Respiratory Mechanics

Question 1

How are respiratory mechanics performed outside of the body, to determine pressure/volume relationships?

Answer 1

Negative pressure is created in a container with the lung.

The change of the volume of the lung is calculated.

Question 2

In respiratory mechanics, as the intrapleural pressure (pressure around the lung) becomes more negative, what happens?

Answer 2

Air flows into the lungs= lung volume increases.

Question 3

Is the change in volume for a given change in pressure constant?

Answer 3

No.

The line produces is not straight.

Question 4

How are pressure and volume related in respiratory mechanics?

Answer 4

At a low lung volume, it takes a big amount of pressure to get a small increase in volume.

Once a little bit of air enters the lungs, a little change in pressure produces a large change in volume.

Thus, it becomes easier to stretch the lungs.

Question 5

When the lungs get close to TLC, what happens?

Answer 5

It becomes hard to stretch (inflate) again.

Thus, a large pressure change will only change the volume a little.

Question 6

What is compliance of the lung?

Answer 6

How easy it is to stretch our lungs.

to calculate=

Change in volume/ change in pressure

Question 7

What is the opposite of compliance?

Answer 7

Elasticity- ability to recoil

Question 8

When is compliance the highest?

Answer 8

When we are in normal breathing range (normal Tidal Volume).

Thus, we dont have to work hard.

Question 9

At either extreme of the pressure/volume relationship curve (sigmoidal), (very small lung volume or very big lung volume), what is compliance?

Answer 9

Compliance is low.

Question 10

What does a high compliance mean?

Answer 10

Very stretchable and easy to inflate.

Question 11

At birth, bb must inflate its lungs for the 1st time. What is the compliance of the lungs for the first breath and how hard does the bb have to work?

Answer 11

Very very low compliance bc lung volume is v low.

BB has to work v hard.

Question 12

Do the lungs inflate and deflate the same?

Answer 12

No.

Thus, exhalation and inhalation is different.

Question 13

What would happen if we inflated the lungs with saline (instead of air)?

Answer 13

Saline allows for high compliance due to there being no air/water surface, so there is no surface tension, allowing rapid intake of saline, exhale also occurs at the same place

Question 14

What is the main reason the inhale and exhale graphs do not align (also know as hysteresis)?

Answer 14

1. Due to surfactant molecules moving one way during inspiration and different during expiration /
2. LaPlaces Law! (P=2T/Radius)

Question 15

Why does the gap between the expiration and inspiration line (hysteresis)?

Answer 15

Surfactant= differences in surface tension

Question 16

Surfactant is not evenly distributed on the alveolar surface, instead it is small droplets randomly positioned. So if the alveolar volume is small…?

Answer 16

the droplets are close together and pull apart during inspiration and fuse together during expiration

Question 17

What is the SLIGHT hysteresis in the saline-filled curve due to?

Answer 17

Resistance caused by tissue sliding over one another. (ST)

Question 18

When there is low compliance, there is ____ stretchability and _____ to inflate… vice versa for high compliance

Answer 18

low stretchability and hard to inflate high stretchability and easy to inflate with high compliance or high slope of deltaV/deltaP

Question 19

What is the pressure/volume relationship for the lungs?

Answer 19

Looks like what we saw for INSPIRATION.

Normal resting point (without the rib cage) is low (because they want to collapse).

Question 20

What is the normal resting point for lungs alone, which is VERY small, referred to as?

Answer 20

Minimal volume.

However, we do not usually see in person because the rib cage is attached.

Question 21

Pressure/volume relationship of the rib cage?

Answer 21

The rib cage wants to move outward (thus, have a larger volume).

The normal resting point of the rib cage when the pressure is 0 cmH20 relaxed.

Question 22

The normal resting point of the lungs alone is quite small and known as the minimal volume(near 0) due to elastic recoil. The rib cage rests?

Answer 22

At a higher volume, where pressure is near 0cmH2O due to orientation of ribs, joints and muscles

Question 23

The elastic recoil of the lungs and rib cage balance each other out at ______

Answer 23

FRC (functional residual capacity). – volume of hair present at the end of a passive expiration.

In this situation, airway pressure goes down to zero, due to elastic recoil of both even each other out.

With forced expiration, goes below FRC –> residiual volume

Question 24

If the lungs could pick, where would they go to? FRC, RV, MV

Answer 24

Minimal volume. They want to be smaller so minimal volume is what they COULD shrink to.

Question 25

So for instance, if there is a pneumothorax, what would happen to the lungs and rib cage, separate?

Answer 25

Rib cage would increase in volume while the lungs would collapse and decrease in volume

Question 26

**How is airway resistance calculated?**

Answer 26

**R= 8\*n\*L/r⁴** ## Footnote ^{Resistance is directly proportional to the [viscosity] and the [length of the tube]. Inversely proportional the [radius of the tube].}

Question 27

**FEV**

Answer 27

**How much a person can breath out during a forced breath*. It is very sensitive to changes in airway resistance.*** **Normally, it takes a person 3 seconds to get out all of the air.** **In one second, a person will get out a substantial amount of air.**

Question 28

What measurements are helpful in identifying changes in pulmonary mechanics?

Answer 28

**1. FEV** **2. How fast the air can be moved out**

Question 29

How we use FEV to determine airway resistance?

Answer 29

FEV1 is the amount of air that is exhaled in the first sentence. **To determine resistance:** **FEV1/FVC** (forced vital capacity: total amount of air we get out in a FEV test)

Question 30

A normal person **~70-80%** of the ____ is exhaled in the 1st second of a forced expiration.

Answer 30

**FVC**

Question 31

What will **FEV1/FVC ratio** look like for someone with an **obstructive dz:** emphysema or athasma?

Answer 31

**It will take longer to get the air out of the lungs.** FVC is reduced because air is trapped in lungs. FEV1 is even more reduced. **Thus, FEV1/FVC ratio is below ~70%**

Question 32

What will **FEV1/FVC ratio** look like for someone with an **restrictive** dz: interstitial lung dz.

Answer 32

**Absolute values of FEV1 and FVC are both reduced** because the lungs cannot expand. But the **ratio is higher than normal (\<90%)** because the elastic recoil of the lungs forces the air out more rapidly.

Question 33

The FEV1/FVC ratio is used to determine what?

Answer 33

**Obstructive or restrictive disease**

Question 34

Normally, the elastic recoil of the lungs would cause what?

Answer 34

**Collapse of the small airway and alveoli.**

Question 35

Why do the aleoli and airways not collapse?

Answer 35

**INTERDEPENDENCE** ## Footnote Shared walls of alveolar and airways prevent collapse because their recoil opposes the recoil of the other aveoli.

Question 36

What would happen if we lost some of the walls?

Answer 36

We would alter or lose forces that COUNTER the collapse of alveoli.

Question 37

Structure and stability of _____ airways and alveoli depend on all of the connecting airways and alveoli.

Answer 37

**SMALL**

Question 38

What happens during COPD?

Answer 38

We lose the alveolar walls due to tissue destruction. As a result, remaining alveoli can collpase.

Question 39

What happens as airway resistance increases?

Answer 39

We need more pressure to cause air to flow into the lungs. Thus, we need more pressure to cause a change in volume

Question 40

Decreased interdepedence means the alveoli are collapsing upon **exhalation**, leading to?

Answer 40

1. **less air being forced out of lung,** 2. **peak and instantaneous ariflow are reduced due to increased airway resistance** 3. **Decreased FVC**

Question 41

What represents the work done to stretch (elastic forces) the lungs/thorax?

Answer 41

0AECD0= work of breathing to overcome the elastic forces (compliance)

Question 42

What 2 forces does breathing overcome?

Answer 42

**1. Elastic** **2. Resitance**

Question 43

What area is the work required to overcome resistive forces?

Answer 43

**ABCEA**

Question 44

Increase in airway resistance means it takes a greater pressure to generate flow into lungs. What do we have to change to change the amount of work being done to stretch the lungs/rib cage?

Answer 44

Change the compliance. Decrease in compliance = work harder to stretch lungs = increase in area (pneumonia, pneumonia, overwight all decrease compliance)

Question 45

On the P/V curve, what would happen if we increased resistance?

Answer 45

Inspiratory loop would become bigger.

Question 46

What is altered the most when you increase resistance?

Answer 46

Expiration because of airway collapse. -shift to the L on the chart

Question 47

Work is done to overcome elastic recoil of the lungs or to overcome the resistance to airflow. What does it mean if the work to exhale due to airway resistance exceeds the work done to inflate the lungs (elastic work)?

Answer 47

**it means that expiration must be active!**

Question 48

If the world to exhale due to airway resistance exceeds the work done to inflate the lungs (elastic), then?

Answer 48

expiration must be active

Question 49

The _______ is the greater effort (bigger area of the curve).

Answer 49

elastic recoil