Lecture 21: Airway Smooth Muscle

Question 1

What could ASM be involved in?

Answer 1

• V’/Q’ matching
• Dead space regulation
• Airway stability
• Foetal Breathing

Question 2

What activates ASM?

Answer 2

• Activated ACh and endothelin

- Local mediators LTC4 and PGF2

Question 3

What inhibits ASM?

Answer 3

• Vasocactive Intestinal Peptide
• NA
• Local mediators NO and PGE2

Question 4

ASM has a ______________ SR

Answer 4

Well-developed

Question 5

ASM is activated when ______________.

Answer 5

You breath

Question 6

In humans lung resistance __________ when ASM is inhibited

Answer 6

Drops by 30%

Question 7

ASM is activated (phasic) during _____________.

Answer 7

Inspiration

Question 8

Contraction of ASM in response to ____________ might improve V’/Q’ matching but requires ____________.

Answer 8

Low CO2

Extreme conditions

Question 9

Airway narrowing reduces __________, which means less __________ but increases ___________ and work to breathe

Answer 9

airway volume
less dead space
resistance

Question 10

At rest, dead space is about ___ of tidal volume

Answer 10

20%

Question 11

During exercise, airways _________ and this _________ dead space we also get a/an __________ in tidal volume

Answer 11

Dilate
More dead space
increased tidal volume

Question 12

Coughing produces ______________ of ASM

Answer 12

Reflex contraction

Question 13

Explain the physics of coughing:

Answer 13

• Airway narrowing increases air velocity and flow

- Increased velocity improves clearance during cough

Question 14

When does compression of the airway occur?

Answer 14

During forced exhalation

Question 15

How does ASM counteract compression?

Answer 15

Increased ASM tone may stabilise the airways during compression

Question 16

How does ASM contribute to foetal development of the lung?

Answer 16

Peristaltic waves move lung fluid/amniotic fluid into the lung periphery and pressurise the buds which may cause growth