ICL 2.3: Lung Volumes & Pulmonary Function Tests

Question 1

what are the reference values for spirometry?

Answer 1

in the USA, ethnically appropriate NHANES III reference equations published in 1999 for those ages 8 – 80 years of age are recommended

it’s based on height, sex, and ethnicity

Question 2

what are the reference values for lung volumes and diffusing capacity?

Answer 2

no specific set of reference equations is recommended (or mandated), however a list of potentially suitable reference equations is available

Question 3

what factors effect the lung function testing that you need to be aware of?

Answer 3

1. vital capacity decreases with age which is normal because lung elasticity decreases
2. residual volume increases with age
3. males have larger lung function than females
4. tall individuals have larger volumes and higher flows; increased weight doesn’t mean that you’ll have higher lung flow
5. lung function values plateau at 20-30 years of age –> lung capacity decreases 30 mLs/year after that
6. african americans have lower spirometry

Question 4

what happens to lung capacity with age?

Answer 4

vital capacity decreases

when the lung volume decreases, the residual volume increases because there’s loss of function

Question 5

what are all the different tests that are done during a pulmonary function test?

Answer 5

1. spirometry
2. flow Volume Loop
3. bronchodilator response
4. lung volumes
5. diffusion capacity (DLCO)
6. bronchoprovocation testing
7. maximum respiratory pressures
8. simple and complex cardiopulmonary exercise testing

Question 6

what is spirometry?

Answer 6

you blow into a machine and it will measure your flow vs. volume

the spirometer can measure up to 8 L with a flow between 0 and 14 L/sec

so the spirometer will give you a graph that is expired time vs. volume

then from this first graph, you can make a volume vs. flow loop (L/sec)

Question 7

what is the FVC?

Answer 7

FVC = forced vital capacity

the whole volume that you can breath out after a deep inspiration

FEV1 is what you blow out in the first second but FVC is another 4/5 seconds and you get a little more air out

Question 8

what is a flow volume and time volume graph for a spirometer?

Answer 8

go watch….

flow volume is a loop

time volume is a curved line that plateaus

Question 9

what is a positive bronchodilator response?

Answer 9

if someone is having bronchospasm, give them a B2 agonists to dilate their bronchioles

if their FEV1 or the FVC increases by 12% or 200 mLs then this is considered a positive bronchodilator response

this means the airway improved and the patient has a reversible illness

Question 10

what is your total lung capacity?

Answer 10

it’s your vital capacity + residual volume

your vital capacity is the volume when you take a really deep breath and blow all the way out

Question 11

what is the expiratory reserve volume?

Answer 11

ESV is the amount you can expire extra after you have normally inspired and expired

it’s the maximal volume of air that can be exhaled from the end-expiratory position

Question 12

what is the functional residual capacity?

Answer 12

FRC = ERV + RV

the amount of air that stays in your lung after you expire normally

it’s the volume in the lungs at the end-expiratory position

slide 10

Question 13

what is inspiratory reserve volume?

Answer 13

the amount of air you can inspire after normal inspiration

it’s the maximal volume that can be inhaled from the end-inspiratory level

slide 10

Question 14

what is the inspiratory capacity?

Answer 14

the amount of air you can inspire after a normal expiration

IC = tidal volume + IRV

Question 15

what is tidal volume?

Answer 15

Tidal volume: that volume of air moved into or out of the lungs during quiet breathing

TV indicates a subdivision of the lung; when tidal volume is precisely measured, as in gas exchange calculation

Question 16

what is residual volume?

Answer 16

the volume of air remaining in the lungs after a maximal exhalation

Question 17

what is total lung capacity?

Answer 17

the volume in the lungs at maximal inflation, the sum of VC and RV

Question 18

what is the maximal voluntary ventilation?

Answer 18

the volume of air expired in a specified period during repetitive maximal effort

Question 19

what is the limitation of spirometry?

Answer 19

you can’t measure the residual volume or diffusion capacity

Question 20

what are the techniques that can be used to measure lung volume?

Answer 20

1. body plethysmography

2. gas dilution

Question 21

what is body plethysmopgrahy?

Answer 21

it’s a measurement of intrathoracic gas volume (thoracic gas volume [TGV]) at the time of airflow occlusion (typically FRC), the compressible gas within the thorax

you ask the patient to sit in a booth and you close the box which is attached to filters and pressure gauges

then you ask the patient to breath in and out and you measure the pressure and volume of the air in the box when the person breaths in vs. out

since the box is a closed space, P1V1=P2V2 and you measure the change in the volume of the whole chest wall and the air surrounding the patient in the box and you can find the residual volume because of this!

Question 22

what are gas dilution techniques?

Answer 22

measures gas volume that communicates via the airways, using a mass balance approach

mass balance equation uses the initial volume and tracer gas concentration, and the final tracer concentration to calculate the volume in the patient’s lungs at the moment the tracer gas breathing began –> assume the tracer gas is largely insoluble, inert, and well mixed in the lung

we use it to measure residual volume – you breath in an inert gas that doesn’t distribute well in the lungs and then you measure the amount of gas that leaves you after expire; whatever didn’t come out is the residual volume

Question 23

how does COPD effect results from body plethysmography vs. gas dilution?

Answer 23

in patients with obstructive lung disease and gas-trapping, functional residual capacity (FRC) determined by plethysmopgrahy may be higher than measured by gas dilution

Question 24

how is diffusing capacity measured?

Answer 24

1. steady-state
2. intra-breath
3. rebreathing
4. single breath

single breath is the most common technique

Question 25

how do you measure diffusing capacity?

Answer 25

you do gas dilution but you give a gas that can diffuse through the epithelium really easily and therefore can go through to the pulmonary capillaries!

so you use CO for this!

after they’ve taken a super deep breath, have them hold their breath so the CO can diffuse from the alveoli to the blood – then once they expire, measure the amount of CO and you know what didn’t come out diffused across the epithelium to the capillaries!

if you have certain diseases that CO can’t diffuse through the lungs, the amount of CO expired will be higher and this means lower diffusing capacity

Question 26

which conditions increase diffusing capacity?

Answer 26

1. polycythemia
2. left to right shunt
3. asthma
4. pulmonary hemorrhage
5. Muller maneuver
6. exercise
7. supine position

Question 27

which conditions decrease diffusing capacity?

Answer 27

1. valsalva maneuver
2. carboxy-hemoglobin
3. lung resection
4. COPD
5. ILD
6. pulmonary vascular disease like emboli, pulmonary HTN, vasculitis
7. anemia
8. submaximal inspiration or respiratory muscle weakness

Question 28

what is respiratory muscle pressure?

Answer 28

this is important for people who have chest wall weakness like someone with MS or is a paraplegic or ALS

how do you know if their lung volume is decreased because of a neurological problem or because of their respiratory muscles?

you put a pressure gauge in their mouth and ask them inspire forcefully which will record negative pressures – then you ask them to expire forcefully which will give out a positive pressure

values of the maximal inspiratory or expiratory pressure decrease with age because muscles weaken with age

so the MIP measures diaphragm function while MEP tells you how good your cough/clearing secretions will be

so a normal MIP excludes inspiratory muscle weakness! BUT a low MIP does not reliably confirm inspiratory muscle weakness

if your MIP is less than 1/3 of normal, it means hypercarbic respiratory failure

Question 29

what positional change signifies inspiratory muscle weakness?

Answer 29

a fall in the FVC from upright to the supine position correlates with significant inspiratory muscle weakness

FVC = forced vital capacity

Question 30

what are airway challenges?

Answer 30

when you give a B2 antagonists to initiate bronchoconstriction!

cold air or methacholine or histamine or B2 blockers

this should cause a 20% drop in the FEV1

so you give a low methacholine concentration via inhalation and slowly increase the concentration and measure the FEV1 as you go – once it drops below 20%, record the dose of methacholine that did the patient dirty

this dose is called the challenge dose!

healthy people can tolerate more than 16 mg/mL – mild asthma will make you drop at 1-4 mg of methacholine

Question 31

what pulmonary function test results indicate that there’s an obstruction?

Answer 31

if the FEV1/VC is less than the 5th percentile of the predicted value for that persons age, gender, height

above 80% is a normal value for FEV1 and as it drops, the obstruction gets worse –> moderate (50-79), severe (30-49), and very severe (<30)

so the classification of obstruction is based on the FEV1 value, not the ratio! as soon as the ratio is under 80 it’s considered obstruction

when you have obstruction, both your FEV1 and VC are decreased bu the FEV1 is decreased to a greater degree which is why the ratio changes with obstruction

Question 32

which lung diseases are obstructive?

Answer 32

1. asthma

2. COPD

Question 33

which lung diseases are restrictive?

Answer 33

restrictive lung disease is usually interstitial lung disease

Question 34

what pulmonary function test results indicate that there’s a restriction?

Answer 34

FEV1 and VC both go down at the SAME rate so the ratio is above 80! –> with obstructive diseases, the FEV1 drops much lower than the VC so the ratio is below 80

so look at the total lung capacity which you measure through body box and it will be low!

Question 35

how will the flow volume curve look like with obstructive vs. restrictive disease processes?

Answer 35

go look at the slide….

slide 30

obstructive = emphysema, variable intrathoracic UAO, and variable extra thoracic UAO graph –> inspiration is totally normal but expiration is difficult

restrictive = restrictive parenchymal lung disease graph –> graph looks totally normal but it’s little

Question 36

which of the following is used to follow disease severity in COPD?

A. diffusing capacity

B. degree of responsiveness to bronchodilators

C. forced vital capacity

D. forced expiratory volume in 1 second

Answer 36

D. forced expiratory volume in 1 second

Question 37

a 22 year old female present to your office for followup of recurrent attacks of acute bronchitis. you suspect asthma. which of the following would you include in your spirometry testing to diagnose asthma?

A. diffusing capacity

B. if no obstruction present, add trial of bronchodilator

C. if no obstruction present, perform methacholine challenge

D. flow volume loop

Answer 37

C. if no obstruction present, perform methacholine challenge

it’s not B because some COPD patents may have a positive bronchodilator response because the treatment helps them! but the methacholine challenge is specific for asthma

you want to see when they hit 20% obstruction with methacholine challenge

Question 38

a 72 year old male patient is admitted to the ICU with respiratory distress. a CXR obtained in the ED demonstrates bilateral pulmonary infiltrates and his DLCO is elevated. what is the most likely diagnosis?

A. pulmonary edema

B. hypersensitive pneumonitis

C. venous thromboembolic disease

D. alveolar hemorrhage

E. interstitial lung disease

Answer 38

D. alveolar hemorrhage