heart)
Stretch receptors as well
Used for detection of venous return
Indirectly monitor mean arterial BP (since it affects venous return)
Type A fibers- fire during atrial depolarization (monitors HR)
Type B fibers- fire during ventricular systole, increase firing during atrial filling (monitors atrial volume (venous return))
Slides 15-19 oct 15
What is the sensor for regulation of cardiovascular function;
Chemoreceptors
3 of 3
Peripheral chemoreceptors located at same locations as baroreceptors
Detect change in PO2, PCO2, and H+ concentration
Primary function is to regulate respiratory activity and maintain blood gas level
Influence medullary cardiovascular centres similar to that of the high pressure baroreceptors
Slides 20-21 oct 15
What are the 4 major factors in the humoral (hormonal) control of cardiovascular function control?
- Catecholamines- majority from adrenal medulla
Epinephrine at very low levels (cause vasodilation, decrease in vascular resistance), epinephrine at medium levels (HR, contractility, AV conduct increased), epinephrine at high levels (CO and vascular resistance increased) - Renin-angiotensin-aldosterone system- slide 30
- Atrial natriuretic peptide (ANP)- slide 31
- Vasopressin- also as antidiuretic hormone (ADH) slide 32
Slides 22-32 oct 15
What all does an increase in venous return do?
Review
Increase preload Stretch myocardial contractile myocytes Increase force of contraction (known as frank starling mechanism) Increase stroke volume Increase cardiac output
What is right ventricular filling (RVEDV)?
What are the 3 parameters of ventricular EDV?
Right ventricular end diastolic volume is a function of venous return
RVEDV = RVESV + venous return
70% of ventricular filling is through passive filling
Function of 3 parameters:
- Ventricular filling pressure- increase in venous return increases right atrial filling pressure which increase EDV
- Ventricular filling time- decrease this and EDV will decrease
- Ventricular compliance- increase in compliance increases overall ventricular volume (EDV)
What is the vascular function curve?
Slides 6-11 oct 17
Model of heart as continuous pump with given output
Venous return=cardiac output at steady state
Increase rate of output (flow)=decrease right atrium pressure (eventually hit negatives, caused by suction within right atrium cause mismatch between high output and low return)
When RAP hits negative it’s a plateau phase
Veins collapse with negative pressure (venous return would be zero)
What is mean systemic filling pressure (MSFP)?
What are the 2 things it is a function of?
The pressure in the cardiovascular system with zero cardiac output
(Usually due to collapse of veins from negative atrial pressure due to mismatch between output and input)
Function of:
- Fluid volume- greater the volume (blood), higher the MSFP
- Overall compliance- lower compliance, higher MFSP
Why does an increase in cardiac output (CO) and decrease in right atrial pressure (RAP) lead to an increase in venous return?
Increase in CO increases blood pressure, which increases the pressure head
Decrease in RAP with increase in pressure head will increase the pressure gradient (driving pressure) between central venous pressure and right atrium
Increase in pressure gradient increases return of blood from peripheral back to right atrium
What is central venous pressure (CVP)?
Blood pressure in the thoracic vena cava in the proximity of the right atrium
Change in CVP (ΔPcv) = change in blood volume (ΔVv) / venous compliance (Cv)
Any increase in central venous volume (Vv) will increase CVP (Pcv) without changing Cv
Decrease in central venous compliance (Cv) increases CVP
Slides 12-15 oct 17
How does changes in blood volume (transfusion, normal, hemorrhage) affect CVP?
*use vascular function graph slide 16 oct 17
Transfusion (increase blood volume) generates higher CVP than normal
Hemorrhage (decrease blood volume) generated lower CVP than normal
How does changes in peripheral resistance (vasodilation, vasoconstriction) affect CVP?
*use vascular function curve slides 17-18 oct 17
At CO=0, they all converge into a single point because there is no change in volume
Vasodilation (increase in blood flow from artery to venous, increase in venous blood) generated higher CVP than normal
Vasoconstriction (decrease blood flow from artery to venous, decrease in venous volume) generates lower CVP
What are 5 things that increase central venous pressure (CVP) through compliance (Cv) or blood volume (Vv)?
- Decrease cardiac output (CO) means heart failure which means blood backing up in venous circulation (increase blood=increase CVP)
- Increase fluid retention means renal failure, increase blood volume increases CVP
- From standing to laying down- blood shift from legs to thoracic region, increase blood volume increase CVP
- Arterial dilation- decrease sympathetic activity, increase compliance & blood volume, increase CVP
- Muscle contraction- walking, increase venous return, increase blood volume, increase CVP
What happens when you combine cardiac function graph and vascular function graph all on one graph?
What happens if you increase CVP to point A (slide 22 oct 17)?
Slides 21-23 oct 17
Shows heart and vasculature are coupled functionally
Intersection of the lines in equilibrium point
Any movement will imitate a sequence of events to restore the system back to equilibrium point
⬆️CVP ⬆️venous return (to point A)
⬆️venous return ⬆️CO (A-B)
⬆️CO ⬇️CVP (B-C)
⬇️CVP ⬇️CO (C-D)
Repeat whole cycle till equilibrium is reached
What happens to cardiac function/vascular function graph when you increase peripheral resistance?
Slide 26 oct 17
Shift both cardiac and vascular function downward
Equilibrium point moved downward with decrease in CO (this is due to increase in afterload)
No change in CVP (therefore heart isn’t able to pump as much blood out because of increase in afterload)
What does heart failure do to the cardiac function/vascular function graph?
Slide 27 oct 17
Shift the cardiac function curve to the right without affecting the vascular function curve
Cause a decrease in CO and an inverse in CVP
What does hypervolemia do to the cardiac function/vascular function graph?
Increase in CO is mainly due to increase in preload
Increase in CVP is mainly due to increase in blood volume
Raises vascular function curve but does not affect cardiac function curve
