Ventilation/Mechanics III Flashcards
Surface Tension in lungs from?
H2O molecules on alveolar walls ->
attracted to other H2O ->
generates collapsing force
Collapsing force is related to radius how?
inversely
Laplace’s Law eqn
P = 2T/r
P = inward (collapsing) pressure T = surface tension force r = radius of alveolar
Small alveoli empty into?
larger alveoli
Atelectasis is?
alveolar collapse (tele = far, tasis = stretching)
Atelectasis opposed by? (2)
1) alveolar surfactant (disrupts interaction w/ H2O)
2) interdependence of alveoli (support ea other)
Surfactant made of? (3)
phospholipid (DPPC)
lipids
proteins
Surfactant made by?
Type II alveolar epithelial cells
Hyaline Membrane Disease is?
infant respiratory distress synd:
premature infants,
alveoli collapse completely,
low surfactant makes difficult to reinflate
Premature Infants surfactant levels?
< 24 wks = none
> 35 wks = sufficient
Surfactant role in surface tension?
equalizes (reduces) surface tension forces in large and small alveoli
↑ compliance
↓ collapse of small alveoli
↓ gas discharge from small to large alveoli
[Surfactant] is high where?
small alveoli
[Surfactant] is related to T (surf tension) how?
inversely
Alveolar collapse inhibited by? (2)
1) surfactant
2) surrounding alveoli (tendency for each to collapse cancel ea other out)
Work of breathing is?
work req’d to move lung and chest wall
Work calculated how?
pressure x vol
Work of breating req’s what % of resting metabolic rate?
2-3%
Total Work =
elastic work + resistance work
Elastic work is?
work needed to expand lung:
65% of total
Elastic work dependent on? (3)
1) surface tension
2) elastic elements in lung
3) lung vol (↑ as vol ↑)
Resistance work (Raw) is?
work needed to move air through airways (overcome airway resistance):
35% of total
Resistant work dependent on? (2)
1) AIRWAY DIAMETER (1/r^4)
2) flow of velocity
(↑ velocity -> ↑ turbulance -> ↑ work)
ºVair (Air flow thru airway) =
(Palv - Pmouth)/Raw
Palv = alveoli air pressure Pmouth = mouth air pressure
Raw =
Raw = 8ηl/πr^4
Airway resistance (AWR) related to lung vol how?
inversely:
AWR ↓ as lung vol ↑
due to radial traction forces expanding the airway
Radial Traction Forces (RTF) are?
force of alveoli supporting ea other
RTF affected by obstructive dx how?
RTF ↓
emphysema: tissue destruction so not available to support
RTF responds to ↑ lung vol how?
RTF ↑
RTF affected by restrictive dx how?
RTF ↑
fibrosis: tissues held firmly by fibers
Obstructive Disease affects airway how? (3)
1) excess secretions
2) thickening of airway wall (edema or hypertrophy)
3) destruction of lung parenchyma (loss of radial traction)
COPD flow/volume curves look like?
volume ↓
flow rate ↓ w/ scooped out on down slope of expiratory curve (middle volumes)
Why do COPD pt’s purse lips to breathe?
on exhalation, ↑ air pressure ->
↓ premature collapse