Lecture 4: Mechanisms of Breathing

Question 1

Which dome of the diaphragm is higher and why?

Answer 1

The right due to the liver

Question 2

What are the attachments of the diaphragm?

Answer 2

Xiphoid surface
Central tendon
Costal margin (inferior 6 ribs and costal cartilage)
Lumbar vertebra - right crus (L1-3/4) and left crus (L1-2/3 i.e. the median arcuate ligament, medial arcuate ligament and lateral arcuate ligament

Question 3

What does the median arcuate ligament arch over?

Answer 3

The top of the aorta

Links the left and right crura

Question 4

What does the medial arcuate ligament arch over?

Answer 4

The psoas major

Question 5

What does the lateral arcuate ligament arch over?

Answer 5

Quadratus lumborum

Question 6

At what level does the IVC pierce the diaphragm?

Answer 6

T8
Slightly to the right
Inside central tendon
Pulls on walls of IVC and opens it up

Question 7

At what level does the oesophagus pierce the diaphragm?

Answer 7

T10
Posterior to central tendon
Slightly to the left
Fibres of right crus sling around it

Question 8

What nerves are the diaphragm innervated by?

Answer 8

The phrenic nerve C3, 4, 5
Motor to all
Sensory to central part and to pericardium

Question 9

Where is pain from the central diaphragm referred to?

Answer 9

C3, 4, 5 dermatomes over the neck and upper limb (phrenic nerve)

Question 10

Where is pain from the peripheral diaphragm referred to?

Answer 10

Dermatomes of the thoracic wall (intercostal nerve)

Question 11

What occurs when P(atm) = P(lungs)?

Answer 11

No movement of air

Question 12

What occurs when P(atm) > P(lungs)?

Answer 12

Air moves into lungs (inspiration)
Increase volume
Decrease pressure

Question 13

What occurs when P(atm)

Answer 13

Air moves out of lungs (expiration)
Decrease volume
Increase pressure

Question 14

What is the main determinant of quiet respiration?

Answer 14

The diaphragm

Question 15

During inspiration the diaphragm ___ and ___ the lungs.

Answer 15

During inspiration the diaphragm contracts and expands the lungs.

Question 16

During expiration the diaphragm ___ and ___ the lungs.

___ of the lungs significantly contributes to expiration.

Answer 16

During expiration the diaphragm relaxes and collapses the lungs.
Elasticity of the lungs significantly contributes to expiration.

Question 17

Describe the pump handle movement of the thoracic cage.

Answer 17

The intercostal muscles and ribs 2-6 pull the sternum forward and upward with expansion in the vertebrosternal plane, increasing AP dimension.

Question 18

Describe the bucket handle movement of the thoracic cage.

Answer 18

Ribs 7 - 10 pull the ribs out laterally in the vertebrocondral plane increasing transverse diameter

Question 19

Which accessory respiratory muscles expand the chest?

Answer 19

Scalene muscles
External intercostals
Internal intercostals (medial to costochondral junction)

Question 20

Which accessory respiratory muscles collapse the chest?

Answer 20

Internal intercostals (lateral to costochondral junction)
Abdominal muscles

Question 21

What are hiccups and why do they occur?

Answer 21

Quick inspirations
Spasmodic contractions of the diaphragm
Occur as a result of irritation of:
- neurons in the phrenic nerve
- the diaphragm muscle
- the respiratory centres in the brainstem