Norm of Pulmonary Function Tests (PFT)
The observed values are reported as percentages of normal with use of prediction equations calculated according to age, height, sex, race, and weight. Results are considered abnormal if they are less than predicted 80% of the calculated values. For spirometry measurement, forced vital capacity, forced expiratory volumes, and peak expiratory flow rates are at predicted value for age, race, sex, and height.
Average Results for Adults
|Tidal volume (VT)||500 cc|
|Expiratory reserve volume (ERV)||1500 cc|
|Residual volume (RV)||1500 cc|
|Inspiratory reserve volume (IRV)||2000 cc|
|Diffusion capacity carbon monoxide||25 mL/min/mm Hg|
|Forced vital capacity (FVC)||>80% of predicted volume|
|Forced expiratory volume (FEV1)||>80% of predicted volume|
|Forced expiratory flow (FEF) 25–75||>50%|
Usage of Pulmonary Function Tests (PFT)
Diagnosis and monitor the progress of pulmonary dysfunction (asthma, bronchitis, bronchiolitis obliterans, emphysema, and myasthenia gravis); quantify the severity of known lung disease; evaluate the effectiveness of medications (bronchodilators); determination of whether a functional abnormality is obstructive or restrictive; identification of clients at high risk for postoperative pulmonary complications; evaluation of the risk of pulmonary resection; used in conjunction with a cardiopulmonary exercise stress test for evaluation of functional ability; serial measurements used to evaluate response to treatment in cardiopulmonary vascular disease.
|Total Lung Capacity (TLC) = (VT + ERV + RV + IRV)
(Total volume of lungs when maximally inflated is divided into four volumes)
|Overdistention of the lungs associated with obstructive disease||Restrictive disease|
|Tidal Volume (VT)
(Volume of air inhaled and exhaled in normal quiet breathing)
|May indicate bronchiolar obstruction with hyperinflation or emphysema||May indicate fatigue, restrictive parenchymal lung disease, atelectasis, cancer, edema, pulmonary congestion, pneumothorax or thoracic tumor; decreased VT necessitates further testing|
|Inspiratory Reserve Volume (IRV)
(Maximum volume that can be inhaled after a normal quiet inhalation)
|n/a||Decreased IRV as an isolated value does not indicate disease|
|Expiratory Reserve Volume (ERV)
(Maximum volume that can be exhaled after a normal quiet exhalation)
|n/a||May occur with obesity, pregnancy, or thoracoplasty|
|Residual Volume (RV)
(Volume remaining in lungs after maximal exhalation)
|Increased RV above 35% of the TLC indicates obstructive disease; RV is also increased with aging||n/a|
|Forced Expiratory Volume (FEV)
(Volume expired during specified time intervals [0.5 and 1 second])
|Restrictive disease||Decreased FEV1 after administration of beta-blockers may indicate presence of bronchospasm and contraindicate continued use of specific pharmacologic therapy involved|
|Forced Expiratory Volume 1 (FEV1)
(Air volume forcefully exhaled in 1 second)
|Restrictive disease||Decreased FEV1 as percentage of vital capacity (FEV1/FVC) indicates obstructive disease:
65%–80% of predicted = mild disease
50%–65% of predicted = moderate disease
<50% of predicted = severe disease
|Functional Residual Capacity (FRC) = (ERV + RV)
(Amount of volume in lungs after normal exhalation)
|Overdistention of lungs associated with chronic obstructive pulmonary disease
|Acute respiratory distress syndrome (ARDS)
Restrictive diseases and mixed obstructive and restrictive diseases
|Inspiratory Capacity (IC) = (IRV + VT)
(Maximum volume that can be inhaled after a normal quiet exhalation; useful in evaluating timeliness of weaning from mechanical ventilation)
|Vital Capacity (VC) = (IRV + VT + ERV)
(Total volume that can be exhaled after maximum inspiration)
|Increased or normal VC and FVC with decreased flow rates indicates obstructive defect (airway diseases)||Decreased VC with normal or increased flow rates indicates restrictive defect (diaphragmatic impairment, drug overdose, head injury, limited thoracic expansion, and neuromuscular disease)|
|Forced Vital Capacity (FVC) (Total volume exhaled forcefully and rapidly after maximum inhalation)||Increased or normal VC and FVC with decreased rates indicates obstructive defect (airway diseases)||With concurrent heart disease, may indicate pulmonary congestion, pleural effusion, cardiomegaly, or muscular weakness|
|Thoracic Gas Volume (TGV)
(Total volume of lungs, including nonventilated and ventilated airways)
|Indicates air trapping caused by obstructive disease and requires special equipment to monitor||n/a|
|Minute Volume (MV) = (Respiratory Rate × VT)
(Total amount of gas breathed during 1 minute)
Metabolic or respiratory acidosis
PEEP causing increased intrathoracic pressure
Pulmonary parenchymal disease
|Maximum Voluntary Ventilation (MVV)
(Maximum volume of gas breathed during rapid, forced breathing in 1 minute under testing conditions)
|Maximum Breathing Capacity (MBC)
(Largest volume of air that can be inhaled and exhaled in 1 minute)
|Peak Expiratory Flow Rate (PEFR)
(Peak flow rate during expiration)
(Ratio of FEV1 to FVC, expressed as a percentage)
|n/a||Obstructive airway disease Obstruction|
|Forced Expiratory Flow (FEF 25–75)
(Average forced expiratory flow during midportion [25%–75%] of forced vital capacity; useful in clients with small airways, such as children)
|n/a||Obstructive airway disease|
Description of Pulmonary Function Tests (PFT)
Pulmonary function tests (PFTs) are several different tests used to evaluate lung mechanics, gas exchange, and acid-base impairment through spirometric measurements, lung volumes, and arterial blood gases. Spirometry testing is included in pulmonary function testing. A spirometer is an instrument that measures lung capacity, volume, and flow rates. The instrument consists of a bell suspended in a container of water. The bell rises and falls in response to the client's breathing. The movement of the bell is recorded on a kymograph or electrical potentiometer. The pattern of the air flow on the graph must be interpreted to identify artifact and abnormalities, such as cough and upper airway obstruction. Full PFTs include measuring the amount of air that can be maximally exhaled after a maximum inspiration and the time required for that expiration and determining the ability of the alveolar capillary membrane to transport oxygen into the blood and carbon dioxide from the blood into the expired air.
Professional Considerations of Pulmonary Function Tests (PFT)
Consent form NOT required.
Pneumothorax, increased intracranial or intraocular pressure, syncope, dizziness, chest pain, paroxysmal coughing, bronchospasm, oxygen desaturation, hypertension, strain on recent abdominal or thoracic incisions, aneurysm rupture.
Relative contraindications include hemoptysis of unknown origin, pneumothorax, unstable cardiovascular status, recent cardiac event or pulmonary embolus, recent eye surgery, concurrent nausea or vomiting, recent thoracic or abdominal surgery, or thoracic, abdominal, or cerebral aneurysm.
- Assess medication record for recent analgesic that may depress respiratory function.
- Bronchodilators and intermittent positive-pressure breathing therapy may be withheld before the tests.
- The client should void and then loosen any restrictive clothing.
- Record the client's age, sex, and race on the test requisition.
- Carefully measure and record weight and height.
- Assess baseline vital signs.
- See Client and Family Teaching.
- Position the client sitting with both feet flat on the floor or standing with something to lean on and a chair behind him or her for use if dizziness occurs.
- Connect the mouthpiece to the spirometer (even in the handled version) and place mouthpiece in the client's mouth.
- Place the clip over the nose so that only breathing through the mouth is possible.
- Instruct the client to breathe through a mouthpiece. Up to eight efforts per measurement period may be needed to obtain results that are reproducible three times.
- Criteria for acceptable test:
- a. Extrapolated volume of 95% of the FVC or 150 cc, whichever is greater.
- b. No false starts.
- c. Rapid start-to-rise time.
- d. No cough.
- e. Exhalation time of at least 6 seconds.
- f. The two largest FEV and FEV1 values vary by no more than 0.200 L.
- g. MVV 12–15 seconds.
- The two highest MVVs are within 10% of each other.
- If the test is ordered to include a bronchodilator, administer bronchodilator and wait 15 minutes before repeating the procedure.
- Assess vital signs every 5 minutes until they return to baseline values.
- Resume normal diet and any bronchodilators or intermittent positive-pressure breathing therapy.
- Results are normally available within 30 minutes. Consideration of client's clinical condition is necessary when one is interpreting results.
- Flush out air at least 5 times in a volume-displacement spirometer to reduce risk of airborne spread of infection to future clients.
- Dispose of or disinfect any portions of the test equipment that come into contact with the client.
Client and Family Teaching
- Withhold short-acting bronchodilator medication for 5 hours before the test or as ordered by physician. Long-acting bronchodilators will be withheld for a longer period of time. If you experience difficult breathing, you should use your bronchodilator.
- Refrain from smoking or eating a heavy meal for 4–6 hours.
- Dentures should not be removed.
- Take a maximal inhalation, hold it, and then maximally and forcibly exhale. A modified technique with an initial forced exhalation followed by a relaxed exhalation continued for as long as possible may be used.
- After a short rest period, the procedure is repeated two more times.
- The procedure takes about 20 minutes.
Factors That Affect Results
- The client's ability to voluntarily and actively participate is essential to complete the indicated tests.
- An inadequate seal around the mouthpiece invalidates the results.
- An ineffective nose clip causes unreliable results.
- Gastric distention, hypoxia, metabolic impairments, narcotic analgesia, pregnancy, and sedatives may alter the results. Fatigue as a result of repeated efforts may also alter the results.
- Daily monitoring and calibration are required to ensure accuracy and reproducibility of spirometry results.
- In one study, obstruction of PFTs included use of tobacco, history of hay fever age, and male sex.
- Bronchodilators administered before the tests may obscure true pulmonary function.
- Herbs or natural remedy effects: In one study, people who received 200 mg of ginseng twice each day for 3 months demonstrated improved FVC, FEV1, and PEFR as well as arterial blood oxygen levels and walking distance.
- Pulmonary function tests are normally performed in a pulmonary laboratory.
- See also Lung scan, Perfusion and ventilation; Diffusing capacity for carbon monoxide (DLCO, transfer factor).