Respiratory Physiology Lecture 2 part 11: More on ventilation

Question 1

What are the two mechanics of ventilation?

Answer 1

• static properties of the lung
• Dynamic properties of the lung

Question 2

Static lung properties

Answer 2

mechanical properties when no air is flowing (Necessary to maintain lung and chest wall at a certain volume)

Question 3

What are the static properties of the lung?

Answer 3

• Intrapleural pressure (PIP)
• transpulmonary pressure (PTP)
• Static compliance of the lung
• Surface tension of the lung

Question 4

Dynamic lung properties

Answer 4

mechanical properties when the lungs are changing volume and air is flowing in and out (Necessary to permit airflow)

Question 5

What are the dynamic properties of the lungs?

Answer 5

– Alveolar pressure (PALV)
– Dynamic lung compliance
– Airway and tissue resistance

Question 6

What are static and dynamic properties of the lung necessary for?

Answer 6

• static: Necessary to maintain lung and chest wall at a certain volume
• dynamic: Necessary to permit airflow

Question 7

What is the main pressure for generating flow?

Answer 7

Alveolar pressure (P_ALV)

Question 8

Ventilation

Answer 8

exchange of air between the atmosphere and the alveoli

Question 9

What kind of flow is ventilation?

Answer 9

bulk flow

Question 10

bulk flow

Answer 10

gas moves from high pressure to low pressure

Question 11

Boyles Law

Answer 11

for a fixed amount of an ideal gas kept at a fixed temperature, P [Pressure] and V [Volume] are inversely proportional

ie. While one increases, the other decreases

Question 12

P1V1= ?? (At constant T)

Answer 12

P1V1 = P2V2 (At constant T)

Question 13

What exerts pressure in lungs?

Answer 13

• Change in lung volume translated into a change in lung pressure according to Boyle’s Law
• Gas molecules are constantly in motion and this motion exerts a pressure

Question 14

Alveolar volume/ pressure during expiration and inspiration

Answer 14

expiration: ⇡ pressure ⇣ volume
inspiration: ⇣ pressure ⇡ volume

Question 15

What produces airflow?

Answer 15

A change in volume, and then in pressure, produces airflow

• Once pressure difference is generated between inside and outside of the lung (alveoli and atm), air moves via bulk flow (F) from a region of high pressure to a region of low pressure

Question 16

F

Answer 16

bulk flow

Question 17

bulk flow (F) = ??

Answer 17

F=ΔP/R

Question 18

What are the two pressures of interest in bulk flow?

Answer 18

Two pressures of interest:

P_alveoli (P_alv) & P_atmosphere (P_atm)

F=(P_alv – P_atm)/R

Question 19

When is F = 0?

Answer 19

When P_atm = P_alv, F = 0

Question 20

What relates the the lungs to the thoracic wall?

Answer 20

The pleurae

Question 21

Pleurae

Answer 21

thin double-layered envelope

Question 22

What are the layers of the pleurae?

Answer 22

visceral pleura & parietal pleura

Question 23

visceral pleura

Answer 23

covers the external surface of the lung

Question 24

Parietal pleura

Answer 24

covers thoracic wall and superior face of the diaphragm

Question 25

What is between the visceral and parietal pleura?

Answer 25

Intrapleural fluid (~ 10 mL)

Question 26

Purpose of intrapleural fluid

Answer 26

Reduces friction of lung against thoracic wall during breathing

(Extremely thin, 5 - 35 μm)

Question 27

What interaction determines lung volume?

Answer 27

Interaction between lungs and thoracic cage determines lung volume

Question 28

What is the elastic recoil of lungs and chest wall?

Answer 28

‒ Lungs → tendency to collapse due to elastic recoil

‒ Chest wall → pulls thoracic cage outward due to elastic recoil

Question 29

Elastic recoil of lungs and chest wall at equalibrium

Answer 29

At equilibrium, inward elastic recoil of lungs exactly balances outward elastic recoil of chest wall

Question 30

How does interaction between lungs and chest wall occur?

Answer 30

Interaction between lungs and chest wall does not occur by direct attachment but through the intrapleural space between visceral and parietal pleurae