respiratory mechanisms

Question 1

airflow in tube definition

Answer 1

the movement of air in a tube where there is a difference of pressures between the ends

Question 2

what does the pressure difference depend upon?

Answer 2

the rate and pattern of airflow

Question 3

two basic types of airflow

Answer 3

laminar flow and turbulent flow

Question 4

laminar flow definition

Answer 4

when the stream lines are parallel to the sides of the tube and is found at low flow rates

Question 5

flow rate definition

Answer 5

the volume/mass of a gas/liquid that moves per unit time

Question 6

what does Poiseuille’s law state?

Answer 6

that flow is related to viscosity, the pressure gradient, length and radius of the tube

Question 7

flow rate equation

Answer 7

Pᴨr^4/8nl

Question 8

resistance equation

Answer 8

8nl/ᴨr^4

Question 9

what is flow rate proportional to?

Answer 9

the pressure gradient

Question 10

why is the tube radius critical?

Answer 10

halving the radius can increase the resistance by x16

Question 11

what happens when flow rate is increased?

Answer 11

the unsteadiness of the laminar flow increases, stream lines separate from the tube walls and local eddies (swirling and reverse currents) form at branches

forms a transitional flow

Question 12

turbulent flow definition

Answer 12

when complete disorganisation of the stream lines is seen at high flow rates

Question 13

what affects the turbulent flow?

Answer 13

viscosity of gas becomes unimportant, however an increase in gas density matters and affects the pressure gradient

Question 14

what determines whether air flow is turbulent or laminar?

Answer 14

Reynolds number

Question 15

How is Reynold’s number calculated?

Answer 15

2rvd/n

r= radius

v= average velocity

d= density

n= viscosity

Question 16

when does turbulence occur?

Answer 16

Re>2000

Question 17

Explain types of flow in the lungs

Answer 17

mainly laminar flow

but the lungs highly complicated branching pattern means that there may be eddies and that the flow is non steady,

complete laminar flow only occurs in the terminal bronchioles

true turbulence may occur in the trachea during exercise, when velocity/flow rate is high

Question 18

what causes wheezing?

Answer 18

occurs during the expiratory phase of respiration due to an obstruction that produces turbulent air flow

Question 19

what does the resistance determine?

Answer 19

the rate of laminar flow down a pressure gradient?

Question 20

causes of airway resistance

Answer 20

• decrease in lung volume increase airway resistance
• upper most parts of the bronchial tree, as in total these have less divisions and thus a smaller radius than the total branches further down. Although the smallest bronchioles have the smallest radius, the very large cross sectional area compensates for this
• segmental bronchi are the site of maximal resistance- 1/3 of total resistance arises from the nose, pharynx and larynx

Question 21

what reduces the resistance caused by the nose, pharynx and larynx?

Answer 21

mouth breathing

Question 22

what is the silent zone?

Answer 22

peripheral airways that contribute very little to resistance, therefore airway disease that begins here is unlikely to produce a difference in resistance that could be detected

Question 23

what does anaphylaxis cause?

Answer 23

bronchiolar contraction that increases airway resistance by reducing the radius

decreases in lung volume compress the airways and increase resistance further

Question 24

what is radial traction?

Answer 24

a force that keeps airways open during lung expansion and volume increases

Question 25

sympathetic control of resistance explained

Answer 25

B2 adrenergic receptor agonists cause bronchodilation, reducing resistance, such as adrenaline and salbutamol can be used as treatments for asthma and COPD

Question 26

parasympathetic control of resistance explained

Answer 26

M2 GPCR, where ACh acts and causes bronchocontriction anticholinergic agents used in COPD

Question 27

how is airway resistance measured?

Answer 27

subject sealed in plethysmograph breathes through a pneumotachograph to measure flow when they breathe, the alveolar pressure falls and the pressure in the box rises alveolar pressure can then be estimated by P1V1=P2V2

Question 28

peak expiratory flow definition

Answer 28

the maximum air flow during forced expiration beginning with the lungs fully inflated

Question 29

what happens to the peak expiratory flow in asthma patients?

Answer 29

lower, due to high resistance

Question 30

what happens to the peak expiratory flow in emphysema?

Answer 30

low lung elasticity, resulting in poor airway support, easy collapse and thus reduced peak expiratory flow

Question 31

what limits the peak expiratory flow rate?

Answer 31

the person's maximum rate of expiration is limited by the compression of the airways by intrathoracic pressure forced expiration intrapleural pressure exceeds airway pressure so the airways would collapse due to the greater positive pressure outside than inside

Question 32

FEV1 definition

Answer 32

the volume of air exhaled in the first second

Question 33

how is peak expiratory flow measured?

Answer 33

spirometry

Question 34

is FEV1 different to forced vital capacity?

Answer 34

yes it is less, however not that much less as the majority of air is expired in the first second

Question 35

what happens to FEV1 and FVC in restrictive diseases?

Answer 35

both are reduced

Question 36

what happens to FEV1 and FVC in obstructive diseases?

Answer 36

both reduced but FEV a lot more than FVC

Question 37

Obstructive disease definition + examples

Answer 37

respiratory disease characterised by airway obstruction asthma, COPD, chronic bronchitis

Question 38

restrictive disease definition + examples

Answer 38

extra pulmonary, pleural or parenchyma respiratory diseases that restrict lung expansion, resulting in a decreased lung volume decreased force vital capacity as physically cannot inhale more and thus expel more pulmonary fibrosis

Question 39

what diseases affect airway resistance

Answer 39

COPD, asthma, emphysema and chronic bronchitis