Circulation and Hemodynamics Flashcards
What are the relative pressures of the following vessels:
Arteries
Arterioles
Capillaries
Veins
high pressure
moderate pressure, Sm.M can moderate
large XS area (low velocity, low pressure)
low pressure, large volume
how do you calculate velocity of blood flow?
V=Q(flow)/A(area)
can be calculated for a single vessel knowing its XS area and flow
OR
knowing total summed XS area of parallel circuits and flow
What is the relationship between flow, pressure, and resistance?
Q=change in P/R
can be determined through individual vessel or segment of vessel or through entire system
What is the equation for cardiac output?
CO=Arterial pressure-venous pressure/TPR
Or CO=BP/TPR
or CO=HRxSV
What is Poiseuille’s law equation for resistance?
What is the relationship between the constants?
R=(8nl)/pir^4)
n=viscosity (dehydration can increase, anemia can decrease)
l=length of vessel (can increase or decrease with body habitus)
pi=is pi
r=radius (vasoconstriction decreases radius, increases resistance, vasodilation increases radius, decreases resistance) *Most significant determinant*
Adding resistance beds in series does what?
Adding resistance beds in parallel does what?
increases resistance (series=R1+R2+R3…)
decreases total resistance (parallel=1/r1+1/r2+1/r3…)
When does blood flow become turbulent?
when velocity is high
when XS area is large
when density is heavy
and/or
when viscosity is low
What equation can predict turbulence?
Reynolds number
Nr=pdv/n
p-denisity, d-diameter, v-velocity, n-viscosity
if greater than 2000, then considered to transition from laminar to turbulent flow
leads to bruit and arteriosclerosis
What is blood vessel compliance?
describes how easy it is to cause a vessel to expand
how much does the vessel expand in response to a given change in lumen hydrostatic pressure
compliance =change in volume/change in pressure
How do you change compliance?
Smooth muscle contraction causes a shift in compliance, moving blood to arterial side and increasing pressure
Describe the pressure changes in the cardiovascular system
pressure gradually drops through the systemic circulation
pulsatile in nature at aortic end due to compliance and distension during ejection and recoil during diastole, lost by arterioles.
What is clinically reported as systolic pressure?
What is clinically reported diastolic pressure?
greatest pressure reached in a large artery
lowest pressure reached in large artery
(120/80, pulse pressure is systolic-diastolic=40, mean pressure = diastolic+1/3 pulse pressure=80+(40/3) = 93.3
Since pulse pressure is dependent on the arterial compliance, what happens when you decrease compliance?
Pulse pressure increases
systolic pressure increases
diastolic pressure stays the same or decreases
How would increased SV or increased R effect this?
What are the three features of venous pressure?
Low pressure, high compliance, large volume
What are the features of atrial pressure?
low and estimated by pulmonary wedge pressure
since the measurement site is a little upstream from the atrium, it is a few mmHg higher than the actual left atrial pressure
This is important because it can be used to determine if someone has heart failure/to what extent
What is the arterial pressure change in the following conditions:
Arteriosclerosis
Aortic Stenosis
Increase arterial pressure
decrease arterial pressure
If you change resistance only and nothing else (no change in compliance) what is the result?
No change in pulse pressure
(not typically seen in nature)
What makes up microcirculation?
arterioles with Sm. M wall
metarterioles with limited Sm. M walls
capillaries with precap. sphincters
How does exchange occur across the capillary wall?
Via clefts
these clefts allow water soluble substances such as glucose, electrolytes etc, through (small in brain, large in liver/gut)
lipid soluble substances such as O2 and CO2 pass thru cell wall and larger things pass through in vesicles
What does the Starling Equation calculate?
Know the equation
flow of water out of the capillary (+) or into the capillary
(-)
based on hydrostatic pressure (BP)
Osmotic pressure (pi)
Jv=Kf (Pc-Pi)-(pic-pii)
Pc-Pi is the HSP
pic-pii is the Osm. P
What can alter hydrostatic pressure or osmotic pressure
edema
Pc can change by elevated venous pressure (heart failure)
Pi can change by restriced lymphatic flow or increased driving force out of capillary
pic can change by decrease in albumin (starvation, liver failure)
pii can change by restricted lymph flow or inflammation
How much lymph is made per day?
about 2-3 liters per day reenters at the subclavian vein
How can tissues “break” from central control in times where one tissue needs more perfusion than another?
local beds can break away from central control when local needs become greater
this does no significantly alter the TPR or other tissues will compensate by further constriction to maintain BP constant in the face of some tissues “breaking” from central control
Describe myogenic control (reflex)
if the blood pressure is elevated, which would otherwise deliver more blood than necessary, arterial walls become stretched and that causes vasoconstriction
the opposite occurs when blood pressure drops (vasodilate as a result)
Describe metabolic control.?
Short: High metabolism stimulates vasodilation, increasing blood flow to area in need
Long: active hyperemia is increasing interstitial concetration of metabolites such as CO2, H, K, lactate and adenosine or decrease in O2 due to increasing metabolism causes smooth muscle of arterioles, metarterioles, and pre-cap. sphincters to relax increasing flow through the area
What is reactive hyperemia?
when vascular obstruction causes build-up of metabolites leading to vasodilation therefore if the obstruction is removed the area is flooded with blood
ex: sitting on your hand for a few minutes and then moving it
What is shear (in terms of local control)
if a vascular bed dilates due to metabolic demand, the flow through upstream arterioles and small arteries would increase
this would increase the shear or wall friction leading to the release of NO which would cause vasodilation and augment the downstream metabolic effect
Histamine and Bradykinin effect blood flow how?
arteriolar vasodilation
increases capillary porosity (Kf) allowing escape of large molecules
causes edema in response to tissue damage
How does serotonin effect blood flow
vasoconstricition in response to tissue damage
What has “mixed” effects on blood flow?
prostaglandin
Describe coronary circulation
- mostly under metabolic control
- left ventricular contraction causes constriction of vasculature msot notably near the endocardial surface
- CA blood flow is lowest during ventricular contraction
What controls cerebral circulation?
mostly metabolic control
Describe Pulmonary circulation
- highest pressures of the pulmonary vascular system are found in the RV and pulmonary artery
- the pressure in the RV varies from 24mmHg to 0-4mmHg
- pressure changes are less in the pulmonary A. (24 to 10-16)
- Avg pressures in the Pulmonary A. is 20mmHg
Is resistance high or low in the pulmonary system?
Resistance is very low in the pulmonary system
How is pulmonary blood flow regulated?
vasoconstriction (alveolar hypoxia)
little sympathetic influence
compliant arterial system, meaning that small changes in mean pressure will dilate arteries, reduce resistance and help maintain pressure low in the face of large changes in flow
How does alpha receptors and beta receptors play a role in blood flow at rest and during f/f responses?
at rest-NE binds alpha receptors
flight/fight-adrenal glands secrete EPI that binds to B2 and cause vasodilation
What is a right to left shunt?
What is a left to right shunt?
blood passing from system veins to systemic arteries without passing through functional lung tissue
blood passing from systemic arteries to systemic veins without passing through a capillary bed for substance exchange
