Pulmonary Function Studies

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.