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Flashcards in 3 Lung Mechanics and Ventilation Deck (25)
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Name the muscles that contract to increase interthoracic volume:

  • External intercostal
  • Diaphragm


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


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


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

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


What happens if the pleural seal is broken?

Air drawn in to intrapleural space due to negative pressure inside

Collapses lung


Define tidal volume:

Volume of air entering and leaving lungs in single breath


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


Name the accessory muscles for inspiration:

  • Sternocleidomastoid
  • Scalene muscles
  • Serratus anterior
  • Pectoralis minor


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

  • Internal intercostals
  • Abdominal wall muscles


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


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


Why does surface tension increase as alveoli size increases?

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

ie smaller alveoli


How does surfactant prevent small alveoli collapsing into big alveoli?

Allows different sized alveoli to have same pressure inside them


What is respiratory distress syndrome?

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


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

Compensates for increase in individual resistance in small airways


Why will a residual volume remain even after forced expriration?

We cannot empty our lungs completely


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


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


What is 'alveolar dead space'?

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



What is physiological dead space?

Alveolar dead space + anatomical dead space


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


What muscles are used during quiet expiration?

No muscles used

Passive and due to elastic recoil


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)


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


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