RS Lec 4 Flashcards
lung compliance (def.) - (3)
- measure of the elastic properties of lungs
- measure of how easily the lungs can expand
- magnitude of change in lung volume produced by change in transpulmonary pressure (slope in P-V curve)
two types of lung compliance
- static compliance
- dynamic compliance
static compliance (def.)
-lung compliance during periods of no gas flow (during inspiratory/expiratory pause)
static compliance determined by
-P/V slope measured at FRC (end of expiratory effort)
dynamic compliance (def.)
-lung compliance during periods of gas flow (inspiration, when Ptp changes)
dynamic compliance reflects
-lung stiffness, airway resistance
dynamic compliance decreases when (2)
lung stiffness/airway resistance increase
dynamic compliance & static compliance relationship
-dynamic compliance is less than/equal to static lung compliance
pressure-volume relationship (1. Stable VL)
-at low lung volumes, difficult to pop open airways, rising Ptp little effect on lung volume
pressure-volume relationship (2. Opening of airways)
-first increases in lung volume open proximal airways, recruitment of other airways
pressure-volume relationship (3. expansion of airways)
-all airways are open, Pip is more negative by chest wall expansions, increases V (linear)
pressure-volume relationship (4. limit airway inflation)
-at high lung volumes, lung compliance decreases
hysteresis
-difference between inflation + deflation compliance paths
greater pressure difference (lung compliance)
-needed to open airway than keep from closing
lung compliance determined by (2)
- elastic components of lungs + airway tissue (elastin + collagen)
- surface tension at air-water interface in alveoli
location of elastic components of airways
-alveolar walls, around vessels, bronchi
elastic behaviour determined by
-geometrical arrangements, not typically elongation of fibers
collagen (twine) characteristics (3)
- high tensile strength
- inextensible
- stiff (low compliance)
elastin (weak spring) characteristics (3)
- low tensile strength
- extensible
- spring- high compliance
emphysema (def.)
-floppy lungs due to elastin destruction + alveolar wall destruction
emphysema effects (3)
- increased compliance, less elastic recoil
- little Ptp changes, large changes in lung volume
- time to fill increased
pulmonary fibrosis (def.)
-collagen deposition in alveolar walls in response to injury, silica dust, asbestosis
pulmonary fibrosis effects (2)
- reduction in lung compliance (stiff lungs)
- large Ptp needed for little changes in Lung volume
Surface tension (amount for elastic recoil)
-2/3 of elastic recoil of lungs, decreases lung compliance
surface tension (def.)
- water molecules at surface attracted to each other
- measure of attracting forces pulling surface molecules together
surface tension is seen at
-air-fluid boundaries (hydrogen bonding of water molecules)
effect of surface tension
-cause the surface to maintain as small an area as possible
saline-filled lung
-surface tension eliminates= small Ptp changes large increase lung volume
alveolar collapse due
-ST created inward recoil
increased pressure needed to balance
-surface tension, reduces tendency to collapse
laplace’s equation
P=2T/r
T- surface tension (c0nstant)
r - radius
P - pressure
smaller alveolar radius —>
-greater pressure needed to keep the bubble inflated
smaller alveoli collapse
into the large ones, T is constant, pressure greater in the smaller bubbles
surfactant produced by
-type II alveolar cells
surfactant action (3)
- lowers the surface tension of the lining
- stabilize alveoli collapse
- increase lung compliance, easier to expand lungs
surfactant made of (molecules) (5)
- phospholipids:
- dipalmitoyl-phosphatidylcholine (DPPC),
- phosphatidyl-choline
- surfactant apoproteins, Ca2+ ions
surfactant properties
-hydrophobic & hydrophilic properties:
enable air-water interface,decreases the density of water molecules, reduces attraction between H20
thickness of surfactant relationship with surface area
- thickness decreases with increasing SA,
- cause increase ST as radius increases
surface tension remains (regardless of radius/size in lungs)
constant, equalize pressures in alveoli of different sizes (no differences in pressure gradient between small/larger alveoli)
surfactant produced during
-last week of gestation
IRDS
- infant respiratory distress syndrome
- lack of surfactant
ventilation (upright lung)
-largest at bottom lung
ventilation (upside down)
-largest at top lung
ventilation (back)
-largest at back of lungs
weight of lungs increase P at bottom effect on Pip
makes Pip less negative, Ptp decrease- able to expand more
Alveoli at bottom
- starting more deflated, can expand more
- bottom regions of lung receive a larger portion of air
