Flashcards in Principles of Blood Flow Deck (21)
Is Blood a Newtonian fluid?
No it is non-Newtonian. (There is no constant viscosity)
What is stage 1 blood flow?
Steady laminar flow in a rigid vessel. Static driving pressure.
What is stage 2 blood flow?
High Reynold's number flow and turbulence. Dynamic pressure.
What is stage 3 blood flow?
Elastic vessel walls and pulsatile pressure.
What is stage 4 blood flow?
Microcirculation and diffusion.
What is blood flow? Describe flow through a series of tubes.
It is the quantity of blood passing a particular observation point in a given time interval (L/min). It is constant
Mathematically how can one describe blood flow in a parallel circuit?
Volume flows are additive. Flow in equals flow out if there are no sources or sinks. Flow across any total cross-sectional area is constant. Generalizes to any number of parallel branches. Flow is the same in the aorta and the pulmonary artery.
What does the parallel architecture of the circulatory system permit?
Redistribution of blood flow
What is the continuity equation?
In tubes with varying cross-sectional area Q=A x v. v=detla x/ delta t.
How is velocity related to the total cross-sectional area?
Inversely proportional v=Q/A. With constant flow a smaller vessel will have blood traveling through it at a higher velocity.
What is transit time? How can it be estimated? What is the transit time for the whole circulation?
It is the time required for a blood cell to travel between two points in the system. t=l/v (length and velocity) t=V/Q (volume and flow). One pass through the entire systemic and pulmonary circulation is about 1 min.
What contributes to resistance of flow?
The walls of the vessel and the viscosity of the blood. They are both frictional forces.
Since the length of blood vessels and the viscosity of blood do not normally change what is the major variable that determines the resistance to the flow?
The radius of blood vessels, primarily the arterioles.
What is Poiseuille's law?
Q= ∆P x (pi r^4/ 8nL). n=viscosity L=length
How is temperature related to viscosity?
They are inversely related. Cold temperatures increase blood viscosity contributing to decreased blood flow in cold hands and feet.
How does blood pressure change along the length of a vessel?
For a given flow a greater pressure drop along the length of the vessel occurs in a longer vessel with a higher viscosity fluid and most severely with a smaller radius.
What is ∆P equal to?
P1-P2 where P1 is the pressure at the beginning of the vessel. P2=P1-(8nQ/πr^4)L
How do you determine resistance for blood vessels in series? What does R equal?
Rtotal = R1 + R2 + R3
Across which vessel is the largest pressure drop if they are all equal lengths?
The smallest vessel will cause the largest drop in pressure (all other variables held constant Q, L, n etc.)
How is resistance for blood flow determined when vessels are in parallel?
1/Rtotal = 1/R1 + 1/R2 + 1/R3 etc. The more branches in a parallel network the lower the total resistance.