Lecture 3 Formulas

Question 1

Laplace’s Law

Answer 1

P=T/R - Column/Tube
P=2T/R - Sphere
P - Pressure
T - Tension
R - Resistance

Question 2

Surfactant

Answer 2

Reduces the surface tension of the fluid within the lungs. As the area of alveoli decrease, the concentration of surfactant increases, thereby decreasing T and P proportionally.

Question 3

PEEP

Answer 3

Decreases closing volume of the alveoli

Question 4

Atelectasis

Answer 4

Collapsing of the alveoli and respiratory bronchioles. This causes V/Q mismatch as a form of a shunt
SHUNT

Question 5

Aorta Aneurysm

Answer 5

Due to Laplace’s law, the aorta normally follows P=T/R.
If a portion of the wall loses tension beyond a certain point, pressure expands the area of the wall until the tension of the tissues balances the constant pressure.
Once the tissue expands it follows P=2T/R

Question 6

Lamina

Answer 6

Lamina is a 1 molecule thick sheet of fluid
Laminar flow normally consists of wrapped concentric cylinders of lamina
Pressure is directly proportional to flow
P/Q = R
ΔP=Q*R (If resistance is a fixed value)

Question 7

Hagen-Poiseuille Equation

Answer 7

Q= (πΔPr^4)/(8ηl)
ΔP=(8ηlQ)/(πr^4)
η - dynamic viscosity
l - length of tube
Flow is proportional to r^4

Question 8

Fanning Equation

Answer 8

Q^2=(KΔP4π^2r^5)/ρl

Flow is proportional to r^2.5

Question 9

Darcy’s Law

Answer 9

Q = ΔP/R
Similar to Ohm’s law but for fluids
Is only applicable to laminar flow.

Question 10

Reynold’s Number

Answer 10

NR = νρd/η

NR>2000 is Turbulent Flow

Question 11

Continuity Equation

Answer 11

v1 x a1 = v2 x a2

Question 12

Bernoulli’s Equation

Answer 12

E = P + pgh + 1/2 pv^2

Question 13

Entrainment ratio

Answer 13

Entrainment ratio = entrained flow / driving flow

1-FiO2/FiO2-.21

Question 14

Red Blood Cells

Answer 14

Diameter of red blood cell is 7 mcm.
Arterioles, capillaries and venules have diameter of 4 mcm to 10 mcm.
Critical closing pressure of arteries is 20 mmHg

Question 15

Hematocrit affect on resistance

Answer 15

Blood is 3 to 4 times more viscous then water. Polycythemic states (Hct 60) can have viscosity as high as 10 times water. Viscosity creates greater resistance to flow

Question 16

Fahraeus-Lindquist Effect

Answer 16

As vessel diameter decreases, the viscosity decreases due to the cells “lining up.” This happens at diameters less than 0.5 mm but greater than the diameter of the red cells.

Question 17

Viscosity increases as blood velocity decreases

Answer 17

Due to Rouleaux formations (cellular aggregations) at low velocity which block vessels.