physiology: lung mechanics Flashcards
Three different pressure considerations important in
ventilation
atmospheric (barometric) pressure intra-alveolar pressure (intrapulmonary pressure) intrapleural pressure (intrathoracic pressure)
Atmospheric Pressure
pressure at sea level….
decreases when…
760mm Mg
as altitude increases
Intra-alveolar Pressure
what is it
it varies with
pressure of air in alveoli (opened system)
phase of respiration
-during INSPIRATION = negative(IAP atmospheric pressure)
what drives ventilation
•Difference between P(alv) and P(atm)
Intrapleural Pressure
what
always…
-pressure inside pleural sac (closed system)
-less than Palv
negative under normal conditions at rest
what does FRC stand for
what does it mean
- functional residual capacity
- volume of air in lungs in between breathes …..Palv = Patm (2.2L)
Factors determining intra-alveolar pressure:
- quality of air
- volume of aveoli
Inspiration:
lungs expand , aveolar volume increases
- alveolar pressure ↓
- pressure gradient is : air into lungs
- quanity of air in alveoli rises
- alveolar pressure↑
expiration
lungs recoil , alveolar volume decreases
- alveolar pressure ↑
- pressure gradiant is lungs to air
- quanity of air in aveoli ↓
- alveolar pressure ↓
Respiratory Muscle Activity During Inspiration
contraction of diaphragm and external intercostal muscles
elevation of rib cage
Respiratory Muscle Activity During Expiration
contraction of internal intercostal muscles and abdominal muscles
Factors Affecting Pulmonary Ventilation
lung compliance- lung expandability , less compliant lungs are more work required for inflation …… (affected by elasticity and tension of lungs)
Airway Resistance….. affected by passive forces, contracile activity of smooth muscles and mucus excretion( increased by pathologies)
Work of breathing is increased in the following situations:
pulmonary compliance ↓
recoil elasticity ↓
airway resistance ↑
