Principles of Circulatory Function Flashcards
What are the principles of circulatory function?
1) rate of flow to vascular bed controlled by tissue demand
2) CO = sum of all local tissue flows
3) arterial pressure controlled independently of CO & local blood flow
Define conductance?
C = (1 / Resistance)
Define flow in terms of P & conductance.
Q = (deltaP) * C
What is Poiseuille’s Law?
small change in vessel diameter = big change in flow
What is flow in terms of Poiseuille’s Law?
Q = (pi * deltaP * r^4) / (8 * n * l)
What is the largest determinant of flow?
vessel diameter
What is conductance proportional to?
d^4
Why does parallel circuitry increase conductance?
decreased resistance!
1/Rt = 1/R + 1/R + 1/R
What is a normal hematocrit?
45
What effect does hematocrit have on flow? At what level is flow stopped?
increased hematocrit = increased viscosity (n) = decreased flow
inhibited @ 60
Why is autoregulation important?
it uncouples pressure & flow
What is the mechanism behind autoregulation?
1) increased o2 + nutrients = contraction
2) stretch-activated Ca++ s.m. channels = contraction
Define critical closing pressure?
If P falls below certain point (60 mmHg), vessel closes & restricts flow completely
What modulates vascular tone?
the SNS
Define blood pressure.
the stored energy generated via the work of the heart
