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
2
Q
What two proteins are responsible for the elastic properties of lungs?
A
- collagen
- elastin
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
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
5
Q
What is the equation for compliance?
A
Compliance = ΔV/ΔP
6
Q
How is airway pressure measured?
A
- in terms of atmosphere pressure [zero]
- above Patm is positive
- below Patm is negative
7
Q
What is transmural pressure?
A
- pressure across the aloveolar wall
- transmural P = intra-alveolar P - extra-alveolar P
8
Q
What is extra-alveolar pressure?
A
intrapleural pressure – the space between lungs and chest wall
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
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
11
Q
Is lung more compliant during expiration or inspiration?
A
expiration
12
Q
What is law of laplace for alveoli?
A
P = 2T/r P = collapsing pressure on alveolus T = surface tension r = radius
13
Q
Does a smaller alveolus or larger alveolus have higher collapsing pressure?
A
smaller alveolus
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
15
Q
2 consequences of surfactant reducing surface tension
A
- stabilizes alveoli against collapse
- promotes compliance –> easier expansion/inspiration, less work to breath
16
Q
What is the equation for respiratory system compliance
A
C respiratory system = C lung + C chest wall
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
18
Q
What is FRC?
A
- functional residual capacity
- the resting/equilibrium volume present in lung after normal breath exhaled
- FRC = ERV + RV
19
Q
What is residual volume [RV]?
A
x
20
Q
What is expiratory reserve volume [ERV]?
A
x
21
Q
What is tidal volume [TV]?
A
x
22
Q
What is inspiratory reserve volume [IRV]?
A
x
23
Q
What is vital capacity [VC]
A
x
24
Q
What is total lung capacity [TLC]?
A
x
25
Is normal intrapleural pressure negative or positive relative to atmosphere? what is it?
- negative relative to atm
| - usually -3 mmHg
26
What does emphysema do to lung compliance? How?
- increase in lung compliance [higher slope]
| - due to loss of elastic fibers
27
What does fibrosis do to lung compliance? how?
- decreases lung compliance [shallower slope]
| - due to excessive collagen
28
What is the equation for flow from resistance?
Flow = ΔP / R
```
ΔP = pressure difference between mouth/nose and alveoli
R = resistance = 8ηl/πr^4
```
29
What is poiseuille's equation for resistance?
R = resistance = 8ηl/πr^4
30
What is the site of highest resistance?
medium sized bronchi
31
True or false: the smallest airways have the highest resistance
false: because even though really small airways so each will have individual high resistance they are arranged in parallel
32
What innervates airway smooth muscle?
- B2 sympathetic receptors: cause bronchial smooth muscle relaxation and bronchodilation
- M parasympathetic receptors: cause arrow narrowing and bronchospasm
33
What two things determine airway resistance
- lung volume
| - viscosity of inspired air
34
What are two ways airway diameter can be altered? what consequences resistance?
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
Why does lung volume determine airway resistance?
- airways are tethered by surrounding lung tissue
| - airway diameter varies with lung volume
36
What is heliox? use?
- helium oxygen mixture, alters air viscosity
| - used for asthmatics in distress
37
What is path of inspiration?
- 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
What happens to intra-thoracic V and P to cause air to rush in during inspiration?
- higher intra-thoracic V
| - lower intra-thoracic P
39
What is path of expiration?
- passive proccess
| - everything reverses as diaphragm comes back, ribs move down and in
40
What helps inspiration in exercise?
- inspiration assisted by external intercostals and accessory muscles
41
What helps expiration in exercise and asthma?
- expiration assisted by internal intercostals and abdominals
42
What are the 2 muscles of active expiration?
- internal intercostal muscles
| - abdominal muscles
43
what are the 2 major muscles of inspiration?
- external intercostal muscles
| - diaphragm
44
what are the 2 accessory muscles of inspiration?
- sternocleidomastoid
| - scalenus
45
What is alveolar pressure at rest?
alveolar p = atmospheric pressure = 0
46
what is intrapleural pressure at rest?
negative
| -5 cm H2O
47
What is transmural pressure at rest?
trasnmural = intra-alveolar - intrapleural = 0 - -5 = +5 cm H2O
48
What is significance of positive transmural pressure at rest?
- positive transmural pressure means expansion
- ensures alveoli stay open
- if transmural P were negative, it would be a collapsing pressure
49
What is alveolar, intrapleural, and transmural pressures at rest?
alveolar: 0
intrapleural: -5
transmural: +5
50
What is alveolar, intrapleural, and transmural pressures in middle of inspiration?
alveolar: -1
intrapleural: -6.5
transmural: +5.5
51
What is alveolar, intrapleural, and transmural pressures in end of inspiration?
alveolar: 0
intrapleural: -8
transmural: +8
52
What is alveolar, intrapleural, and transmural pressures in middle of expiration?
alveolar: +1
intrapleural: -6.5
transmural: +7.5
53
What is alveolar, intrapleural, and transmural pressures at end of expiration?
End of respiration = rest state
alveolar: 0
intrapleural: -5
transmural: +5
54
What is significance of alveolar pressure = 0 at end of inspiration?
means you have no flow.
55
When is intrapleural pressure most negative?
at end of inspiration
56
What happens to pressures in forced expiration?
- get really high intra-alveolar pressure
| - net positive transmural pressure
57
What happens in COPD in forced expiration?
- get not as high alveolar pressure in the part thats obstructed so get negative transmural pressure there
