Lung Function Tests

Question 1

What are pulmonary function tests?

Answer 1

Pulmonary function tests (PFTs) are noninvasive tests that show how well the lungs are working. The tests measure lung volume, capacity, rates of flow, and gas exchange. This information can help your healthcare provider diagnose and decide the treatment of certain lung disorders.

Question 2

What are the different lung volumes?

Answer 2

Four standard lung volumes, namely:

tidal (TV), inspiratory reserve (IRV), expiratory reserve (ERV), and residual volumes (RV) are described in the literature.

Alternatively, the standard lung capacities are inspiratory (IC), functional residual (FRC), vital (VC) and total lung capacities (TLC)

Question 3

What are the different methods for measuring all lung volumes?

Answer 3

• Body plethysmography
• Nitrogen washout
• Inert gas dilution techniques

Question 4

What are lung volume patterns?

Answer 4

• Normal
• obstructive - An obstructive defect is indicated by a low forced expiratory volume in one second/forced vital capacity (FEV1/FVC) ratio, which is defined as less than 70% or below the fifth percentile
• restrictive - A restrictive pattern is indicated by an FVC below the fifth percentile
• neuromuscular

Question 5

How do you measure ventilatory function?

Answer 5

 Determination of lung volumes (under static conditions)

 Determination of forced expiratory flow rates (under dynamic conditions

 Lung volumes and measurements are interpreted by comparing the values measured with the values expected given the age, height, sex, and race of the patient.

Question 6

What is a volume-time curve?

Answer 6

Spirogram (volume time curve) measures respired volume against time. FEV 1 and FVC are the traditional measures. This figure also demonstrates measurement of inspiratory capacity (I.C).

Question 7

What is pneumotahography?

Answer 7

The pneumotachograph is a device that measures airflow quantitatively by detecting flow of respiratory gases and comparing it to the pressure drop against a small resistive field.

Question 8

What is spirometry?

Answer 8

Spirometry is a simple test used to help diagnose and monitor certain lung conditions by measuring how much air you can breathe out in one forced breath.

How is a spirometry test performed?

In a spirometry test, while you are sitting, you breathe into a mouthpiece that is connected to an instrument called a spirometer.

The spirometer records the amount and the rate of air that you breathe in and out over a period of time.

When standing, some numbers might be slightly different.

Question 9

What are the indications for spirometry?

Answer 9

Indications :

• Evaluate respiratory symptoms, signs, abnormal laboratory or radiographic findings
• Assist in diagnosing respiratory diseases
• Monitor respiratory disease activity and response to therapy
• Determine respiratory disease stage and prognosis
• Evaluate the pulmonary effects of occupational, environmental, and drug exposures
• Provide objective assessment of impairment or disability
• Evaluate risk prior to lung resection surgery
• Assist in smoking-cessation efforts

Question 10

What is spirometry performance?

Answer 10

Very popular devices

The volume accuracy of the spirometer should be checked at least daily with a 3-L syringe.

Acceptability :

• maximal inspiration to total lung capacity (TLC)
• an abrupt, maximally forceful exhalation; and
• exhalation continuing to residual volume (exhalation time of greater than 6 seconds or a plateau on the volume-time curve)
• absence of cough, glottic closure, or hesitation during the maneuver; an air leak from the mouth or nose
• minimum of three acceptable maneuvers

Question 11

How does a normal spirometry curve look like?

Answer 11

Most spirometers display the following graphs, called spirograms:

a volume-time curve, showing volume (litres) along the Y-axis and time (seconds) along the X-axis.

a flow-volume loop, which graphically depicts the rate of airflow on the Y-axis and the total volume inspired or expired on the X-axis.

Question 12

What does a spirometry curve with insufficient cooperation look like?

Answer 12

little dips

Question 13

What is spirometry performance?

Answer 13

Test repeatability:
After three acceptable spirograms, apply the following criteria:

1.The two largest values of FVC are to be within 0.15L of each other
2.The two largest values of FEV1 are to be within 0.15L of each other

Question 14

How do you interpret changes in lung function tests?

Answer 14

Changes in lung function can be due to:

Technical factors from either the instrument, the technician, or the subject;
Disease-related changes

Lung function variability increases over time and is generally greater in subjects with disease than in normal subjects.

Question 15

What are the different normal spirometric values?

Answer 15

 FVC - forced vital capacity

 FEV1 - forced expiratory
volume for the first second

 FEV1 /FVC - 0.75 to 0.80

 The FEF25-75% is often considered a more sensitive measurement of early airflow obstruction, particularly in small airways.

PEF - the biggest flow rate during the forced expiration

FEF 75,50,25 are flow rates when in the lung are 75, 50 and 25% of the air left (not expired)

Question 16

What is the clinical utility of lung volume testing restrictive patterns?

Answer 16

Lung resection

Restrictive pattern caused by decreased lung compliance:
- Interstitial lung disease

Decreased chest wall compliance:
- kyphoscoliosis 
- ankylosing spondylitis 
- pleural effusions 
- fibrothorax, thoracoplasty 
morbid obesity

Question 17

What is the clinical utility of lung volume testing obstructive patterns?

Answer 17

• COPD
• Bronchial Asthma
• Chronic bronchitis, Bronchiectasis

Question 18

What are obstructive patterns of abnormal function?

Answer 18

Obstructive pattern - decrease in expiratory flow rates

 decreased FEV1, FEV1 /FVC, and FEF25-75%

 decreased flow rates for any given lung volume

 normal or increased TLC, elevated RV, increased RV /TLC

 decreased VC

Question 19

What are restrictive patterns of abnormal function?

Answer 19

• Decrease in lung volumes, primarily TLC and VC as well as RV
• Preserved FEV1/FVC
• The flow-volume curve is tall (preserved flow rates) but narrow (decreased lung volumes)

Question 20

What are bronchoprovocation tests categories?

Answer 20

The methacholine challenge test (also known as a bronchoprovocation test) is used to diagnose asthma.

It can find out how “reactive” or “responsive” your lungs are to things you inhale that can cause asthma symptoms.

These symptoms include cough, a tight feeling in your chest, and shortness of breath.

Question 21

What are the indications and contraindications for bronchial provocation tests?

Answer 21

Indications:

• Establishing a diagnosis of asthma when atypical features are present
• Evaluating the possibility of occupational asthma
• Monitoring asthma therapy:
• Objectively assessing asthma severity

Contraindications:

• Severe airflow limitation (FEV1 < 50% or <1.0L)
  Recent upper or lower respiratory tract infection (within 6wk)
• Acute coronary syndrome or stroke within 3 months
• Severe hypertension

Question 22

What is a methacholine inhalation challenge?

Answer 22

• The test consists of performing spirometry at baseline and then after each dose of nebulized methacholine.

An initial methacholine concentration of 0.031mg/mL or 0.0625mg/mL is used and subsequent doses are increased by two- to fourfold until the FEV1 falls by 20% from the baseline value or a concentration of 16mg/mL is reached

Question 23

What is diffusing capacity?

Answer 23

Diffusion capacity assesses how well a tracer gas in inspired air can cross from the air into the blood.

The test measures the absorption of a low concentration of carbon monoxide in inhaled air by hemoglobin in red blood cells that circulate through pulmonary capillaries.

The diffusing capacity for carbon monoxide (DlCO) provides a quantitative measure of gas transfer in the lungs.

CO is used in the test.

The amount of gas transferred across a membrane is directly proportional to the tissue surface area, diffusion constant, and the difference in gas partial pressure and is inversely proportional to the tissue thickness.

Question 24

What are the physiological sources of variability in the measurement of DICO?

Answer 24

Age

Gender

Ethnicity

Hemoglobin concentration

Carboxyhemoglobin
concentration

Altitude and inspired
oxygenconcentration

Circadian rhythm

Menstrual cycle

Smoking history

Exercise

Body position

Bronchodilation

Question 25

What is the clinical utility of diffusing capacity?

Answer 25

A low DlCO with normal spirometry suggests:

• Pulmonary vascular disease, (significant reduction in DlCO and normal spirometry and lung volumes)
• Early interstitial lung disease,
• Emphysema associated with a restrictive lung process,
• Anemia (reduced hemoglobin), or elevated carboxyhemoglobin level.
• A low DlCO in the setting of obstruction, defined as a FEV1/FVC ratio below the LLN, suggests a diagnosis of emphysema.
• A low DlCO in the setting of restriction, is seen in various interstitial lung diseases, neuromuscular disease, chest wall abnormalities, and severe congestive heart failure.
• Diffusing capacity is valuable in monitoring disease progression in patients with idiopathic pulmonary fibrosis and sarcoidosis

Question 26

What is an alveolocapillary block?

Answer 26

Impaired diffusion of gases between the air in the alveolar spaces and the blood in alveolar capillaries;

block can be caused by edema, cellular infiltration, fibrosis, or tumor, and results in undersaturation of peripheral arterial blood with oxygen