Respiratory 4 Flashcards
What does high compliance mean
Easy to inhale
Hard to exhale
Low elastance
What does low compliance mean
Hard to inhale
Easy to exhale
High elastance
What is another important determinant of compliance and lung elastic recoil
Surface tension at air water interface of the airways
What is surface tension
Measure of force acting to pull a liquids molecules together at an air-water interface
What did Von Neergard find
Way easier to inflate if their was liquid
Found fluid lining the inner walls of alveoli
What is structure of alveoli
Alveoli wall then liquid layer then air inside
What would happen if alveoli only had water lining walls
The pull inward would be so strong alveoli would collapse
Where is fluid found in alveoli
Lining the inner walls
What happens when intermolecular force pulls the surface molecules downward
The molecules that remain at surface develop opposing force, surface tension
What is surfactant
Detergent-like molecule secreted by type II alveolar cells
- 90% phospholipids, 10% proteins
What is role of surfactant
Reduce surface tension and disrupt intermolecular bonds
- reduce surface tension to ~25 dynes/cm or less
What are the regions of the surfactant molecules and where do they sit
Hydrophilic end stays in water and hydrophobic goes into air
- sit between adjacent water molecules so they can’t form bonds
What are 2 things surfactant does
- Increases compliances (reduces inward pressure)
- Ensures alveoli of all size inflate (smaller have greater concentration of surfactant)
What do alveoli of different radius have in common
Same surface tension so there’s equal inward pressure and small ones wont empty into large ones
What ensures two alveoli inflate and have adequate surface area for exchange even when one is blocked or smaller alveolus
The rapidly expanding one will put a “brake” on expansion by increasing surface tension and elastic recoil
The slowly expanding one will have less diluted surfactant causing no “brake” in expansion
What is infant respiratory distress syndrome
Premature: insufficiency of surfactant production and immaturity of lungs
- alveoli collapse
- prevalence decreases with gestational age
- decrease compliance, increase elastance
Prevention of infant respiratory distress
Glucocorticoid injection
Treatment of infant respiratory distress syndrome
- artificial surfactant
- continuous positive airway pressure (CPAP)
- intubate
Where does 90% of airway resistance occur in healthy individual
Trachea and bronchi
- is constant
- smallest total cross sectional area
What is airway resistance based on
Poiseuille’s equation
Resistance increases when length and viscosity increase
Resistance decreases when increase in radius
What is air flow determined by
Pressure gradient at start vs end
Resistance (length, viscosity, radius)
Factors that affect airway resistance
- length of system: constant
- viscosity of air: constant (humidity or altitude alter)
- diameter of airways (constant in healthy)
- upper airways: physical obstruction (mucus, etc.)
- bronchioles: bronchoconstriction (parasympathetic, histamine), bronchodilation (CO2, epinephrine)
What is the site of variable resistance
Bronchioles
What is common control of bronchoconstriction/dilation (smooth muscle control)
- paracrine control, CO2 being major one
High levels = dilation (reduce resistance, get rid of CO2)
Low levels = constriction
