Pulmonary Function Tests

Question 1

Functions of the lungs?

Answer 1

1. Gaseous exchange
2. Acid base balance
3. Oxygen in
4. Carbon dioxide out

Question 2

How do the lungs perform their functions?

Answer 2

air moves to the area of gas exchange
- this requires working respiratory muscles and a normal ribcage

Question 3

What are the conducting airways?

Answer 3

1. trachea
2. lobar bronchi
3. segmental bronchi
4. subsegmental bronchi
5. small bronchi, bronchioles and terminal bronchioles

Question 4

What are pulmonary function tests?

Answer 4

objective methods to assess lung function
- primary function = gas exchange

Question 5

Examples of PFTs?

Answer 5

1. spirometry
2. lung volumes by helium dilution or body plethysmography
3. blood gases
4. exercise tests
5. diffusing capacity
6. bronchial challenge testing
7. pulse oximetry

Question 6

Indications for PFTs?

Answer 6

1. Diagnosis and monitoring of disease
2. Disability/impairment evaluation
3. Insurance
4. Public health such as surveys and occupational health issues
5. Derivation of reference equations
6. Legal reasons

Question 7

What is pulse oximetry?

Answer 7

Non-invasive procedure that estimates O2 sats of Hb in pulsating arterial blood

Question 8

Describe a pulse oximeter?

Answer 8

Has a microprocessing unit that is connected to a sensor probe containing Light Emiiting diode (LED) and a photodetector

Question 9

How does a pulse oximeter work?

Answer 9

• Light is transmitted at 660nm (red) and 940nm (infrared)
• The amount of light absorbed in the light above is compared to give O2 sats

Question 10

Accuracy of a pulse oximeter?

Answer 10

Accuracy – at +/-2% for sats >70% but 3% between 50 to 70%

Question 11

Factors that affect pulse oximetry?

Answer 11

1. Temp, pH, PaCO2 and 2,3-DPG as in the oxygen dissociation curve
2. Nail polish that absorbs light in similar wavelengths
3. Other abnormal species of hemoglobin eg COHb or MetHb
4. Penumbra (paene – almost, umbra - shade) effect refers to poor placement of the Pulse oximeter resulting in poor illumination of the photodetector by the LED

Question 12

What is spirometry?

Answer 12

Measurement of volume of air that can be inhaled or exhaled
Note: cannot measure any volume that includes Residual Volume (RV)
– volume of air that remains in the lungs after maximal exhalation

Question 13

What are the 4 lung volumes?

Answer 13

1. inspiratory reserve volume
2. tidal volume
3. expiratory reserve volume
4. residual volume

Question 14

What are the 4 lung capacities?

Answer 14

1. vital capacity
2. inspiratory capacity
3. functional residual capacity
4. total lung capacity

Question 15

What are the 2 ways to record results of a forced vital capacity maneuver?

Answer 15

1. flow volume curve
   - flow meter measures flow rate in L/s upon exhalation; flow plotted as function of volume
2. classic spirogram
   - volume as a function of time

Question 16

Measurements obtained from the FVC curve?

Answer 16

1. FEV1
2. FEF 25-75%
3. FEV1/FVC

Question 17

What is FEV1?

Answer 17

the volume exhaled during the first second of the FVC maneuver

Question 18

What is FEF 25-75%?

Answer 18

the mean expiratory flow during the middle half of the FVC maneuver - reflects flow though the small (<2 mm in diameter) airways

Question 19

What is FEV1/FVC?

Answer 19

the ratio of FEV1 to FVC X 100 (expressed as a percent)

Question 20

Describe the FEV1/FVC ratios corresponding to the ages <40 to >60 years?

Answer 20

1. <40 years old – at least 75% FVC should be exhaled
2. 40 to 60 years old – 70% to 80% FVC to be exhaled
3. > 60 years old – 65%

Question 21

What are the FEV1/FVC ratios that coincide with mild, moderate and severe obstruction?

Answer 21

1. 60 to 70% - mild obstruction
2. 40 to 60% - moderate
3. <40% - severe

Question 22

Differentials for obstructive diseases?

Answer 22

1. Bronchospasm
2. Asthma
3. Emphysema

Question 23

Differentials of restrictive diseases?

Answer 23

1. Scoliosis
2. Lung resection
3. Neuromuscular diseases
4. Interstitial fibrosis

Question 24

What is the spirometry pre and post bronchodilator?

Answer 24

1. obtain flow-volume loop
2. administer a bronchodilator
3. obtain the flow-volume loop again a minimum of 15 minutes after administration of the bronchodilator
4. calculate percent change in FEV1
   - FEV1 = [(FEV1 Post - FEV1 Pre)/FEV1 Pre] X 100
5. reversibility is with 12% or greater change

Question 25

Advantages of flow volume loops?

Answer 25

1. Shape – shows adequacy of the expiratory effort, early termination of effort drops abruptly, coughing and extra breaths are also picked 2. Small airway obstruction – the expiratory effort is long, upwardly-concave indicating low flow rates of the FVC, consistent with small airways obstruction. 3. Upper airway obstruction – flattens the peak. Both the expiratory and inspiratory phases are flattened (in fixed obstruction eg tracheal stenosis) 4. Variable upper airway obstruction (eg bilateral vocal cord paralysis) affects the inspiratory limb – flattening it

Question 26

Contraindications to spirometry?

Answer 26

1. Acute disorders affecting test performance eg nausea, vomiting, vertigo 2. Hemoptysis of unknown origin 3. Pneumothorax 4. Recent abdominal or thoracic surgery 5. Recent myocardial infarction/ unstable angina 6. Thoracic aneurysms 7. Recent eye surgery (to prevent increased intra-ocular pressure)

Question 27

Describe the diffusing capacity of the lungs?

Answer 27

1. Uses Carbon monoxide inhaled – a 10-second breath hold at full inspiration – DLCO 2. CO has high affinity for Hb and therefore not affected by pulmonary blood flow but surface area and nature of air-blood interface around the alveolar-capillary membrane NB. Affected by smoking, age, height