Respiratory Cycle Mechanics

Question 1

What is intrapleural pressure?

Answer 1

• intrathoracic pressure

- pressure everywhere in the thorax except lumen of blood vessels, lymphatics, or airways

Question 2

What is a normal intrapleural pressure at rest?

Answer 2

-5 cm water

Question 3

What is alveolar pressure?

Answer 3

• pressure within alveoli (759-761 mm Hg)

- decrease to -1 cm water during inhalation and increases to +1 cm water during exhalation

Question 4

What is tidal volume?

Answer 4

volume of air per normal breath

normal is 500 mL

Question 5

What is alveolar ventilation?

Answer 5

• process by which gas moves b/w alveoli and external environment
• tidal volume minus dead space

Question 6

What is minute ventilation?

Answer 6

• volume of air inhaled every minute
• normal is 7L/min

-tidal volume multiplied by RR

Question 7

What is transpulmonary pressure?

Answer 7

-the pressure difference b/w the air spaces (alveolar pressure) and the pressure surrounding the lung (pleural pressure)

Question 8

Delineate how ventilation occurs, using volume and pressure.

Answer 8

• ctx of inspiratory muscles causes thoracic volume to increase, thus pressure decreases and air enters lungs
• relaxation causes thoracic volume to decrease, thus pressure increases and air exits lungs

Question 9

How does intrapleural pressure change during the course of one breath?

Answer 9

• intrapleural pressure begins at -5 cm water during rest

- decreases to -8 cm water during inhalation

Question 10

How does the alveolar pressure change during the course of one breath?

Answer 10

• begins at 0 cm water at rest
• decreases to -1 cm water during inhalation
• decreases to +1 cm water during exhalation

Question 11

What is minute alveolar ventilation?

Answer 11

• volume of air that enters the alveoli per minute
• (tidal volume minus dead space) multiplied by RR
• dead space is body weight in lbs … in mL

Question 12

What is anatomical dead space?

Answer 12

• space in respiratory system other than alveoli

- 1 mL per 1 lb of body weight

Question 13

What is alveolar dead space?

Answer 13

• alveoli that receive air, but not blood

- should be almost nothing in a health person b/c most alveoli have a capillary by them

Question 14

What is physiological dead space?

Answer 14

-air that functionally doesn’t participate in gas exchange

Question 15

True or False: lungs inflate and deflate following the same pattern

Answer 15

False

Question 16

True or False: lung compliance is low at low lung volumes

Answer 16

True, at low lung volumes, lungs must worker harder to get only a little increase in volume

-harder to stretch the lungs

Question 17

True or False: compliance of the lungs is higher during the mid-point of inhalation

Answer 17

True, once there’s a little more air in the lungs, a little pressure will produce a large volume change

-easier to stretch the lungs

Question 18

True or False: lung compliance is low at high lung volumes

Answer 18

True, as lung expands towards TLC, it becomes difficult to stretch again

-small change in pressure only produces a small change in volume

Question 19

What is lung compliance?

Answer 19

the ability of the lung to stretch

• opposite of elasticity
• change in volume divided by the change in pressure

Question 20

What is lung elasticity?

Answer 20

• lung’s ability to recoil

- opposite of compliance

Question 21

If the lungs were not coupled to the chest wall, what would be the lungs normally tendency?

Answer 21

-lungs on their own want to collapse

Question 22

If the chest wall wasn’t coupled to the lungs, what would be its normal tendency?

Answer 22

-chest wall on its own wants to expand

Question 23

At what point during the respiratory cycle do the recoil of the lungs exactly balance out the tendency of the chest wall to expand?

Answer 23

FRC, the volume at the end of a normal exhalation

Question 24

What does the FEV1/FVC ratio look like in obstructive lung diseases vs. restrictive lung diseases?

Answer 24

• FEV1/FVC ratio is decreased in obstructive diseases

- FEV1/FVC ratio is normal (or maybe increased) in restrictive diseases

Question 25

Why might the FEV1/FVC ratio in restrictive diseases increase?

Answer 25

• exhalation may be favored

- FVC may be decreased

Question 26

Describe what interdependence does for small airways and alveoli.

Answer 26

• structural stability depends on all connecting airways and alveoli
• elastic recoil in one alveolus is countered by the recoil of alveoli with shared walls

Question 27

Describe what work is done during breathing.

Answer 27

• work is done to overcome the elastic recoil of lungs
• work is done to overcome resistance to air flow

-work done to overcome elastic recoil is greater than the work to overcome resistive forces