PULMONARY FUNCTION TESTS IN BRONCHIAL ASTHMA: A PRACTICAL APPROACH • Asthma is a chronic inflammatory disease of the airways. • The basic functional abnormality of symptomatic asthma is diffuse airway narrowing increase in resistance airflow limitation hyperinflation, gas trapping increase in the work of breathing.

• Clinically characterized by recurrent: Wheeze – Difficult breathing – cough ( night).

Value of PFTs in BA I. Diagnosis of BA. • Evidence of AWO (reversibility – variability). • No AWO (bronchoprovocation tests). II. Differential diagnosis. • Restrictive lung diseases. • Other obstructive lung diseases.

III. Treatment. • Classification of severity selection of line of

treatment. • Monitoring the response of treatment. IV. Pre-operative assessment.

I. PFTs in diagnosis of BA: 1. Evidence of airflow obstruction: 2. Evidence of variability:

In asthmatics overnight lung functions falls as much as 50%.

Measuring the variability in lung function provides an indirect assessment of airway hyperresponsiveness.

The magnitude of this incidence variation correlates with the degree of airway reactivity.

It can be assessed by PEFR measurement.

The PEFR variability may be calculated from at least 2 values (morning and night), using the following formula:

A diurnal variation in PEFR of more than 20% in considered to be diagnostic of asthma (morning dipping is most characteristic of BA).

3. Evidence of reversibility:

At least 15% improvement of PEFR after inhalation of a bronchodilator or in response to a trial of glucocorticoid therapy favors a diagnosis of asthma.

A) Response to bronchodilators: B) Response to corticosteroid treatment:

• Stop use of all bronchodilators before the test. • Use standard dose of inhaled bronchodilator

(200 g salbutamol). • FEV1 or PEFR is recorded before and at

intervals after the drug is taken (15 – 20 minutes).

• ATS defines a significant brochodilator response as one in which the FEV1 or FVC increases by 12% and 200 ml.

• Patients, with persistent airflow obstruction considered possibly to result from asthma and who fail to respond to an inhaled bronchodilator, require a trial of corticosteroid therapy.

• Prednisolone, in a dose of 20-40 mg/day (single or divided doses) for 1 week to few weeks.

• Pretrial measurements should be recorded for at least 1 week at a time when the patient’s clinical condition is stable.

• PEF should be recorded as the best of three attempts at least twice a day before and during the therapeutic trial.

• An improvement of airflow in response to corticosteroid therapy is

an indication of asthma ( PEFR > 20%).

4. Bronchial challenge test: Bronchial provocation test/ bronchial inhalation challenge/ methacholine challenge/ histamine challenge

Purpose • To detect asthma when it is suspected despite normal pulmonary function • To identify substances or exposures that trigger asthma attacks, particularly

in people with occupational asthma • To evaluate the effectiveness of drugs in preventing airway constriction

How it works? • The test replicates in a controlled setting the conditions in the environment

that may be causing your airways to constrict.

Preparation

Certain drugs, particularly bronchodilators, must be avoided prior to the test.

Do not smoke or take caffeine for six hours before the test.

Avoid exercise and exposure to cold air for two hours before the test.

Test procedure 1. Baseline pulmonary function tests are performed using a spirometer. 2. If it is necessary to test the effectiveness of a drug in preventing airway constriction, you will receive the drug before

continuing the test. 3. You breathe in aerosolized methacholine through a nebulizer for about two minutes. Then, after a 30-second wait,

you exhale forcefully through the mouthpiece. 4. Other substances suspected of causing airway constriction, such as chemicals in the workplace, may be used in

subsequent tests 5. Spirometry tests are repeated 6. The tests may be repeated with higher concentrations of methacholine, colder air, or after more strenuous exercise After the test • You remove the nose clip, and are free to resume normal activities. • You may wheeze or cough for 30 to 60 minutes after the test, and may need a bronchodilator to decrease symptoms Interpretation

The results before and after the challenge (the tested exposure) are compared. If your lung function dropped 20% or more after exposure to cold, exercise, methacholine, or to whatever substance is used for the test, your airways are abnormally sensitive to these exposures.

The target is to reach 20% decrease in FEV1 (called provocative concentration (PC) for a 20% fall in FEV1 {PC 20 – FEV1} ).

Diagnosis of asthma, however, can only be made after test results are correlated with your symptoms, because

abnormal sensitivity of the airways may be present in various disorders, including, among others, chronic

obstructive pulmonary disease, bronchiolitis, and cystic fibrosis.

1. If PC20 –FEV1 < 1 mg/ml the test provides strong confirmation of

clinical diagnosis of asthma.

2. If PC20 –FEV1> 8 mg/ml; asthma is unlikely.

3. Negative MCT excludes asthma with 95% certainty.

4. PC20-FEV1 is 2.5 mg/ml; severe BHR. 5. PC20-FEV1 is 10 mg/ml; moderate BHR. 6. PC20-FEV1 is 25 mg/ml; mild BHR.

If the patient reaches the highest concentration (25 mg/ml) w/o significant change in FEV1 (20% or more), the test is Negative.

Factors affecting results • Failure to follow instructions, such as not holding your breath or exhaling with maximum force. • Anxiety or fatigue. • Recent or current chest infection, a cold, or other respiratory disease. • Bronchodilators, sedatives, and other drugs that may affect breathing. • Other procedures, such as positive-pressure-breathing therapy, performed a few hours before the test. Advantages: It's highly reliable Disadvantages • There is a risk of causing severe airway constriction. • Results can only be interpreted in the light of symptom

II. PFTs for differential diagnosis of BA: A) Restrictive lung disease

B) Other obstructive lung disease.

III. PFTs in treatment of BA: 1) Classification of severity before treatment:

STEP 1 Intermittent

STEP 2 Mild Persistent

STEP 3 Moderate Persistent

STEP 4 Severe Persistent

FEV1 predicted > 80% > 80% 60-80% < 60%

PEF % of personal best > 80% > 80% 60-80% < 60%

PEF or FEV1 variability < 20% 20-30% > 30% > 30%

2) Assessment of exacerbation severity:

Function assessment Mild Moderate Severe

PEF % predicted or % personal best

> 80% Approx. 50-80% Or response lasts < 2 hrs

< 50% predicted or personal best

PaO2 (on air) Normal) > 60 mmHg < 60% mmHg possible cyanosis

SaO2 % (on air) > 95% 91-95% < 91%

PaCO2 < 42 mmHg < 42 mmHg > 42 mmHg

3) Monitoring the response of treatment: • In addition to assessing symptoms, it is also important to periodically assess pulmonary function. The main methods

are spirometry and peak flow monitoring. A) Spirometry tests: to be done

1. at the time of initial assessment 2. after treatment is initiated and symptoms and PEF have stabilized 3. at least every 1 to 2 years to assess the maintenance of airway function.

B) Peak flow monitoring: Provides a simple, quantitatives, and reproducible measure of the existence and severity of airflow obstruction. PEF can be measured with inexpensive and portable peak flow meters. PEF used in: • Patients with moderate to severe persistent asthma should learn how to

monitor their PEF and have a peak flow meter at home. • Peak flow monitoring during exacerbations of asthma: 1. Severity of the exacerbation. 2. Guide therapeutic decisions.

PEF can be used to help the patient in: 1. Learn what makes your asthma worse. 2. Decide if your treatment plan is working

well. 3. Decide when to add or stop medicine. 4. Decide when to seek emergency care.

The Peak Flow Zone System: The personal best peak flow number is the highest peak flow number the patient can achieve over a 2- to 3- week period when his asthma is under good control. Good control is when he feel good and do not have any asthma symptoms.

Green zone Yellow zone Red Zone

more than ___ L/min 80% of personal best number

between ___ L/min 50% to <80% of personal best number

below ___ L/min 50% of your personal best number

signals good control signals caution signals a medical alert.

No asthma symptoms are present.

asthma may not be under good day-to-day control.

Ask doctor if you need to change/ increase the daily medicines.

Call your doctor/ ER

ask what to do

go directly to the hospital emergency.

Take the medicines as usual. take a short-acting inhaled beta2-agonist right away.

must take a short-acting inhaled beta2-agonist (quick-relief medicine) right away.

IV. Pre-operative assessment. Guidelines for estimating postoperative risks:

Pulmonary function abnormalities in asthma

Test Findings Comments

Spirometry FEV1 FVC

FEV1/FVC FV Loop

NL/

NL/

NL/ NL/expiratory flow limitation

12% and 200 ml after BD

12% and 200 ml after BD

Lung volumes TLC FRC RV

NL/

NL/

NL/

15-20% after BD

15-20% after BD

Diffusion (Dlco) NL/

Airway resistance NL/ sGaw may be NL/

Bronchial challenge Methacholine

Exercise

PC20 FEV1

FEV1

< 8 mg/mL, PC40 < 8 mg/mL

10-15% after exercise

Pressure-volume curve NL/shifted upward, possibly with increased slope (compliance)