Pulmonary Function Test

Tidal Volume (TV)

Amount of air in or out during quiet breathing (500mL)

Inspiratory reserve volume (IRV)

The maximum amount of air that can be inhaled after a normal tidal inhalation (3000mL)

Expiratory reserve volume (ERV)

The maximum amount of air that can be exhaled after a normal tidal exhalation (1200mL)

Residual Volume (RV)

The amount of air that remains in the lungs after forced exhalation, typically around 1200 mL.

Total Lung Capacity (TLC)

• The total volume of air contained in the lungs after maximum inhalation, typically around 6000 mL.

• VT+IRV+ERV+RV

• 120% of predictive value or higher is called hyperinflation (Obstructive)

• 80% or less is seen in Restrictive Lung disease, such as pulmonary fibrosis, atelectasis

Inspiratory Capacity (IC)

Maximum amount of air that can be inspired following normal, quiet expiration. (i.e. patient inhales maximally at the end of normal expiration)

Functional Residual Capacity (FRC)

• Volume of air remaining in the lungs at the end of normal, quiet expiration (ERV+RV)

• Normal range is 80-120%, increase in FRC represents hyperinflation of the lungs (obstructive)

Vital Capacity (VC)

Maximum amount of air that can be exhaled by forceful effort after a maximum inspiration, done slowly

Forced Vital Capacity

• Maximum volume of air the patient can exhale as forcefully and as quickly as possible

• Reduced in both obstructive and restrictive diseases

Forced expiratory volume in one second (FEV1)

• Volume of air that is exhaled during the first second of the FVC and reflects the airflow in the large airways

• FEV1/FVC = Normal is 70-80%

• FEV1/FVC = below 70% in obstructive diseases

• FEV1/FVC = normal or above 80% in restrictive diseases

Forced mid-expiratory flow (25%-75%)

• Flow rate found in the middle portion of the FVC curve (flow volume loop

• Marker for small airways obstruction, maybe the first to show in presence of disease

• normal is 4L/sec

• In obstructive lung disease: there is scooping of the curve

Maximum Inspiratory Pressure (MIP)

• Measure of the Inspiratory muscle strength and therefore has a close relationship with diaphragmatic strength

• Individuals are asked to perform a forceful inspiration after a complete expiration

• Normal values

  • Males: -80 cmH2O

  • Females: -70 cm H2O

Maximum Expiratory Pressure (MEP)

• Measure of strength of the abdominal and internal intercostal muscles which produce forced expiration

• Individuals are asked to perform forceful expiration after maximum inspiration

  Normal values

  • Males: +130 cmH2O

  • Females: +100 cm H2O

Maximum Voluntary Ventilation (MVV)

• Measures the maximum breath capacity of the patient (Endurance of the diaphragm)

• Patient is asked to breath as hard and fast as possible for 12 seconds (V is recorded and multiplied by 5 to convert the findings to L/minute)

• MVV = FEV1 × 35

Diffusion Capacity of the lungs for carbon monoxide (DLCO)

• A measure of the lungs' ability to transfer gas from inhaled air to the bloodstream, specifically assessing how well carbon monoxide can move across the alveolar-capillary membrane.

• Normal DLCO is between 80-120%

• Patients with COPD who is most likely to become hypoxic during exercise have DLCO values of less than 55% of the predicted

Severity of Obstruction (GOLD criteria for COPD)

• FEV 1: 80-100% predicted: Mild (Stage I)

• FEV 1: 50-80% predicted: Moderate(Stage II)

• FEV 1: 30-50% predicted: Severe (Stage III)

• FEV 1: <30% predicted: Very severe (Stage IV)