Spirometry will provide the following information:
- FVC (Forced Vital Capacity): The maximum amount of air that can be forcefully exhaled from a maximal inspiration.
- FEV1 (Forced Expiratory Volume 1sec): The volume of air forcefully expired in the first second of a forced vital capacity maneuver.
- FEV1/FVC%: The FEV1 compared to the FVC. This is expressed as a percentage.
- PEF (Peak Expiratory Flow): Maximal flow rate achieved during a forced maneuver. This can be expressed in liters per second or liters per minute. Small portable Peak Flow Meters are used for following asthmatics.
- FEF 25-75% (Forced Expiratory Flow 25-75%): Average flow rate during the middle half of a forced expiratory maneuver. This measures flow rates within the small airways.
Flow volume curve
A physician may want to evaluate a patient's upper airway; a Flow Volume Loop (FVL) is then requested. An FVL measurement includes all the above data plus measurements of a maximal inspiration. The patient performs an FVC and follows it with a maximal inspiration. This test can provide valuable data in a diagnosis or severity of tracheal stenosis or vocal cord disorder.
The UW Health Pulmonary Function Lab utilizes two methodologies for lung volumes. Plethysmography is the preferred method because it measures not only the ventilated area of the lung but also any trapped air in the lung. This methodology is more accurate in an individual with an obstructive disorder. Helium Dilution is the second method used when a subject is physically unable to get into the plethysmograph, is claustrophobic or has difficulty coordinating a VTG (Volume of Thoracic Gas) maneuver.
The below measurements are obtained when ordering Lung Volumes:
- SVC (Slow Vital Capacity/VC - Vital Capacity): Volume of gas measured from a maximal inspiration followed by a maximal expiration.
- IC (Inspiratory Capacity): Volume of air that can be inspired from resting end-expiration.
- ERV (Expiratory Reserve Volume): Volume of gas that can be expired from resting end- expiration.
- Vt (Tidal Volume): Normal resting breathing.
- IRV (Inspiratory Reserve Volume): Inspired volume of air from the top of resting breathing.
- VTG (Volume of Thoracic Gas) or FRC (Functional Residual Capacity): Volume of air remaining in the lungs from resting end-expiration. FRC He - measured by Helium Dilution, FRC pl - measured by plethysmography.
- RV (Residual Volume): Volume of air remaining in the lungs following maximal expiration.
- TLC (Total Lung Capacity): Total amount of air in the lungs from maximal inspiration.