Lecture 3.2: Lung Mechanics Flashcards

1
Q

By what mechanism is air drawn into the lungs?

A

Air is drawn into the lungs by expanding the volume of the thoracic cavity

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2
Q

What is Pleural Fluid?

A

A thin layer of fluid between visceral and parietal pleura ensures that lungs fill thoracic cavity and change volume as thorax does

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3
Q

What happens if the integrity of the pleural seal is broken?

A

• Lungs will tend to collapse (due to elastic recoil)
• Pneumothorax

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4
Q

What is the Mechanism of Breathing In?

A

• Active
• Mainly by contraction of diaphragm (flattening)
• External intercostal muscles contract

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5
Q

What is the Mechanism of Breathing Out?

A

• Breathing out to resting expiratory level is passive just stop breathing in
• Diaphragm relaxes
• Internal intercostal muscles contract

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6
Q

What is the Mechanism of Forced Expiration?

A

• Requires force
• Exerted by abdominal muscles and internal intercostal muscles
• Then inspiration to resting expiratory level is passive

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7
Q

What is Lung Compliance?

A

• The stretchiness of the lungs is known as compliance
• Volume change per unit pressure change
• Higher compliance means easier to stretch

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8
Q

Are lung airways elastic?

A

• Airways have elastic walls

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9
Q

If lung airways are elastic, why are they also stiff?

A

• Compliance reduced by surface tension of lining fluid

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10
Q

What is Surface Tension?

A

• Interactions between molecules at surface of a liquid
• Makes the surface resist stretching
• Higher the surface tension the harder the lungs are to stretch

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11
Q

What effect do Detergents have Surface Tension?

A

• Reduce surface tension by disrupting interactions between surface molecules
• The Lung has a mixture of detergents

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12
Q

What is a Surfactant? What do they do? What in the Lungs produces Surfactants?

A

• Surfactant (mixture of phospholipids & proteins, with detergent properties)
• Reduces surface tension when lungs are deflated (but not when fully inflated)
• So little breaths are easy
• Big breaths are hard
• Produced by Type 2 Alveolar Cells

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13
Q

What is Hysteresis? When is the most lost?

A

• The energy put into stretching a film of surfactant
• Is not all recovered when the film recoils
• This loss is greatest when tidal volume is maximal
• Another reason why little breaths are best

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14
Q

What is Asthma?

A

• Disease of the airways
• Narrowing of airways causes obstruction
• Makes hard to expel air
• Air retained in lungs (gas trapping)
• Makes lungs bigger thus harder to expand

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15
Q

What is Laplace’s Laws Equation?

A

• Pressure = 2 x surface tension/radius
• P= 2T/R
• Big bubbles have low pressure (R large)
• Little bubbles have high pressure (R small)

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16
Q

What is the Law of Bubbles?

A

• If a big bubble is connected to a small bubble
• Air will flow from high pressure to low
• Small bubble collapses into big
• ‘Big bubbles eat little bubbles’

17
Q

Why does Laplace’s Law not apply to the Lungs?

A

• Alveoli form an interconnecting set of bubbles
• If Laplace’s law applied big alveoli would eat little ones
• Thus the lungs become a physical impossibility

18
Q

What stops the ‘Bubble Law’ from occurring?

A

• As alveoli get bigger
• Surface tension in their walls increases because surfactant is less effective
• So pressure stays high
• And stops them eating little alveoli

19
Q

What is Respiratory Distress Syndrome? Who is affected by it?

A

• Babies born prematurely
• Have too little surfactant
• Lungs very stiff
• Few, large alveoli
• Breathing and gas exchange compromised

20
Q

What is Poiseuille’s Law? What is its relevance?

A

• Resistance = 8 x viscosity of air x length of tube/ (radius)^4
• Airway resistance is the pressure difference between the alveoli and the mouth
divided by flow rate and is determined by Poiseuille’s Law

21
Q

Where is Airway Resistance highest and lowest in the Lungs?

A

• Highest resistance in the trachea
• Lowest resistance in the small airways
• So breathing is easy

22
Q

Obstructive vs Restrictive Airway Disease

A

Obstructive lung diseases include conditions that make it hard to exhale all the air in the lungs
People with restrictive lung disease have difficulty fully expanding their lungs with air