Work of breathing (physio)

Question 1

What is compliance?

Answer 1

Stretchability of chest wall and lungs

Question 2

What is airway resistance?

Answer 2

Resistance to flow of air

Question 3

How does compliance affect air flow?

Answer 3

Increased compliance -> air flows in more easily

Question 4

What can cause compliance of chest wall to decrease?

Answer 4

Skeletal deformities of ribs and spine

Question 5

Measure of lung stretchability

Answer 5

Change in lung vol/unit change in airway pressure

Question 6

How does compliance affect work of breathing?

Answer 6

Decreased compliance -> decreased stretchability -> increased work of breathing

Question 7

What is elastic recoil?

Answer 7

Due to elastic fibres in lung tissue

Ability to recoil after stretching force is released

Question 8

What is a major determinant for compliance of the lungs?

Answer 8

Surface tension of alveoli

Question 9

How is surface tension (T) generated in alveoli?

Answer 9

Attractive forces btw adjacent molecules pull alveolar surface tgt

Question 10

How is pressure (P) generated within alveoli?

Answer 10

Surface tension causes alveoli to contract -> air within alveoli contract -> pressure generated

Question 11

Describe pressure in a smaller alveoli

Answer 11

Smaller alveoli has higher pressure -> empty into bigger alveoli

Question 12

R/s btw pressure (P), tension (T) and radius (r)

Answer 12

P directly proportional to T/r
- P directly proportional to T
- P inversely proportional to r

Question 13

Why do smaller alveoli have tendency to collapse?

Answer 13

Surface tension forces create pressure that is higher in smaller alveoli
- more subatmospheric (distending) pressures needed to keep small alveoli distended (stretched)

Question 14

How to improve compliance?

Answer 14

Reduce T -> reduce P -> increases compliance

NOTE: r cannot be changed

Question 15

How to reduce alveolar surface tension?

Answer 15

Surfactant -> disperse themselves btw liquid molecules -> decrease attractive forces btw them -> reduce surface tension of alveoli -> prevent collapse

Question 16

How does narrowing of the airways change resistance?

Answer 16

Increases resistance

Question 17

Ways that airways can be narrowed

Answer 17

Contraction of smooth muscle of bronchioles

Mucus accumulation

Decreased lung vol -> decreased size of bronchioles

Question 18

How does increased resistance affect work of breathing?

Answer 18

Increases work of breathing (to draw air into lungs)

Question 19

What mediates bronchoconstriction?

Answer 19

Parasympathetic nerves

Question 20

What mediates bronchodilation?

Answer 20

Sympathetic mediators

Question 21

What does FEV1 refer to?

Answer 21

Forced expiratory vol of air exhaled in 1 sec after full inspiration

Question 22

What is FVC?

Answer 22

Forced vital capacity -> total vol expired forcefully after full inspiration

Question 23

Why do we measure forced expiratory volumes?

Answer 23

Picks up changes in resistance to airflow and compliance of lungs

Question 24

What happens to FEV1 and FVC when lung compliance decreases?

Answer 24

Both values decrease
- high recoil -> can’t expand properly -> lung vol small -> total exhaled air decrease

Question 25

What happens to FEV1 and FVC when airway resistance increases?

Answer 25

Narrow airways -> slow exhalation -> FEV1 decrease Narrow airways -> can't exhale completely -> FVC decrease

Question 26

Effects of cigarette smoke on the respiratory sys

Answer 26

Cumulative irritation of airways and lungs Chronic inflammation of airways and lungs Increased mucus secretion Depressed ciliary fn Lung diseases -> COPD and lung cancer

Question 27

What is barrel chest and which grp of pts is it seen in?

Answer 27

Hyperinflation of lungs and chest Pts w/ COPD

Question 28

How do COPD pts get barrel chest?

Answer 28

Airways narrowed in COPD -> air trapping during expiration