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Physiology Part 2 > Lec 32 Respiratory mechanics > Flashcards

Lec 32 Respiratory mechanics Flashcards

1
Q

What are the two major forces to overcome to inhale

A
  • elasticity: lungs and chest wall resist stretch, passively return to equilibrium after expanded or compressed
  • resistance: viscosity of inhaled air, flow dependent airway resistance
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2
Q

What two proteins are responsible for the elastic properties of lungs?

A
  • collagen

- elastin

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3
Q

What two forces oppose each other in lung to keep it in equilibrium

A

lung tissue elastic recoil = force inward wanting to collapse

chest wall = exerts force outward wanting to expand

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4
Q

What is compliance? its relationship to elasticity?

A
  • measure of stiffness, an intrinsic property of lung or chest wall that depends on amount of elastic tissue
  • measured as change in volume per unit change in pressure
  • compliance is inversely correlated with elastance
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5
Q

What is the equation for compliance?

A

Compliance = ΔV/ΔP

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6
Q

How is airway pressure measured?

A
  • in terms of atmosphere pressure [zero]
  • above Patm is positive
  • below Patm is negative
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7
Q

What is transmural pressure?

A
  • pressure across the aloveolar wall

- transmural P = intra-alveolar P - extra-alveolar P

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8
Q

What is extra-alveolar pressure?

A

intrapleural pressure – the space between lungs and chest wall

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9
Q

How to measure lung compliance experimentally?

A
  • excised lung placed in jar
  • space outside lung mimics intrapleural pressure
  • vacuum pump simulated changed in intrapleural pressure
  • vol of lung measured by spirometer
  • lung inflated by increasing negative pressure outside
  • lung deflated by reducing negative pressure outside
  • slope of P vs V is compliance
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10
Q

What is hysteresis? what causes it?

A
  • difference in pressure required for inflation compared to deflation
  • lung is more compliant during expiration than inspiration [high slope, bigger volume for same pressure]
  • caused by surface tension at liquid-air interface
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11
Q

Is lung more compliant during expiration or inspiration?

A

expiration

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12
Q

What is law of laplace for alveoli?

A 
P = 2T/r
P = collapsing pressure on alveolus
T = surface tension
r = radius
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13
Q

Does a smaller alveolus or larger alveolus have higher collapsing pressure?

A

smaller alveolus

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14
Q

What is surfactant?

A
  • reduces surface tension and thus collapsing pressure at air-liquid interface
  • its an amphipathic phospholipid - one end hydrophilic and one end hydrophobic
  • improves lung compliance
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15
Q

2 consequences of surfactant reducing surface tension

A
  • stabilizes alveoli against collapse

- promotes compliance –> easier expansion/inspiration, less work to breath

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16
Q

What is the equation for respiratory system compliance

A

C respiratory system = C lung + C chest wall

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17
Q

How does compliance of respiratory system compare to that of chest wall and lung?

A
  • chest wall and lung have equivalent compliance [same slope]
  • combined compliance of respiratory system is less that of other structure alone
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18
Q

What is FRC?

A
  • functional residual capacity
  • the resting/equilibrium volume present in lung after normal breath exhaled
  • FRC = ERV + RV
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19
Q

What is residual volume [RV]?

A

x

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20
Q

What is expiratory reserve volume [ERV]?

A

x

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21
Q

What is tidal volume [TV]?

A

x

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22
Q

What is inspiratory reserve volume [IRV]?

A

x

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23
Q

What is vital capacity [VC]

A

x

24
Q

What is total lung capacity [TLC]?

A

x

25
Q

Is normal intrapleural pressure negative or positive relative to atmosphere? what is it?

A
  • negative relative to atm

- usually -3 mmHg

26
Q

What does emphysema do to lung compliance? How?

A
  • increase in lung compliance [higher slope]

- due to loss of elastic fibers

27
Q

What does fibrosis do to lung compliance? how?

A
  • decreases lung compliance [shallower slope]

- due to excessive collagen

28
Q

What is the equation for flow from resistance?

A

Flow = ΔP / R

ΔP = pressure difference between mouth/nose and alveoli
R = resistance =  8ηl/πr^4
29
Q

What is poiseuille’s equation for resistance?

A

R = resistance = 8ηl/πr^4

30
Q

What is the site of highest resistance?

A

medium sized bronchi

31
Q

True or false: the smallest airways have the highest resistance

A

false: because even though really small airways so each will have individual high resistance they are arranged in parallel

32
Q

What innervates airway smooth muscle?

A
  • B2 sympathetic receptors: cause bronchial smooth muscle relaxation and bronchodilation
  • M parasympathetic receptors: cause arrow narrowing and bronchospasm
33
Q

What two things determine airway resistance

A
  • lung volume

- viscosity of inspired air

34
Q

What are two ways airway diameter can be altered? what consequences resistance?

A
  1. loss of surrounding lung parenchyma: loss of radial traction on airway –> airway narrowing, increased airway resistance. ex. emphysema
  2. pulmonary resistance increases radial traction, get larger airway diameter at given lung volume and decreased airway resistance
35
Q

Why does lung volume determine airway resistance?

A
  • airways are tethered by surrounding lung tissue

- airway diameter varies with lung volume

36
Q

What is heliox? use?

A
  • helium oxygen mixture, alters air viscosity

- used for asthmatics in distress

37
Q

What is path of inspiration?

A
  • diaphragm contracts
  • abdominal contents pushed down
  • ribs lift up and out
  • get increased intra-thoracic V and thus lower intra-thoracic P causing air to rush in
38
Q

What happens to intra-thoracic V and P to cause air to rush in during inspiration?

A
  • higher intra-thoracic V

- lower intra-thoracic P

39
Q

What is path of expiration?

A
  • passive proccess

- everything reverses as diaphragm comes back, ribs move down and in

40
Q

What helps inspiration in exercise?

A
  • inspiration assisted by external intercostals and accessory muscles
41
Q

What helps expiration in exercise and asthma?

A
  • expiration assisted by internal intercostals and abdominals
42
Q

What are the 2 muscles of active expiration?

A
  • internal intercostal muscles

- abdominal muscles

43
Q

what are the 2 major muscles of inspiration?

A
  • external intercostal muscles

- diaphragm

44
Q

what are the 2 accessory muscles of inspiration?

A
  • sternocleidomastoid

- scalenus

45
Q

What is alveolar pressure at rest?

A

alveolar p = atmospheric pressure = 0

46
Q

what is intrapleural pressure at rest?

A

negative

-5 cm H2O

47
Q

What is transmural pressure at rest?

A

trasnmural = intra-alveolar - intrapleural = 0 - -5 = +5 cm H2O

48
Q

What is significance of positive transmural pressure at rest?

A
  • positive transmural pressure means expansion
  • ensures alveoli stay open
  • if transmural P were negative, it would be a collapsing pressure
49
Q

What is alveolar, intrapleural, and transmural pressures at rest?

A

alveolar: 0
intrapleural: -5
transmural: +5

50
Q

What is alveolar, intrapleural, and transmural pressures in middle of inspiration?

A

alveolar: -1
intrapleural: -6.5
transmural: +5.5

51
Q

What is alveolar, intrapleural, and transmural pressures in end of inspiration?

A

alveolar: 0
intrapleural: -8
transmural: +8

52
Q

What is alveolar, intrapleural, and transmural pressures in middle of expiration?

A

alveolar: +1
intrapleural: -6.5
transmural: +7.5

53
Q

What is alveolar, intrapleural, and transmural pressures at end of expiration?

A

End of respiration = rest state

alveolar: 0
intrapleural: -5
transmural: +5

54
Q

What is significance of alveolar pressure = 0 at end of inspiration?

A

means you have no flow.

55
Q

When is intrapleural pressure most negative?

A

at end of inspiration

56
Q

What happens to pressures in forced expiration?

A
  • get really high intra-alveolar pressure

- net positive transmural pressure

57
Q

What happens in COPD in forced expiration?

A
  • get not as high alveolar pressure in the part thats obstructed so get negative transmural pressure there

Physiology Part 2 (19 decks)

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