Physics

Question 1

Boyle’s Law

Answer 1

For a fixed mass at constant temperature, the product of pressure and volume is constant.

P1V1 = P2V2

Question 2

Charles’ Law

Answer 2

At constant pressure, volume of a fixed amount of gas is directly proportional to its absolute temperature (kelvin)

V1/T1 = V2/T2

Question 3

Laplace’s Law (for a sphere)

Answer 3

The surface tension of the sphere is directly proportional to the radius of the sphere and pressure within the sphere.

T = (1/2) PR
T = surface tension
P = pressure within sphere
R = radius of sphere

For us: relationship between intra-alveolar pressure, surface tension, and the radius of the alveoli. T= surface tension, P = intra-alveolar pressure, R = radius of alveoli. Surface tension forces tend to favor alveolar collapse.

Can also think of this as:
Pressure = 2 x surface tension / radius

Question 4

Bernoulli equation (modified)

Answer 4

Defines the pressure drop (or gradient) across an obstruction, narrowing, or stenosis.
deltaP = 4Vsquared

delta P = pressure gradient
V is the measured velocity across the stenosis using Doppler echo

Ex: pt with AS has peak velocity across AoV of 4 m/sec. if BP is 130/80, what is peak pressure in left ventricle?
deltaP = 4 x 4squared
= 64
So 130 + 64 = 194 mmHg