Key Equations

Question 1

What is Dalton’s law?

Answer 1

The idea that the pressure exerted by each gas in a mixture of gases is independent of the pressure exerted by other gases.

Question 2

What is Boyle’s law? Give an equation also.

Answer 2

The pressure of a fixed amount of gas in a container is inversely proportional to the container’s volume.

P1V1 = P2V2

Question 3

What is Henry’s law?

Answer 3

At equilibrium, the partial pressures of gas molecules in the liquid and gaseous phases must be identical.

Question 4

Give the alveolar gas equation.

Answer 4

PAO2 = PiO2 - PaCO2/R

R = respiratory exchange ratio

Question 5

Give the equation for calculating pressure.

Answer 5

pressure = flow x resistance

Question 6

Give the Law of Laplace.

Answer 6

P = 2T/r

P = pressure
T = surface tension
r = radius

Question 7

What is lung compliance?

Answer 7

The change in lung volume caused by a given change in transpulmonary pressure.

The greater the lung compliance, the more readily the lungs are expanded.

Question 8

Give two determinants of lung compliance.

Answer 8

1. Stretchability of lung tissue. Thicker the tissue, the less stretchy = decrease in lung compliance
2. Surface tension of alveoli. Water lines the alveoli. The surface tension of water is high. Type II pneumocytes produce surfactant to reduce the surface tension and increase lung compliance. Surfactant decreases when breaths are small and constant.