Mechanics of breathing

Question 1

What is the difference between obstructive and restrictive conditions?

Answer 1

Restrictive- reduced total lung capacity e.g. pulmonary fibrosis or pneumothorax
Obstructive- lung capacity the same but obstruction of airways so takes longer to breathe (reduced FEV1/FVC ratio) e.g. asthma, COPD, lung cancer

Question 2

On inspiration is atmospheric or alveolar pressure higher?

Answer 2

atmospheric

Question 3

What is the equation for flow?

Answer 3

Flow = k x Δ pressure x radius of tube^4
—————————————————–
Length of tube

Question 4

What is the implication of r^4 in the flow equation?

Answer 4

A small change in radius has a big effect

Question 5

In quiet breathing which muscles are used on inspiration?

Answer 5

Diaphragm, external intercostal to stabilise rib cage

Question 6

During quiet breathing which muscles are used for expiration?

Answer 6

Elastic recoil of tissues

Question 7

When inspiring with a lot of effort, which muscles are used?

Answer 7

diaphragm, external intercostals lift and expand rib cage, accessory muscles, neck muscles, shoulder girdle muscles.

Question 8

When expiring with a lot of effort which muscles are used?

Answer 8

Internal intercostal and abdominal wall

Question 9

Which nerve innervates the diaphragm and where does it originate?

Answer 9

Phrenic, C3, C4, C5

Question 10

Which nerves supply the intercostal muscles?

Answer 10

Segmental thoracic nerves

Question 11

What equipment can be used to assess the volume of air moving in and out of the lungs?

Answer 11

Spirometer

Question 12

What is tidal volume? What is its normal value?

Answer 12

colume of air moved in/out during normal breathing. 6-7 ml/Kg at rest, 15ml/Kg during exercise

Question 13

What is inspiratory reserve volume? What is a normal value?

Answer 13

As deep a breath as possible after normal expiration. (does not include tidal volume.) For 70kg male 3000ml

Question 14

What is expiratory reserve volume? What is a normal value?

Answer 14

After normal inspiration, as deep a breath out as possible. In 70kg male 1500ml (NB not as much as IRV)

Question 15

What is residual volume? What is a typical value for it?

Answer 15

Air left in the lungs after full expiration. In 70kg male 1000ml

Question 16

Tidal volume + IRV + ERV + residual volume =

Answer 16

Total lung capcity

Question 17

Tidal volume + IRV + ERV =

Answer 17

Vital capacity (typically 5000ml in 70kg male)

Question 18

ERV + residual volume =

Answer 18

Functional residual capacity

Question 19

What is FVC?

Answer 19

Forced vital capacity

Question 20

What is FEV1?

Answer 20

Forced expiratory volume in 1 second

Question 21

What is a peak flow meter used to measure?

Answer 21

Peak expiratory flow rate

Question 22

Would an FEV1/FVC ratio more than 0.7 indicate an obstructive or restrictive condition?

Answer 22

Restrictive

Question 23

What unit do peak flow meters use?

Answer 23

L/min or L/sec

Question 24

True or false- peak expiratory flow rate varies throughout the day and night

Answer 24

True- highest reading in evening, lowest early morning

Question 25

Is the bronchoconstriction in asthma reversible?

Answer 25

Yes

Question 26

What is hysteresis in the context of lungs?

Answer 26

The work of breathing in is greater than the work of breathing out. At any given pressure there is less air in the lungs on inspiration/ it takes a lower pressure to reach the same volume. This occurs due to the elastic nature of the tissues.

Question 27

What is the definition of compliance in the context of lungs? What is the equation?

Answer 27

The change in lung volume per unit change in intrathoracic pressure. C= ΔV/ΔP
If compliance is low a small change in pressure results in a large change in volume.
Curve on a pressure/volume graph- the flatter the curve the stiffer the lungs (high compliance)

Question 28

How is compliance measured?

Answer 28

Volume by spirometry, pressure by oesophageal balloon.

Question 29

What are 3 conditions that can reduce compliance?

Answer 29

Circumferential burn
Pulmonary fibrosis
Kyphoscoliosis

Question 30

Which condition can increase compliance?

Answer 30

Emphysema

Question 31

Do alveoli have a larger volume at the top or bottom of the lung? Why?

Answer 31

Top. Due to gravity- ones at the bottom are squashed by weight of the lung (but therefore have more capacity to stretch)

Question 32

What happens if the closing capacity of alveoli is at a higher volume than functional residual capacity?

Answer 32

Some lung regions poorly ventilated and not all alveoli participate.

Question 33

Why is surfactant produced in the alveoli?

Answer 33

Pressure decreases as radius increases or surface tension decreases. Surfactant reduces surface tension in alveoli. There is more of it in smaller alveoli, therefore pressure between alveoli of different sizes is equalised. It increases compliance and helps maximum number of alveoli to participate. Prevents atelectasis.

Question 34

Which cells produce surfactant?

Answer 34

Type II pneumocytes.

Question 35

In what condition is respiratory surfactant deficient?

Answer 35

Infant respiratory distress syndrome

Question 36

What is the composition of surfactant?

Answer 36

90% phospholipid, 10% protein

Question 37

Work = ?

in breathing?

Answer 37

volume x pressure

Question 38

What type of air flow, laminar or turbulent, requires the least work?

Answer 38

Laminar

Question 39

At rest what percentage of energy expenditure is on breathing?

Answer 39

2-5%

Question 40

At maximal hyperventilation what percentage of energy expenditure is on breathing?

Answer 40

30%

Question 41

How is work minimised in restrictive conditions?

Answer 41

Frequent breaths of small volume

Question 42

How is work minimised in obstrutive conditions?

Answer 42

Infrequent large volume breaths.