Pulmonary Mechanics 1

Question 1

What is eupnea?

Answer 1

Normal quiet breathing (7.5 L/min). Inspiration is active but expiration is passive.

Question 2

Which muscles are used during eupnea?

Answer 2

The diaphragm may be the only active inspiratory muscle. Expiration is due to the passive recoil of the lung and the chest wall without the participation of expiratory muscles.

Question 3

In terms of active and passive describe inspiration and expiration in a eupneic patient:

Answer 3

Inspiration is active while expiration is passive.

Question 4

What is hyperpnea?

Answer 4

Active breathing like during exercise. Deeper and faster than normal (120 L/min max).

Question 5

What muscles are used during inspiration in a hyperpnic patient?

Answer 5

Inspiration is aided by the contraction of the external intercostals which lift the ribs upwards and outward to expand the chest cavity to accommodate the larger volumes of air.

Question 6

What are the accessory muscles of inspiration and what do they function to achieve?

Answer 6

Sternocleidomastoid - lifts
sternum scalene - lifts upper ribs
Facial neck and head also have some function.
They are all used to reduce the resistance to airflow.

Question 7

What muscles are used during expiration in a hyperpnic patient?

Answer 7

The internal intercostals and all four of the abdominal muscles are used.

Question 8

For active inspiration what intercostal muscles are used?

Answer 8

The external intercostals

Question 9

For active expiration what intercostal muscles are used?

Answer 9

Internal intercostals

Question 10

What is tachypnea?

Answer 10

More rapid breathing than normal

Question 11

What is hypoventilation? What does it lead to?

Answer 11

It is inadequate ventilation due to breathing too slowly. Leads to alveolar hypoxia, hypercapnea (elevated CO2 levels), and respiratory academia.

Question 12

What is hyperventilation? What does it lead to?

Answer 12

Breathing faster than required for oxygenation leads to alveolar hypocapnea (low CO2) and reparatory alkalemia.

Question 13

Alveolar pressure is one of three pressures that drive breathing, what is it? What happens to it during the breathing cycle.

Answer 13

It is the pressure inside of the alveolar sacs and that pressure varies during the breathing cycle. During inspiration Palv < Patm. During expiration Palv > Patm

Question 14

Intrapleural pressure is one of three pressure that drive breathing, what is it? How does it change during the breathing cycle?

Answer 14

It is the pressure in the space outside the lung but within the chest wall. Contraction of the diaphragm exerts an expansive force on the intrapleural space, thus decreasing its pressure, making it more negative, and acting to inflate the lung.

Question 15

External pressure is one of three pressure that drive breathing, what is it? How does it change during the breathing cycle?

Answer 15

It is usually the atmospheric pressure which is constant during the reparatory cycle, however, if a weight is placed on the chest then the external pressure on the chest wall is greater than Patm and is referred to as body surface pressure.

Question 16

What is transmural pressure? What is an outwardly directed transmural pressure, what about inward? (positive or negative)

Answer 16

Pressure across and elastic vessel is defined as internal minus external pressure. Outwardly directed transmural pressures are regarded as positive while inwardly directed transmural pressures are negative.

Question 17

What is the formula for Transmural chest wall pressure Pc?

Answer 17

Pc = Ppl - Patm. Sets degree of inflation of chest wall.

Question 18

What is transmural lung pressure Pl?

Answer 18

It is the transmural pressure across the lung and is the difference between alveolar and intrapleural pressures. Sets degree of inflation of lung. It must always be positive to maintain inflation

Question 19

What is the formula for Transmural lung pressure Pl?

Answer 19

Pl = Palv- Ppl.

Question 20

What is chest wall pressure?

Answer 20

Is the transmural pressure across the chest wall and is the difference in pressure between the intrapleural space and atmospheric or body surface pressure. Pc is negative at rest.

Question 21

What is the total transmural pressure Pt?

Answer 21

Also called the relaxation pressure. It is the total transmural pressure across the lung and the chest wall. The total pressure is the difference between alveolar and atmospheric pressure and is equal to the sum of the lung pressure and the chest wall pressure.

Question 22

What is the formula for total transmural pressure Pt?

Answer 22

Pt = Palv - Patm = Pc + Pl

Question 23

At rest what is the positive outward lung pressure balanced by?

Answer 23

The inward passive elastic recoil pressure of the lung.

Question 24

What balances the negative inward chest wall pressure?

Answer 24

It is balanced by the passive outward elastic recoil pressure of the chest wall.

Question 25

If the intrapleural space is exposed to atmospheric pressure what will happen?

Answer 25

The lung will collapse inward while the chest wall will spring outward.

Question 26

What would the compliance of one lung be comported to the compliance reported for both lungs?

Answer 26

It would be 1/2. Don’t forget this. This is due to half the volume being in each lung.

Question 27

The lung and the chest wall are compliant in series, what does this mean?

Answer 27

You can add their pressures together.

Question 28

What is the formula for total compliance?

Answer 28

Ct = ∆V/ ∆Pt = ∆V/ ∆Palv

Question 29

What is the formula for lung compliance?

Answer 29

Cl = ∆V / ∆Pl. ∆Pl = Pl final - Pl initial

Question 30

What is the formula for chest wall compliance?

Answer 30

Cc= ∆V/ ∆Pc. ∆Pc = Ppl - Patm

Question 31

When thinking about the lung and the chest wall they can both be thought of as springs, describe each.

Answer 31

The lung is a one way spring which is always trying to move in. The chest is a two way spring.

Question 32

What happens to lung compliance in fibrosis?

Answer 32

It is decreased making it difficult to inspire

Question 33

What happens to lung compliance in emphysema?

Answer 33

It is increased making it difficult to exhale

Question 34

Increasing lung compliance will do what to FRC and TLC? Decreasing Cl will do what?

Answer 34

Increase will increase both while decrease will decrease both.

Question 35

What does surfactant function to do? What effect does it have on compliance?

Answer 35

It lowers the surface tension of the lung and increases compliance.

Question 36

What would happen if someone had a deficiency in surfactant?

Answer 36

It increases the surface tension of alveoli and thus increases their elastic recoil and tends to deflate the lung.

Question 37

Which bubble has higher pressure if they both have the same surface tension, a small bubble or a larger bubble?

Answer 37

The smaller bubble. Air would flow from the small to the bigger one. This is from Laplace’s law P = 2T/r . This is what happens without surfactant.

Question 38

What does surfactant do to the issue of different size spheres and pressure?

Answer 38

With surfactant larger alveolus has pressure equal to smaller alveolus and the two are stable. The surface tension increases with radius because a larger area dilutes surfactant, giving less surfactant per unit area and an increased surface tension and pressure.