Physiology Lecture 2: Lung Dynamics

Question 1

2 factors that govern lung dynamics

Answer 1

1. Physical characteristics of the airways
2. Lung parenchyma (accomodates changes in lung volume)

Question 2

Describe Poiseuille flow

Answer 2

Perfectly laminar flow in which the gas in the center of the tube moves fastest (minimum energy)

Question 3

When is laminar flow most likely to occur

Answer 3

When the flow rate is low and the tube diameter is small

Question 4

In laminar flow, if the tube radius is halved, how much must the driving pressure be increased by in order to maintain the same flow?

Answer 4

16 times

Question 5

Mean forward velocity of fluid or gas at any point in tubular flow

Answer 5

Equal at all points

Question 6

How does the driving pressure vary in turbulent flow?

Answer 6

Varies with the square of the flow

Question 7

When is turbulent flow most likely to occur

Answer 7

When the flow rate is high and the tube diameter is large

Question 8

How to determine likelihood of laminar vs. tubular flow

Answer 8

Reynold’s number (using airway size “r” and speed of air “v”)

Higher reynold’s number = more turbulent flow

Question 9

Reynold’s number equation

Answer 9

2rvd/n

Where:

• r = radius
• v = velocity
• d = gas density
• n = gas viscosity

Question 10

Driving pressure across the airways in the lungs (equation)

Answer 10

ΔP = k₁V + k₂V²

Question 11

Resistance equation

Answer 11

R = ΔP/V

Question 12

2 types of pulmonary resistance

Answer 12

1. Airway resistance
2. Tissue resistance

Question 13

Define airway resistance

Answer 13

Loss of energy as air flows through the airways

Question 14

Define tissue resistance

Answer 14

Loss of energy as lung tissue changes length and volume (elastic energy)

Energy is dissipated as fibres and molecules move past each other

Question 15

Equatioin for resistance in Poiseuille flow

Answer 15

L= tube length

n = viscosity

r = tube radius

Question 16

2 effects of airway branching

Answer 16

1. Velocity of air movement decreases as the diameter of individual airways decreases (thus favorign laminar flow)
2. Total cross-sectional area of the airways increases = reduce resistance

Question 17

Effect of tube arrangement

Answer 17

Tubes in parallel = lower airway resistance

Question 18

Describe the respiratory cycle curves of volume, pleural pressure, flow, and alveolar pressure

Answer 18

Question 19

3 factors upon which maximum expiratory flow depends

Answer 19

• Airways resistance
• Elastic recoil of the lungs
• Expiratory muscles

Question 20

4 reasons for expiratory flow limitation

Answer 20

• Airways are compressible tubes subject to narrowing by increased pleural pressure = choke points
• Driving pressure diminished as lung volume decreases and elastic recoil falls
• P dissipates in the airways as E is lost, overcoming R
• Raw increases at lower lung volumes as parenchymal tethering effect on airways diminishes and airway caliber decreases

Question 21

How can forced expiratory flow-volume curves detect diseases

Answer 21

Elastic recoil or airway resistance diseases can be detected since elastic recoil pressure and airway resistance between the alveolus and the “choke point” determine flow in the effort-independent portion of the curve