Cardiology II Flashcards
Circuits in Series
- Flow must be equal
- CO of R & L heart are inter-dependent bc of their series arrangement
Hemodynamics
- Blood flows in a CLOSED system
- Blood is non-compressible
- Blood is heterogenous
- Vessels are compliant, not rigid
Large artery
- Thick walled
- Under high pressure
Large vein
- Thin walled
- Under low pressure
Area & volume in blood vessels
- Capillaries have biggest cross sectional area
- Veins contain greatest amount of blood
Flow equation
Q = ∆P/R
- Q = flow
- P = pressure
- R = resistance
Flow (Q)
How much travels
- volume flow per unit time
Velocity (v)
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
Velocity equation
v = Q/A
- A = total cross sectional area of tube through which blood flows
Flow vs velocity
- 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.
Smallest vessel
aorta
Medium vessel
all of the arteries
Largest vessel
all of the capillaries
Why is velocity the slowest in the capillaries?
Total cross-sectional area of ALL capillaries combined is huge!
Laminar flow
- Streamline
- Concentric lamina slide past 1 another
- Viscous forces dominate
Turbulent flow
- Eddy currents
- Noisy
- Larger pressure required to maintain constant flow through turbulent areas
- Inertial forces dominate
When is flow turbulent?
If Reynold’s # is > 3000
Reynold’s equation
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
When is flow laminar?
If Reynold’s # is < 2000
Anemia
- Associated w/ decreased hematocrit, mass of RBCs, & viscosity
- Decreased viscosity –> increase in Re
What does anemia cause?
Turbulent flow & functional murmurs
Thrombi
Blood clots in the lumen of vessels
- Diameter narrows, increasing blood velocity at the site of thrombus
Flow vs pressure
Flow is dependent upon pressure difference
Pressure gradient equation
∆P = (P1 - P2)
- Direction: high to low pressure
Flow vs resistance
Increasing resistance –> decreased flow
Resistance equation
R = ∆P/Q
What is the major mechanism for changing resistance in the CV system?
Changing resistance of blood vessels (mainly arterioles)
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!
Resistance (Poiseuille) equation
R = nl8/r4π
Series (vascular beds)
Blood flows from 1 vessel to another in sequence
Parallel (vascular beds)
Blood flow is distributed simultaneously among parallel vessels
Series resistance
- Sequential arrangement
- Total resistance = sum of individual resistances
Effects of sequential arrangement
- Total flow through each level of the system is the same
- Pressure decreases progressively
Parallel resistance
- Simultaneous arrangement
- Total resistance is less than any individual resistances
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
Control of BP
- Baroreceptor reflex: Neurally-mediated, reacts in seconds
- Renin-angiotension-aldosterone system: Hormonally mediated, reacts in minutes to hours
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
Baroflex via ANS
- Decrease PNS to heart –> HR increases
- Increase SNS to blood vessels –> BP increases
Systolic pressure
- Highest arterial pressure during cardiac cycle
- Pressure in artery after blood has been ejected from LV during systole
Diastolic pressure
- Lowest arterial pressure during cardiac cycle
- Pressure in artery when no blood is being ejected from LV
- DBP decreases when TPR decreases
What happens at the initiation of exercise?
Muscle mechanoreceptors & chemoreceptors trigger reflexes that send afferents to the motor cortex
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
Why is increase in VR essential?
Provides increased EDV (needed to produce increase in SV & CO)
- Frank-starling mechanism
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
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
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
VO2 max
Point at which O2 consumption fails to rise despite increased exercise intensity or power output
- O2 consumption shows a plateau
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
