Surface tension/airway resistance

Question 1

define surface tension

Answer 1

forces due to favorable water-water interactions and unfavorable air-water interactions

Question 2

how does the alveolus form favorable interactions between air-water?

How does increased surface tension affect lung compliance

Answer 2

incr surface tension

decr lung compliance b/c water layer in smaller alveoli has a smaller surface area to volume ratio so surface tension prevents expansion

Question 3

how does saline-filled lung differe from air-filled lung

Answer 3

fluid into alveoli provides alternate way to reduce liquid-air interface by creating deeper water layers

water from pulmonary capillary

Question 4

how does surface tension affect small alveoli

Answer 4

collapse of small alveoli (high P due to P = 2T/R) and pressure gradient forces pressure into larger alveoli

Question 5

What is surfactant?

What does it do?

Answer 5

mix of lipids + proteins iwth polar and non-polar ends

intercalates between water molec, decr attractive forces

increased effect at smaller alveoli

Question 6

Effect of surfactant

Answer 6

1) incr lung compliance
2) prevent collapse of small alveoli
3) prevent accum of fluid inside alveoli

Question 7

what is disease characterized by surfactant deficiency?

Answer 7

respiratory distress syndrome – stiff, noncompliant lungs prone to collapse

Question 9

Respiratory airways provide ____

Flow always from __ to ___

Answer 9

resistance, R

high to low pressure

Question 10

Flow equation for laminar flow

relationship between airway resistance to radius

Answer 10

Flow = (P2 - P1) / R

R proportional to 1/r^4

Question 11

compare laminar to turbulent flow

most air flow in airways is ___

Answer 11

flow < (P2 - P1) / R

transitional (between laminar and turbulent)

Question 12

Chemical factors that affect airway resistance

All act by doing what?

Answer 12

affecting smooth muscle tone of bronchioles

Question 13

What are examples of bronchoconstrictors

Answer 13

Parasympathetic Nervous system (acetycholine)

Histamine (asthma)

Question 14

what are examples of bronchodilators

Answer 14

sympathetic nervous system (epinephrine/norepinephrine via beta adrenergic receptors)

agonists for beta adrenergic receptors (isproteronol, albuterol)

CO2 in bronchioles

Question 15

Mechanical factors that affect airway resistance

Answer 15

1) mucous (bronchitis)
2) lung volumes
3) dynamic airway collapse

Question 16

how does lung volume affect airway resistance

implications for obstructive disease?

Answer 16

incr lung volume, decr resistance

patient with obstructive disease breath at higher lung volumes

(deleterious for muscle forces needed to inflate lungs)

Question 17

Discuss dynamic airway collapse

when does it occur?

how does your body create a positive PIP

Answer 17

PTP = PAW -PIP

if you have positive PIP –> airway collapse

if expiratory muscles used, chest wall exert force on intrapleural space or during coughing

Question 18

Airway is ___ when PAW > PIP

Airway is ___ when PAW < PIP

Answer 18

open

closed

Question 19

Healthy person, quiet breathing

What is PIP? Open or close airway?

Answer 19

negative PIP pulls airway open

Question 20

Healthy person, forced expiration

what happens to PIP?

Open or close airway

Answer 20

Chest wall exerts force on intrapleural space
–> PIP positive

positive PIP collapses airway

Question 21

what happens to emphysema, quiet expiration

Primary problem

Compensation

Answer 21

Primary problem–> , decr tendency of lungs to deflate/recoil, employ use muscles in forced expiration, lose connective tissue supporting airway –> PIP = positive

Compensation = positive PIP collapses airway

Question 22

why do emphysemic patients exhale through pursed lips?

Answer 22

exhaling through pursed lips incr airway pressure, decr probability of airway collapse