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Flashcards in 3 Lung Mechanics and Ventilation Deck (25)
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1

Name the muscles that contract to increase interthoracic volume:

  • External intercostal
  • Diaphragm

2

The lung tissue has a natural elastic recoil, meaning that it has a tendency to want to collapse in. So what keeps the lungs against the chest wall?

Pleural fluid found between visceral and parietal pleura: seal between lung and thoracic wall

 

Lungs expand w./ thoracic cavity

Surface tension between pleural surfaces

3

What is the resting expiratory level?

(Tendency to always want to return to this state)

  • State of equilibrium
  • Point before inspiration, just before expiration

Forces= equal and opposite

  1. Lung recoil- in and up
  2. Chest wall- out
  3. Diaphragm- down

4

Why is the pressure in the intrapleural space always negative (relative to atmospheric pressure)?

  • Elastic recoil of lungs- inward
  • Chest wall- outward

5

What happens if the pleural seal is broken?

Air drawn in to intrapleural space due to negative pressure inside

Collapses lung

6

Define tidal volume:

Volume of air entering and leaving lungs in single breath

7

Forced inspiration and expiration uses the lung reserve volume but requires the helps of accessory muscles. When might these muscles be used?

  • Exercise
  • Diseases affecting lungs

8

Name the accessory muscles for inspiration:

  • Sternocleidomastoid
  • Scalene muscles
  • Serratus anterior
  • Pectoralis minor

9

Name the accessory muscles for expiration (no longer passive):

  • Internal intercostals
  • Abdominal wall muscles

10

Compliance of the lung is determined by:

  • Elastic tissue of lung
  • Surface tension forces of fluid lining alveoli

What is compliance?

Stretchiness of lung

Volume change per unit pressure change

11

What is the function of surfactant? (secreted by type 2 pneumocytes in lungs)

  1. Reduces surface tension acting on alveoli (ie increases compliance)
    1. Surface tension limits expansion of alveoli- decrease compliance
  2. Has detergent properties
  3. Stabilises lungs- prevent small alveoli collapsing into bigger ones

12

Why does surface tension increase as alveoli size increases?

Surfactant more effective at disrupting surface tension when molecules= closer together 

ie smaller alveoli

13

How does surfactant prevent small alveoli collapsing into big alveoli?

Allows different sized alveoli to have same pressure inside them

14

What is respiratory distress syndrome?

  • Condition seen in premature babies
  • Surfactant= absent until fetus> 25 weeks
  • Lack of surfactant= Respiratory distress syndrome

15

Why is the parallel arrangement of small airways in the lungs significant?

Compensates for increase in individual resistance in small airways

16

Why will a residual volume remain even after forced expriration?

We cannot empty our lungs completely

17

Find each of the following on the graph:

  • Inspiratory capacity
  • Functional residual capacity
  • Vital capacity
  • Total lung volume

  • Inspiratory capacity: inspiratory reserve + tidal volumes
  • Functional residual capacity: vol of air in lungs at end of quiet expiration
  • Vital capacity: Inspiratory capacity + expiratory reserve volume
  • Total lung volume: Vital capacity + reserve volume

18

With relation to the respiratory system, what is 'anatomical dead space'?

Conducting airways- where no gas exchange occurs

...therefore only part of tidal volume used for gas exchange

19

What is 'alveolar dead space'?

Air in alveoli- not perfused / damaged alveoli- no gas exchange

 

20

What is physiological dead space?

Alveolar dead space + anatomical dead space

21

Fill in the x values in the following equations:

Tidal vol = Anatomical dead space + X

Total pulmonary ventilation =x respiratory rate

X = (Tidal volume - alveolar dead space) x respiratory rate

 

 

 

Tidal vol = Anatomical dead space + alveolar ventilation

Total pulmonary ventilation = Tidal volume x respiratory rate

Alveolar ventilation  = (Tidal volume - alveolar dead space) x respiratory rate

22

What muscles are used during quiet expiration?

No muscles used

Passive and due to elastic recoil

23

As the alveolus expands, does the surface tension increase or decrease?

Increases as surfactant molecules= further apart

(So less force required to expand smaller alveoli)

24

Apart from the energy expended on muscle contraction, what other work must be done on inspiration (2)?

  • Force air through airways
  • Work against elastic nature of lungs

25

Where does the majority of the resistance against air flow reside in the respiratory tracts?

Upper respiratory tract 

Due to parallel arrangement of the small airways

Except when small airways= compressed during forced expiration