6. Mechanics of Breathing

Question 1

What is the goal of breathing?

Answer 1

Movement of O2 into body and elim. of CO2 waste out of body

Question 2

How does thoracic cage when coupled overlying muscles play into mechanics of breathing?

Answer 2

Contraction of accessory muscles gen. F + causes change in size of thoracic cage –> vacuum in pleural space comm. this F to lungs –> lung expansion

Question 3

When are accessory muscles recruited for breathing?

Answer 3

When require more ventilation/gas exchange in lungs. In pt w disease or increased O2 requirements, muscles may get overtaxed –> resp. failure

Question 4

What are the major muscle(s) of the thoracic cage?

Answer 4

Diaphragm + external intercostal muscles

Question 5

What are the accessory muscles of inspiration?

Answer 5

Sternocleidomastoid + scalene muscles (pull ribs upwards –> increase A-P girth of chest)

Question 6

What are the accessory muscles of expiration?

Answer 6

Abd. muscles + internal intercostal muscles (pull ribs downwards –> decrease A-P girth of chest)

Question 7

What links the chest wall + lungs?

Answer 7

Pleural space

Question 8

At rest, is there a P gradient b/w atm + thoracic space?

Answer 8

No

Question 9

When chest cavity expands, is there a P gradient?

Answer 9

Yes, decrease in P w/in thoracic space causes air to flow in thru airway from atm

Question 10

What two pleurae make up the pleural space?

Answer 10

Parietal (chest wall) + visceral (lungs) pleurae

Question 11

What does pleural space allow transmittance of?

Answer 11

Negative P gen. by expansion of chest wall

Question 12

Describe the mechanism of action of pleural space and how it contributes to breathing.

Answer 12

Expansion of chest pulls on parietal pleura, which gen. negative P within pleural space. This vacuum force pulls on visceral pleura, causing lung expansion + decrease in P within lungs –> airflow in.

Question 13

What happens during violation of pleura?

Answer 13

Loss of negative space + collapse of lung! Pneumothorax!

Question 14

What are the three types of pneumothoraces?

Answer 14

1. Closed/tension
2. Open/”sucking” chest wound
3. Spontaneous

Question 15

What is a closed/tension pneumothorax?

Answer 15

Violation in pleural space but chest wall intact –> not in direct contact w atm; air can leak into pleural space + increase P w/in chest (tension pneumo)

Every time pt breaths, pneumo worsens + P increases –> requires chest tube to relieve P

Question 16

What is an open pneumothorax?

Answer 16

Opening in chest wall + potentially in lung as well –> allows air to move from atm into pleural space –> collapsed lung; sucking chest wound occurs when hole cont. from chest wall + thru lungs (air comes in through chest wall + out through airway)

Question 17

What is a spontaneous pneumothorax?

Answer 17

Resulting from rupture of lung due to pulmonary blebs or weaknesses in lung

Question 18

What is the result of a collapsed lung?

Answer 18

Impaired gas exchange

Question 19

What is more severe: tension or open pneumothorax?

Answer 19

Tension

Question 20

What is a common treatment for bilateral open pneumothorax?

Answer 20

Placing chest tube into pleural space to suck out air until wound heals + lungs can fully expand

Question 21

How does the increased P in tension pneumothorax affect physiology?

Answer 21

Increased P in pleural space if great enough can push against other side of chest (mediastinal shift) –> P against heart + great vessels –> impairs fxn of heart, arterial blood out of heart, + venous drainage of heart –> –> cardiac arrest!