Vascular pt 2 Flashcards
Transmural (intravascular) pressure
• The ΔP between the intravascular (inside) and tissue (outside) pressure
explain Perfusion (driving) pressure
- The ΔP between arterial and venous ends of a blood vessel
* Generated by contracting heart and elastic arteries.
Wall distension depends on
compliance.
• Veins expand easily to store blood because of high
compliance and low transmural pressures. (These two are determined by CO & R)
explain Gravity (hydrostatic) pressure
- ΔP is proportional to the height of the column of blood in the body; exists in absence of blood flow
- Pressure lowest in head, highest in feet
3 BLOOD PRESSURE CHARACTERISTICS
Perfusion (driving) pressure
Transmural (intravascular) pressure
Gravity (hydrostatic) pressure
TRANSMURAL PRESSURE (P) generates stress (S) within wall; it is a function of
radius (R) and wall thickness (w). Based on LaPlace equation: T=PR and S=T/w. • S = P x R/w
• Vessels that produce little stress and can tolerate high pressures are
– small vessels eg. capillaries (low R)
– thick walled vessels eg. aorta (large w)
characteristics of Perfusion pressure are ?
directed along the length of the vessel (kinetic energy)
• Important pressure for direction O2 and nutrients to tissues
• Not affected by change in radius
characteristics of Transmural pressure?
directed against the wall (potential energy)
• Important in smoothening pressure pulses.
According to Bernoulli’s principle: Perfusion & transmural pressures vary with velocity of flow, why?
– Increased velocity decreases the lateral, transmural pressure thus, more fluid energy is in the form of forward kinetic energy, and less as sideways, potential energy.
– In dilated vessels, there is more ___ and is potentially dangerous in aneurysms
transmural (lateral) pressure
Pressure gradient (ΔP) across a blood vessel depends on its
resistance.
Aorta has high pressure due to ?
cardiac output and low compliance of aorta.
Arterioles form the largest drop in pressure (ΔP) across the vascular system due to ?
high resistance.
Capillary pressure drops due to ?
friction and outward filtration of fluid
Venules & Veins: pressure decreases with increased ?
compliance
Blood pressure is a key index of CV health, since it can reflect changes in ?
cardiac output (CO) and total peripheral resistance (TPR).
___ is the average pressure in a cardiac cycle.
Mean Arterial Pressure (MAP)
Diastolic P + 1/3 (systolic - diastolic pressure)
MAP rises with either increased CO or TPR.
MAP rises with either increased
CO or TPR
____ is the difference between systolic and diastolic pressures.
Pulse pressure
• PP=Ps-Pd
____ is proportional to stroke volume (SV) and inversely proportional to compliance (C)
Pulse Pressure
• PP = SV / C
Stretch-ability” of blood vessels walls; it is the inverse of elasticity (resistance to stretch).
Dependent on pliability of tissues: elastic fibers, smooth muscle, CT, etc
compliance
During systole, arteries expand due to the presence of ?
elastic fibers
__and continuous propulsion smoothen out the blood flow pulsations
elasticity
absorption of pressure waves by the__ is dependent on the ___ of the vessel.
elasticity
compliance
___ depends on the ratio of elastic to collagen fibers in the extracellular matrix
Compliance
A relative increase in___ will limit expansion and reduce compliance
collagen
Dampening of the pressure oscillations made by the heart is also called the ?
Windkessel effect
explain the “second heart beat” during diastole
During diastole, contraction of aortic elastic fibers generate a pressure wave that propagates through the rest of the arteries.
– Elasticity absorbs the energy of the pressure wave (potential energy) and releases it during diastole (kinetic energy)
Pulses are not completely flattened until they reach the?
small arteries and arterioles
Decreasing the compliance of arteries has two effects:
Increases arterial systolic pressure
Decreases arterial diastolic pressure because there is less elastic recoil
Elasticity normally absorbs and diminishes some of the pressure . A narrower, stiff, non-compliant artery has an ?
inherently greater resistance and generates a greater ΔP.
low compliance generates a higher___ and a lower___ pressure
systolic
diastolic
Increased SV increases PP and MAP by increasing the___ level.
systolic
Decreased compliance increases PP by increasing___ and decreasing____ pressures. Decreased compliance indicated by increase of slope.
systolic
diastolic
C=ΔV/ΔP
PP amplitude and wave form are indices of ?
vascular compliance.
PP is a better index in ?
people over 60 (more atherosclerosis)
Diastolic pressure is a better index for ?
younger people (more vascular resistance)
Low compliance increases ___
PP amplitude
-Arteriosclerosis: low compliance leads to an increased PP (decreased diastolic pressure not always present)
Low stroke volume decreases__?
PP amplitude
• Aortic stenosis: decreased SV leads to reduced PP
• Hypothyroidism: low heart contractility and low SV leads to a reduced PP
explain Pulse waves
• It’s what you feel at an artery not caused by blood flow.
• Pulse wave travels 15 or more times more rapidly than blood flow
• A wave of distension travels to peripheral vessels, accelerating as it goes.
– Aorta: 3-6 m/s
– Large arteries: 7-10 m/s
– Small arteries: 15-35 m/s
Increasing resistance along the arterial tree causes ?
the increased velocity
Decreased compliance as one ages causes
an increase in pulse wave amplitude
Arterial pulse waveform has 2 components:
• Forward (incident) traveling wave when the left ventricle contracts
• Reflected (rebound) wave returning from the periphery.
– In a compliant arterial tree, the reflected wave coincides with the diastole and augments perfusion of the coronary arteries.
___ reflects off aortic and other vascular
bifurcations or regions of high resistance
Pulse wave
__is the sum of the reflected wave and the forward wave, separated by a dicrotic notch
Waveform
Decreased arterial compliance____ velocity of both
forward (incident) and reflected pulse waves
increases
– With age the reflected wave appears earlier and the dicrotic notch disappears
Accelerated reflected wave has two actions:
– It is added to the forward wave to increase systolic
pressure amplitude (increase risk of stroke)
– It shifts to the earlier systolic phase such that there is less pressure during subsequent diastole for coronary artery perfusion.
Decreased compliance is due to
- Vasoconstriction / atherosclerosis
* Reduction in dilatory responses
Vasodilation reduces the amplitude and velocity of the reflected wave, enhancing the dicrotic notch. This is due to?
– Nitric oxide (NO) vasodilation of artery; NO is released from endothelium in response to cardiac pulse pressure
– Decreased sympathetic activity
Vasoconstriction increases speed of return of rebound wave & diminishes the dicrotic notch. This is due to:
– Decreased NO responsiveness to pulse pressure due to damaged blood vessels
– Increased sympathetic activity
– Atherosclerosis
