Lecture 6 - Overview of Cardiovascular Physiology Flashcards
1
Q
Other than bringing oxygen and nutrients to tissues and taking away wastes, what are some other functions of the CV system?
A
- Endocrine signaling
- Thermoregulation
- Facilitate the immune response
- Hemostasis
2
Q
What is hemostasis?
A
Process which causes bleeding to stop
3
Q
What are the 3 major parameters to measure CV function?
A
- Pressure
- Flow
- Resistance
4
Q
2 possible units for blood pressure?
A
mmHg (or Torr) and cmH2O
5
Q
What is blood pressure?
A
Measure of the force exerted by blood per unit area on vessel walls
6
Q
Which pressure are we the most interested in clinically?
A
Arterial BP
7
Q
How is arterial BP expressed?
A
Systolic P/diastolic P
8
Q
What is the mean arterial pressure?
A
Arterial pressure integrated over the course of one cardiac cycle of systole and diastole
9
Q
How to approximate the mean arterial pressure at a normal heart rate?
A
MAP = diastolic P + 1/3 pulse pressure
10
Q
Systole?
A
Period of cardiac contraction and ejection
11
Q
Diastole?
A
Period of cardiac relaxation and filling
12
Q
Normal BP for an adult?
A
120/80
13
Q
Why is MAP not the average of systolic and diastolic pressures?
A
Because diastole lasts a little longer than systole in the cardiac cycle
14
Q
Systolic pressure?
A
Highest arterial BP observed when the heart is ejecting blood
15
Q
Diastolic pressure?
A
Lowest arterial BP observed when the heart is filling up with blood
16
Q
Pulse pressure?
A
Systolic P - Diastolic P
17
Q
What is blood flow?
A
BV passing through a portion of the circulation per unit time (Q)
18
Q
Blood flow 2 units?
A
mL/min or L/min
19
Q
What equation relates flow, pressure, and resistance? Analogy to this equation?
A
Q = ΔP/R
Analogy: Ohm’s Law = I = V/R
20
Q
Most important cardiac flow rate?
A
Cardiac output
21
Q
What is cardiac output?
A
Flow rate from 1 ventricle
22
Q
Equation to calculate cardiac output?
A
CO = HR x SV
23
Q
Normal CO value?
A
5L/min
24
Q
What is the stroke volume?
A
Volume ejected by 1 ventricle in 1 beat
25
Normal SV for a 170 lb person?
70 mL
26
What is the cardiac index (CI)?
CO normalized for body surface area
27
Formula for CI?
CI = CO / m^2
28
CI for 170 lb person?
CI = 5/1.5 = 3.3 L/min/m^2
29
What is the stroke index (SI)?
SV normalized for body surface area
30
Formula for SI?
SI = SV/ m^2
31
What is blood velocity?
Speed at which blood flows
32
What is another word for resistance?
Impedance
33
What is the unit of resistance?
mmHg/mL/min
34
Unit of resistance of the systemic circulation?
PRU = peripheral resistance units
35
Normal resistance of the systemic circulation?
0.02 PRU
36
How do valves work?
They passively respond to pressure gradients
37
Unit of blood velocity?
cm/s
38
What is resistance to blood flow a property of?
Fluid AND vessel
39
Is ALL of the blood in the ventricles ejected with contraction?
NOPE
40
What is the end diastolic volume (EDV)?
Amount of blood in ventricle following atrial contraction during diastole
41
What is the end systolic volume (ESV)?
Residual amount of blood in ventricle following ventricular contraction during systole
42
What is the ejection fraction?
Proportion of end diastolic volume ejected during systole
43
Equation for ejection fraction?
Ejection fraction = SV/EDV
44
Equation for end diastolic volume?
EDV = SV + ESV
45
Describe the timing of the electrical and mechanical events taking place in the heart?
Electrical events precede and initiate the mechanical ones
46
What is the blood transit time?
Average time for a particle of blood to pass from one point to the another in the circulation
47
Is the CO of the RV = to the CO of the LV?
YESSS
48
Describe the pressure and resistance of the systemic circulation.
High pressure
| High resistance
49
Describe the pressure and resistance of the pulmonary circulation.
Low pressure
| Low resistance
50
Is the overall circulatory pathway a circuit in parallel or in series? What does this mean?
Series
CO = venous return
51
Is regional circulation in parallel or in series? What does this mean?
Parallel
Individual organs can adjust their flow individually via dilation/constriction of the arterioles
52
% of cardiac output going to the brain? VO2?
13%
VO2: = 21%
53
% of cardiac output going to the coronary circulation? VO2?
4%
VO2 = 11%
54
% of cardiac output going to the liver and GIT? VO2?
24%
VO2 = 23%
55
% of cardiac output going to skeletal muscles? VO2?
21%
VO2 = 27%
56
% of cardiac output going to the kidneys? VO2?
20%
VO2 = 7%
57
% of cardiac output going to the skin and other organs? VO2?
18%
VO2 = 11%
58
Why is the venous system sometimes called the capacitance system?
Because it can function as a reservoir for blood, i.e. if you lose blood or if the flow rate increases (e.g. during exercise), sympathetic NS will contract veins to release blood to make up for it to maintain BP homeostasis
59
What % of the blood is found in the venous system?
64%
60
What vessels account for most of the resistance of the CV system?
1. Small arteries/arterioles: 47%
2. Capillaries: 27%
3. Large arteries: 19%
4. Veins: 7%
61
Breakdown % of blood in systemic vs pulmonary circulation? How is this possible if CO of RV = CO of LV?
Systemic circulation => 90% of the blood
Pulmonary circulation => 10% of the blood
Possible because the pulmonary circulation is low pressure and resistance
62
Which CV vessels regulate blood flood to specific regional circuits? How?
Arterioles by dilating or constricting to decrease or increase resistance
63
Pulmonary arterial pressure?
25/10 mmHg
64
Pulmonary MAP?
15 mmHG
65
Where is the largest pulse pressure found in the CV system? What is it? Why?
LV: 120
Required to pump blood into the aorta and setting up the pressure gradient for flow through the systemic circulation
66
Which vessels make up the distributing system?
Arteries
67
Which vessels make up the collecting system?
Veins
68
Which vessels make up the exchange system?
Capillaries
69
% of cardiac output going to the lungs?
100%
70
Pressure higher in atria or ventricles?
Ventricles
71
Diastolic P in LV? Why?
0 mmHg
To allow LV to fill up
72
How is systemic arterial pressure commonly measured?
Indirectly via a BP pressure cuff, a sphygomomanometer:
Cuff applies a pressure of around 180 mmHg until flow is stopped in the arm (no more sound), then pressure is slowly released until sound is heard like a beat, demonstrating intermittent flow = systolic pressure. Then, no more sound will be heard once the flow is constant = diastolic pressure
73
How are arterial and venous pressures directly measured?
Direct catheterization
74
What vessels/heart compartments can be measured by direct catheterization and advancing it in retrograde direction?
Arteries, aorta, and LV
75
What vessels/heart compartments can be measured by direct catheterization and advancing it in anterograde direction?
Veins, RA, RV, and pulmonary arteries
76
Is it possible to measure pulmonary venous and LA pressures by direct catheterization?
NOPE
77
How are pulmonary veins and LA pressures measured?
Indirect measurement of pulmonary capillary wedge pressure
78
Which vessels/heart compartment cannot be measured via direct catheterization?
Pulmonary veins and LA
79
Where is the lowest pulse pressure found in the CV system? What is it?
RV
20 mmHg
80
Normal venous pressure?
2-6 mmHg
81
What is another name for a pulmonary artery catheter?
Swan-Ganz catheter
82
When is a pulmonary artery catheter used to measure wedge pressure?
For heart patients, for example during heart failure
83
Where is a pulmonary artery catheter first introduced?
A large vein
84
What pressures can a pulmonary artery catheter measure? What else?
Veins, RA, RV, PA, PV/LA (wedge pressure), and filled LV + CO
85
What are the 5 tubes contained in a pulmonary catheter? What do we call this? What else does the catheter include?
1. Thermistor
2. Balloon port
3. Filament
4. PA distal
5. Infusion port
=> multi-lumen smooth catheter (each tube ends at different places)
+ Balloon on the outside of the catheter at its tip
86
Describe the steps to measure pulmonary artery pressure using a pulmonary artery catheter.
1. Advance catheter to RV
2. Slightly inflate balloon to help utilize blood flow to gain entry into the pulmonary artery (like a sail) and advance it as far as you can (2nd or 3rd generation branch of pulmonary artery)
3. Fully inflate balloon until flow in the artery is blocked
4. This will cause the pressure beyond the catheter tip to fall and equilibriate with the downstream pressure = capillary wedge pressure = pressure of pulmonary veins and LA
87
When using a pulmonary catheter, how can one tell at which location it is?
The pressure at the tip reflects its location
88
PA normal pressure?
25/10 mm
89
How would the LA pressure be affected if the LV is failing to pump blood?
Would be elevated
90
During diastole, what pressures equilibriate?
Those in the ventricles, atria, and large vessels feeding into the atria
91
When using a pulmonary arterial catheter, does the balloon inflation affect the patency of the lumen through which pressure is measured?
NOPE
92
What is another name for wedge pressure measurement?
Hemodynamic assessment
93
For how long are pulmonary catheters usually left in the patient?
Couple days with balloon NOT inflated (inflate periodically)
94
Normal RA pressure?
9/4 mmHg
95
Normal LA pressure (wedge)?
12/5 mmHg
96
Normal RV end-diastolic pressure?
< 6 mmHg
97
Normal LV end-diastolic pressure?
< 12 mmHg
98
How is cardiac output measured?
1. With a pulmonary arterial catheter in the pulmonary artery using an indicator dilution technique
2. By employing Fick's principle
99
Is CO in pulmonary artery = CO in aorta?
YUP
100
What is the curve duration when using the indicator-dilution method?
Time from injection until concentration has reached 0 (will need to be extrapolated)
101
What is the actual equation to measure CO using the indicator-dilution technique?
I/C.T
```
I = mass of indicator injected
C = mean dye concentration
T = duration of 1st circulation
```
102
Other 2 names for curve duration when using the indicator-dilution method?
Duration of 1st circulation = duration of primary curve
103
Describe the indicator dilution technique to measure CO.
1. Indicator dye is injected into the RV
2. Serial measurements of concentration are made in the pulmonary artery
3. Average indicator concentration and the duration of the first-circulation curve are used to calculate PA flow = CO
104
How will the concentration of dye in the PA fluctuate during the indicator-dilution method to measure CO?
Starts at 0 => reaches maximum => goes back down to a minimum => goes back up again because of recirculation
105
Describe the thermal dilution technique to measure CO.
1. Cold or room temperature saline is injected into the RV
2. Serial measurements of temperature are made in the pulmonary artery
3. Temperature deflection and the duration of the first-circulation curve are used to calculate PA flow = CO
106
What is the Fick principle?
Amount of substance added or removed to or from an organ = blood flow x (a-v)
(a-v) = difference in concentration across the organ between arteries and veins
107
How is Fick's principle used to calculate CO?
CO = blood flow across the lungs = amount of oxygen consumed (mL/min) / (a-v)O2
```
a = systemic arterial oxygen concentration (sampled from any artery)
v = pulmonary arterial oxygen concentration
```
108
Why is pulmonary arterial O2 concentration used in CO measurement using the Fick principle instead of the venous O2 concentration?
Because complete mixing of venous blood from various systemic regional circulations might not be accomplished until that point in the circulation
109
5 other techniques used to measure blood flow?
1. Plethysmography
2. Doppler flow meter
3. Electromagnetic flow
4. Echocardiography
5. fMRI
110
Do all circulatory pathways have the same transit time through the entire systemic circulation?
NOPE
111
How to use the indicator dilution technique when all you have is the curve produced?
CO = amount of indicator added / area under first circulation curve
112
What is 1 mmHg?
The pressure generated by elevating a column of mercury by 1 millimeter
113
What is VO2 a measure of?
Oxygen utilization
114
Normal RV pressure?
25/0 mmHg
115
Normal LV pressure?
120/0 mmHg
116
What would a continuous murmur in the second left intercostal space adjacent to the sternum mean? How would this affect CO?
Murmur near trunk of the pulmonary artery => patent ductus arteriosus so blood is being mixed between the aorta and the pulmonary artery causing the CO to appear to be higher when calculating CO with Fick's principle because (a-v) will be lower
117
When using a pulmonary arterial catheter, does the the balloon inflation affect the patency of the lumen through which pressure is measured? Explain.
The balloon is around the outside the catheter, which isn't weak enough to be collapsed by that balloon. Imagine a blood pressure cuff that is inflated, but still letting blood pass beneath it.
118
When are the pressures in the pulmonary vein, LA and LV very close?
Toward the end of diastole
119
Units for O2 consumption?
mL O2/min
120
What is pulse pressure a function of? What are the most important determinants in a healthy individual?
1. Stroke volume***
2. TPR***
3. Aortic distensibility
4. Heart rate
5. Ejection velocity
121
Which part of the pulmonary circuit has the highest pulse pressure?
RV
122
What other pressures is the RV diastolic pressure equal to?
CVP = RA diastolic
123
What other pressures is the LV diastolic pressure equal to?
LA diastolic = PAP diastolic
124
What is pulse pressure a surrogate for?
SV
