Normal Physiology 3 - Lung Dynamics

Question 1

What determine the nature of the flow (laminar vs turbulent)

Answer 1

The size of the airways - the bigger the airway the more turbulent the airflow

Question 2

How can we know if the flow is laminar?

Answer 2

the flow stream lines become parallel to the sides of the tube

Question 3

where is the flow with the highest velocity in laminar flow

Answer 3

in the middle

Question 4

What is the velocity in a turbulent flow?

Answer 4

the mean forward velocity of the gas is the same at any point in the flow, whether central or near the walls

Question 5

What should the driving pressure be in laminar vs turbulent flow to get the same flow rate?

Answer 5

you need a higher driving pressure to maintain the same flow rate in a turbulent flow

Question 6

As the tube gets smaller, how does the driving pressure (or the resistance) needs to change in order to keep the same airflow? (during laminar flow)

Answer 6

The driving pressure varies directly with the tube length and inversely with the fourth power of tube radius, so you would need an increased pressure

Question 7

So if the radius of the tube is halved (in laminar flow) what happens to the driving pressure?

Answer 7

driving pressure must be increased 16 fold to maintain the same amount of air flow

Question 8

When is laminar flow most likely to occur

Answer 8

when the flow rate is low and when the tube diameter is small (the opposite for turbulent flow)

Question 9

What is the effect of gas density on air flow?

Answer 9

The denser the gas, the more turbulent the flow will be.

So if you want to help a patient with an obstruction, give them a mix of he and O so that the flow is less turbulent and so more efficient

Question 10

What’s reynold number

Answer 10

the higher reynolds number the more turbulent the flow

Question 11

who to you calculate resistance

Answer 11

R = deltaP / flow

Question 12

how does the tube geometry affects the total resistance ?

Answer 12

Tubes connected in parallel allows for a lower total airways resistance despite the fact that the individual airways are getting smaller

(in serie = higher total airway resistance
in parallel = lower total airway resistance)

Question 13

So where is the airway resistance the greateast between trachea, bronchus and alveoli ducts?

Answer 13

trachea, alveolar ducts are numerous and in parallel, so the total surface area is bigger, so then the total airway resistance is smaller

Question 14

what happens to velocity of air flow as the diameter of individual airways decreases?

Answer 14

As the diameter decreases, the velocity decreases, thus favouring laminar flow and thus more energitically efficient - overall resistance decreases

Question 15

What is the interdependence between the airways and the parenchyma?

Answer 15

Airway resistance changes with lung volume

Question 16

explain relation between airway resistance and lung volume

Answer 16

• As lung volume increases, airways are being pulled open by the alveolar attachments on the membranous bronchioles and also helped with the effect of negative intrathoracic pressure on airways.

Question 17

Study this graph.

Answer 17

Question 18

How can we calculate total pulmonary resistance

Answer 18

With the pressure gradient between the mouth and the pleural space

Question 19

and to measure airway resistance (Raw)?

Answer 19

by determining the pressure gradient between the mouth and the alveoli

Question 20

What is the major component of pulmonary resistance

Answer 20

airways resistance - loss of energy as air flows through the airways

Question 21

What are the determinents of maximum expiratory floe?

Answer 21

• airways resistance
• elastic recoil of the lungs
• expiratory muscle strength (up to a point)

Question 22

what is expiratory flow limitation

Answer 22

No matter how hard the expiratory muscles push, flow will not increase any further.

no matter how hard a person forces air out of their lungs, the gas will not come out faster

Question 23

Explain that graph

Answer 23

At lung volumes greater than 75% of VC (low pleural pressure) airflow increases progressively with increasing pleural pressure.

At volumes of lets say 25% of VC, airflow levels off as pleural pressure exceeds atmospheric pressure (t’as pas besoin de forcer pour que l’air sorte)

Question 24

When is the effort dependent phase?

Answer 24

Early in the forced expiration (at higher lung volume), blow harder and you get more airflow

Question 25

When is the effort-independent phasse?

Answer 25

Occurs later during the forced expiratory maneuver (at intermediate and lower lung volume), no matter how hard one blows, beyond a certain point there is no further increase in flow at that lung volume

Question 26

By what is determined the flow during the effort-independent portion of the flow-volume curve?

Answer 26

• Elastic recoil pressure of the lung
• Resistance of the airways

Question 27

So if a disease affects elastic recoil and/or airway resistance, how can we see it?

Answer 27

Will be detectable on forced expiratory flow volume curves

Question 28

What is the more widely used measurement in pulmonary medicine?

Answer 28

FEV1

Question 29

What means a low FEV1/FVC ratio?

Answer 29

• When low, indicates it is taking longer than usual for air to get out (decreased flow)
• when high, can also indicate a problem

Question 30

FVC?

Answer 30

the VC during a forced maneuver

Question 31

ratio with obstruction

Answer 31

lower then predicted

Question 32

ratio with restriction

Answer 32

higher than predicted

Question 33

Identify the curves:

Answer 33