Ch. 7 West

Question 1

What is the most important muscle of breathing, which nerves supply it, and what does muscle contraction result in?

Answer 1

Diaphragm
Supplied by the phrenic nerves from C3-5
When it contracts, the abdominal contents are forced downward and forward, and the vertical dimension of the chest cavity is increased, and the ribs are lifted and moved out.

Question 2

When one side of the diaphragm is paralyzed, it moves ____ with respiration rather than moving ____ because the intrathoracic pressure falls.

Answer 2

It moves up rather than down
This is known as paradoxical movement

Question 3

Which muscles are accessory muscles of inhalation?

Answer 3

Scalene muscles (elevate first two ribs)
Sternocleidomastoids (raise the sternum)

Question 4

What are the accessory muscles of exhalation?

Answer 4

Accessory muscles of exhalation include the four abdominal muscle groups: rectus abdominis, external oblique, internal oblique, and transverses abdominis.

Question 5

What is hysteresis?

Answer 5

The pressure-volume curves that the lung follows during inflation and deflation are different.
The lung volume at any given pressure during deflation is larger than during inflation

Question 6

What is the transpulmonary pressure?

Answer 6

It is equal to the pressure around the lung when the alveolar pressure is atmospheric.

Question 7

What is compliance?

Answer 7

The slope of the pressure-volume curve

Compliance = ΔV/ΔP

The change in volume for the change in pressure

Question 8

What are some factors which can lead to decreased compliance?

Answer 8

Increased fibrous tissue in the lung (pulmonary fibrosis)
Alveolar edema which prevents the inflation of some of the alveoli
Compliance falls if the lung remains unventilated for a long time particularly if the volume is low; may be due to atelectasis.
Compliance can also be reduced somewhat if the pulmonary venous pressure is increased and the lung is engorged with blood.

Question 9

What factors can increase compliance?

Answer 9

Normal aging lung
Emphysema

Question 10

T/F: The pressure-volume curve is nonlinear and the lung becomes more stiff at higher volumes

Answer 10

True

Question 11

T/F: Elastic behavior of the lung depends on both structural proteins (collagen, elastin) and surface tension

Answer 11

True

Question 12

Laplace’s Law

Answer 12

P = 4T/r

P = pressure
T = surface tension
r = radius

Question 13

Surfactant works by…

Answer 13

Lowering the surface tension of the alveolar lining fluid

Question 14

What are the two types of alveolar epithelial cells and some of their characteristics

Answer 14

Alveolar type I epithelial cells: shaped like a fried egg, long cytoplasmic extensions spread out thinly over the alveolar walls

Alveolar type II epithelial cells: more compact, lamellate bodies within them that are extruded into the alveoli and transform into surfactant

Question 15

T/F: Low surface tension in the alveoli increases the compliance of the lung and reduces the work of expanding it with each breath.

Answer 15

True

Question 16

Absence of surfactant results in what negative consequences?

Answer 16

Decreased lung compliance
Alveolar atelectasis
Alveoli fill with transudate

Question 17

Intrapleural pressure is less _____ at the bottom of the lung than it is at the top of the lung.

Answer 17

Intrapleural pressure is less negative at the bottom of the lung than it is at the top of the lung.

Question 18

T/F: Because of the nonlinear pressure-volume curve, alveoli at the base expand more than do those at the apex

Answer 18

True

Question 19

TF: At FRC, the inward pull of the lung is balanced by the outward spring of the chest wall.

Answer 19

True

Question 20

T/F: The lung retracts at all volumes above minimal volume.

Answer 20

True

Question 21

Poiseuille equation explaining laminar flow

Answer 21

R = 8nl/Πr^4

Where R = flow resistance
n = viscosity
l = length
r = radius

***Radius is crucial! If radius is halved, resistance increases 16-fold!

Question 22

Turbulent flow has different properties than laminar flow; list some differences.

Answer 22

Viscosity of the gas is relatively unimportant
Increase in gas density increases the pressure drop for a given flow
Turbulent flow does not have the high axial flow velocity that is characteristic of laminar flow

Question 23

What is the factor that determines whether or not flow will be laminar?

Answer 23

Reynold’s number

Re = 2rvd/n

Where r = radius
d = density
v = average velocity
n = viscosity

Turbulence most likely to occur when flow rate is high and the tube has a large diameter. A low-density gas (helium) tends to produce less turbulence.

Question 24

High Reynolds numbers suggest….

Answer 24

Intertial forces dominate over viscous forces, i.e. turbulent flow more likely

Question 25

What are the two main reasons that intrapleural pressure falls during inspiration?

Answer 25

As the lung expands, elastic recoil increases, leading to negative intrathoracic pressures. In addition, the reduction in alveolar pressure causes a further fall in intrapleural pressure

Question 26

Which airway segments (upper/large, medium sized bronchi, lower/smallest) contribute most to airway resistance?

Answer 26

The medium-sized bronchi

Question 27

T/F: The peripheral airways contribute very little to resistance, therefore they could be diseased for a longer time before becoming clinically evident.

Answer 27

True

Question 28

When the lung volume increases, how does this alter the caliber of the bronchi?

Answer 28

Increases their caliber due to radial traction applied by surrounding lung tissues

Question 29

Which nerve controls motor innervation to the bronchial smooth muscle?

Answer 29

Vagus nerve

Question 30

Which receptors in the lung control bronchial smooth muscle constriction/relaxation?

Answer 30

Stimulation of the β2 receptors relaxes the smooth muscle in the bronchi, blood vessels and uterus.

Question 31

What nervous system activity causes bronchoconstriction?

Answer 31

Parasympathetic activity, as does ACh

Question 32

T/F: Breathing in a dense gas increases resistance.

Answer 32

True

Question 33

How does dynamic compression of airways work and what does it result in

Answer 33

• Limits air flow in healthy subjects during forced expiration
• May occur in diseased lungs at relatively low expiratory flow rates
• During dynamic compression, flow is determined by alveolar pressure minus intrapleural pressure (not mouth pressure) and is therefore independent of effort
• Is exaggerated in disease states such as emphysema due to reduced elastic recoil of the lungs and loss of radial traction on the airways

Question 34

As compliance decreases, the PV curve shifts ____

Answer 34

To the right, “sad bunny”
As compliance decreases, volume control ventilation yields higher and higher peak airway pressure in order to achieve the same volume

As compliance decreases in pressure control ventilation, this yields less and less volume for the same pressure level.

Question 35

Inspiration is _____, expiration at rest is ______.

Answer 35

Active
Passive

Question 36

The recoil pressure of the lung is determined by the elastic tissue and the ___ ____ of the alveolar lining.

Answer 36

Surface tension

Question 37

T/F: Pulmonary surfactant is a phospholipid produced by type II alveolar epithelial cells

Answer 37

True

Question 38

T/F: At FRC, the inward recoil of the lung and the outward recoil of the chest wall are balanced.

Answer 38

True

Question 39

T/F: The driving pressure during forced exhalation is alveolar minus intrapleural pressure.

Answer 39

True