7. Physics of Breathing Flashcards
What is distensibility?
Describes how structures deform in response to applied force; can be visualized by plotting vol changes w/ applied P’s
What is elasticity (E)?
How much an object resists + recovers from deformation produced by a F
E = dP/dV [cmH2O/L]
What is compliance (C)?
Amount of deformation per unit F applied; PV graph of compliance curve flattens out at both extremes –> 2ppl reaching TLC + RV
C = 1/E = dV/dP
What is transmural P?
Difference between alveolar + intrapleural P
Define residual vol (RV).
Lowest lung vol
Define total lung capacity (TLC).
Vol when lung is fully expanded
What happens to vol changes as P’s increase?
As P’s increase, vol increases at a slower rate –> takes more + more P to increase vol by same amt. Want to breath in middle part of P-V graph b/c most efficient (mild sigmoid shape)
(T/F) At any given pt, chest wall + lungs want to go in opp directions.
True
(T/F) Chest wall always wants to expand.
False, at TLC, chest wall actually wants to expand in –> helps w passive exhalation –> move back down to balanced state
What happens to chest wall recoil as lungs expand?
The chest wall’s desire to recoil becomes less + less as vol increases –> building potential E for lungs but releasing F that causes chest wall to want to expand out.
What does a P-V curve look like for lungs?
As P’s increase, vol’s initially increase very quickly and then slow down
What does a P-V curve look like for chest wall?
As P’s increase, vol’s initially increase slowly, and then becomes faster
What term describes the balance between inward pull of lungs and outward pull of chest wall?
Functional residual capacity (FRC)
What is the transmural P when at FRC? Pleural P?
0
Negative P; w inspiration, pleural P became more negative while w expirations, pleural P became more positive
How do you calculate transmural P’s?
Subtract alveolar P’s from P sure. alveoli
What is the purpose of hysteresis loop?
PV curve for inflation and deflation of lungs, reflecting a collection of alveoli; slope = measures compliance
What does LePlace’s Law describe?
As volume in alveoli decreases, ST increases. HOWEVER, total amt surfactant remains the same, which means increased amt surfanctant per unit area.
Pressure = Tension/radius –> P = 2T/r
What two major components reflect lung’s elastic recoil?
Tissue’s elasticity + surface T
During normal TV resp., alveolar radius change from 0.05 to 0.1mm, which supposedly necessitates 7.5mmHg (15mmHg –> 7.5mmHg). However, this doesn’t doesn’t occur. Why?
Surfactant coating inside of alveoli decreases the necessary P from 7.5mmHg to 1mmHg.
Without surfactant, P in smaller alveoli would be greater causing movement of air from small to large alveoli. HOWEVER, with surfactant, P’s remain about same b/w the two diff sized alveoli since T decreases for smaller alveoli.. This helps prevent further collapse when alveoli get smaller during expiration.
What is alveolar interdependence?
Expanded alveoli in one area helps stent open an alveoli dir. adjacent to it
