Mechanics of breathing

Question 1

compliance

Answer 1

• how easy it is to inflate the lungs
• the slope of the pressure volume curve
• Volume change per unit of pressure change
  
  • Change in V/Change in P

Question 2

recoil

Answer 2

how well the lungs go back to original shape after inflating

Question 3

Which law allows breathing to work?

Answer 3

Boyle’s Law

P₁ x V₁ = P₂ x V₂

Question 4

what are the major muscles of inspiration?

Answer 4

diaphragm

external intercostals- raise the ribs up, increase thoracic cavity space

Question 5

What are the accessory muscles of inspiration?

Answer 5

Sternocleidomastoid

scalenes- pull up first rib (all ribs follow)

Question 6

What are the accessory muscles of expiration?

Answer 6

Abdominals- force internal muscles up, making thoracic cavity smaller

internal intercostal muscles

Question 7

Explain intrapulmonary pressures that occur with normal breaths

Answer 7

• Inspiration- inspiratory muscles contract and chest expands.
  
  • bigger volume = lower pressure; air flows into lungs until pressure equals atmospheric pressure
• Expiration- inspiratory muscles relax
  
  • recoil of lung causes alveolar pressures to exceed atmospheric pressure, causing air to flow out of lungs

Question 8

what causes the “suction” that keeps the lungs against the chest wall?

What forces work against that, trying to collapse the lung?

Answer 8

Intrapleural pressure space between the lung and thorax

4 mmHg lower than intrapulmonary pressure

alveolar surface tension and lung elasticity want to pull the lungs to collapse

Question 9

At what point in the breathing cycle is the intrapulmonary pressure the lowest?

Answer 9

halfway into inspiration

*the inspiratory muscles have created more space, but air has not yet come in

Question 10

At what point in the breathing cycle is the intrapulmonary pressure the highest?

Answer 10

halfway into exhalation

*the inspiratory muscles have relaxed, decreasing the space available and increasing the pressure, but the air has not yet escaped.

Question 11

what happens when air enters the pleural cavity?

Answer 11

Negative pressure is lost, causing lung to collapse. Mediastinum shits toward other side because the negative pressure on that side is unopposed.

Question 12

Regional differences in ventilation

Answer 12

• intrapleural pressure is less negative at the bottom of the lungs due to the weight of the lung
• lung is easier to ventilate at low volumes than at high volumes
• the apex has a big resting volume and smaller changes occur in inspiration

Question 13

How is Laplace’s law applied to the lungs?

Answer 13

When the radius of the alveoli is smaller, more pressure is required to open it up.

P = 4T/r

T = surface tension

**If radius decreases by half, pressure increases x2

Question 14

hysteresis

Answer 14

• when comparing the volume and pressure on inhalation to exhalation, the pressures will differ at the same volume
• pressures are higher during inhalation
  
  • this is caused by the surface tension
• Lungs inflated with saline have greater compliance (the mouse video)

Question 15

What happens in the absence of surfactant?

Answer 15

• reduction of lung compliance
• alveolar atelectasis
• pulmonary edema

Question 16

How do you determin resistance and flow?

What is the greatest factor?

Answer 16

Pouseuille’s law

greatest factor is airway diameter

Q = (Change in pressure * πr⁴⁾/n*8*L

n=viscosity of air

Question 17

what is the site of major airway resistance?

Answer 17

medium sized bronchi

*similary to capillaries, the resistance is high, but there are so many bronchi that the overall resistance is low

Question 18

Where is the resistance low?

Answer 18

in the very small airways

Question 19

Airway resistance _________ as lung volume ________ because airways are _________

Answer 19

Airway resistance decreases as lung volume increases because airways are pulled open

Question 20

What controls the bronchial smooth muscle?

Answer 20

ANS

Question 21

Breathing a dense gas _______ resistance as breathing a less dense gas ________ it. Example?

Answer 21

Breathing a dense gas increases resistance as breathing a less dense gas decreases it. Example: Helium

Question 22

What characterizes restrictive lung disease?

Answer 22

reduced functional volume/compliance of the lungs; Difficult to get air into the lungs

Ex fibrosis and asbestosis

Question 23

What characterizes obstructive lung disease?

Answer 23

reduced flow rate; eventualy causing increased compliance. Difficult to get air out of the lungs

Ex. COPD and asthma

Question 24

FEV

What happens to the FEV in COPD?

Answer 24

Forced expiratory volume

FEV is reduced and the FEV/FVC ratio is less than the normal value of 75%

FVC = Forced vital capacity

Question 25

What happens to the FEV/FVC ratio in in restrictive lung disease?

Answer 25

The FEV and FVC are both reduced so the ratio is the same

Total lung capacity and residual lung capacity is decreased. (residual the most)