Ventilation and Compliance

Question 1

Describe what it means by tidal volume?

Answer 1

TV - Tidal Volume. The volume of air breathed in or out of the lungs at each breath.

500ml

Question 2

Describe what it means by expiatory reserve volume?

Answer 2

ERV - Expiratory Reserve Volume. The maximum volume of air which can be expelled

1100ml

Question 3

Describe what it means by inspiratory reserve volume?

Answer 3

IRV - Inspiratory Reserve Volume. The maximum volume of air which can be drawn

3000ml

Question 4

Describe what it means by residual volume?

Answer 4

RV - Residual Volume. The volume of gas in the lungs at the end of a maximal expiration.

1200ml

Question 5

Describe what it means by vital capacity?

Answer 5

VC - Vital Capacity = tidal volume + inspiratory reserve volume + expiratory reserve volume.

Question 6

Describe what it means by total lung capacity?

Answer 6

TLC - Total Lung Capacity = vital capacity + the residual volume.

Question 7

Describe what it means by inspiratory capacity?

Answer 7

IC - Inspiratory Capacity = tidal volume + inspiratory reserve volume.

Question 8

Describe what it means by function residual capacity?

Answer 8

FRC - Functional Residual Capacity = expiratory reserve volume + residual volume.

Question 9

Describe what it means by FEV1?

Answer 9

FEV1 = Forced Expired Volume in 1 second

Question 10

Describe what it means by FEV1:FVC?

Answer 10

Fraction of Forced Vital Capacity expired in 1 second.

Question 11

What does it mean by anatomical dead space and what is the value for this?

Answer 11

Anatomical dead space volume is ~150 mL and is the volume of gas occupied by the conducting airways that cannot undergo gas exchange.

Question 12

What does ventilation refer to?

Answer 12

Ventilation refers to the movement of air in and out of the lungs (breathing).

Question 13

What are the two types of ventilation and describe each one

Answer 13

Pulmonary (minute) ventilation – total air movement in and out of the lungs

Alveolar ventilation – fresh air (with high O2 content) getting to the alveoli and therefore available for gas exchange.

Question 14

What does hypoventilation mean?

Answer 14

Hypoventilation is when our alveolar ventilation is low.

Question 15

What does hyperventilation mean?

Answer 15

Hyperventilation is when our alveolar ventilation is high.

Question 16

How can alveolar ventilation be calculated?

Answer 16

Alveolar ventilation (mL/min) can be calculated by the respiratory rate (breathes per minute) and the air to alveoli (mL/min).

Question 17

What does partial pressure mean and what unit is it expressed by?

Answer 17

The partial pressure of a gas in a mixture of gases is equivalent to the percentage of that particular gas in the entire mixture multiplied by the pressure of the whole mixture.

Pressure is common expressed in mmHg or kPa units (normally use mmHg)

Question 18

T/F All gas molecules exert same pressure, so partial pressure increases with increasing [gas]mixture

Answer 18

TRUE

Question 19

What are the normal values for alveolar PO2 and CO2

Answer 19

PO2 = 100mmHg (13.3 kPa)

PCO2 =40mmHg (5.3 kPa)

Question 20

What happens to the PO2 and PCO2 during hyperventilation?

Answer 20

PO2 increases to 120mmHg

PCO2 falls to 20mmHg

Question 21

What happens to the PO2 and PCO2 during hypoventilation?

Answer 21

PO2 falls to 30mmHg

PCO2 increases to 100mmHg

Question 22

What cells are the alveolar walls made of?

Answer 22

Type I -thin walled
- cells which permit gas exchange

Type II - cells which secrete surfactant fluid

Question 23

What is surfactant and describe its function

Answer 23

Surfactant is a detergent-like fluid produced by type II alveolar cells. This reduces the surface tension on alveolar surface membrane thus reducing the tendency for alveoli to collapse.

Question 24

Why is it important to reduce surface tension?

Answer 24

Surface tension is the attraction of one water molecule to the other molecules. Since the alveoli is lined with fluid that is largely water-based with the water molecules arranged in a sphere around the alveoli, the attraction between these molecules causes a force that leads to the alveoli to collapse.

Question 25

Why is surfactant more effective in smaller alveoli?

Answer 25

The molecules of the surfactant are closer together therefore more concentrated

Question 26

What law determined the pressure required to keep an alveoli open and stop from collapsing?

Answer 26

The law of LaPlace

P=2Tr

P-pressure
T-surface tension
r-radius

Question 27

Describe the surfactant production in a fetus

Answer 27

Surfactant production starts at week 25 of gestation and is complete at abut week 36 (40 weeks = full term). Stimulated by the thyroid hormone and cortisol which increases towards the end of pregnancy. Premature babies surfer Infant Respiratory Distress Syndrome (IRDS).

Question 28

What is the definition of compliance

Answer 28

Compliance is the change in volume relative to the change in pressure so essentially how much does volume change for any given change in pressure.

(represents the stretchability of the lung not the elasticity

Question 29

Define high-compliance

Answer 29

large increase in lung volume for a small decrease in inter-plueral (ip) pressure.

Question 30

Define low-compliance

Answer 30

small increase in lung volume for large decrease in ip pressure

Question 31

Why does it require a greater change in pressure from FRC to reach a particular lung volume during inspiration than to maintain that pressure during expiration?

Answer 31

This is because inspiration requires work to overcome the tissue inertia and also to drive air into the lungs.

Expiration requires less work due to the elastic recoil of the lungs.

Question 32

What can affect compliance?

Answer 32

Emphysema - causes expiration to be difficult leading to either same or increased compliance

Fibrosis - causes inspiration to require more effort thus decreasing compliance

Question 33

What is the difference between static or dynamic spirometry?

Answer 33

Static – where the only consideration made is the volume exhaled

Dynamic – where the time taken to exhale a certain volume is what is being measured

Question 34

What factors are being measured in spirometry

Answer 34

FEV1= forced expiratory volume in 1 second (fit, healthy males: 4.0L)

FVC= forced vital capacity (fit, healthy males: 5.0L)

FEV1/FVC= 80% in a healthy individual.

Question 35

What does Dalton’s law state?

Answer 35

the total pressure of a gas mixture is the sum of the pressures of the individual gases. (partial pressure)

Question 36

What is FEF?

Answer 36

Forced expiratory flow (FEF25%-75%). Average expiratory flow over the middle of an FVC. Correlates with FEV1, but changes are generally more striking, however “normal” range is greater.