Pulmonary mechanics and ventilation (physio)

Question 1

What happens when air is inspired?

Answer 1

Diaphragm and inspiratory chest wall muscles contract -> chest cavity expand

Lungs expand -> intrathoracic vol increase -> air pressure in lungs decrease

Pressures in thorax and pleural cavity decrease

Active -> contract

Question 2

What happens when air is expired?

Answer 2

Diaphragm and inspiratory chest wall muscles relax

Lungs recoil -> form smaller vol -> air pressure in lungs increase

Pressures in thorax and pleural cavity increase

Passive -> relax

Question 3

What happens when ventilation is stimulated (i.e: exercise)?

Answer 3

Extra muscles are recruited in inspiration and expiration -> enhance movement of chest wall
- stronger inspiratory effort -> increase lung vol further -> increased air drawn into lungs per unit time
- stronger expiratory efforts -> decrease lung vol further -> increased air expelled from lungs per unit time

Question 4

What is pleura space?

Answer 4

Potential space btw 2 layers
- 2 layers in very close contact -> glide over one another

Question 5

What is intrapleural pressure?

Answer 5

Pressure in the pleural space

Question 6

What is pressure in the lungs like before inspiration?

Answer 6

No net flow btw alveoli and atmosphere -> intra-alveolar pressure similar to atmospheric pressure

Intrapleural pressure is neg -> created by lung recoil against chest wall

Question 7

How does pressure in the lungs change during inspiration?

Answer 7

Chest wall, pleura and lungs expand

Intra-alveolar pressure decrease -> become less than atmospheric pressure -> air flows in

Intrapleural pressure decrease -> become more neg

Question 8

How does pressure change during expiration?

Answer 8

Chest wall, pleura and lungs recoil

Intra-alveolar pressure increase -> become more than atmospheric pressure due to additional air taken in during inspiration -> air flows out

Intrapleural pressure returns to original levels

Question 9

How can the pleural space expand?

Answer 9

Filled w/ excess fluid

Filled w/ excess air

Question 10

What happens when the pleural space expands?

Answer 10

Intrapleural pressure increase -> lung collapses/have difficulty expanding -> disrupts ventilation

Question 11

How does pressure change during a pneumothorax?

Answer 11

Air flow in from atmosphere into pleural space/leak out from punctured lung into pleural space -> intrapleural pressure increase -> lung collapse

Question 12

What affects ventilation?

Answer 12

Changes in thoracic vol and pressure

Integrity of lungs and pleura, muscles and innervation, rib cage

Question 13

What is physiologic dead space?

Answer 13

Vol of air breathed in that does not undergo gas exchange w/ blood

Question 14

Why does dead space exist?

Answer 14

Not all air taken in undergoes gas exchange as it doesn’t reach alveoli due to anatomic dead space (air in airways up to respi bronchioles, just short of alveoli)

Question 15

What is tidal vol at rest (TV)?

Answer 15

Vol of air entering respi sys at each resting breath/exiting respi sys on passive expiration

Question 16

What is inspiratory reserve vol (IRV)?

Answer 16

Extra air entering lungs w/ maximal inspiration (on top of TV)

Question 17

What is expiratory reserve vol (ERV)?

Answer 17

Extra air expelled from lungs w/ maximum expiration (aft passive expiration)

Question 18

What is residual vol (RV)?

Answer 18

Vol of air left in lungs aft max expiration -> prevent lungs from collapsing

Question 19

Factors affecting ventilation vol

Answer 19

Size
- small size person -> smaller ventilation vol

Age

Physical fitness
- less fit -> smaller ventilation vol

Gender
- male usually have larger ventilation vol thn women
-ERV and IRV higher as men have more muscular framework and muscular chest wall -> take in additional vol of air during forceful inspiration/exhale additional vol of air during forceful expiration

Question 20

How can tidal vol change?

Answer 20

Depends on how much ventilation is stimulated (eg: activity of a person -> resting TV < exercising TV as exercising TV recruits other lung vol at rest)

Question 21

What affects ability to ventillate?

Answer 21

Factors which affect breathing
- properties of chest wall
- muscle power -> whether it’s adequate for breathing movement
- skeletal deformities -> hinder breathing movement
- properties of lungs
- resistance to air flow -> high -> more difficult to breathe
- areas of stiffness -> hard to expand lung
- areas of collapse -> predispose to difficulty in expansion
- restriction of diaphragm movement

Question 22

What is hyperventilation?

Answer 22

Increased ventilation

Question 23

What is hypoventilation?

Answer 23

Decreased ventilation

Question 24

What is tachypnoea?

Answer 24

Increased rate of breathing/respi rate

Question 25

What is dyspnoea?

Answer 25

Distressful sensation of breathing

Question 26

Define minute ventilation

Answer 26

TV of air breathe per min

Question 27

Formula to calc minute ventilation

Answer 27

TV x respi rate

Question 28

Define alveolar ventilation

Answer 28

Volume of air that reaches alveoli per min
- component of min. ventilation that can undergo gas exchange

Question 29

Formula to calc alveolar ventilation

Answer 29

(TV - dead space) x breaths per min