Respiratory Physiology - Ventilation

Question 1

Weibel’s model of airways

Answer 1

Idealised model of the airways with 23 levels of branching (23 airway generations)

Question 2

Total cross sectional area of lung with subsequent airway generations

Answer 2

Exponentially increases
Significantly increased area as reach respiratory zone

Question 3

Implication of significant increase in total cross sectional area (eg as reach respiratory zone)

Answer 3

Decreased forward flow of air through airways

Question 4

Mechanism of gas transfer from conducting zone to respiratory zone

Answer 4

Diffusion of air due to large increase in cross sectional area

Question 5

Implication of gas diffusion and lung disease

Answer 5

Pollutants collect in junction between anatomical dead space and respiratory zone as larger particles diffuse less easily

Question 6

Typical tidal volume

Answer 6

6-8 ml/Kg
Average size adult ~500 ml

Question 7

Typical Alveolar gas volume

Answer 7

3000 ml

Question 8

Typical anatomical dead space volume

Answer 8

150 ml

Question 9

Typical pulmonary capillary blood volume

Answer 9

70 ml

Question 10

Pulmonary blood flow per minute definition and typical value

Answer 10

Cardiac output
~ 5 L/min

Question 11

Alveolar ventilation calculation

Answer 11

(Tidal volume - Anatomic dead space) x RR

Eg. typically:
(500 ml - 150 ml) x 15 = 5250 ml

Question 12

Alveolar ventilation definition

Answer 12

Volume of fresh gas reaching blood/air barrier each minute

Question 13

Typical Ventilation perfusion ratio

Answer 13

Alveolar ventilation per minute / Pulmonary blood flow per minute

As per previous flashcards roughly = 5250 / 5000 ml/min
Roughly = 1

Question 14

Spirometry measurements and definitions diagram

Answer 14

Question 15

Measurements that cannot be measured using spirometry

Answer 15

Functional residual capacity
Residual volume

Question 16

How to measure Functional Residual Capacity and Residual Volume

Answer 16

Helium dilution

Question 17

Why is helium used for helium dilution measurement of FRC and RV

Answer 17

Helium very insoluble to not taken up by blood

Question 18

Helium dilution calculation graphic

Answer 18

Question 19

Helium dilution calculation explained

Answer 19

Concentration of helium equilibrates across box and lungs, and as not taken up by lung then concentration can be used to calculate lung volume

Question 20

Boyle’s Law (for gases)

Answer 20

Pressure x Volume is constant at a constant temperature

I.e if gas is in fixed space and volume decreases, pressure must increase and vice versa

Question 21

Newer method of calculating FRC and RV

Answer 21

Question 22

Tidal volume calculation

Answer 22

Dead space volume + Alveolar gas volume

Question 23

Where does expired CO2 come from

Answer 23

Alveoli - no CO2 comes from dead space as no gas exchange occurs there

Question 24

Alveolar ventilation equation use

Answer 24

Calculate alveolar ventilation as it is difficult to measure anatomic dead space

Question 25

Alveolar ventilation equation

Answer 25

Alveolar ventilation = K x CO2 ventilation / PACO2 (alveolar but is essentially equal to arterial PCO2 in healthy individuals)

I.e PaCO2 is inversely proportional to alveolar ventilation

K is a constant
V dot is volume per unit of time

Question 26

FCO2

Answer 26

Fractional concentration of CO2

Fractional concentration adds up to 1 rather than percentage which adds up to 100

Question 27

Tidal volume range

Answer 27

6-8 ml/kg

Question 28

Inspiratory reserve volume range

Answer 28

30 - 40 ml/kg

Question 29

Expiratory reserve volume range

Answer 29

20 ml/kg

Question 30

Residual volume range

Answer 30

20 ml/kg

Question 31

Vital capacity range

Answer 31

60 ml/kg

Question 32

Functional residual capacity range

Answer 32

35 - 45 ml/kg

Question 33

Total lung capacity range

Answer 33

90 ml/kg