Respiratory System 4

Question 1

What is alveolar pressure immediately before inspiration?

Answer 1

Equal to atmospheric pressure, so there’s no air flow , because there is no driving pressure from the atmosphere to the lungs (intrapleural pressure is about 4mmHg below atmospheric pressure)

Question 2

When does inspiration start?

Answer 2

When contraction of the inspiratory muscles (primarily the diaphragm) enlarges the thoracic cavity

Question 3

What happens as thoracic volume increases?

Answer 3

The intrapleural pressure becomes more sub-atmospheric and the lungs expand

Question 4

What does the increase in lung volume cause?

Answer 4

Alveolar pressure to decrease and air moves into the lungs

Question 5

When does air-flow cease?

Answer 5

When alveolar pressure returns to atmospheric pressure

Question 6

What happens when inspiration terminates?

Answer 6

The diaphragm relaxes, intrapleural pressure rises and the lungs recoil. The gases in the alveoli are compressed which elevates alveolar pressure above atmospheric pressure, driving air from the lungs to the atmosphere

Question 7

What do the negative values of air-flow during inspiration indicate?

Answer 7

That air is flowing from atmosphere into the lungs

Question 8

What do the positive values of air-flow during inspiration indicate?

Answer 8

That air flows in the opposite direction during expiration

Question 9

What is tidal volume (Vt)?

Answer 9

The total volume of air moving into (and out of) the lungs in a single breath

Question 10

What factors affect the exchange of air?

Answer 10

Muscular effort
Lung characteristics;
- compliance (change of V per change of P)
- resistance (change of P per change of flow)
- dead space (Vd)
- diffusion

Question 11

What is the inverse of compliance?

Answer 11

Elastance (reflecting the stiffness of the lung tissue)

Question 12

What is the inverse of resistance?

Answer 12

Conductance

Question 13

What is compliance?

Answer 13

A measure of the distensibility of the lungs and the chest wall and is defined as the change in volume that accompanies a small change in pressure

Question 14

What is the equation for compliance?

Answer 14

Change in volume/change in pressure

Question 15

When is compliance high (or elastance low)?

Answer 15

If a small change of pressure brings about a large change of volume

Question 16

When is compliance low?

Answer 16

If it requires a large change of pressure to achieve a small change of volume

Question 17

What is compliance given by?

Answer 17

The slope of a graph of volume as a function of pressure

Question 18

At FRC, what would an increase in filling pressure by 5mmHg cause?

Answer 18

An increase of a excised lung by about 25% of total lung capacity

Question 19

What characterises emphysema?

Answer 19

Greatly increased compliance (loss of elastic fibres)

Question 20

What are lungs like at low lung volume?

Answer 20

Very incompliant

Question 21

Why are low lung volumes incompliant?

Answer 21

Because most alveoli have collapsed so that relatively large pressure is required to overcome surface tension in order to reopen them

Question 22

What happens once the lungs are open?

Answer 22

They distend relatively easily until they are near full inflation

Question 23

Why does the deflation curve differ from the inflation curve?

Answer 23

Due to surface tension

Question 24

Is there less effort to inflate lungs filled with saline or air?

Answer 24

Saline (hysteresis is much less evident)

Question 25

What does air flow into and out of the lungs depend on?

Answer 25

The pressure difference between the atmosphere and alveoli and in the resistance to flow through the airways

Question 26

Where is resistance greatest?

Answer 26

In the medium sized tertiary (segmental) bronchi

Question 27

What else contributes significant resistance to air flow?

Answer 27

Mouth and nose

Question 28

When does resistance decrease?

Answer 28

As total cross-sectional area increases in smaller respiratory pathways

Question 29

What is asthma characterised by?

Answer 29

Sporadic bronchi-constriction that increases airway resistance

Question 30

What is an anatomic deadspace?

Answer 30

The volume of conducting airways (no exchange of respiratory gases occurs in this volume)

Question 31

What is dead space volume an obligatory consequence of?

Answer 31

Tidal ventilation

Question 32

What does the presence of an anatomic deadspace do?

Answer 32

Dilutes each tidal inspiration with alveolar air remaining from the previous expiration

Question 33

At rest, what does Vd (150ml in a healthy adult) comprise of the Vt?

Answer 33

One third, about 500ml

Vt= 1/3 alveolar air (exhaust) + 2/3 fresh air

Question 34

What is diffusion described by?

Answer 34

Fick’s law

Question 35

What is the process of diffusion?

Answer 35

The movement of oxygen and CO2 between the alveoli and pulmonary capillary and from systemic capillary blood to the cells by the process of diffusion

Question 36

What is the volume of gas transported across a membrane, such as the alveolar-pulmonary capillary interface per unit time directly related to?

Answer 36

1. Driving pressure or difference in partial pressure of the gas across the membrane
2. The area of the membrane

Question 37

What is the volume of gas transported across a membrane, such as the alveolar-pulmonary capillary interface per unit time inversely related to?

Answer 37

1. The length of the diffusion pathway (thickness of the membrane)
2. The square root of the molecular weight of the gas

Question 38

Who does respiratory distress syndrome occur in?

Answer 38

Premature babies

Question 39

What happens in respiratory distress syndrome?

Answer 39

In the alveoli, the air-water interface creates surface tension, in order to inflate an alveolus, sufficient pressure must be developed to overcome both the elastic recoil of lung tissue and the air-water surface tension
-pulmonary surfactant reduces surface tension (its absence in premature babies causes respiratory distress syndrome)

Question 40

What is emphysema?

Answer 40

It’s characterised by the destruction of alveolar and peribronchial tissue, so, upon expiration, the bronchioles collapse, trapping air in downstream alveoli and, as a consequence, FRC increases (barrel-chest), thereby disadvantaging the muscles of inspiration

Question 41

What is asthma?

Answer 41

Characterised by bronchiolar constriction (smaller r), therefore there’s increased R, and thus, increased P to achieve Vt, and therefore more muscular effort

Question 42

What is pulmonary edema characterised by?

Answer 42

Increases diffusion distance