Statics 1

Question 1

Draw lung volumes and capacities chart:

Answer 1

Question 2

Lung capacities are always the sum of:

Answer 2

two or more volumes

Question 3

Volume in our lungs increases when:

Answer 3

pressure in the lungs decreases

Question 4

Functional residual capacity (FRC):

Answer 4

• the volume of gas remaining in the lungs after a normal tidal expiration (passive expiration)

Question 5

Is there any airflow into or out of the lungs at FRC?

Answer 5

No. Avleolar pressure = atmospheric pressure (0).

Question 6

State of the lung and the chest wall at the end of expiration (FRC), when all the respiratory muscles are relaxed:

Answer 6

• inward elastic recoil of lung balanced by outward elastic recoil of chest wall.
• alveolar pressure equal to atmospheric pressure, no airflow occurs.
• transmural pressure negative.

Question 7

Negative-pressure breathing:

Answer 7

• lowering alveolar pressure below atmospheric pressure to create air flow into the lungs

Question 8

Positive-pressure ventilation:

Answer 8

• Air flow into the lungs caused by raising the pressure at the nose and mouth above alveolar pressure.

Question 9

Steps in inspiration (muscles, pressures, etc.):

Answer 9

1. contraction of muscles of inspiration.
2. intrapleural pressure becomes more negative.
3. transmural pressure difference increases.
4. alveoli distend, decreasing alveolar pressure below atmospheric pressure, which causes air to flow into alveoli.

Question 10

Transmural Pressure =

Answer 10

Transmural Pressure = P_inside - P_outside

(alveolar pressure - intrapleural pressure)

Question 11

How does transmural pressure increase?

Answer 11

• inspiratory muscles contract, expanding the thoracic volume and increasing the outward stress on the lung, the intrapleural pressure becomes more negative.
• TP = alveolar pressure - intrapleural pressure

Question 12

Boyle’s Law in relation to breathing/alveoli:

Answer 12

P = 1/V

• as the alveolar volume increases, alveolar pressure decreases.
• when alveolar pressure drops below atmospheric pressure, inspiration occurs.

Question 13

What causes negative intrapleural pressure at rest, and what is the resting negative intrapleural pressure value?

Answer 13

• Value: –3 to –5 cm H2O.
• Caused by the mechanical interaction between lung and chest wall.
• Elastic recoil of lung pulls inward.
• Elastic recoil of chest wall pulls outward.

Question 14

Alveolar pressure equation:

Answer 14

intrapleural pressure + alveolar elastic recoil pressure

• creating a more negative intrapleural pressure will create a negative alveolar pressure and pull air into the alveoli from the atmosphere.

Question 15

How do alveoli located centrally in the lung expand in response to a more negative intrapleural pressure?

Answer 15

• structural interdependence of alveolar units.
• Alveolar septa transmit the pressure difference across the outermost alveoli to inner alveoli.

Question 16

Difference between inner and outer alveoli due to structural interdependence in negative-pressure breathing:

Answer 16

• mechanical stress transmitted from exterior alveoli (those closest to the chest wall) to more interior alveoli, so the exterior alveoli might be more distended.

Question 17

Difference between inner and outer alveoli due to structural interdependence in positive-pressure ventilation:

Answer 17

• Lungs must push against diaphragm and rib cage to move them.
• Outermost alveoli might be more compressed than those more interior.

Question 18

Status of the lungs at FRC:

Answer 18

• end of passive expiration.
• inspiratory muscles relaxed.
• alveolar pressure equal to atmospheric pressure (0).
• no air movement occurs.

Question 19

The inward elastic recoil of lung is equal to:

Answer 19

• transmural pressure difference
• (Alveolar pressure - Intrapleural Pressure)

Question 20

The muscles of inspiration include:

Answer 20

1. diaphragm
2. external intercostals
3. sternocleidomastoid
4. trapezius
5. muscles of vertebral column

Question 21

Primary muscle of inspiration:

Answer 21

diaphragm

Question 22

When a person is in the supine position, the diaphragm is responsible for how much of the air that enters the lungs during normal quiet breathing (eupnea)?

Answer 22

2/3

Question 23

When a person is standing or seated in an upright posture, the diaphragm is responsible for how much of the air that enters the lungs during normal quiet breathing (eupnea)?

Answer 23

1/3 to 1/2

Question 24

Accessory inspiratory muscles and when they become activated:

Answer 24

• activated when tidal volume needs to be increased.
  
  • sternocleidomastoid
  • trapezius
  • muscles of vertebral column

Question 25

Expiration is mainly driven by:

Answer 25

* elastic recoil of alveoli. * this decreases alveolar volume, which increases alveolar pressure above atmospheric and leads to air flowing out of alveoli. ## Footnote **PASSIVE PROCESS**

Question 26

Describe the dashed line and solid line in this graph:

Answer 26

* dashed line predicts the changes in intrapleural pressure necessary to overcome the elastic recoil of alveoli. * solid line more accurate; includes additional pressure work that must be done to overcome resistance to airflow and tissue resistance.

Question 27

Changes in intrapleural pressure during inspiration:

Answer 27

* Contraction of the inspiratory muscles causes intrapleural pressure to continuously become more negative as the lungs are pulled open and the alveoli are distended.

Question 28

When is intrapleural pressure the most negative?

Answer 28

at the end of inspiration

Question 29

Changes in alveolar pressure during inspiration:

Answer 29

* 0 at start of inspiration. * becomes more negative, and then less negative. * 0 at end of inspiration and start of expiration.

Question 30

When is there no airflow into or out of the lungs?

Answer 30

* when alveolar pressure = atmospheric pressure. * end of expiration. * end of inspiration.

Question 31

Lung compliance is:

Answer 31

* the ease at which the lung volume can be expanded.

Question 32

Lung elastance is:

Answer 32

* the natural ability of the lung to return to its original shape after some external force which has acted upon it is removed.

Question 33

Compliance equation:

Answer 33

C = ∆V/∆P

Question 34

Draw lung pressure/volume graph for inspiration and expiration (isolated lungs):

Answer 34

Slope = compliance (∆V/∆P)

Question 35

Difference in distensibility of the lungs at low and high volumes:

Answer 35

* **Low volumes:** lung distends easily * **High volumes:** distensible components of alveolar walls have already been stretched, and large increases in transpulmonary pressure yield only small increases in volume.

Question 36

Why is there a difference in curve for inflation and deflation of the lungs in the graph below?

Answer 36

**DIFFERENCE IS CALLED HYSTERESIS.** 1. Surfactant has less effect on decreasing surface tension during inspiration. 2. Recruitment of alveoli during inspiration requires more energy/work.

Question 37

Equation to determine total compliance:

Answer 37

Question 38

Transmural pressure difference for lungs:

Answer 38

alveolar pressure - intrapleural pressure

Question 39

Transmural pressure difference for chest wall:

Answer 39

intrapleural pressure - atmospheric pressure

Question 40

Draw compliance curves for normal lung, emphysema, and fibrosis:

Answer 40

* emphysema = more compliance * fibrosis = less compliance

Question 41

Emphysema increases the compliance of the lungs because:

Answer 41

* it destroys the alveolar septal tissue that normally opposes lung expansion. * decreased alveolar elastic recoil.

Question 42

Fibrosis decreases the compliance of the lungs becuase:

Answer 42

* it makes the lungs less compliant, or “stiffer.” * increase alveolar elastic recoil.

Question 43

Why does compliance change at different lung volumes?

Answer 43

* Alveoli are more compliant and have less elastic recoil at low volumes. * Alveoli become less and less compliant as volume increases and also have more elastic recoil.

Question 44

Woman inspires 500ml from spirometer. Intrapleural pressure before inspiration (-5). End inspiration (-10). What is lung compliance?

Answer 44

Question 45

Normal pulmonary compliance value:

Answer 45

0.1 - 0.2 L/cm H2O