Principles of Pulmonary Function Testing

Question 1

Describe spirometry testing procedure and purpose.

Answer 1

performed by measuring the volume of air exhaled during forced expiration, patient must inhale maximally and exhale with maximal effort for as long as possible

spirogram is a very sensitive test to detect abnormalities in lung mechanics

Question 2

2. Describe spirometry patterns of obstructive lung disease.

Answer 2

as obstruction is more severe the FVC decreases and the concave shape of the terminal expiratory F-V curve becomes more pronounced

Question 3

3. Illustrate flow-volume loops curves in obstructive and restrictive patterns of disease

Answer 3

obstructive curves show low flow, and high volumes (short with a wide base) with a curvilinear effort independent phase, vital capacity is reduced due to hyperinflation

restrictive flow-volume curves show high flow, low volume (high peak narrow base), reduced TLC, steep decent in effort independent phase

Question 4

4. Describe the differences between intrathoracic and extrathoracic airway obstruction.

Answer 4

variable intrathoracic lesions will cause a shelf on the expiratory limb (reduced traction on exhale causes lesion to obscure lesion)

variable extrathoracic lesions will cause shelf on the inspriratory limb, pressure differential on inhalation will cause collapse of airway at level of obstruction

Question 5

5. Distinguish between different methods of measuring lung volumes.

Answer 5

plethysmography can measure the lung volume whereas spirometry can only measure vital capacity

FRC, TLC and RV cannot be measured by spirometry and can be measured by plethysmography, the most accurate method of measurement esp with airflow obstruction

other methods include Closed-Circuit Helium dilution and Open-circuit nitrogen washout (rarely used)

Question 6

6. Summarize type of disease processes can lead to a reduction diffusion capacity.

Answer 6

1. anemia
2. decreased area of diffusion: emphysema, surgical resection, bronchial obstruction or multiple pulmonary emboli
3. increased thickness of alveolar-capillary membrane: CHF, fibrosis, sarcoidosis, asbestosis
4. Misc: high CO back pressure from smoking, pregnancy, ventilation-perfusion mismatch

Question 7

What is FEV1 and why is it useful?

Answer 7

forced expiratory volume in the first second of spirometry testing

it is the best characterized and most reproducible test of pulmonary function

Question 8

What is FEV1/FVC ratio and how does it change with obstructive and restrictive disease?

Answer 8

ratio of forced expiration in one second over total expiration volume; ratio decreases significantly with obstructive disease but stays high in restrictive disease due proportional reduction in volumes

Question 9

What are the 3 main questions to ask regarding airflow obstruction on spirogram?

Answer 9

1. is there airway obstruction (normally >70-75%
2. in the case of obstruction, how severe? (severe is 35-49% and very severe is <35%)
3. is the obstruction fixed or reversible (do bronchodilators help?)

Question 10

What are the key’s to performing an acceptable spirometry?

Answer 10

1. maximal inspiration
2. blast air out as fast as possible
3. continue for at least 6 s.
4. two largest of 3 maneuvers differ by less than 150mL
5. no obvious back extrapolation error, evidence of expiratory plateau

Question 11

What is the effort dependent portion of a flow-volume curve?

Answer 11

the initial slope of the F-V curve will be less steep and the PEF will not be reached if effort is not maximal

in the non-effort dependent portion, dynamic compression contributes to independent decline in flow rates

all inspiratory flow-volume curves vary with effort and are considered effort-dependent

Question 12

How would you partition the flow v. volume curve to understand contributions by small airways?

Answer 12

by leaving off FEV1 and looking at the flow between 25th and 75th quartiles, you can see the flow contributed by small airways (<2mm)

Question 13

Contrast obstructive and restrictive lung disease.

Answer 13

obstructive of air flow results in trapping in the lungs, airways close prematurely at high lung volumes (hallmark decrease in FEV1/FVC ratio)

restrictive lung expansion causes a decrease in lung volumes (and decrease in TLC and FVC)

Question 14

Restrictive lung disease is defined by TLC _____%

Answer 14

<80%; total lung capacity is measured by the greatest lung volume achieved by maximum voluntary inspiration

Question 15

In _____ ______ disease, the RV is increased (called “air trapping”) due to cessation of flow after a prolonged expiration at very low flow rates with patchy closure of airways (dynamic obstruction).

Answer 15

severe obstructive disease leads to increase RV

Question 16

Name several conditions that result in restrictive pulmonary disease.

Answer 16

parenchymal removal or destruction

parenchyma infiltrate (inflammation ro fibrosis)

extra pulmonary deformity (effts chest wall or pleura

reduced force due to peripheral and central nervous system respiratory muscles

Question 17

How do capacities vary in restrictive disease caused by parenchymal process v. extra-pulmonary deformity? (concerning disease of pleura, best wall or neuromuscular disease)

Answer 17

disease of pleura lead to a proportionate reduction in all lung volumes

disease of the chest wall: normal FRC, low TLC and high RV (stiff chest wall) or low FRC and low TLC, normal RV (obesity)

neuromuscular disease: TLC is limited, RV is increased while FRC is normal

Question 18

How would you rate someone’s diffusion capacity?

Answer 18

<40% predicted severe