What is a Pulmonary Function Test?

Pulmonary function tests are one of the necessary tests for respiratory diseases. It is mainly used to detect the patency of the airways and the size of lung capacity. For early detection of lung and airway lesions, assess the severity and prognosis of the disease, assess the efficacy of drugs or other treatment methods, identify the cause of dyspnea, and diagnose lesions Sites, assessment of lung function tolerance to surgery or labor intensity tolerance, and monitoring of critically ill patients have important clinical value.

Basic Information

Chinese name

Pulmonary function tests

Clinical significance

Early detection of lung and respiratory disease

Clinical significance of pulmonary function test

1. Early detection of lung and respiratory diseases such as chronic bronchitis, emphysema, bronchial asthma, and interstitial lung disease.
2. Identify the cause of dyspnea and determine the location of airway obstruction.
3. Assess the severity of the lung disease. .
4. Assess tolerance for surgery (especially chest surgery) and the possibility of complications after surgery.
5. People with long-term smoking should also have regular lung function tests to observe the situation of impaired lung function and urge patients to make up their mind to quit smoking.
6. Monitoring of critical patients.
7. It helps to determine the severity of COPD and to formulate a corresponding treatment plan based on the severity of the disease.

Pulmonary function check items

(I) Lung Volume Function 1. Tidal Volume (VT)
(1) Concept: The amount of air in and out of the lungs for a calm breath.
(2) Clinical significance: It is mainly respiratory muscle function that affects tidal volume.
(3) Reference value: about 500 ml for adults.
2. Respiratory Volume (ERV) and Inspiratory Volume (IRV)
(1) Concept: The volume of supplemental exhalation is the maximum volume that can be exhaled at the end of calm exhalation, and the volume of inspiratory volume is the maximum volume that can be inhaled after calm inhalation.
(2) Clinical significance: When the function of inspiratory muscles and expiratory muscles is weakened, the volume of supplemental expiratory volume and the volume of inspiratory volume are decreased.
(3) Reference value: Compensatory expiratory volume: 1603 ± 492mL for males and 1126 ± 338mL for females.
Inspiratory volume: 2160mL for men and 1400mL for women.
3. Deep Inspiratory Capacity (IC)
(1) Concept: The maximum amount of air that can be inhaled for the quiet end of breath.
(2) Clinical significance: The main factor affecting the inspiratory volume is inspiratory muscle strength. Factors such as reduced thoracic and lung activity, increased elastic retraction of the lung tissue, and airway obstruction can also reduce deep inspiration.
(3) Reference value: 2617 ± 548mL for males and 1970 ± 381mL for females.
4. Vital Capacity (VC)
(1) Concept: The vital capacity is the maximum amount of air that can be exhaled after the maximum inhalation.
(2) Clinical significance: The decrease in vital capacity is mainly seen in various restrictive ventilation disorders, followed by respiratory muscle dysfunction; airway obstruction also has a slight effect on vital capacity.
(3) Reference value: 4217 ± 690mL, female 3105 ± 452mL; measured / predicted value <80% is abnormal, 60% to 79% is slightly reduced, 40% to 59% is moderately reduced, 40% is severe reduce.
5. Functional residual gas volume (FRC) and residual gas volume (RV)
(1) Concept: Functional residual capacity refers to the amount of air remaining in the lungs after calm exhalation, and residual capacity refers to the amount of air remaining in the lungs after maximum exhalation.
(2) Clinical significance: increase, suggesting hyperinflation in the lungs, seen in obstructive emphysema and partial obstruction of the airways; decrease, seen in diffuse restrictive lung disease and acute respiratory distress syndrome.
(3) Reference value: FRC: male 3112 ± 611mL, female 2348 ± 479mL
RV: 1625 ± 397mL for men, 1245 ± 336mL for women
6. Total lung (TLC)
(1) Concept: the full amount of air contained in the lungs after deep inhalation. It is the sum of vital capacity and residual gas volume.
(2) Clinical significance: TLC increases, mainly seen in obstructive emphysema; TLC decreases, seen in restrictive lung disease.
(3) Reference value: 5766 ± 782mL for males and 4353 ± 644mL for females.
(B) Pulmonary ventilation function 1. Pulmonary ventilation (1) Concept: Pulmonary ventilation includes resting minute ventilation (VE) and maximum ventilation (MVV) per minute.
(2) Clinical significance: Reduced MVV is seen in airway obstruction and reduced lung tissue elasticity; decreased respiratory muscle strength and respiratory insufficiency; thoracic, pleural, diffuse interstitial disease and large-scale pulmonary parenchymal disease
(3) Reference value: 104 ± 2.71L / min for males; 82.5 ± 2.17L / min for females, an abnormality below 80%.
2. Forced vital capacity (FVC)
(1) Concept: refers to the total amount of air that can be exhaled at the maximum force and speed after inhaling deeply to the total lung volume. The commonly used clinical indicators are the forced expiratory volume in one second (FEV1.0) and the ratio of forced expiratory volume in one second to forced vital capacity (FEV1.0 / FVC%).
(2) Clinical significance: Obstructive ventilation disorder: FEV1.0 / FVC% decreased; Restrictive ventilation disorder: FEV1.0 / FVC% increased.
(3) Reference value: FEV1.0: 3197 ± 117mL / s for males, 2314 ± 48mL / s for females; FEV1.0 / FVC%:> 80%.
3. Maximum expiratory volume (MMEF or MMF)
(1) Concept: It is the average flow rate of 25% and 75% of forced expiratory vital capacity calculated from the FVC curve.
(2) Clinical significance: MMF decreases the response to increase in small airway resistance.
(3) Reference value: 3452 ± 1160mL / s for males and 2836 ± 946mL / s for females.