Ventilation and Pressure

Question 1

Ventilation

Answer 1

• Process of moving air in and out of lungs
• Controlled by mechanical properties of lung and chest wall
• Can be used to assess respiratory health

Question 2

Lung volume periods

Answer 2

1.tidal volume
2. functional residual capacity
3. total lung capacity
4. vital capacity
5.residual volume

Question 3

Tidal volume

Answer 3

-air in/out with normal breath

Question 4

Functional residual capacity (FRC)

Answer 4

-amount of air in thorax after normal expiration

Question 5

Total lung capacity (TLC)

Answer 5

• Total volume of gas inside lungs after maximum inhalation

**Used in humans a lot, but obviously can’t ask an animal to take full breath

Question 6

Vital capacity (VC)

Answer 6

-maximum amount of air that can be moved

Question 7

Residual volume (RV)

Answer 7

-amount of air in lung that cannot be exhaled

Question 8

Functional reserve capacity (FRC) and CPR

Answer 8

• The air that remains in lungs after expiration (lungs are always filled with gas)
• Reason you have approximately 5 mins after someone stops breathing to attempt CPR

Question 9

Air movement

Answer 9

• Only moves where there is a difference in gas pressure
• Moves from high to low

Question 10

Dalton’s Law

Answer 10

Total pressure= sum of the partial pressures of individual gases

Question 11

Gases within air

Answer 11

• O2
• CO2
• H2O
• N2 (inert, just exists)

Question 12

Pressure distribution in ambient (dry) air

Answer 12

• Lower levels of CO2
• No H2O pressure

Question 13

Pressure distribution of moist tracheal air

Answer 13

-H2O displaces O2 as O2 is humidified (more H2O, slightly less O2)

Question 14

Pressure distribution of alveolar gas

Answer 14

-CO2 displaces O2 due to gas exchange (increase in CO2, decrease in O2)
-H2O pressure still present

Question 15

Pressure distribution in systemic venous blood vs. systemic arterial blood

Answer 15

• Venous: less O2, more CO2
• Arterial: more O2, less CO2

Question 16

Visceral pleura pressure

Answer 16

-continuous serous membrane tissue covering the lungs
-elastic recoil pressure (tends to collapse); pulls lung away from chest wall

Question 17

Parietal pleura pressure

Answer 17

• Continuous serous membrane tissue covering the chest cavity
• Elasticity of the chest wall tends to spring out; push outwards

Question 18

Ventilation mechanics at rest (pressure)

Answer 18

-both pleura are attached to each other by serous fluid and are opposing forces pulling on the intrapleural “space” (theoretical because they are attached) creating a vacuum
-generates a net negative pressure preventing the lungs from collapsing

Question 19

Ventilation mechanics at rest (airflow)

Answer 19

-no airflow because the alveolar pressure is EQUAL to atmospheric pressure

Question 20

Atmospheric pressure

Answer 20

760mm Hg

Question 21

Ventilation mechanics during inspiration (pressure)

Answer 21

-contraction of external intercostal muscles move ribs craniolaterally & diaphragm moves caudally causing the attached pleura to pull outwards, expanding the lungs
-lung expansion=increased lung volume
-due to Boyle’s law, increased lung volume results in decreased pressure in alveolar and intrapleural space (net negative in intrapleural and alveolar spaces compared to atmospheric pressure)

Question 22

Ventilation mechanics during inspiration (airflow)

Answer 22

Negative pressure in both intrapleural and alveolar space compared to atmospheric pressure

-difference drives airflow into the lungs, and oxygen in the alveolar participates in gas exchange
-stops when alveolar and atmospheric pressure are equal

Question 23

Boyles Law

Answer 23

P1V1=P2V2
-volume increases, than pressure decreases

Question 24

Ventilation mechanics during expiration (pressure)

Answer 24

-relaxation of external intercostal and diaphragm results in elastic compression of lung (passive in most animals)
-due to Boyle’s law, decrease in volume results in increased pressure in alveolar and intrapleural space. Results in positive pressure in alveolar space (and still negative but slightly increased pressure in intrapleural space)

Question 25

Ventilation mechanics during expiration (airflow)

Answer 25

-Alveolar pressure is greater than atmospheric pressure, so airflow (including CO2) will exit the respiratory system

Question 26

Why is the intrapleural pressure almost always net negative?

Answer 26

Needs to be negative to keep the alveoli open so atmospheric pressure always needs to be greater than intrapleural pressure
- Will be most negative during inspiration, least negative at rest or during forced expiration

Question 27

Ventilation mechanics during forced expiration (pressure)

Answer 27

-contraction of abdominal muscle forces abdominal viscera against diaphragm and internal intercostal muscle to depress the ribcage and reduce thoracic size
- Due to Boyle’s law, decreased volume, results in increased pressure
-net positive pressure in both alveolar and intrapleural space compared to atmospheric pressure

Question 28

Ventilation mechanics during forced expiration (airflow)

Answer 28

-very high positive pressures in both alveolar and intrapleural spaces result in a forceful airflow out of lungs

• coughing, and during exercise

Question 29

Transmural pressure

Answer 29

=P(alveolar) – P(intrapleural)

-drives distention (how well alveoli stay open) in alveoli. They cannot expand by themselves, they are very compliant and passively expand due to distending pressure

Question 30

Positive transmural pressure

Answer 30

-must be positive to keep alveoli open
- the greater the transmural pressure, the greater the distending force and therefore the more expanded and larger the alveoli (impacts gas exchange)

Question 31

Effects of gravity on pressure

Answer 31

• explained by slinky model (distance between coils decreases further down due to gravity)
  -decreased volume near bottom and therefore increased pressure. Higher pressure near the bottom so smaller net pressure difference relative to atmospheric pressure

Question 32

Gravity effect on alveolar size

Answer 32

Alveolar size is larger in the cranial/dorsal half

• due to transpulmonary pressure being affected by gravity. Since volume decreases further down, an increase in intrapleural pressure occurs resulting in a decreased transpulmonary pressure

Question 33

Alveolar pressure at rest

Answer 33

-always equal to 0

Question 34

Pneumothorax

Answer 34

-puncture of intrapleural space results in loss of negative pressure caused by equalization with atmospheric pressure

-Results in loss of positive transmural pressure which is required to keep lungs open. This loss causes lung collapse, chest wall springing out, and prevention of chest from expanding