pulmonary function tests

pulmonary

[pul´mo-ner″e] 1. pertaining to the lungs" >lungs; called also pulmonic and pneumonic.2. pertaining to the pulmonary artery.pulmonary acid aspiration syndrome a disorder produced as a complication of inhalation of gastric contents; it may progress to a syndrome resembling acute respiratory distress syndrome.pulmonary alveolar proteinosis a disease of unknown etiology marked by chronic filling of the alveoli with a proteinaceous, lipid-rich, granular material consisting of surfactant and the debris of necrotic cells. Some patients have a history of exposure to irritating dusts or fumes. The condition is treated by whole lung lavage with balanced salt solution; most patients need repeated lavage.pulmonary artery the large artery originating from the superior surface of the right ventricle of the heart and carrying deoxygenated blood to the lungs for oxygenation; it starts as the pulmonary trunk, which divides between the fifth and sixth thoracic vertebrae to form the right pulmonary artery that enters the right lung and the left pulmonary artery that enters the left lung. See Appendix 3-1.pulmonary circulation the circulation of blood to and from the lungs. Unoxygenated blood from the right ventricle flows through the right and left pulmonary arteries to the right and left lungs. After entering the lungs, the branches subdivide, finally emerging as capillaries which surround the alveoli and release the carbon dioxide in exchange for a fresh supply of oxygen. The capillaries unite gradually and assume the characteristics of veins. These veins join to form the pulmonary veins, which return the oxygenated blood to the left atrium. See also circulatory system.pulmonary function tests tests used to evaluate lung mechanics, gas exchange, pulmonary blood flow, and blood gases and pH. They are used to evaluate patients in the diagnosis of pulmonary disease, assessment of disease development, or evaluation of the risk of pulmonary complications from surgery.Lung Volumes and Capacities. The total lung capacity (TLC) is divided into four volumes. The tidal volume (V_T) is the volume inhaled or exhaled in normal quiet breathing. The inspiratory reserve volume (IRV) is the maximum volume that can be inhaled following a normal quiet inhalation. The expiratory reserve volume (ERV) is the maximum volume that can be exhaled following a normal quiet exhalation. The residual volume (RV) is the volume remaining in the lungs following a maximal exhalation. The vital capacity (VC) is the maximum volume that can be exhaled following a maximal inhalation; VC = IRV + V_T + ERV. The inspiratory capacity (IC) is the maximum volume that can be inhaled following a normal quiet exhalation; IC = IRV + V_T. The functional residual capacity (FRC) is the volume remaining in the lungs following a normal quiet exhalation; FRC = ERV + RV.
The vital capacity and its components are measured using a spirometer, which measures the volumes of air inhaled and exhaled. The functional residual capacity is usually measured by the helium dilution method using a closed spirometry system. A known amount of helium is introduced into the system at the end of a normal quiet exhalation. When the helium equilibrates throughout the volume of the system, which is equal to the FRC plus the volume of the spirometer and tubing, the FRC is determined from the helium concentration. This test may underestimate the FRC of patients with emphysema. The FRC can be determined quickly and more accurately by body plethysmography. The residual volume and total lung capacity are determined from the functional reserve capacity.Forced Vital Capacity (FVC). In the forced vital capacity maneuver, the patient exhales as forcefully and rapidly as possible, beginning at maximal exhalation. Several parameters are determined from the spirogram. The forced vital capacity is the total volume of air exhaled during the maneuver; it is normally equal to the vital capacity. The forced expiratory volume (FEV) is the volume expired during a specified time period from the beginning of the test. The times used are 0.5, 1, 2, and 3 seconds; corresponding parameters are FEV_0.5, FEV_1.0, FEV_2.0, and FEV_3.0. The maximal expiratory flow is the slope of the line connecting the points where 200 ml and 1200 ml have been exhaled; it is also called FEF_200–1200 (forced expiratory flow). The maximal midexpiratory flow is the slope of the line connecting the points where 25 per cent and 75 per cent of the forced vital capacity have been exhaled; it is also called FEF_25–75%.Maximal Voluntary Ventilation (MVV). This is the maximal volume of air that can be breathed by the patient, expressed in liters per minute; it was formerly called maximal breathing capacity. The patient breathes as rapidly and deeply as possible for 12 to 15 seconds and the volume exhaled is determined by spirometry.Predicted Values. Because the results of pulmonary function tests vary with size and age, the normal values are calculated using prediction equations or nomograms, which give the normal value for a specific age, height, and sex. The prediction equations are derived using linear regression on the data from a population of normal subjects. The observed values are usually reported as a percentage of the predicted value.Interpretation. These tests provide evidence of impairment of ventilatory function; they do not point to specific disease processes. Abnormal test results may show either an obstructive or a restrictive pattern; sometimes both are present.The Obstructive Pattern. This pattern occurs when there is airway obstruction from any cause, as in asthma, bronchitis, emphysema, or advanced bronchiectasis; these conditions are grouped together in the nonspecific term chronic obstructive pulmonary disease. In this pattern, the residual volume is increased and the PV/TLC ratio is markedly increased. Owing to increased airway resistance, the flow rates are decreased. The FEV/FVC ratios, maximal midexpiratory flow, and maximal expiratory flow are all decreased; FEV_1.0/FVC is less than 75 per cent.The Restrictive Pattern. This pattern occurs when there is a loss of lung tissue or when lung expansion is limited as a result of decreased compliance of the lung or thorax or of muscular weakness. This pattern occurs in conditions such as pectus excavatum, myasthenia gravis, diffuse idiopathic interstitial fibrosis, and space-occupying lesions (tumors, effusions). The vital capacity and forced vital capacity are less than 80 per cent of the predicted value, but the FEV/FVC ratios are normal. The total lung capacity is decreased and the RV/TLC ratio is normal.pulmonary vein any of the four large veins (two right and two left branches) that carry oxygenated blood from the lungs to the left atrium of the heart. See anatomic Table of Veins in the Appendices.

pulmonary function tests

A range of tests of the efficiency of the lungs and of diagnostic procedures to detect lung disease. They include tests of chest expansion, air lung volume, the maximum volume of air that can be expired (vital capacity), the peak air flow rate achievable (see PEAK FLOW METER) and tests of blood concentrations of oxygen and carbon dioxide.

Figure 1 Examples of PFT results presented in graphic form.

Figure 2 showing lung volumes measured during PFT.

Pulmonary Function Studies

Synonym/acronym: Pulmonary function tests (PFTs).

Common use

To assess respiratory function to assist in evaluating obstructive versus restrictive lung disease and to monitor and assess the effectiveness of therapeutic interventions.

Area of application

Lungs, respiratory system.

Contrast

None.

Description

Pulmonary function studies provide information about the volume, pattern, and rates of airflow involved in respiratory function. These studies may also include tests involving the diffusing capabilities of the lungs (i.e., volume of gases diffusing across a membrane). A complete pulmonary function study includes the determination of all lung volumes, spirometry, diffusing capacity, maximum voluntary ventilation, flow-volume loop, and maximum expiratory and inspiratory pressures (See Figure 1 showing lung volumes measured during PFT). Other studies include small airway volumes.

Pulmonary function studies are classified according to lung volumes and capacities, rates of flow, and gas exchange. The exception is the diffusion test, which records the movement of a gas during inspiration and expiration. Lung volumes and capacities constitute the amount of air inhaled or exhaled from the lungs; this value is compared to normal reference values specific for the patient’s age, height, and gender. The following are volumes and capacities measured by spirometry that do not require timed testing.

Tidal Volume	TV	Total amount of air inhaled and exhaled with one breath
Residual Volume	RV	Amount of air remaining in the lungs after a maximum expiration effort; this indirect type of measurement can be done by body plethysmography (see monograph titled “Plethysmography”)
Inspiratory reserve volume	IRV	Maximum amount of air inhaled at the point of maximum expiration
Expiratory reserve volume	ERV	Maximum amount of air exhaled after a resting expiration; can be calculated by the vital capacity (VC) minus the inspiratory capacity (IC)
Vital capacity	VC	Maximum amount of air exhaled after a maximum inspiration (can be calculated by adding the IC and the ERV)
Total lung capacity	TLC	Total amount of air that the lungs can hold after maximum inspiration; can be calculated by adding the vital capacity (VC) and the residual volume (RV)
Inspiratory capacity	IC	Maximum amount of air inspired after normal expiration; can be calculated by adding the inspiratory reserve volume (IRV) and the tidal volume (TV)
Functional residual capacity	FRC	Volume of air that remains in the lungs after normal expiration can be calculated by adding the residual volume (RV) and expiratory reserve volume (ERV)

The volumes, capacities, and rates of flow measured by spirometry that do require timed testing include the following:

Forced vital capacity in 1 sec	FEV1	Maximum amount of air that can be forcefully exhaled after a full inspiration
Forced expiratory volume	FEV	Amount of air exhaled in the first second (can also be determined at 2 or 3 sec) of forced vital capacity (FVC), which is the amount of air exhaled in seconds, expressed as a percentage
Maximal midexpiratory flow	MMEF	Also known as forced expiratory flow rate (FEF_25–75), or the maximal rate of airflow during a forced expiration
Forced inspiratory flow rate	FIF	Volume inspired from the RV at a point of measurement (can be expressed as a percentage to identify the corresponding volume pressure and inspired volume)
Peak inspiratory flow rate	PIFR	Maximum airflow during a forced maximal inspiration
Peak expiratory flow rate	PEFR	Maximum airflow expired during FVC
Flow-volume loops	F-V	Flows and volumes recorded during forced expiratory volume and forced inspiratory VC procedures
Maximal inspiratory-expiratory pressures		Strengths of the respiratory muscles in neuromuscular disorders
Maximal voluntary ventilation	MVV	Maximal volume of air inspired and expired in 1 min (may be done for shorter periods and multiplied to equal 1 min)

Other studies for gas-exchange capacity, small airway abnormalities, and allergic responses in hyperactive airway disorders can be performed during the conventional pulmonary function study. These include the following:

Diffusing capacity of the lungs	DL	Rate of transfer of carbon monoxide through the alveolar and capillary membrane in 1 min
Closing volume	CV	Measure of the closure of small airways in the lower alveoli by monitoring volume and percentage of alveolar nitrogen after inhalation of 100% oxygen
Isoflow volume	isoV	Flow-volume loop test followed by inhalation of a mixture of helium and oxygen to determine small airway disease
Body plethysmography		Measure of thoracic gas volume and airway resistance
Bronchial provocation		Quantification of airway response after inhalation of methacholine
Arterial blood gases	ABGs	Measure of oxygen, pH, and carbon dioxide in arterial blood

Values are expressed in units of mL, %, L, L/sec, and L/min, depending on the test performed.

Note: See figure 1 showing some examples of PFT results presented in graphic form; the graphs assist in interpreting the findings and establishing the diagnosis of respiratory conditions.

This procedure is contraindicated for

high alertPatients with cardiac insufficiency, recent myocardial infarction, and presence of chest pain that affects inspiration or expiration ability.

Indications

Detect chronic obstructive pulmonary disease (COPD) and/or restrictive pulmonary diseases that affect the chest wall (e.g., neuromuscular disorders, kyphosis, scoliosis) and lungs, as evidenced by abnormal airflows and volumes
Determine airway response to inhalants in patients with an airway-reactive disorder
Determine the diffusing capacity of the lungs (DCOL)
Determine the effectiveness of therapy regimens, such as bronchodilators, for pulmonary disorders
Determine the presence of lung disease when other studies, such as x-rays, do not provide a definitive diagnosis, or determine the progression and severity of known COPD and restrictive pulmonary disease
Evaluate the cause of dyspnea occurring with or without exercise
Evaluate lung compliance to determine changes in elasticity, as evidenced by changes in lung volumes (decreased in restrictive pulmonary disease, increased in COPD and in elderly patients)
Evaluate pulmonary disability for legal or insurance claims
Evaluate pulmonary function after surgical pneumonectomy, lobectomy, or segmental lobectomy
Evaluate the respiratory system to determine the patient’s ability to tolerate procedures such as surgery or diagnostic studies
Screen high-risk populations for early detection of pulmonary conditions (e.g., patients with exposure to occupational or environmental hazards, smokers, patients with a hereditary predisposition)

Potential diagnosis

Normal adult lung volumes, capacities, and flow rates are as follows:

TV	500 mL at rest
RV	1,200 mL (approximate)
IRV	3,000 mL (approximate)
ERV	1,100 mL (approximate)
VC	4,600 mL (approximate)
TLC	5,800 mL (approximate)
IC	3,500 mL (approximate)
FRC	2,300 mL (approximate)
FVC	3,000–5,000 mL (approximate)
FEV₁/FVC	81%–83%
MMEF	25%–75%
FIF	25%–75%
MVV	25%–35% or 170 L/min
PIFR	300 L/min
PEFR	450 L/min
F-V loop	Normal curve
DCOL	25 mL/min per mm Hg (approximate)
CV	10%–20% of VC
V_iso	Based on age formula
Bronchial provocation	No change, or less than 20% reduction in FEV₁

Note: Normal values listed are estimated values for adults. Actual pediatric and adult values are based on age, height, and gender. These normal values are included on the patient’s pulmonary function laboratory report.CV = closing volume; DCOL = diffusing capacity of the lungs; ERV = expiratory reserve volume; FEV₁ = forced expiratory volume in 1 sec; FIF = forced inspiratory flow rate; FRC = functional residual capacity; FVC = forced vital capacity in 1 second; F-V loop = flow-volume loop; IC = inspiratory capacity; IRV = inspiratory reserve volume; MMEF = maximal midexpiratory flow (also known as FEF_25–75); MVV = maximal voluntary ventilation; PEFR = peak expiratory flow rate; PIFR = peak inspiratory flow rate; RV = residual volume; TLC = total lung capacity; TV = tidal volume; VC = vital capacity; V_iso = isoflow volume. (See figure 2)

Normal findings

Normal respiratory volume and capacities, gas diffusion, and distribution
No evidence of COPD or restrictive pulmonary disease

Abnormal findings related to

Allergy
Asbestosis
Asthma
Bronchiectasis
Chest trauma
Chronic bronchitis
Curvature of the spine
Emphysema
Myasthenia gravis
Obesity
Pulmonary fibrosis
Pulmonary tumors
Respiratory infections
Sarcoidosis

Critical findings

N/A

Interfering factors

The aging process can cause decreased values (FVC, DCOL) depending on the study done.
Inability of the patient to put forth the necessary breathing effort affects the results.
Medications such as bronchodilators can affect results.
Improper placement of the nose clamp or mouthpiece that allows for leakage can affect volume results.
Confusion or inability to understand instructions or cooperate during the study can cause inaccurate results.
Exercise caution with patients who have upper respiratory infections, such as a cold or acute bronchitis.

Nursing Implications and Procedure

Pretest

Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
Patient Teaching: Inform the patient this procedure can assist in assessing lung function.
Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
Obtain a history of the patient’s cardiovascular and respiratory systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
Review the procedure with the patient. Address concerns about pain related to the procedure and explain that no discomfort will be experienced during the test. Explain that the procedure is generally performed in a specially equipped room or in a health-care provider’s (HCP’s) office by an HCP specializing in this procedure and usually lasts 1 hr.
Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
Record the patient’s height and weight.
Instruct the patient to avoid bronchodilators (oral or inhalant) for at least 4 hr before the study, as directed by the HCP.
Instruct the patient to refrain from smoking tobacco or eating a heavy meal for 4 to 6 hr prior to the study. Protocols may vary among facilities.

Intratest

Potential complications: N/A
Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
Ensure the patient has complied with dietary and medication restrictions and pretesting preparations.
Obtain an inhalant bronchodilator to treat any bronchospasms that may occur with testing.
Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
Instruct the patient to void and to loosen any restrictive clothing.
Instruct the patient to cooperate fully and to follow directions.
Place the patient in a sitting position on a chair near the spirometry equipment.
Place a soft clip on the patient’s nose to restrict nose breathing, and instruct the patient to breathe through the mouth.
Place a mouthpiece in the mouth and instruct the patient to close his or her lips around it to form a seal.
Tubing from the mouthpiece attaches to a cylinder that is connected to a computer that measures, records, and calculates the values for the tests done.
Instruct the patient to inhale deeply and then to quickly exhale as much air as possible into the mouthpiece.
Additional breathing maneuvers are performed on inspiration and expiration (normal, forced, and breath-holding).

Post-Test

Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
Assess the patient for dizziness or weakness after the testing.
Allow the patient to rest as long as needed to recover.
Instruct the patient to resume usual diet and medications, as directed by the HCP. Inform the patient of smoking cessation programs as appropriate.
Recognize anxiety related to test results, and be supportive of perceived loss of independent function. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

Related tests include α₁-AT, anion gap, arterial/alveolar oxygen ratio, biopsy lung, blood gases, bronchoscopy, carboxyhemoglobin, chest x-ray, chloride sweat, CBC, CBC hemoglobin, CBC WBC count and differential, CT angiography, CT thoracic, culture and smear for mycobacteria, culture bacterial sputum, culture viral, cytology sputum, echocardiography, ECG, Gram stain, IgE, lactic acid, lung perfusion scan, lung ventilation scan, MR angiography, MRI chest, osmolality, phosphorus, plethysmography, pleural fluid analysis, potassium, PET chest, pulse oximetry, sodium, and TB skin test.
Refer to the Cardiovascular and Respiratory systems tables at the end of the book for related tests by body system.