PULMONARY FUNCTION TEST

PULMONARY FUNCTION TEST – (Abnormal Findings, Description, Calculation of Total Lung Capacity, Calculation of Vital Capacity, Age Related Changes, Client Preparation, Procedure, Gas Exchange/Diffusing Capacity of the Lung, Inhalation Tests (Bronchial Provocation Studies), Post-Procedural Tests and Contraindications

Pulmonary function test are done using a spirometer that measures the amount of air a patient can move in and out and how fast he or she can process it. The patient breathes into a mouthpiece and performs several different breathing maneuvers that are explained by the technician performing the test.

By measuring the patient’s airflow and comparing the results with predicted values for each patient’s height, weight, age, and gender, valuable information can be obtained concerning whether the patient has mild, moderate or severe obstructive or restrictive lung disease

ABNORMAL FINDINGS

• Pulmonary fibrosis
• Interstitial lung diseases
• Tumor
• Chest wall trauma
• Emphysema
• Chronic bronchitis
• Asthma
• Inhalant pneumonitis
• Postpneumonectomy
• Bronchiectasis
• Airway infection
• Pneumonia
• Neuromuscular disease
• Hypersensitivity bronchospasm

DESCRIPTION

Pulmonary function test (PFT) is performed in a pulmonary function laboratory. After preparing the client, a nose clip is applied and the unsedated client breathes into spirometer or body plethysmograph, a device for measuring and recording lung volume in liters versus time in seconds. The clients is instructed how to breathe for specific tests; for example, to inhale as deeply as possible and then exhale to the maximal extent possible. Using measured lung volumes, respiratory capacities are calculated to assess pulmonary status

CALCULATION OF TOTAL LUNG CAPACITY

The total lung capacity (TLC) is the total volume of the lung at their maximum inflation. The four values are used to calculate TLC

• Total volume (TV): the volume inhaled and exhaled with normal quite breathing (also called tidal volume)
• Inspiratory reserve volume (IRV): the maximum amount that can be inhaled over and above a normal inspiration
• Expiratory reserve volume (ERV): the maximum amount that can be exhaled following a normal inhalation
• Residual volume (RV): the amount of air remaining in the lungs after maximal exhalation

ABBREVIATIONS USED IN PULMONARY FUNCTION TEST

• FEV₁ – Forced expiratory volume in one second
• FVC – Forced vital capacity
• VC – Vital capacity (forced or relaxed)
• PEF – Peak (maximum) expiratory flow rate
• TLC – Total lung capacity
• FRC – Functional residual capacity
• RV – Residual volume
• TCO – Gas Transfer factor for carbon monoxide
• DCO – Diffusing capacity for carbon monoxide
• KCO – Transfer Coefficient for carbon monoxide (TCO/liter lung volume)

CALCULATION OF VITAL CAPACITY

Vital capacity (VC) is the total amount of air that can be exhaled after a maximal inspiration; it is calculated by adding together the IRV, TV and ERV

• Inspiratory capacity: it is the amount of the air can be inhaled following a normal quiet exhalation. It is calculated by adding the TV and IRV
• Functional residual capacity (FRC): it is the volume of air left in the lungs after a normal exhalation. The ERV and RV are added to determine
• Forced expiratory volume (FEV₁): it is the amount of air that can be expelled in 1 second
• Forced vital capacity (FVC): it is the amount of air that can be exhaled forcefully and rapid after maximum air intake
• Minute volume (MV) is the total amount or volume of air breathed in minute. In older clients, residual capacity is increased and vital capacity is decreased. These age-related changes result from the following

AGE RELATED CHANGES

• Calcification of the costal cartilage and weakening of the intercostals muscles, which reduce movement of the chest wall
• Vertebral osteoporosis, which spinal flexibility and increases the degree of kyphosis, further increasing the anterior posterior diameter of the chest
• Diaphragmatic flattening and loss of elasticity

CLIENT PREPARATION

• Explain the test to the client
• Inform the client that cooperation is necessary to obtain accurate results
• Instruct the client not to use bronchodilators or smoke for 6 hours after this test (if required by physician)
• Tell the client to withhold the use of small-dose meter inhalers and aroused therapy before this study
• Measure and record the client’s height and weight before this study to determine the predicted values
• List on the laboratory slip any medications the client is taking

PROCEDURE

Spirometry and Airflow Rates

• The unsedated client is taken to the pulmonary function laboratory
• The client breaths through a sterile mouthpiece and into a spirometer to measure and record the desired values
• The client is asked to inhale as deeply as possible. This is repeated several times (usually two to three times). The two best are used for calculations. This test may be repeated with bronchodilators if the client’s values are deficient
• From this, the machine computes FVC, FEV₁, FEV₁/FVC, PIFR, PEFR and MMEF
• The client is asked to breathe in and out as deeply and frequently as possible for 15 seconds. The total volume breathed is recorded and multiplied by 4 to obtain the MVV
• The client is asked to breathe in and out normally into the spirometer and then exhale forcibly from the end tidal volume expiration point. This provides measurement of ERV
• The client is asked to breathe in and out normally into the spirometer and then inhale forcibly from the end tidal volume expiration point. This provides measurement of IC
• The client is asked to breathe in and out maximally (but not forced). This is a measure of VC and the calculated TLC

GAS EXCHANGE/DIFFFUSING CAPACITY OF THE LUNG (D₁)

• The D₁ of CO is usually measured by having the client inhale a CO mixture
• D₁ CO is calculated with an analysis of the amount of CO exhaled compared with the amount inhaled. Some procedures require arterial blood gas to be performed at the same time as the gas exchange maneuvers

INHALATION TESTS (BRONCHIAL PROVOCATION STUDIES)

• These tests also may be performed during pulmonary function studies to establish a cause-and-effort relationship in some clients with inhalant allergies
• The methacholine or histamine challenge test is typically used to detect the presence of hyperactive airway diseases. This test would not be indicative for a client known to have asthma
• Care is taken during the challenge test in reverse any severe bronchospasm with prompt administration of an inhalant bronchodilator (e.g. isoproterernol)

POST-PROCEDURAL CARE

Note that clients with severe respiratory problems are occasionally exhausted after the testing and will need rest

CONTRAINDICATIONS

• Clients who are in pain because of the inability to cooperate by deep inspiration and expiration
• Clients who are unable to cooperate because of age or mental incapacity