11/20/2014 Medical Physiology: Hemodynamics Barry Knox Flashcards
Write flow equation
Q = A x v
Write Ohm’s Law of Fluids
Q = change in P/R
Why can blood flow through an individual organ be considered to be flow through a series network?
- consecutive vascular network directs blood in the organ from arteries to veins
- there can be dramatic differences in resistance in different organs –> allows changes in control of blood flow even though the mean arterial blood pressure is relatively constant
Who determines the overall resistance of any organ and why?
Arterioles resistance (controlled by arteriolar radius) –> they have the largest resistance compared to other vessels
Cite a major control point in cardiovascular physiology
Contraction or relaxation of the smooth muscles in the arteriolar wall
Define total peripheral resistance (TPR)
Overall resistance to flow through the circulation
In what kind of network are organs arranged?
Parallel
*the resistance of each organ contributes to the TPR according to the inverse relationship
Why does any pressure difference comes only from frictional losses from circulation?
Because the aortic valve and the right atrium are at the same height
What is total flow equal to (approximately, if we talk about the entire circulatory system)?
Cardiac output
*assuming central venous pressure = 0
What is mean arterial pressure equal to?
CO (cardiac output) X TPR (total peripheral resistance)
What is the normal value of TPR at rest?
- 2 PRU
* 0.42 (exercise)
* 2.1 (hypertension)
What does the slope of P vs. Q graph represent?
1/R
How does R behave in exercise and hypertension compared to rest?
R (hypertension) > R (rest) > R (exercise)
Define viscosity
A measure of intermolecular attractions in the liquid, which determines the steepness of the velocity gradient
*different from density
Define density
Also called specific gravity, and which is defined as the mass per unit volume (g/ml)
Differentiate between laminar and turbulent flow
- Laminar (silent) flow –> flow is proportional to ∆P –> breaks down when velocity reaches a critical point –> Re flow above critical point of velocity –> effective resistance increases –> causes significant losses of kinetic energy –> Q proportional to the square root of ∆P –> Re>3000
- For the same ∆P, there is less flow when flow is turbulent than when laminar
What is the Reynolds number?
Critical parameter that characterizes flow (Re)=disruptive forces/cohesive forces
disruptive forces=2rvp (radius,velocity,density)
cohesive forces=n (viscosity)
What are auscultatory sounds?
The surfaces of constant velocity (spirals, swirls, and eddies) heard in turbulent flow with a stethoscope
Define murmurs (bruits)
Audible sounds due to vibrations in heart or vessel walls; not usually heard under resting conditions
Define “innocent” systolic murmurs
Occur when cardiac output increases during exercise, causing turbulent aortic flow during systole