Respiratory Mechanics Flashcards

1
Q

Relationship between pressure and volume at low lung volumes?

A

At low lung volumes, it takes a fairly big pressure change to make a small increase in volume

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2
Q

What happens once there is some air in the lungs?

A

Once there is some air in the lungs, a little pressure change produces a large volume change-in other words, it becomes easy to stretch the lungs

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3
Q

When the lung gets close to the TLC?

A

It again becomes difficult to inflate-so a large pressure change produces a small change in volume

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4
Q

Compliance of the lungs

  • What is it?
  • How is it measured?
A
  • Measure of the “stretchability” of the lungs

- (change in volume)/(change in pressure)

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5
Q

When is compliance highest?

A
  • The compliance of the lungs is highest in the normal breathing range
  • Don’t have to work particularly hard to get a decent Vt
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6
Q

What happens to compliance at either extreme (too small or too large)?

A

Compliance is low-have to work harder to inflate the lungs at low or high volumes

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7
Q

Thought question

  • What is the compliance of the lungs for the first breath?
  • How hard does the baby have to work?
A
  • Prior to the first breath, lung volume is very low, compliance is low, and the effort to breath is high
  • With successive breaths, the baby’s lungs inflate and become more compliant, so work decreases
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8
Q

Describe the pressure-volume curve of the normal lung and explain the differences observed in inspiration versus expiration
-Respiratory mechanics: pressure and volume relationships

A
  • Something really interesting happens when we allow our lung model to “exhale”-The lung doesn’t deflate the same way it inflated
  • Even better, if we inflate the lungs with saline (rather than air), the whole shape changes and the lung mostly deflates the same way it inflated
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9
Q

Why is surfactant important?

A

Alleviates surface tension-reduces tension in the smallest alveoli more than in larger alveoli

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10
Q

The difference in the inspiratory and expiratory lines on the graph is mostly due to?

A

the presence of surfactant

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11
Q

Hysteresis

A

difference between inspiration and expiration

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12
Q

It is believed that the hysteresis is due to?

A

the molecules of surfactant moving one direction during inspiration but coming back a different way

  • surfactant is not evenly distributed on the alveolar surface
  • small droplets randomly positioned
  • if the alveolar volume is small, the droplets are close together and pull apart during inspiration/fuse during expiration
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13
Q

The slight hysteresis of the saline filled curve is due to?

A

the resistance of the tissue sliding over one another

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14
Q

Define compliance

-equation?

A

change in volume/change in pressure

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15
Q

What does low compliance mean?

A

Low stretchability; hard to inflate

(high compliance is the opposite)

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16
Q

Compare and contrast the compliance of the lung vs. the rib cage vs. the intact system

  • Be able to draw the figure!
  • Lungs?
A

Lungs have lots of elastic fibers so they “want” to get smaller (minimal volume)

17
Q

Rib cage

A

Due to joint arrangement in body wants to get larger

18
Q

Intact system

A

The elastic recoil of the lungs and the rib cage exactly counter each other at FRC

19
Q

What happens in a pneumothorax?

A

The lungs get smaller and the rib cage gets larger

20
Q

Airway resistance equation

A

R=(8(viscosity)(tube length))/r^4

21
Q

Contraction of bronchial (airway) smooth muscle changes the radius of the airway and therefore?

A

changes the resistance

22
Q

Forced expiratory volume

A
  • Very helpful in identifying changes in the pulmonary mechanics
  • Both the FEV itself (total volume out) and how fast the air can be moved out of the lungs is important
23
Q

FEV1

A

The amount of air that can be exhaled in the first second is used as one measure of pulmonary function

24
Q

FEV1:FVC

-normal?

A

about 80% of the FVC is exhaled in the first second of expiration

25
Q

FVC, FEV1, and FEV1:FVC in patients with obstructive disease

-2 obstructive diseases?

A
  • 2 obstructive diseases-asthma and emphysema
  • It takes far longer to get air out of the lungs
  • The FVC is reduced because the air is trapped
  • FEV1 is even more reduced
  • FEV1:FVC is below 70%
26
Q

FVC, FEV1, and FEV1:FVC in patients with restrictive disease

-Restrictive disease?

A
  • Interstitial fibrosis
  • FVC and FEV1 are both reduced due to inability of the lungs to expand
  • FEV1:FVC ratio is higher than normal (>90%) because the elastic recoil of the lungs forces the air out more rapidly
27
Q

Describe the control of airway resistance

A

Via the smooth muscle and ANS

28
Q

Define interdependence

A
  • The structural stability of the small airways and alveoli depends on all the connecting airways alveoli
  • The elastic recoil in one alveolus is countered by the elastic recoil of an alveolus with shared walls
29
Q

Describe how interdependence influences airway resistance

A

-If you lose the alveolar walls (due to age, smoking, etc) remaining alveoli can collapse during expiration

30
Q

Describe the work of breathing and how it influences normal respiratory processes

A
  • Work is done to overcome the elastic recoil (emphysema) of the lungs or resistance to airflow
  • The elastic recoil is the greater effort (bigger area of the curve)
31
Q

Describe the factors that alter the work of breathing

A

?

32
Q

What happens to air flow as intrapleural pressure becomes more negative?

A

Air flows into the lungs