pulmonary function tests(redirected from lung function)
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.
pulmonary function testsA 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.
Pulmonary Function Studies
Area of applicationLungs, respiratory system.
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 (FEF25–75), 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
- Patients with cardiac insufficiency, recent myocardial infarction, and presence of chest pain that affects inspiration or expiration ability.
- 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)
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)|
|MVV||25%–35% or 170 L/min|
|F-V loop||Normal curve|
|DCOL||25 mL/min per mm Hg (approximate)|
|CV||10%–20% of VC|
|Viso||Based on age formula|
|Bronchial provocation||No change, or less than 20% reduction in FEV1|
- Normal respiratory volume and capacities, gas diffusion, and distribution
- No evidence of COPD or restrictive pulmonary disease
Abnormal findings related to
- Chest trauma
- Chronic bronchitis
- Curvature of the spine
- Myasthenia gravis
- Pulmonary fibrosis
- Pulmonary tumors
- Respiratory infections
- 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
- 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.
- 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).
- 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 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.