Mechanics of Breathing

Question 1

What are the main muscles of inhalation? Two additional accessory muscles for inhalation?

Answer 1

diaphragm and external intercostals

scalenes and sternocleidomastoids

Question 2

What direction does the diaphragm move if the phrenic nerve is damaged? Why?

Answer 2

The diaphragm is paralyzed and moves up with inspiration because of the negative pressure in the thoracic cavity pulling it upwards

Question 3

Why is expiration typically a passive function?

Answer 3

the lung has elastic recoil, making it want to shrink

Question 4

During exercise expiration is an active process with what muscles?

Answer 4

mainly the abdominal muscles (rectus abdominus and obliques) and internal intercostals

Question 5

The pressure differential required to inflate the lung is _____ than that required to deflate it.

Answer 5

greater - remember that deflation is a passive process for the lung due to the elastic recoil

Question 6

This means the graphs of negative pressure vs volume is different for exhalation and inhalation. What is this called?

Answer 6

hysteresis

Question 7

Why does lung volume NEVER go to 0?

Answer 7

Because exhalation makes the pressure in the thoracic cavity increase, which collapses some small airways, leading to a blockage of air movement

Question 8

What is compliance?

Answer 8

the relationship of volume change per pressure change

Question 9

Is lung compliance typically high or low?

Answer 9

high - about 200 ml/cm H20

Question 10

What disease will reduce compliance? What disease will increased compliance?

Answer 10

reduced compliance - fibrosis

increased compliance - COPD

Question 11

What are two physical characteristics of the lung that cause it’s elastic recoil?

Answer 11

1. lots of elastin and collagen

2. surface tension of alveoli

Question 12

Why do people with COPD need to work hard to expire?

Answer 12

COPD lungs have lost some of the elastin and collagen in the lung, which means they’ve lost some of that elastic recoil and expiration isn’t just a passive process for them

Question 13

What is surface tension (in general0?

Answer 13

attraction between adjacent molecules - in this case H2O

Question 14

What does the law of laplace mean for the lung?

Answer 14

T = Pxr/2 for a sphere

means that 2 conected alveoli would have different pressures if one had a smaller radius than the other, which would result in smaller alveoli emptying into larger ones

Question 15

What alters surface tension to prevent this?

Answer 15

surfactant

Question 16

surfactant at low volumes or high volumes?

Answer 16

low volumes

Question 17

WHat is surfactant/

Answer 17

dipalmitoyl phosphatidylcholine

Question 18

How do they think it works?

Answer 18

detergent that provides a physical barrier preventing the water moleucles from interacting at small volumes = no surface tension

Question 19

Where is intrapleural pressure more negative - the base or the apex of the lung? Which has a smaller residual volume

Answer 19

apex of the lung is more negative

base has smaller residual volume

Question 20

Why do people with COPD purse their lips while breathing?

Answer 20

The increased pressure associated with exhalation results in collapse of airways at fucntional residual capacity in people with COPD, so they purse their lips to increase resistance to flow and thus increase the pressure in the airways to work against that compression

Question 21

What happens to resistance as you branch on down the bronchial tree?

Answer 21

resistance decreases because the cross sectional area (radius) increases

Question 22

So what is the major site of resistance in the lung?

Answer 22

medium-sized bronchi

Question 23

Why does airway resistance decline at larger lung volumes?

Answer 23

the negative pressure from inhalation pulls the vessels open

the increased size of the lung (radial traction of tissue) also pulls airways open

Question 24

Does parasympathetic activity increase or decrease airway resistance?

Answer 24

increases it

Question 25

How does parasympathetic acitviyt increase airway resistance?

Answer 25

acetylcholine on muscarinic receptors, increases IP3, increases Ca, leading to contraction and airway constriction
(carried by vagus)

Question 26

How does sympathetic stimulation decrease airway resistance?

Answer 26

Epinephrin on beta 2 receptors increases cAMP, which leads to airway dilation

Question 27

What happens to the rate of flow during forced expiration?

Answer 27

it is initially rapid and then falls - one cannot overcome this fall in expiratory flow because it’s caused by compression of airways when the thoracic volume is decreased to expel air

Question 28

What is the FEV1?

Answer 28

it’s the forced expiratory volume that occurs in the first second of expiration after a maximal inhalation - usually about 80% of the forced vital capacity?

Question 29

What will the FEV1 be in COPD?

Answer 29

they will have a low FEV1 AND a low FEV1/FVC (mostly normal FVC though)

Question 30

What will the FEV1 be in restrictive diseases?

Answer 30

low FEV1 and FVC, but that means the FEV1/FVC ratio is normal