Cardiology II Flashcards
1
Q
Circuits in Series
A
- Flow must be equal
- CO of R & L heart are inter-dependent bc of their series arrangement
2
Q
Hemodynamics
A
- Blood flows in a CLOSED system
- Blood is non-compressible
- Blood is heterogenous
- Vessels are compliant, not rigid
3
Q
Large artery
A
- Thick walled
- Under high pressure
4
Q
Large vein
A
- Thin walled
- Under low pressure
5
Q
Area & volume in blood vessels
A
- Capillaries have biggest cross sectional area
- Veins contain greatest amount of blood
6
Q
Flow equation
A
Q = ∆P/R
- Q = flow
- P = pressure
- R = resistance
7
Q
Flow (Q)
A
How much travels
- volume flow per unit time
8
Q
Velocity (v)
A
How fast it travels
- rate of displacement of blood per unit time
- Inversely proportional to TOTAL cross- sectional area
- Fastest in aorta & slowest in capillaries
9
Q
Velocity equation
A
v = Q/A
- A = total cross sectional area of tube through which blood flows
10
Q
Flow vs velocity
A
- If flow through a tube is constant, then velocity increases as total x-sectional area decreases
- As vessel diameter increases, velocity of flow through the vessel decreases.
11
Q
Smallest vessel
A
aorta
12
Q
Medium vessel
A
all of the arteries
13
Q
Largest vessel
A
all of the capillaries
14
Q
Why is velocity the slowest in the capillaries?
A
Total cross-sectional area of ALL capillaries combined is huge!
15
Q
Laminar flow
A
- Streamline
- Concentric lamina slide past 1 another
- Viscous forces dominate
16
Q
Turbulent flow
A
- Eddy currents
- Noisy
- Larger pressure required to maintain constant flow through turbulent areas
- Inertial forces dominate
17
Q
When is flow turbulent?
A
If Reynold’s # is > 3000
18
Q
Reynold’s equation
A
Re = vpD/n
- v = velocity
- p = fluid density
- D = tube diameter
- n = viscosity
- If Re is greater than 2000, there is an increasing likelihood that blood flow will become turbulent
19
Q
When is flow laminar?
A
If Reynold’s # is < 2000
20
Q
Anemia
A
- Associated w/ decreased hematocrit, mass of RBCs, & viscosity
- Decreased viscosity –> increase in Re
21
Q
What does anemia cause?
A
Turbulent flow & functional murmurs
22
Q
Thrombi
A
Blood clots in the lumen of vessels
- Diameter narrows, increasing blood velocity at the site of thrombus
23
Q
Flow vs pressure
A
Flow is dependent upon pressure difference
24
Q
Pressure gradient equation
A
∆P = (P1 - P2)
- Direction: high to low pressure
25
Flow vs resistance
Increasing resistance --> decreased flow
26
Resistance equation
R = ∆P/Q
27
What is the major mechanism for changing resistance in the CV system?
Changing resistance of blood vessels (mainly arterioles)
28
Resistance to blood flow
- R is directly proportional to viscosity
- R is directly proportional to length
- R is inversely proportional to the 4th power of the radius ** MOST IMPORTANT!
29
Resistance (Poiseuille) equation
R = nl8/r4π
30
Series (vascular beds)
Blood flows from 1 vessel to another in sequence
31
Parallel (vascular beds)
Blood flow is distributed simultaneously among parallel vessels
32
Series resistance
- Sequential arrangement
| - Total resistance = sum of individual resistances
33
Effects of sequential arrangement
- Total flow through each level of the system is the same
| - Pressure decreases progressively
34
Parallel resistance
- Simultaneous arrangement
| - Total resistance is less than any individual resistances
35
Effects of simultaneous arrangement
- Mean pressure in each artery will be close to mean pressure in the aorta
- Adding a new resistance to the circuit decreases total resistance
36
Control of BP
- Baroreceptor reflex: Neurally-mediated, reacts in seconds
| - Renin-angiotension-aldosterone system: Hormonally mediated, reacts in minutes to hours
37
Baroreceptors
- Mechanoreceptors located in carotid sinus & aortic arch
- Sensory afferents carry pressure info to CV centers in brainstem
- CV centers coordinate a ∆ in output of ANS
- Efferent neurons direct ∆s in heart & blood vessels
- Strongest stimulus = rapid ∆ in pressure
38
Baroflex via ANS
- Decrease PNS to heart --> HR increases
| - Increase SNS to blood vessels --> BP increases
39
Systolic pressure
- Highest arterial pressure during cardiac cycle
| - Pressure in artery after blood has been ejected from LV during systole
40
Diastolic pressure
- Lowest arterial pressure during cardiac cycle
- Pressure in artery when no blood is being ejected from LV
- DBP decreases when TPR decreases
41
What happens at the initiation of exercise?
Muscle mechanoreceptors & chemoreceptors trigger reflexes that send afferents to the motor cortex
42
Motor cortex
Directs responses to increase sympathetic outflow to the heart & blood vessels
- Heart = increase HR & contractility
- Blood vessels = arteriolar constriction & venoconstriction
- Venoconstriction increases VR to heart
43
Why is increase in VR essential?
Provides increased EDV (needed to produce increase in SV & CO)
- Frank-starling mechanism
44
Local responses in skeletal & cardiac muscle
- Metabolites build up (lactate, K+, nitric oxide, adenosine)
˚ Leads to vasodilation of arterioles
˚ Increases local blood flow to muscles
- Prominent response --> Decrease in TPR
- Dominate in heart
˚ Vasodilation mediated by adenosine & decreased PO2
˚ Leads to increased coronary blood flow
45
Pulse pressure increase in exercise
- Large amount of elastic tissue in arteries --> stiff & noncompliant
- During systole, blood is rapidly ejected into aorta/arteries --> arterial pressure increases from lowest (diastole) to highest (systole)
- Magnitude of increase = pulse pressure
- PP depends on SV & compliance of arteries
- PP increases in exercise bc SV increases
46
Cutaneous blood flow
- Exhibits a biphasic response to exercise
- Early – vasoconstriction of cutaneous arterioles occurs as a result of the sympathetic alpha1 receptor activity
- As exercise progresses, body temp increases secondary to O2 consumption
47
VO2 max
Point at which O2 consumption fails to rise despite increased exercise intensity or power output
- O2 consumption shows a plateau
48
O2 exchange in lungs
- Restores PO2 to its normal arterial value of 100mmHg
- In exercise, while venous PO2 is lower than normal, rapid diffusion of O2 from alveolar gas raises PO2 in arterial blood back to normal
- Only compromised in people w/ lung disease
