7. Physics of Breathing

Question 1

What is distensibility?

Answer 1

Describes how structures deform in response to applied force; can be visualized by plotting vol changes w/ applied P’s

Question 2

What is elasticity (E)?

Answer 2

How much an object resists + recovers from deformation produced by a F

E = dP/dV [cmH2O/L]

Question 3

What is compliance (C)?

Answer 3

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

Question 4

What is transmural P?

Answer 4

Difference between alveolar + intrapleural P

Question 5

Define residual vol (RV).

Answer 5

Lowest lung vol

Question 6

Define total lung capacity (TLC).

Answer 6

Vol when lung is fully expanded

Question 7

What happens to vol changes as P’s increase?

Answer 7

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)

Question 8

(T/F) At any given pt, chest wall + lungs want to go in opp directions.

Answer 8

True

Question 9

(T/F) Chest wall always wants to expand.

Answer 9

False, at TLC, chest wall actually wants to expand in –> helps w passive exhalation –> move back down to balanced state

Question 10

What happens to chest wall recoil as lungs expand?

Answer 10

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.

Question 11

What does a P-V curve look like for lungs?

Answer 11

As P’s increase, vol’s initially increase very quickly and then slow down

Question 12

What does a P-V curve look like for chest wall?

Answer 12

As P’s increase, vol’s initially increase slowly, and then becomes faster

Question 13

What term describes the balance between inward pull of lungs and outward pull of chest wall?

Answer 13

Functional residual capacity (FRC)

Question 14

What is the transmural P when at FRC? Pleural P?

Answer 14

0

Negative P; w inspiration, pleural P became more negative while w expirations, pleural P became more positive

Question 15

How do you calculate transmural P’s?

Answer 15

Subtract alveolar P’s from P sure. alveoli

Question 16

What is the purpose of hysteresis loop?

Answer 16

PV curve for inflation and deflation of lungs, reflecting a collection of alveoli; slope = measures compliance

Question 17

What does LePlace’s Law describe?

Answer 17

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

Question 18

What two major components reflect lung’s elastic recoil?

Answer 18

Tissue’s elasticity + surface T

Question 19

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?

Answer 19

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.

Question 20

What is alveolar interdependence?

Answer 20

Expanded alveoli in one area helps stent open an alveoli dir. adjacent to it