Mechanics of breathing 2

Question 1

What kind of pressure allows the lungs to expand?

Answer 1

a negative pressure

Question 2

What is Pip?

Answer 2

intrapleural pressure

Question 3

what forces cause Pip to be** negative**?

Answer 3

• elastic recoil of the lungs - collapse inwards (pulling lungs outwards)
• elastic recoil of the chest wall - expand outwards
• these forces balance out at rest

Question 4

What is the equation of the transpulmonary pressure volume?

Answer 4

Ptp = Palv - Pip

Question 5

what does Pcw stand for?

Answer 5

• chest wall pressure

Question 6

Describe the pressure- volume relationship

Answer 6

as the pressure decreases around the lung, volume of the lung increases

Question 7

what is hysteresis?

Answer 7

• the difference between inspiratory and expiratory compliance

Question 8

what is lung compliance?

Answer 8

the magnitude of change in lung volume produced by a given change in intrapleural/transpulmonary pressure

Question 9

what is the equation for compliance?

Answer 9

C= delta V / delta P

Question 10

what does a greater lung compliance mean?

Answer 10

the greater the lung compliance the **easier it is to expand **the lungs at a given change in pressure

Question 11

what does it indicate if the lung compliance is** lower than normal**?

Answer 11

• this indicates that the lung is stiffer

Question 12

What is an example of a disorder that is associtated with poor compliance?

Answer 12

pulmonary fibrosis

Question 13

what is an example of a condition that is associated with increased compliance?

Answer 13

• emphysema (air sacs in the alveoli are damaged)

Question 14

what is emphysema?

Answer 14

• air sacs in alveoli are damaged
• air sacs weaken and rupture which creates larger air spaces instead of many small ones

Question 15

what are the **2 major determinants **of lung compliance?

Answer 15

1. stretch capacity of the lung tissue
2. surface tension

Question 16

what is surface tension?

Answer 16

• surface tension is the force acting on the surface of a liquid in an air-water interface

Question 17

How does surface tension form?

Answer 17

• when you breathe in,** air contains water vapour**
• the water molecules line the alveoli and are attrcated to each other creating strong forces that try to form spheres

Question 18

What does the law of laplace describe?

Answer 18

• describes the relationship between pressure (P), surface tension (T) and the radius of the alveolus (r)

Question 19

what is the collapsing pressure?

Answer 19

the pressure required to prevent collapse of the sphere

Question 20

what happens to the collapsing pressure if the surface tension (T) increases or the** radius of a sphere decreases**?

Answer 20

the collapsing pressure increases

Question 21

why do smaller alveoli have a greater collapsing pressure?

Answer 21

• they have a decreased radius
• they have a greater tendency to collapse

Question 22

What is surfactant produced by?

Answer 22

type II pneumocytes

Question 23

what is surfactant a mixture of?

Answer 23

mixture of both lipids and proteins

Question 24

what does the hydrophilic end of surfactant do?

Answer 24

the hydrophillic end inserts into the water layer lining the alveoli and **reduces surface tension **

Question 25

What are the physiological advantages of surfactant?

Answer 25

• surfactant reduces surface tension and prevents alveolar collapse
• increases the** stability of the alveoli**
• if you lower the surface tension, you increase the compliance of the lungs, which reduces the worl of expanding the lung with each breath

Question 26

what could be the consequences of a** loss of surfactant**?

Answer 26

• low compliance - stiff lungs
• surface tension is high and therefore difficult to expand lungs
• premature babies born - surfactant is not acquired yet and they may develop respiratory distress syndrome

Question 27

what happens if air is inrtoduced into the pleural space?

Answer 27

• pressure is raised, lung collapses and chest wall springs out
• causes pneumothorax