Lecture 1: Respiratory Cycle and Mechanics

Question 1

What does Boyle’s law say?

Answer 1

Pressure of gas is inversely proportional to volume

Question 2

What happens when lung volume increases?

Answer 2

Pressure in lungs decrease so air can enter lungs

Question 3

What happens when lung volume decreases?

Answer 3

Pressure in lungs increases so air can exit lungs

Question 4

What happens during inspiration?

Answer 4

• Inspiratory muscles (external intercostal muscles) contract
• Diaphragm descends
• Thoracic volume increases
• Intrapleural pressure and alveolar pressure decreases
• Chest wall and lungs will expand due to coupling (lungs want to collapse)

Question 5

Where is parietal fluid found?

Answer 5

Between parietal and visceral pleura

Question 6

What is intrapleural pressure?

Answer 6

Pressure everywhere in thorax except lumens of blood vessels, lymphatics, and airways

Question 7

What is the intrapleural pressure at rest?

Answer 7

-5 cm H2O

Question 8

What is the intrapleural pressure during inspiration?

Answer 8

Reaches -8 cm H2O

Question 9

What is the alveolar pressure at rest?

Answer 9

0 cm H20

Question 10

What is the alveolar pressure during inspiration?

Answer 10

-1 cm H20

Question 11

What happens during expiration?

Answer 11

• Passive so expiratory muscles not always used
• Diaphragm ascends
• Thoracic volume decreases
• Intrapleural pressure and alveolar pressure increases
• Chest wall and lungs will shrink due to coupling

Question 12

What is the intrapleural pressure during expiration?

Answer 12

Goes back to rest (-5 cm H2O)

Question 13

What is the alveolar pressure during expiration?

Answer 13

Reaches +1 cm H2O

Question 14

What four things does the respiratory cycle show change in?

Answer 14

1) Volume
2) Alveolar Pressure
3) Intrapleural Pressure
4) Air Flow

Question 15

What is minute ventilation?

Answer 15

Volume of air inhaled every minute

Question 16

How do you calculate minute ventilation?

Answer 16

V(dot) = Tidal Volume x frequency

Question 17

What is the normal value of minute ventilation?

Answer 17

7 L/min or 7000 mL/min

Question 18

What is anatomic dead space?

Answer 18

Space in the lungs designed not exchange oxygen

• first 16 generations of airway do not have alveoli
• called anatomic since it is not designed for air exchange

Question 19

How do you calculate anatomic dead space?

Answer 19

Weight of person –> anatomic dead space

Example: 120 lb person has 120 mL of anatomic dead space

Question 20

What is alveolar dead space?

Answer 20

Alveoli that should do gas exchange but doesn’t (increases in diseased state)
-this should in theory not exist

Question 21

What is physiological dead space?

Answer 21

anatomic dead space + alveolar dead space

total parts of the respiratory system that don’t do gas exchange

Question 22

How do you calculate minute alveolar ventilation?

Answer 22

V(dot alv) = (Tidal volume-anatomic dead space volume) x (frequency)

Question 23

When is it easiest for lungs to stretch during inspiration?

Answer 23

After there is a little air in the lungs, a small change in pressure can lead to a huge increase in volume of lungs

Question 24

What is hysteresis?

Answer 24

volume change allowed by surfactant between inspiration and expiration

lung filled with saline will not have hysteresis (gap) in between since surface tension is high = not enough change in volume to expand the lung

Question 25

What allows hysteresis to occur?

Answer 25

Surfactant: reduces tension and keeps alveoli open

Question 26

What is compliance?

Answer 26

Measure of stretch ability of lungs

Question 27

Where is compliance high in lungs?

Answer 27

Tidal volume (middle)
-easy to inflate

Question 28

How is compliance calculated?

Answer 28

Compliance = (Δ volume)/(Δ pressure)

Question 29

What is the opposite of compliance?

Answer 29

Elasticity: recoil ability

Question 30

How does fibrosis affect compliance?

Answer 30

Lowers compliance

-lungs have to work harder to bring in air

Question 31

How does age affect compliance?

Answer 31

Compliance increases with age

-less elastin and more collagen

Question 32

How does emphysema affect compliance?

Answer 32

Increases compliance

-easier to bring air but air has no where to go since there is an increase in dead space

Question 33

Where do recoil of lungs and chest wall balance each other?

Answer 33

Functional residual capacity (FRC)

Question 34

When a pneumothorax occurs, what happens to chest wall and lungs?

Answer 34

Lungs: get smaller
Chest wall: expand
*both get their wish

Question 35

How is airway resistance calculated?

Answer 35

Resistance = (8 x viscosity of x length of tube) / (radius^4)

Question 36

What prevents alveoli to collapse?

Answer 36

Interdependence

-shared walls of alveolar and airways prevent collapse as recoil opposes each other

Question 37

What does work of breathing mean?

Answer 37

Breathing does work to overcome resistive and elastic forces

resistive - resistance to expansion aka resistance to inspiration
elastic - resistance to recoil aka resistance to expiration

Question 38

How do you interpret a work of breathing graph?

Answer 38

1. Figure out if condition resists expansion (inspiration_ or recoil (expiration)
2. Know which curve represents work of inspiration and expiration. Find the relevant curve and analyze how it changed.

inspiration changes up and right direction, expiration changes down and left direction