pulmonary function tests correct version

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Interpreting Spirometry Results

Spirometry requires considerable patient effort and cooperation. Therefore, results must

be assessed for validity before they can be interpreted. Inadequate patient effort can lead to

misdiagnosis and inappropriate treatment.

To determine the validity of spirometric results, at least three acceptable spirograms

must be obtained. In each test, patients should exhale for at least six seconds and stop when there

is no volume change for one second. The test session is finished when the difference between the

two largest FVC measurements and between the two largest FEV1 measurements is within 0.2 L.

If both criteria are not met after three maneuvers, the test should not be interpreted. Repeat

testing should continue until the criteria are met or until eight tests have been performed. The

lines of the flow-volume curve are free of glitches and irregularities. The volume-time curve

extends longer than six seconds, and there are no signs of early termination or cutoff.

If the test is valid, the second step is to determine whether an obstructive or

restrictive ventilatory pattern is present.

Restrictive ventilatory pattern can be:

Parenchymal

• Sarcoidosis

• Pneumoconiosis

•Pulmonary fibrosis

• Interstitial lung disease

Extraparenchymal

• Neuromuscular diseases

• Affections of thoracic cage: kyphosis, scoliosis, obesity

The characteristic element is reduction of lung volumes, especially TLC and VC.

In parenchymal restrictive ventilatory disease RV is generally low and expiratory flows

are maintained (FEV1 is normal). Curve flow/volume shows imbalance between flows and lungvolumes – the curve is relatively high, but narrow.

In extraparenchymal restrictive ventilatory disease, dysfunction can be predominantly

during inspiration or combined (inspiration and expiration).

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The inspiratory restrictive dysfunction can be due to weak inspiratory muscles, rigid

thoracic cage and the lung, which is normal, is under insufficient force. In consequence TLC is

low, RV is not usually affected and expiratory flow is conserved.

In combined restrictive dysfunction the ability to expire to RV is limited (RV is high).

FEV1/FVC is variable, depending on respiratory muscles strength. If this strength is significantly

low, the ratio will be low, in the absence of obstruction. If muscles strength is conserved, but

thoracic cage is rigid, the ratio will be normal or high.

A reduced FEV1 and absolute FEV1/FVC ratio indicates an obstructive ventilatory

pattern. A Tiffeneau index (FEV1/FVC x 100) of less than 70% is very suggestive for

obstructive lung disease. VC is often low in obstructive disease, because of important increase of

RV, but with insignificant change of TLC.

When the FVC and FEV1 are decreased, the distinction between an obstructive and

restrictive ventilatory pattern depends on the absolute FEV1/FVC ratio. If the absolute

FEV1/FVC ratio is normal or increased, a restrictive ventilatory impairment may be present.

However, to make a definitive diagnosis of restrictive lung disease, the patient should be referred

to a pulmonary laboratory for static lung volumes. If the TLC is less than 80 percent, the pattern

is restrictive, and diseases such as pleural effusion, pneumonia, pulmonary fibrosis, and

congestive heart failure should be considered.

Bronchodilator challenge testing is recommended to detect patients with reversible

airway obstruction (e.g., asthma). A bronchodilator is given, and spirometry is repeated after

several minutes. The test is positive if the FEV1 increases by at least 12 percent and the FVC

increases by at least 200 mL. The patient should not use any bronchodilator for at least 48 hours

before the test. A negative bronchodilator response does not completely exclude the diagnosis of

asthma.

The mid-expiratory flow rate (FEF 25–75%) is the average forced expiratory flow rate

over the middle 50 percent of the FVC. It can help in the diagnosis of an obstructive ventilatory

pattern. Because it is dependent on FVC, the FEF 25–75% is highly variable. In the correct

clinical situation, a reduction in FEF25–75% of less than 60 percent of that predicted and an

FEV1/FVC ratio in the low to normal range may confirm airway obstruction.

The maximal voluntary ventilation (MVV) maneuver is another test that can be used to

confirm obstructive and restrictive conditions. The patient is instructed to breathe as hard and fast

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as possible for 12 seconds. The result is extrapolated to 60 seconds and reported in liters per

minute. MVV generally is approximately equal to the FEV1. A low MVV can occur in

obstructive disease but is more common in restrictive conditions. If the MVV is low but FEV1

and FVC are normal, poor patient effort, a neuromuscular disorder, or major airway lesion must

be considered.

Once the ventilatory pattern is identified, the severity of the disease must be determined.

The obstructive syndrome is considered to be:

• Mild – if FEV1/FVC ratio = 60-75%

• Moderate – if FEV1/FVC ratio = 40-60%

• Severe – if FEV1/FVC ratio < 40%

The final step in interpreting spirometry is to determine if additional testing is needed to

further define the abnormality detected by spirometry. Measurement of static lung volumes,

including FRC, is required to make a definitive diagnosis of restrictive lung disease.

Table 1. Ventilatory dysfunction

Ventilatory dysfunction

TLC RV VC FEV1/ FVC

Obstructive N / ↑ ↑ ↓ ↓

Restrictive

Parenchymal ↓ ↓ ↓ N / ↑

Extraparenchymal affection of

inhaling

↓ N / ↓ ↓ N

Extraparenchymal affection of

inhaling + exhaling

↓ ↑ ↓ Variable

Mixed ventilatory dysfunction

• Low VC

• Low FEV1/FVC

• Very low FEV1

Diagnostic is not certain without the evidence of restrictive component (low TLC)

• E.g. lung tuberculosis + chronic bronchitis

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Fig.1 Flow-volume in obstructive lung disease is concave, FEF25-75 too low, FVC normal

Fig.2 Volume-time curve in obstructive lung disease: FEV1 low, FET ( Forced Expiratory Time)

higher due to the lower flow but equal volume.

Fig.3 Variable Extrathoracic Obstruction. Typically the expiratory part of the F/V-loop is

normal: the obstruction is pushed outwards by the force of the expiration. During inspiration the

obstruction is sucked into the trachea with partial obstruction and flattening of the inspiratory

part of the flow-volume loop. This is seen in cases of vocal cord paralysis, extrathoracic goiter and laryngeal tumors.

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Fig.4 Variable Intrathoracic Obstruction. A tumor located near the intrathoracic part of thetrachea is sucked outwards during inspiration with a normal morphology of the inspiratory part

of F/V-loop. During expiration the tumor is pushed into the trachea with partial obstruction andflattening of the expiratory part of the F/V loop.

Fig.5 Flow-volume in restrictive lung disease - shape normal, FVC low. Total lung volume is

low, which results in a low FVC. PEF can be normal or low. FEV1 is equally lowered than FVC,so the Tiffeneau index will be normal or even raised.

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Fig. 6 Volume-time curve in restrictive lung disease - FEV1 too low, FET normal

Fig. 7 Fixed Large Airway Obstruction. This can be both intrathoracic as extrathoracic. The

flow-volume loop is typically flattened during inspiration and expiration. Examples are tracheal

stenosis caused by intubation and a circular tracheal tumor.

Fig.8 Mixed Lung Disease Often patients will show signs of both obstructive and restrictive lungdisease. The flow-volume loop will have characteristics of both syndromes - FVC, FEV1 and

FEF25-75 too low.

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Diagnostic algorithm

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Investigation of asthma

Allergens

Extrinsic allergens include:

• pollen

• animal dander

• house dust or mold

• kapok or feather pillows

• food additives containing sulfites

• other sensitizing substances.

Intrinsic allergens include:

• irritants

• emotional stress

• fatigue

• endocrine changes

• temperature variations

• humidity variations

• exposure to noxious fumes

•

anxiety• coughing or laughing

• genetic factors

Laboratory Studies

• Laboratory assessments and studies are not routinely indicated for asthma, but they may

be used to exclude other diagnoses.

• Blood eosinophilia greater than 4% or 300-400/µL supports the diagnosis of asthma, but

an absence of this finding is not exclusionary. Eosinophil counts greater than 8% may be

observed in patients with concomitant atopic dermatitis. This finding should prompt an

evaluation for allergic bronchopulmonary aspergillosis or eosinophilic pneumonia.

• Total serum immunoglobulin E levels greater than 100 IU are frequently observed in

patients experiencing allergic reactions, but this finding is not specific for asthma and

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may be observed in patients with other conditions (eg, allergic bronchopulmonary

aspergillosis). A normal total serum immunoglobulin E level does not exclude the

diagnosis of asthma.

• In assessing asthma control, the British Thoracic Society recommends using sputum

eosinophilia determinations to guide therapy. An improvement in asthma control, a

decrease in hospitalizations, and a decrease in exacerbations were noted in those patients

in whom sputum-guided therapy was used. A controlled prospective study has shown that

adjusting inhaled corticosteroid (ICS) treatment to control sputum eosinophilia - as

opposed to controlling symptoms, short-acting beta-agonist (SABA) use, nocturnal

awakenings, and pulmonary function - significantly reduced both the rate of asthma

exacerbations and the cumulative dose of inhaled corticosteroids.

Imaging Studies

• In most patients with asthma, chest radiography findings are normal or may indicate

hyperinflation. Findings may help rule out other pulmonary diseases such as allergic

bronchopulmonary aspergillosis or sarcoidosis, which can manifest with symptoms of

reactive airway disease. Chest radiography should be considered in all patients being

evaluated for asthma to exclude other diagnoses.

• Sinus CT scanning may be useful to help exclude acute or chronic sinusitis as a

contributing factor. In patients with chronic sinus symptoms, CT scanning of the sinuses

can also help rule out chronic sinus disease.

Other Tests

• Allergy skin testing is a useful adjunct in individuals with atopy. Results help guide

indoor allergen mitigation or help diagnose allergic rhinitis symptoms. The allergens that

most commonly cause asthma are aeroallergens such as house dust mites, animal danders,

pollens, and mold spores.

• Two methods are available to test for allergic sensitivity to specific allergens in the

environment: allergy skin tests and blood radioallergosorbent tests (RAST).

• In patients with asthma and symptoms of gastroesophageal reflux disease (GERD), 24-

hour pH monitoring can help determine if GERD is a contributing factor.

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Procedures

• Pulmonary function testing (spirometry)

o Spirometry assessments should be obtained as the primary test to establish the

asthma diagnosis. Spirometry should be performed prior to initiating treatment in

order to establish the presence and determine the severity of baseline airway

obstruction. Optimally, the initial spirometry should also include measurements

before and after inhalation of a short-acting bronchodilator in all patients in whom

the diagnosis of asthma is considered. Spirometry measures the forced vital

capacity (FVC), the maximal amount of air expired from the point of maximal

inhalation, and the FEV1. A reduced ratio of FEV1 to FVC, when compared with

predicted values, demonstrates the presence of airway obstruction. Reversibility is

demonstrated by an increase of 12% and 200 mL after the administration of a

short-acting bronchodilator.

o The assessment and diagnosis of asthma cannot be based on spirometry findings

alone because many other diseases are associated with obstructive spirometry

indices.

o As a preliminary assessment for exercise-induced asthma (EIA), or exercise-

induced bronchospasm (EIB), perform spirometry in all patients with exercisesymptoms to determine if any baseline abnormalities (ie, the presence of

obstructive or restrictive indices) are present.

• Methacholine- or histamine- challenge testing

o Bronchoprovocation testing with either methacholine or histamine is useful when

spirometry findings are normal or near normal, especially in patients with

intermittent or exercise-induced asthma symptoms. Bronchoprovocation testing

helps determine if airway hyperreactivity is present, and a negative test result

usually excludes the diagnosis of asthma.

o Trained individuals should perform this asthma testing in an appropriate facility

and in accordance with the guidelines. Methacholine is administered in

incremental doses up to a maximum dose of 16 mg/mL, and a 20% decrease in

FEV1, up to the 4 mg/mL level, is considered a positive test result for the presence

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of bronchial hyperresponsiveness. The presence of airflow obstruction with an

FEV1 less than 65-70% at baseline is generally an indication to avoid performing

the test.

• Exercise testing

o Exercise spirometry is the standard method for assessing patients with exercise-

induced bronchospasm. Testing involves 6-10 minutes of strenuous exertion at 85-

90% of predicted maximal heart rate and measurement of postexercise spirometry

for 15-30 minutes. The defined cutoff for a positive test result is a 15% decrease

in FEV1 after exercise.

o Exercise testing may be accomplished in 3 different ways, using cycle ergometry,

a standard treadmill test, or free running exercise. This method of testing is

limited because laboratory conditions may not subject the patient to the usual

conditions that trigger exercise-induced bronchospasm symptoms, and results

have a lower sensitivity for asthma compared with other methods.

• Eucapnic hyperventilation

o Eucapnic hyperventilation with either cold or dry air is an alternate method of

bronchoprovocation testing.

o It has been used to evaluate patients for exercise-induced asthma and has been

shown to produce results similar to those of methacholine-challenge asthmatesting.

• Peak-flow monitoring

o Peak-flow monitoring is designed for ongoing monitoring of patients with asthma

because the test is simple to perform and the results are a quantitative and

reproducible measure of airflow obstruction.

o It can be used for short-term monitoring, exacerbation management, and daily

long-term monitoring. Peak-flow monitoring should not be used as a substitute for

spirometry to establish the initial diagnosis of asthma.

o Results can be used to determine the severity of an exacerbation and to help guide

therapeutic decisions as part of an asthma action plan.

• Guidelines for the use of peak-flow meters for asthma

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o Advise the patient to use the peak-flow meter upon awakening in the morning

before using a bronchodilator.

o Instruct the patient on how to establish a personal best peak expiratory flow (PEF)

rate.

o Inform the patient that a peak flow of less than 80% of the patient's personal best

indicates a need for additional medication and a peak flow below 50% indicates

severe exacerbation.

o Advise the patient to use the same peak-flow meter over time.

• Exhaled nitric oxide

o Exhaled nitric oxide analysis has been shown to predict airway inflammation and

asthma control; however, it is technically more complex and not routinely used in

the monitoring of patients with asthma.

o A prospective, controlled study has shown that when inhaled corticosteroid

asthma treatment was adjusted to control the fraction of exhaled nitric oxide, as

opposed to controlling the standard indices of asthma, the cumulative dose of ICS

was reduced, with no worsening of the frequency of asthma exacerbations.

Medical Care

The latest version of the goals for successful assessment and management of asthma outlined in

the 2008 US National Heart, Lung, and Blood Institute publication "Global Strategy for AsthmaManagement and Prevention" include the following :

• Achieve and maintain control of asthma symptoms

• Maintain normal activity levels, including exercise

• Maintain pulmonary function as close to normal as possible

• Prevent asthma exacerbations

• Avoid adverse effects from asthma medications

• Prevent asthma mortality

Overall management of asthma should incorporate the following 4 treatment components:

• Objective measures of lung function

• Environmental control measures and avoidance of risk factors

• Comprehensive pharmacologic therapy

• Patient education

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