Week 21: (B) Dynamic Mechanics of Breathing

Question 1

What are the 3 factors of dynamic force?

Answer 1

Resistance
Flow
Turbulence

Question 2

What is dynamic force?

Answer 2

How gas moves through the airways

Question 3

What is Poiseuille’s Law? RESISTANCE

Answer 3

Suggests smallest tubes have greatest airway resistance…….but there are lots of them so the cumulative resistance is actually lower.

Question 4

What part of the airways has the highest resistance?

Answer 4

Upper airways 90%

Question 5

What are the factors that influence resistance?

Answer 5

• Lung volume and branching
• Bronchiolar smooth muscle tone
• Density and viscosity of gases

Question 6

What effects density and viscosity of gases?

Answer 6

• Affected by altitude.
• Important consideration in artificial environments (Space, deep sea).
• Laminar flow is a function of gas viscosity but turbulent flow depends on gas density

Question 7

What lines the upper airway?

Answer 7

smooth muscle

Question 8

What causes a decrease in the radius of the ‘tube’ ?

Answer 8

muscular contraction

Question 9

What induces the smooth muscle contraction in the airways?

Answer 9

• Parasympathetic activity,
• Ach neurotransmission
• Irritants (smoke, allergens),
• Decreased alveolar PCO2

Question 10

What causes an increase in the radius of the ‘tube’?

Answer 10

muscular relaxation

Question 11

What induces the smooth muscle relaxation in the smooth muscle?

Answer 11

• Sympathetic activity
• Pulmonary stretch (see last slide),
• NAdr (neural – weak)
• Adr (b2 – circulating, strong) [and Salbutamol].

Question 12

What are the effects of beta blockers (propanol) for asthmatic people?

Answer 12

Muscle spasms that make it difficult to breathe.

Cause constriction of the airways

Question 13

What is the effect of hyper reactivity of smooth muscle?

Answer 13

contracts more intensely with duration of exposure

HYPERTROPHY

Question 14

What causes allergic inflammation of the airways? (2)

Answer 14

1) Dust mite fecal allergen
Der p 2, 5
2) Cat saliva allergen
Fel d 1

Question 15

What are the consequences to an allergic inflammation of the airways?

Answer 15

Hyper-reactivity of airway smooth muscle contraction
Bronchial smooth muscle thickening
hypertrophy

Question 16

What is the effect of contraction of parabronchial smooth muscle?

Answer 16

raises upper airway resistance

Question 17

Where is the bulk of resistance?

Answer 17

trachea and branch generation 5

Question 18

Gas moves into the lungs via convection until when?

Answer 18

low resistance zone when it moves via diffusion

Question 19

What is the low resistance zone?

Answer 19

moves at crows oxygen permeation co-efficient
O2 moves forward at its own molecular rate of diffusion through bulk air.

Loses its convection effect, moves to respiratory acinus by diffusion as it moves into its own molecular velocity

Question 20

In normal lungs where is the low resistance zone located ?

Answer 20

respiratory acinus

Question 21

What is the effect of the upper airway resistance in the position of the low resistance zone? (asthma)

Answer 21

-Occurs at around branch 9 instead of ~19. meaning it has to diffuse at the slower rate for longer. need to difuse along branch 9-17 .

-Gas fails to penetrate to distal regions of respiratory
zone causing alveolar pCO2 to rise. decrease pH acidification

-Lung ceases to oxygenate Hb efficiently due to
Reversal of proper alveolar Bohr and Haldane
effects

Question 22

What is turbulence?

Answer 22

breath sounds

Question 23

What happens to convection, low resistance zone etc. when we exercise?

Answer 23

raise convection in the lung
molecular velocity occurs in the acinus zone
the O2 travels further into the acinus zone so gas exchange is quicker, less time in slow diffusion.
hence why we breathe heavier and quicker.

Question 24

What factors effect the flow resistance of the tubes in the airways?

Answer 24

Laminar flow
Transitional flow
Turbulent flow (lots of eddies)

Question 25

How do you measure airway resistance of whole body?

Answer 25

Whole Body Plethysmography

Question 26

How does the whole body plethysmography work?

Answer 26

enclosed space, breath in against a closed shutter. lung volume increases causing arterial pressure to decrease. Due to no airflow, mouth pressure = arterial pressure. The inspiration causes change in box pressure is proportional to the negative change in arterial pressure (decrease arterial pressure) --> thus the change in box pressure provides a measure of arterial P

Question 27

What happens to resistance during inhalation?

Answer 27

Airway Resistance Falls as Gas Flow and Lung Volume Increase.

Question 28

What happens to the airway size during inhalation?

Answer 28

As lungs expand airways | are also physically widened.

Question 29

What happens to resistance as lung volume increases?

Answer 29

as lung vol increases, resistance decreases

Question 30

How does resistance of the upper airways help with exhalation?

Answer 30

helps to keep airway pressure high to maximise gas movement out of alveoli

Question 31

What is dynamic compression?

Answer 31

``` Dynamic compression of the airways results when intrapleural pressure equals or exceeds alveolar pressure, which causes dynamic collapsing of the lung airways Contraction of smooth muscle The force (pressure) of the alveoli pushing air out must overcome the resistance of the upper airways. ```

Question 32

What is an Eddie in fluid dynamics?

Answer 32

The swirling of a gas and the reverse current created when the gas is in a turbulent flow regime. Lots of eddies make up a turbulent flow

Question 33

What causes wheezing in the lungs?

Answer 33

Laminar flow is complicated by dichotomous branching and associated with Eddies and turbulence that can occur in the lung and are influenced by airway smooth muscle contraction.

Question 34

What is the driving pressure in the airways?

Answer 34

driving pressure of gas movement through the airways is going to be a product of laminar flow.

Question 35

What is Laminar flow?

Answer 35

Type of fluid (gas or liquid) flow in which the fluid travels smoothly or in regular paths, in contrast to turbulent flow, in which the fluid undergoes irregular fluctuations and mixing.

Question 36

What is transitional flow?

Answer 36

A mixture of turbulent flow and laminar, usually laminar at the edges and turbulent at the centre

Question 37

What is turbulent flow?

Answer 37

chaotic and rough movement of particles through a region.

Question 38

What are the steps in inspiration?

Answer 38

expanding chest cavity, reduce Pip significantly. pulls airway pressure down below atmospheric P, gas will enter airways (enter conducting zone) alveolar pressure = -15

Question 39

What happens in early inhalation?

Answer 39

No gas movement, holding breath for a moment before exhale interpleural pressure is negative due to tethering of lung to chest wall (expand and lower pressure) airway pressure zero along mouth alveolus

Question 40

What are the steps in expiration?

Answer 40

- Lungs collapse under elastic recoil (product of elastin fibre + surface tension) - Inward collapse produces dynamic compression of lung. -Interpleural pressure increases (+10) in the alveolus. P in respiratory zone above atmospheric. =DYNAMIC COMPRESSION

Question 41

What is gas movement completely dependent on? exhale

Answer 41

On dynamic compression in the alveoli to move across zones. | Where gas begins to meet the increasing resistance of the conducting zone, we need extra force (dynamic compression)

Question 42

What's COPD characterised by?

Answer 42

``` increased resistance to air flow as they suffer from collapse of elastic structure in the airways and build up of mucous. 1. Alveoli destruction 2. Reduced surface area 3. Reduced elasticity ```

Question 43

What is airflow like in moderate COPD?

Answer 43

turbulent flow of gas, as it moves against the collapsed structures and increase mucous in the airways

Question 44

What is airflow like in severe COPD?

Answer 44

Inhalation phase not as turbulent as moderate expiration- protracted, turbulent and a lot of resistance pressure Can breathe in ok but gas that enters their airways becomes trapped there, unable to remove easily due to increased resistance = gas trapping

Question 45

Why do people with COPD purse their lips?

Answer 45

- To main airway P high all the way through the conducting zone of the lungs. - Never actually get the fall-off that we see in the normal expiration. - maximum point of resistance up from airway to mouth

Question 46

Why do people with COPD hunch over?

Answer 46

- Using dynamic compression by hunching over to raise airway P as above Pip all the way through the airways - Produce their own dynamic compression.

Question 47

What is a name for a person with COPD pursed lips and pinched over?

Answer 47

"blue puffer"

Question 48

What is an equation for work of the lung?

Answer 48

pressure* volume | pressures are always changing

Question 49

What is the work for breathing (inspiration)?

Answer 49

-Energy input required to overcome elastic component ADD - Energy input required to overcome surface tension

Question 50

What is the work for breathing (expiration)?

Answer 50

Energy input to overcome airway and tissue resistance

Question 51

What is the difference between panting and deep breathing?

Answer 51

panting: overcoming surface tension of the lung | Deep breathing: overcoming elastic fibre components