Hemodynamics Flashcards
(51 cards)
What is velocity?
rate of displacement over time (distance per unit time)
What is flow?
volume per unit time
What is the equation for velocity in a conduit of varing CSA?
v = Q/A
For a given constant flow, how does velocity vary with respect to CSA?
inversely proportional
What does flow depend on?
the pressure gradient of the fluid and the dimensions of the entire CV system
How do velocity and area relate?
the ratio of the cell’s velocity past one cross section relative to that past cross section depends on the inverse ratio of the respective areas
V1/V2 = A1/A2
What does the velocity area rule (V1/V2 = A1/A2) pertain regardless of?
whether a given CSA applies to a system that consists of a single large tube or to a system made up of several smaller tubes in parallel
How is lateral/static pressure measured?
measured with tubes tangential to the direction of flow
How is total pressure measured?
three pitot tubes face upstream
What does dynamic pressure reflect?
the kinetic evergy of the flowing fluid
What is the equation for the dynamic compoenent of total pressure?
Pdyn = pv^2/2
p - density
pressure change -> velocity change. -> CSA change -> narrowing/widening of vessel
What does the area/volume of fluid in a tube determine?
lateral/static pressure
less volume (narrower tube) = decrease in static pressure
What changes when CSA changes resutling in a velocity change?
alters the dynamic component of pressure
What results in lateral and dynamic pressure when a vessel narrows?
pressure gradient difference
increase in velocity
dynamic component will increase
lateral component will decrease
How does peak velocity change in the ascending vs descending aorta?
In the descending thoracic aorta, the peak velocity is substantially less than in the ascending aorta
* lesser velocities have been recorded in more distal arterial sites
At what site does the dynamic pressure component attain higher values?
site of constriction it may attain substantial values
* most locations, it is a negligible fraction regardless of the orientation of the pressure probe
How does aortic stenosis affect dynamic and lateral pressure?
the entire output of LV is ejected through a narrow aortic valve orfice (calcified)
The high flow velocity is associated with a large kinetic energy -> the lateral pressure is correspondingly reduced (dynamic is increased)
What lateral pressure is recorded when two probes are both in the LV?
same pressures recorded
What lateral pressure is recorded when one probe is in the LV and the other is at the aortic valve?
The lateral pressure during ejection is much less than in the ventricular cavity
- increased velocity of flow in narrow valve orifice
What lateral pressure is recorded when one probe is in the LV (close to the aortic valve) and the other is in the aorta?
The pressure difference was even more pronounced
- substantial energy was lost through friction (viscosity) as blood flowed rapidly through the narrow aortic valve
What is Poiseuille’s law?
for steady laminar flow of a Newtonian fluid through a cylindrical tube flow (Q):
- varies directly to pressure difference
- varies directly to the fourth power of the radius of the tube
- varies inversely to the length of the tube
- varies inversely to the viscosity of the tube
What is the equation of Poiseuille’s law?
Q = pie(Pi-Po)r^4/8nl
What are characteristics of laminar flow?
when the thin layer of fluid in contact with the wall adheres to the wall and is motionless
the layer of fluid just central to the external laminate must shear against this motionless layer and moves slowly at a finite velocity
more central layers move progressively more rapidly
maximal velocity is at the center of the stream (and equal to twice the mean velocity of flow across the entire CSA of the tube)
How do fluid elements progress through laminar flow?
they remain in one lamina (streamline) as the fluid progresses longitudinally along the tube
