RS Lec 3 Flashcards
static properties of lungs (def.)
-mechanical properties when no air is flowing (needed to maintain lung + chest wall @ certain volume)
things that make up static properties of lung
- intrapleural pressure (Pip)
- transpulmonary pressure (Ptp)
- static compliance of lung
- surface tension of the lung
dynamic properties of lungs (def.)
-mechanical properties when the lungs are changing volume and air is flowing in and out (necessary to permit airflow)
things that make up dynamic properties of lung
- alveolar pressure (Palv)
- dynamic lung compliance
- airway +tissue resistance
boyle law
-fixed amount of air at constant temp – pressure is inversely proportional to V
↓V leads to ↑ Palv=
expiration
↑V leads to ↓ Palv=
inspiration
difference is pressure generated …
air moves via bulk flow from high pressure to low pressure
Palv < Patm
inspiration (increase in thoracic volume)
Palv > Patm
expiration (decrease in thoracic volume)
Bulk flow (F)
-F= (Palv- Patm)/R
lung pressures that affect INS, EXP
- intrapleural pressure (Pip)
- alveolar pressure (Palv)
- transpulmonary pressure (Ptp)
pleurae (def.)
-thin double-layered envelope between intrapleural fluid
visceral pleura (def.)
-covers external surface of lung
parietal pleura (def.)
-covers thoracic wall + superior face of diaphragm
intrapleural fluid (10 ml) reduces
-friction of lungs during breathing (thin space- 5 to 35 um)
lung volume determined by interaction between…
- lung + thoracic cage via intrapleural space
tendency of lungs
collapse due to elastic recoil
tendency of chest wall
-outward due to elastic recoil
at equilibrium (tendency of lungs/chest wall)
-inward elastic recoil (lungs) balances outward recoil (chest)
Intrapleural pressure (Pip) (3)
- pressure within pleural cavity
- changes with breathing but always subatmospheric due to opposite recoil
- relative vacuum
if Pip = Palv
-lungs would collaspe
alveolar pressure (Palv) (3)
- pressure of air inside the alveoli, dynamic element in producing airflow
- when airways are open Patm = Palv
difference between alveolar pressure + atmospheric pressure
-controls gas-exchange between lungs + atmosphere
transpulmonary pressure (Ptp)
- force responsible for keeping the alveoli open, difference between Palv and Pip
- static parameter, does not cause airflow but determines lung volume
Inspiration actions
- diaphragm + INS intercostal contracts
- thorax expand
- Pip more subatmospheric
- increase Ptp
- lungs expand
- Palv subatmospheric (flow from high to low)
- air flow in alveoli
expiration actions
- diaphragm + INS intercostal stop contracting
- chest wall recoil inward
- Pip back to regular subatmospheric value
- Ptp back to preINS value
- lungs recoil
- Palv increases (compressed air) > Patm
- air flow out of lungs
airway resistance is generally
small
resistive forces (airflow)
- inertia of RS (negligible)
- friction (1. lung tissue past itself, 2. lung +chest wall (IP fluid ↓ friction)
- frictional resistance to flow of air through airways (80%)
airflow resistance sensitive to
-changes in radius when flow is not laminar
laminar airflow
- little energy lost to resistance
- happens in smallest airways
transitional airflow
- produces vortices- resistance increases
- happens in most of bronchial tree (intermediate airways)
turbulent airflow
- resistance to airflow is the highest
- happens in large airways
- linear air velocities is high
laminar flow (poiseuille’s law)
- proportional to viscosity of gas, length of tube
- inversely proportional to r^4
resistance in airways in upper air passages/large airways
0.6
resistance in airways small airways (#)
0.3
terminal bronchioles arranged in parallel
- lower aggregate R
- parallel: 1/R= 1/R1 + 1/R2 +…
- in series: R= R1 +R2 +…
small airways determine airflow resistance because they are easily occluded by…
- smooth muscle contraction in walls
- edema occurring in walls of alveoli + bronchioles
- mucus collecting in lumen of bronchioles
