Review of Pulmonary Physiology

Question 1

Is it inspiration or expiration which is normally completely passive? Which muscles assist if need be?

Answer 1

Expiration -> elastic return

Assistance via abdominal muscles

Question 2

What is transpulmonary pressure?

Answer 2

Pressure inside alveoli (filling pressure in lungs) - pressure outside in the pleura (negative intrapleural pressure)

Question 3

What is the slope of the pressure / volume curve and where is it generally measured?

Answer 3

Compliance (change in Volume / change in pressure)

Generally measured at functional residual capacity (FRC)

Question 4

What is hysteresis? Why does it occur? What redues it?

Answer 4

Tendency of it being more difficult to inflate the lung (Takes more pressure) than to deflate it

Occurs because of surface tension caused by air-water interface tends to pull downward and deflate the alveoli, which are harder to inflate after being deflated.

Reduced by surfactant

Question 5

What controls the size of the lung at lower than FRC?

Answer 5

The chest wall, which wants to elastically recoil to above FRC

The lung wants to collapse to minimum volume

Question 6

What controls the size of the lung near TLC?

Answer 6

both the elastic recoil of the chest wall and the lung, as they are both overstretched

Question 7

What pressures are equal at FRC?

Answer 7

Elastic recoil of the chest wall (intrapleural - atmospheric) = elastic recoil of lungs (alveolar - intrapleural)

Question 8

What is La Place’s relationship and how is related to surfactant?

Answer 8

P =2T/r

if surface tensions were equal in small vs large alveoli, greater filling pressures would be required to inflate the smaller alveoli.

Surfactant helps reduce T more the small your alveoli, keeping filling pressures equal no matter alveolar size.

Question 9

What is the resistance formula for the lungs?

Answer 9

R = P/V

Where P = pressure difference and V = airflow

Think of this is a rearrangement of V=IR, where current = airflow, and voltage = pressure difference

Question 10

Why is it easier to detect diseases of the upper airway faster than lower airway?

Answer 10

Up to the carina (bifurcation cartilage of the trachea), resistances add in series
-> shared airway, blocking one thing will greatly increase resistance

past the carina, resistances add reciprocally (in parallel)

Question 11

Where is the airways is flow laminar vs turbulent? What is the most important factor in determining this resistance?

Answer 11

Small, peripheral airways -> laminar

Large airways in series -> turbulent, when Reynolds’ number is >2000

Size of the tube’s lumen is most important

Question 12

What is the Bernoulli effect? Clinical significance?

Answer 12

With flow from a larger to a small cross-sectional area, velocity of flow must increase to maintain the same bulk flow. This results in a pressure drop and major energy expenditure from the small to the large airways.

Question 13

What type of disease increases airway resistance?

Answer 13

An obstructive process

Question 14

What is the problem with restrictive processes?

Answer 14

Elastic recoil -> loss of compliance or stretch.

-> by definition reduces total lung capacity

Question 15

How are lung volume and resistance related?

Answer 15

inversely -> as lung volume decreases, resistance increases

Question 16

What is meant by effort dependence vs effort independence?

Answer 16

For the first 25% of the expiratory flow curve, increasing the intrapleural pressure more will increase flow more. However, at a certain point, an increase in intrapleural pressure will not generate a greater expiratory flow. This is called “effort independent” expiratory flow.

Question 17

Will peak flow rate vary with effort?

Answer 17

Yes - peak flow varies with effort, but the latter end of the curve will always follow the same expiratory rate decrease regardless

Question 18

What is the best explanatory theory as to why expiratory flow limitation occurs?

Answer 18

Wave speed theory -> physical characteristics of the tube and substance flowing create a “speed limit” which is called the choke point

Question 19

What is frequency dependence of compliance?

Answer 19

A way proposed to detect early COPD which doesn’t work that well.

Breathing faster traps more air in the lungs, so delta V appears to drop despite high inspiratory pressures. This only happens in obstructive conditions. (dynamic compliance is decreased)

Question 20

What is the rate constant of an alveolus?

Answer 20

The time it takes to empty or fill an alveolus.

RC

R = resistance, C = compliance. Increasing resistance or increasing compliance will increase the filling / emptying time.

Stiffer lungs with lower resistance will empty faster

Question 21

Which areas of the lungs have the greatest filling and ventilation?

Answer 21

Apex - consistently the most full, due to most negative intrapleural pressures higher in the lungs

Base - greatest change in ventilation over the inspiration / expiration cycle. This is good because they also receive the most blood flow.

Question 22

What is the nitrogen washout curve / what explains closing volume?

Answer 22

Put a patient on one breath of 100% O2, the slowly exhale while expired volume and nitrogen concentration are measured.

Phase 1 - 100% O2 from dead space
Phase 2 - Rapid increase in nitrogen as lung units start emptying
Phase 3 - plateau
Phase 4 - when near RV, the apex of the lungs which carried high N2 air from the anatomical deadspace begin contributing. From where this nitrogen upslope begins to the end of expiration (RV) is called closing volume.

Question 23

What is the usefulness of closing volume?

Answer 23

In disease states, the closing volume inflection point is met closer and closer to FRC instead of RV.

Question 24

What are the two important curves made in spirometry?

Answer 24

Volume vs time

Flow rate vs volume

Question 25

What is a normal FEV1.0?

Answer 25

75% Forced Vital Capacity (seen by first second in volume vs time curve)

Question 26

What are the spirometry hallmarks of an obstructive process?

Answer 26

FEV1 = reduced
FVC = normal or reduced
FEV1/FVC = reduced

Question 27

What are the spirometry hallmarks of a restrictive process?

Answer 27

FEV1 = normal or reduced
FVC = greatly reduced
FEV1/FVC = normal or increased

Question 28

What does it mean when both inspiration and expiration curves are equally diminished in peak flow vs volume?

Answer 28

Fixed obstruction of the upper area (in series) i.e. vocal cords or trachea

Question 29

What does it mean when only inspiration is diminshed and expiration curve is normal in peak flow vs volume?

Answer 29

Vocal cord weakness, expiration not affected

Question 30

What is the definition of functional residual capacity in terms of lung volumes?

Answer 30

FRC = Residual volume + expiratory reserve volume

FRC is the volume remaining at the end of a normal tidal breath

Question 31

What is the definition of vital capacity in terms of lung volumes?

Answer 31

VC = TLC - RV

TLC = total lung capacity

Question 32

What is total lung capacity in terms of lung volumes (do not use capacities)

Answer 32

TLC = RV + ERV + TV + IRV

TV = tidal volume

Question 33

How does helium dilution measure lung volumes and what is its problem?

Answer 33

Start with known concentration of helium, breath til it comes to equilibrium, and use Boyle’s law (C1V1 = C2V2) to determine the volume change

Problem -> tends to underestimate lung volumes in bad lungs which have a lot of dead space which are not ventilated

Question 34

What is the most accurate way of measuring all the gas in the thorax?

Answer 34

Body plethysmograph

Question 35

What is the idea behind diffusing capacity for carbon monoxide?

Answer 35

Normally, a single breath of carbon monoxide should be fully absorbed, and none will be present in exhaled gas, assuming no problems at all with the lungs or cardiovascular system. It is a very sensitive but nonspecific test.

Values lower than 100% absorption indicate a problem

Question 36

What is the clinical utility of diffusing capacity for carbon monoxide?

Answer 36

If spirometry shows a restrictive process:

• > Low DLCO suggests parenchymal disease
• > normal DLCO suggests chest wall disease

Question 37

In an obstructive process, will DLCO be lower in emphysema or asthma?

Answer 37

Emphysema -> less ability of gas to mix with lung parenchyma

Question 38

What does an elevated RV with a low TLC suggest?

Answer 38

Neuromuscular disease

• > cannot fully inspire to TLC
• > Cannot use accessory muscles to fully exhale

Question 39

What are the causes of increased TLC?

Answer 39

1. Obstructive lung diseases

2. Acromegaly - increased size of lung parenchyma

Question 40

How do emphysema, asthma, and chronic obstruction lead to increased TLC?

Answer 40

Emphysema - decreased lung elastic recoil
Asthma - increased chest wall recoil, increased FRC (only in acute attacks)
Chronic obstruction - air trapping and increased RV