Static lung volumes

What determines FRC and how does that change w/ age?

FRC:

• Determined by interaction between ribcage flexibility and lung elasticity

  • Ribcage always want to EXPAND (due to tension in costal cartilage)

  • Lungs always want to COLLAPSE (b/c they are elastic and stretched in the thorax)

  • FRC is determined by the balance of these two forces

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As We Age:

• lung elastic recoil lessens → FRC rises

Desribe the absolute and relative pressures present in the thoracic cavity

Describe the muscles of:

• Inspiration

• Expiration

Inspiration:

• Diaphragm

• Scalenes

  • Lifts R1,R2

• Sternocleidomastoid

  • Lift sternum upward and outward

• External Intercostals

  • Fiber direction: Down and forward (hands in pockets)

  • Elevate ribs

• Neck and back musculature

  • Posture allows better lung inflation

• Bronchial smooth muscle

  • Bronchodilation reduces airway resistance

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Expiration:

• Abdominal muscles: increase abdominal cavity pressure

  • Internal/external obliques

  • Rectus abdominus

  • Transverse abdominus

• Internal intercostals

  • Fiber direction: Down and back

  • Depress ribs

• Neck and back musculature

  • Postural Changes

1. Describe the importance of P_TP in lung-chest wall interactions

2. What happens in Pneumothorax?

3. What happens as lung volume rises?

A positive Transpulmonary Pressure (P_TP) is necessary to maintain lung volume:

• P_TP = P_A – P_PL 

• Alveoli naturally wants to collapse due to Elastic Forces (P_EL)

• Alveoli stays open b/c lung is adhered to chest wall via the negative pressure in Pleural Space 

• As long as PTP is positive, lung stays open

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Pneumothorax:

• air enters the pleural space → pressure becomes equal to atmospheric and the lung → P_TP = 0 → Lungs collapse

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Lung Volume:

• When Lung volumes rise, PTP must rise as PEL increases as the lung is stretched further

1. Draw out the PV graph depicting Transpulmonary Pressure, Intrapleural Pressure, and Lung Volume (TLC)

2. Why do we breath from FRC?

FRC:

• We breath from here b/c this makes expiration at rest is passive

  • Due to elastic recoil

  • Minimizes the work of breathing

Draw out the graph depicting compliance of Normal, Emphysema, and Fibrosis. Describe why the lines are shaped that way

Emphysema:

• Increased compliance

• Destruction of elastic tissue

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Fibrosis:

• Reduced compliance

• Increased deposition of fibrous tissue

1. What is Hysteresis?

2. Describe the mechanism that causes hysteresis

Hysteresis: difference between the inspiratory pressure-volume curve and the expiratory due to inspiration being “harder” to do then expiration

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Mechanism:

• Inspiration:

  • changes in surface tension*

  • overcoming the elastic recoil

• Expiration:

  • Elastic nature of the lung → work done on the lung during inspiration is partially “given back” during expiration

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*= the attraction of water molecules to one another

1. What does Surfactant do?

2. How?

3. Importance?

4. How is it produced?

5. What is the effect of lung volume on surface tension?

Surfactant reduces surface tension:

• By replacing water molecules at the air-liquid interface

• Mechanism:

  • surfactant molecules have hydrophobic tails → Pulls it towards surface → Reduces attraction of water molecules from one another @ surface

• Importance:

  • allows work of breathing to be minimized

• Production:

  • produced in type II pneumocytes in ER

  • Stored in lamellar bodies

    • Exocytose and “spread” into alveolar surface

    • Tubular myelin = reservoir for surfactant and helps to spread surfactant rapidly

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Lung Volume on Surface Tension:

• Inspiration → Alveoli Inflates → increases distance between surfactant molecules → Surface Tension Rises → puts a brake on inspiration (as well as elastic recoil)

• Expiration → Vice Versa

• Thus: surfactant also helps the alveoli maintain a uniform size

1. Draw out the graph depicting Compliance of Chest Wall and Lung as a function of Pressure Vs Volume (Vital Capacity)

2. Describe the three curves

3. Where is FRC on this graph?

   1. What must happen if we go above/below FRC

Chest Wall:

• Wants to expand (aids inspiration); after a certain point, it wants to recoil inwards (aids expiration)

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Lung:

• always want to collapse to it’s minimal volume

  • will never get there as that point is w/in residual volume

• Tendency of elastic recoil aids expiration

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Solid Line = Combined chest wall and lung pressure volume curve

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FRC:

• volume at a Pressure of zero

• balancing point between the tendency for the lung to collapse inward and the ribcage to expand outward

• To go above FRC

  • We need to expand chest wall and lung, so P_TP becomes more positive

• To go below FRC

  • P_TP becomes less positive

1. What is specific Compliance?

2. Why is this important

Compliance = Lung Volume/Pressure

Specific Compliance = Lung Compliance/Lung volume

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Why is this important:

• For people w/ less lung volume (due to disease, surgery, etc), it appears that compliance decreases as lung volume decreases; This shouldn’t happen as compliance is an intrinsic property of the lung’s tissue, not dependent on size

• The fall in “regular” compliance is due to the fact that the smaller lungs are always closer to TLC as they have to use a lot more of their available volume to perform the duties of the lung

• Specific Compliance fixes this; Once we apply the appropiate volume, it turns out that everybody has the same value of Specific Compliance.