Mechanics of Breathing II Flashcards
What allows the lungs to expand?
negative pressure
What forces inter pulmonary pressure to be -ve?
Elastic recoil of lungs - collapse inwards
Elastic recoil of chest - expand outwards
What happens when pleural membranes move apart?
Increase interpleural space volume -> reduces pressure
What determines airflow?
Difference in pressure between alveoli and atmosphere
What is transpulmonary pressure?
Pressure holding lung open -> determines lung volume
Ptp = Palv - Pip
What does chest wall pressure oppose?
Outward elastic recoil of chest wall
Pcw = Pip - Patm
What is the equation for airflow?
F = Palv-Patm/R
What is Pip and Palv at end of expiration?
Pip = -4mmHg
Palv = 0
What does pressure changes of Pip, Palv and Ptp show?
Different phases of the respiratory cycle
When does air flow stop moving down its pressure gradient?
When intrapleural pressure = atmospheric pressure
When does gas flow stop moving down its pressure gradient during expiration?
Until intrapulmonary pressure is 0
Why is lung volume never zero?
Some air in lung without any expanding pressure
Why is inspiratory volume less than expiratory in intrapleural pressure?
Elastic recoil on expiration always less than pressure require to inflate lungs
What is lung compliance?
Magnitude of change in lung volume produced by a given change in intrapleural/transpulmonary pressure
C = ∆V/ ∆P
What does the greater compliance mean?
Easier it is to expand the lungs at a given change in pressure
What is normal compliance?
200mls.cmH2O^-1
What is the consequence of higher expanding pressure?
Lungs are stiffer = less compliannt
What is a restrictive disorder?
Pulmonary fibrosis
What are 2 features of pulmonary fibrosis?
Deposition of fibrotic tissue
Hard to distend
What is a disease associated with increased compliance?
Emphysema - alveoli air sacs are damaged
What happens in emphysems?
Inner walls of air sacs weaken and rupture - creating larger air spaces
What are 2 major determinants of compliance?
Stretchability of lung tissue
Surface tension
What is surface tension?
Force acting on surface of a liquid in an air-water interface within alveoli
What law describes surface tension?
Law of Larplace
P=2T/r
r - radius of alveoli
What causes the collapsing pressure to increase according to Law of Larplace?
Surface tension increasing
Radius of sphere decreases
Do smaller or larger alveoli have a greater tendency to collapse (greater collapsing pressure)?
Smaller
What is surfactant made up of?
Lipids and proteins
What cell secretes surfactant?
Type II pneumocytes
How does surfactant reduce surface tension?
Hydrophilic end inserts into water layer lining alveoli -> inhibit water molecules coming close together
What stimulates surfactant secretion?
Taking a deep breath
What are 3 advantages of surfactant?
Reduces surface tension
Prevents alveolar collapse
Increases stability
What does loss of surfactant cause?
Low compliance - stiff lungs
Alveoli filled with water
Common with premature babies
What happens when air is introduced into pleural space?
Raised pressure -> lung collapse -> chest wall springs out -> pneumothorax
