PULMONARY FUNCTION TEST

Prepared By:Sharmin Susiwala

DEFINITION:

• Pulmonary Function Testing (PFT) is a complete evaluation of the respiratory system including patient history, physical examinations, chest x-ray examinations, arterial blood gas analysis, and tests of pulmonary function.

• The primary purpose of pulmonary function testing is to identify the severity of pulmonary impairment.

• Pulmonary function testing has diagnostic and therapeutic roles and helps clinicians answer some general questions about patients with lung disease.

INDICATIONS:• Pulmonary function testing is a diagnostic and management tool used for a

variety of reasons.• Pediatric neuromuscular disorders• Neuromuscular disorders such as Duchenne muscular Dystrophy.• Musculoskeletal deformities such as kyphoscoliosis contribute to restrictive lung

disease.• Pulmonary function testing in patients with neuromuscular disorders helps to

evaluate the respiratory status of patients at the time of diagnosis, monitor their progress and course, evaluate them for possible surgery, and gives an overall idea of the prognosis.

• Other indications• Chronic dyspnea• Asthma• Chronic obstructive pulmonary disease• Restrictive lung disease• Preoperative testing• Impairment or disability

MEASUREMENTS:• There are four lung volumes and four lung capacities. • A lung capacity consists of two or more lung volumes.

• The lung volumes are:1. Tidal volume (VT)

2. Inspiratory reserve volume (IRV)3. Expiratory reserve volume (ERV)4. Residual volume (RV).

• The four lung capacities are:1. Total lung capacity (TLC)2. Inspiratory capacity (IC)3. Functional residual capacity (FRC)4. Vital capacity (VC).

1. Tidal volume: It is the volume of air moved into or out of the lungs during quiet breathing. Value: 500 ml

2. Inspiratory reserve volume: It is the maximal volume that can be inhaled from the end-inspiratory level(after the inspiration of a normal tidal volume). Value: 3100 ml

3. Expiratory reserve volume: It is the maximal volume of air that can be exhaled from the end-expiratory position(after the expiration of a normal tidal volume). Value: 1200 ml

4. Residual volume: It is the volume of air remaining in the lungs after a maximal exhalation. Value: 1200 ml

1. Total lung capacity: It is the volume in the lungs at maximal inflation or maximum amount of air that can fill the lungs. Value: 6000 ml (TLC = TV + IRV + ERV + RV).

2. Vital capacity: It is the total amount of air that can be expired after fully inhaling. Value: 4800 ml (VC = TV + IRV + ERV = approximately 80 percent TLC). The value varies according to age and body size.

3. Inspiratory capacity: It is the maximum amount of air that can be inspired. Value: 3600 ml (IC = TV + IRV).

4. Functional residual capacity: It is the amount of air remaining in the lungs after a normal expiration. Value: 2400 ml (FRC = RV + ERV)

SPIROMETRY

• Spirometry (meaning the measuring of breath) is the most common of the pulmonary function tests (PFTs), measuring lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled.

• Indications:• Spirometry is indicated for the following reasons: to diagnose or manage asthma to detect respiratory disease in patients presenting with symptoms of

breathlessness, and to distinguish respiratory from cardiac disease as the cause to measure bronchial responsiveness in patients suspected of having asthma to diagnose and differentiate between obstructive lung disease and restrictive

lung disease to follow the natural history of disease in respiratory conditions to assess of impairment from occupational asthma to identify those at risk from pulmonary barotrauma while scuba diving to conduct pre-operative risk assessment before anaesthesia or cardiothoracic

surgery to measure response to treatment of conditions which spirometry detects

• Spirometer• The spirometry test is performed

using a device called a spirometer, which comes in several different varieties. Most spirometers display the following graphs, called spirograms:

• a volume-time curve, showing volume (liters) 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.

flow-volume loop

• Parameters• The most common parameters measured in spirometry

are 1. Vital capacity (VC), 2. Forced vital capacity (FVC), 3. Forced expiratory volume (FEV) at timed intervals of

0.5, 1.0 (FEV1), 2.0, and 3.0 seconds, 4. Forced expiratory flow 25–75% (FEF 25–75) and 5. Maximal voluntary ventilation (MVV),[5] also known as

Maximum breathing capacity.* Functional residual capacity (FRC) cannot be measured

via spirometry, but it can be measured with a plethysmograph or dilution tests (for example, helium dilution test)

• Forced vital capacity (FVC)• Forced vital capacity (FVC) is the volume of air that can forcibly be blown out

after full inspiration, measured in liters. • FVC is the most basic maneuver in spirometry tests.• Forced expiratory volume in 1 second (FEV1)• FEV1 is the volume of air that can forcibly be blown out in one second, after full

inspiration. • Average values for FEV1 in healthy people depend mainly on sex and age.• Values of between 80% and 120% of the average value are considered normal.• FEV1/FVC ratio (FEV1%)• FEV1/FVC (FEV1%) is the ratio of FEV1 to FVC. • In healthy adults this should be approximately 75–80%. • Forced expiratory flow (FEF)• Forced expiratory flow (FEF) is the flow (or speed) of air coming out of the lung

during the middle portion of a forced expiration. • It can be given at discrete times, generally defined by what fraction remains of

the forced vital capacity (FVC). • The usual intervals are 25%, 50% and 75% (FEF25, FEF50 and FEF75), or 25%

and 50% of FVC.

• Forced inspiratory flow 25–75% or 25–50%• Forced inspiratory flow 25–75% or 25–50% (FIF 25–75% or 25–50%) is similar to

FEF 25–75% or 25–50% except the measurement is taken during inspiration.• Peak expiratory flow (PEF)• Peak expiratory flow (PEF) is the maximal flow (or speed) achieved during the

maximally forced expiration initiated at full inspiration, measured in liters per minute.

• Maximum voluntary ventilation (MVV)• Maximum voluntary ventilation (MVV) is a measure of the maximum amount of air

that can be inhaled and exhaled within one minute. • For the comfort of the patient this is done over a 15 second time period before

being extrapolated to a value for one minute expressed as liters/minute. • Average values for males and females are 140–180 and 80–120 liters per minute

respectively.Measurement

Approximate valueMale Female

Forced vital capacity (FVC) 4.8 L 3.7 L

Tidal volume (Vt) 500 mL 390 mLTotal lung capacity (TLC) 6.0 L 4.7 L

Incentive Spirometer

Peak expiratory flow

• The peak expiratory flow (PEF), also called peak expiratory flow rate (PEFR) is a person's maximum speed of expiration, as measured with a peak flow meter, a small, hand-held device used to monitor a person's ability to breathe out air.

• It measures the airflow through the bronchi and thus the degree of obstruction in the airways

• Measurement• The highest of three readings is used as the recorded value of the Peak

Expiratory Flow Rate. • Peak flow readings are often classified into 3 zones of measurement

according to the American Lung Association; green, yellow, and red. Doctors and health practitioners can develop an asthma management plan based on the green-yellow-red zones.

Zone Reading Description

Green Zone80 to 100 percent of the usual or normal peak flow readings are clear.

indicates that the asthma is under good control.

Yellow Zone 50 to 79 percent of the usual or normal peak flow readings

Indicates caution. It may mean respiratory airways are narrowing and additional medication may be required.

Red ZoneLess than 50 percent of the usual or normal peak flow readings

Indicates a medical emergency Severe airway narrowing may be occurring and immediate action needs to be taken.

Arterial Blood Gases• An arterial blood gas (ABG) test measures the acidity (pH) and the levels of oxygen and carbon

dioxide in the blood from an artery. • This test is used to check how well your lungs are able to move oxygen into the blood and remove

carbon dioxide from the blood.• As blood passes through your lungs, oxygen moves into the blood while carbon dioxide moves out

of the blood into the lungs. • An ABG test uses blood drawn from an artery, where the oxygen and carbon dioxide levels can be

measured before they enter body tissues. • An ABG measures:1. Partial pressure of oxygen (PaO2). This measures the pressure of oxygen dissolved in the blood

and how well oxygen is able to move from the airspace of the lungs into the blood.2. Partial pressure of carbon dioxide (PaCO2). This measures how much carbon dioxide is dissolved

in the blood and how well carbon dioxide is able to move out of the body.3. pH. The pH measures hydrogen ions (H+) in blood. The pH of blood is usually between 7.35 and

7.45. A pH of less than 7.0 is called acid and a pH greater than 7.0 is called basic (alkaline). So blood is slightly basic.

4. Bicarbonate (HCO3). Bicarbonate is a chemical (buffer) that keeps the pH of blood from becoming too acidic or too basic.

5. Oxygen content (O2CT) and oxygen saturation (O2Sat) values. O2 content measures the amount of oxygen in the blood. Oxygen saturation measures how much of the hemoglobin in the red blood cells is carrying oxygen (O2).

• Importance:• An arterial blood gas (ABG) test is done to:• Check for severe breathing problems and lung diseases,

such as asthma, cystic fibrosis, or chronic obstructive pulmonary disease (COPD).

• See how well treatment for lung diseases is working.• Find out if you need extra oxygen or help with

breathing (mechanical ventilation).• Find out if you are receiving the right amount of oxygen

when you are using oxygen in the hospital.• Measure the acid-base level in the blood of people who

have heart failure, kidney failure, uncontrolled diabetes, sleep disorders, severe infections, or after a drug overdose.

• Measurements • A sample of blood from an artery is usually taken from the inside of the wrist

(radial artery), but it can also be taken from an artery in the groin (femoral artery) or on the inside of the arm above the elbow crease (brachial artery).

• Pulse oximetry plus transcutaneous carbon dioxide measurement is an alternative method of obtaining measurement.

• Results• An arterial blood gas (ABG) test measures the acidity (pH) and levels of

oxygen and carbon dioxide in the blood.• NormalPartial pressure of oxygen

(PaO2):Greater than 80 mm

Hg (greater than 10.6 kPa)Partial pressure of carbon

dioxide (PaCO2): 35-45 mm Hg (4.6-5.9 kPa)

pH: 7.35-7.45

Bicarbonate (HCO3): 23-30 mEq/L (23-30 mmol/L)

Oxygen content (O2CT): 15-22 mL per 100 mL of blood (6.6-9.7 mmol/L)

Oxygen saturation (O2Sat): 95%-100% (0.95-1.00)