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FSM Pulmonary > Mechanics > Flashcards

Mechanics Flashcards

1
Q

What keeps the lungs and chest wall together?

A

Surface tension from fluid in the pleura

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2
Q

What are two ways to measure intrapleural pressure (PIP)?

A

1) Catheter in intrapleural space 2) Balloon in thoracic esophagus to measure pressure (reflects changes in PIP, not absolute value)

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3
Q

What direction do the lungs tend to move when free of tension? The chest wall?

A

Lungs - collapse Chest wall - expand These two forces compromise at the functional residual capacity (FRC).

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4
Q

What is a typical PIP?

A

-3 to -6 cm H2O

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5
Q

What is transpulmonary pressure?

A

PA - PIP. The pressure that inflates the lungs.

  • PIP is negative, so it tends to expand lungs.
  • When glottis open, PA = PB (equilibrium), so transpulmonary pressure is just - PIP.
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6
Q

What is transthoracic pressure?

A

PIP - PB. The force acting on the thoracic wall.

  • PIP is negative, so it pulls the chest wall inward.
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7
Q

What is transrespiratory pressure?

A

PA - PB. The potential pressure gradient for flow into or out of alveoli, aka difference between alveolar and atmospheric pressure when relaxed.

  • If this P is negative, gas will flow into alveoli (when glottis opens) - If this P is positive, gas will flow out of lungs.
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8
Q

What is the opposite of compliance?

A

Elastance (this is not intuitive like how we typically think of elastic things!)

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9
Q

What things decrease compliance?

A
  • Respiratory distress syndrome
  • Edema
  • Atelectasis (alveolar collapse)
  • Fibrosis
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10
Q

What is the term for alveolar collapse?

A

Atelectasis

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11
Q

What things increase compliance?

A
  • Age
  • Emphysema
  • Increasing body size
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12
Q

What creates surface tension?

A

Asymmetric IMFs (yayyy little molecules interacting) between gas and liquid. This causes molecules on the surface to have attraction to the liquid below, so they are pulled down and the top becomes denser.

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13
Q

What is the Law of Laplace for curved interfaces (like bubbles)?

A

P = 4T/R T = tension in wall R = radius of curvature (for a sphere, it is 2T/R vs bubbles have two surfaces)

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14
Q

Does a small or a large soap bubble have a greater internal pressure?

A

The small bubble, because of the law of Laplace (P = 4T/R, pressure is inversely proportional to radius). This is important because it means smaller alveoli tend to collapse! So surfactant is crucial for them.

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15
Q

What is the mechanical difference between air and saline-filled lungs?

A

Saline eliminates the fluid-air interface, so there is no longer any surface tension.

This means the lungs are more compliant, so we know that surfactant/surface tension is important for recoil.

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16
Q

What is hysteresis?

A

The difference in P-V relationship in the lungs in inflation vs deflation.

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17
Q

What causes hysteresis?

A

At the minimal lung volume, the surfactant is all clumped together and completely covers the alveolar surface, so there is effectively no surface tension. As the lung volume increases, the surface area stretches out so the molecules of surfactant spread out more so their concentration decreases (even though extra molecules are brought up to the surface from micelles). This means that surface tension decreases as we inspire.

As we expire, the surfactant molecules get compressed together, decreasing surface tension, so the lungs are more compliant.

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18
Q

What are three things surfactant does?

A

1) Reduces alveolar surface tension
2) Preserves alveolar integrity
3) Prevents continuous transudate (edema) from pulmonary capillaries to alveoli

This last thing is because it provides a force to oppose the oncotic pressure of blood so that reabsorption doesn’t occur

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19
Q

What is surfactant made of?

A

Lipoprotein complex - 30% protein, 70% phospholipid (mostly dipalmitoyl phosphatidyl choline)

20
Q

Which type of pneumocytes make surfactant?

A. Type 1

B. Type 2

A

B, Type 2

21
Q

What time in gestation does surfactant become functional?

A

Around week 30

22
Q

Which is the proper alignment of surfactant at the air/water interface?

(water aka alveolus)

A. phospholipid head - air, tail - water

B. phospholipid head - water, tail - air

A

B. phospholipid head - water, tail - air

23
Q

What is the normal compliance of the chest wall?

A

0.2 L/cm H2O

24
Q

What is the typical compliance of the chest wall and lung together near FRC?

A

0.1 L/cm H2O

(The compliance of both in isolation is about 0.2 L/cm H2O, but adding compliance in series means 1/Ctot = 1/Clung + 1/Cchest)

25
Q

Where is the ventilation highest when upright?

A

The base. Gravity compresses the alveoli against the diaphragm, decreasing the PIP gradient, and making the alveoli more compliant (starting from smaller volume, so they can expand more). This is in the middle of the compliance curve, where compliance is high.

26
Q

Why is the apex of the lung least ventilated at FRC when upright?

A

Negative PIP gradient is greatest, so lung is in the upper part of the compliance curve (where it flattens), so it has low compliance.

27
Q

Where is the greatest ventilation when at RV and upright?

A

The apex - The abdominal muscles push up so the base is compressed, PIP is positive at the base, and the airways at the base are closed, so the lower lung will not be ventilated. The apex is now on the steep part of the compliance curve.

28
Q

What factors affect airway resistance?

A
  • Lung volume
  • Bronchial smooth muscle tone (autonomic reflexes from lung stretch, local mediators)
  • Gas density (turbulence) or viscosity (laminar)
    *
29
Q

What causes PIP to change non-linearly during the respiratory cycle (why does it not follow the straight lines)?

A

Tissue and airway resistance affects the PIP, making pressure lower with inspiration and higher with expiration.

30
Q

What is the relationship between flow/ventilation and the change in pressure in the airways (compressible tubes)?

A

Non-linear: there is a limit to flow maximum, due to airway compression when the PIP exceeds the airway pressure. The maximum flow is proportional to lung volume.

Airway compression depends on lung volume - tethers are stretched and make the airway stiffer, so it is less compressible with large volumes.

31
Q

Which part of the lung is most susceptible to dynamic compression?

A

The base because??

32
Q

What causes the effort independent portion of the flow volume curve?

A

Dynamic compression of the airways.

As effort increases, PIP increases, so compression is increased and ventilation is limited.

33
Q

Which part of the respiratory cycle exhibits changes in the flow-volume relationship?

A

Expiration - there are effort dependent and effort independent portions of the curve

34
Q

What happens to FRC with obstruction to expiration?

A

FRC will increase, which increases elastic recoil to help the expiration effort and reduce dynamic compression.

35
Q

How are the compliances of the two lungs arranged? The lung and chest wall?

A

The two lungs are in parallel (add C+C), while the lungs and chest wall are in series (add 1/C).

36
Q

What does tethering do?

A

Pulls open airways to decrease resistance at larger volumes. This also decreases compliance.

37
Q

What is the effect of tissue and airway resistance on the PIP during a respiratory cycle (think of that multicomponent graph)?

A

Resistance means that more pressure is required to achieve flow, so the PIP will be more negative DURING inspiration and more positive DURING expiration (curved/hatched lines).

At the beginnings/ends of inspiration/expiration, there is no effect of resistance on PIP.

38
Q

How are gas velocity and pressure related (think Bernoulli)?

A

The pressure will be lower (lateral pressure = pressure out on the walls of the tube) where velocity is higher.

39
Q

What is dynamic compression?

A

Compression with forced expiration, when the pressure outside the airway is higher than inside, so airways collapse.

40
Q

What are two reasons that all expiratory curves combine into the shared effort-independent slope?

A

1) Elastic recoil increases with greater stretch (so with more effort, there is more driving force)
2) At large volumes, there is less dynamic compression because there is more tethering and the airways are held open. As you expire and volume decreases, airway compression increases.

41
Q

What is the maximum amount of air you can exhale?

A

VC - vital capacity

42
Q

What is the minimum amount of air that can be left in the lungs, even with maximum effort?

A

RV - residual volume

43
Q

What makes up the inspiratory capacity?

A

Inspiratory reserve + tidal volume

44
Q

What is a normal tidal volume?

A

0.4-0.5 L

45
Q

What makes up the vital capacity?

A

IC+ERV

46
Q

What makes up the TLC?

A

IC+FRC

aka VC+RV

47
Q
A

FSM Pulmonary (3 decks)

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