L3 Ventilation and Lung Mechanics

Question 1

Flow Rate Equation

Answer 1

F = (P1-P2)/R

R = resistance to flow

Question 2

Pressure in the alveoli can be described according to Boyle’s law. What does this law state?

Answer 2

The pressure of a gas is inversely proportional to the volume.

(As volume decreases, pressure increases and vice versa)

Question 3

What equation is associated with Boyle’s law?

Answer 3

P = nRT/V

n = number of moles of gas

R = gas constant

T = absolute temp (Kelvin)

V =volume

Question 4

What are the 2 possible reasons for a collapsed lung?

Answer 4

1) Elastic recoil

2) Surface tension - liquid droplets draw the alveolar membranes together, resulting in alveolar collapse

Question 5

What 2 factors normally prevent collapse of the lung?

Answer 5

1) Surfactant

2) Intrapleural pressure

Question 6

What is ‘compliance of the lungs and thorax’?

Answer 6

The ability to expand. Measured in terms of increased lung volume per unit of pressure change in intrapulmonary pressure.

For every 1cm increase in the intrapulmonary pressure, the lungs volume will increase by the compliance volume.

Units of compliance = L/cm

Normal = 0.13L/cm

Question 7

What instrument is used to measure the flow of air into and out of the lungs?

Answer 7

Spirometer

Question 8

What volumes make up the pulmonary volumes?

Answer 8

1) Tidal
2) Inspiratory reserve
3) Expiratory reserve
4) Residual

Question 9

What are the pulmonary capacities?

Answer 9

1) Inspiratory
2) Functional residual (total air left in lungs after a normal expiration)
3) Vital (total air that can be exhaled after a maximal inspiration)
4) Total lung

Question 10

What is the ‘minute respiratory volume’?

Answer 10

Total volume of air that passes through the respiratory system per minute.

Normally around 6L.

Question 11

What are dead air spaces?

Answer 11

Regions in the respiratory system where gas exchange does not take place

Question 12

What is the difference between anatomical dead air space and physiological dead air space?

Answer 12

Anatomical: volume taken up by nasal cavities to terminal bronchioles (~150ml).

Physiological: anatomical dead air space PLUS volume of non-functioning alveoli.

In a very healthy person, these could both be identical values. Usually the physiological is higher.

Question 13

How is the volume of air available for gas exchange calculated?

Answer 13

Alveolar Ventilation Rate (AVR)

AVR = RR(TV - DAS)

RR = respiratory rate (breaths/min)
TV = tidal volume (ml/resp)
DAS = dead air space (ml/resp)