From the Guidelines
Timed vital capacity (TVC) is not a standard term in pulmonary function testing, but it can be considered as the volume of air a person can exhale in a specific time period, typically measured as forced vital capacity (FVC) or forced expiratory volume in one second (FEV1) 1.
Definition and Measurement
Timed vital capacity is essentially a measure of the volume of air that can be exhaled from the lungs after a maximal inhalation, and it is typically measured using spirometry. The most common parameters measured are FEV1 and FVC, which are used to diagnose and monitor respiratory conditions such as asthma, COPD, and restrictive lung diseases.
- The FEV1/FVC ratio is particularly valuable in diagnosing obstructive lung disease, with values below 70% suggesting airflow obstruction 1.
- The test is non-invasive, relatively quick to perform, and provides immediate results that guide clinical decision-making in respiratory medicine.
Clinical Significance
The measurement of timed vital capacity, or more specifically, FVC and FEV1, is crucial for assessing disease severity, monitoring progression, and evaluating response to treatments such as bronchodilators or anti-inflammatory medications.
- The GOLD 2025 report recommends using pre-BD spirometry to rule out COPD and post-BD measurements to confirm the diagnosis, which can help reduce clinical workload and limit COPD overdiagnosis 1.
- The use of post-BD values ensures that volume responders are not overlooked and provides a more accurate diagnosis of COPD.
Diagnostic Criteria
The diagnostic criteria for COPD using spirometry are based on the FEV1/FVC ratio, with a threshold value of <0.7 indicating airflow obstruction.
- The GOLD 2025 report recommends that the presence or absence of airflow obstruction should be confirmed by repeat spirometry on a separate occasion if the post-BD FEV/FVC ratio is between 0.60 and 0.80 1.
- The ATS/ERS technical statement on the standardisation of spirometry contains a grading system for the quality of the test session, which can help provide a level of confidence that the results represent the best performance of the individual 1.
From the Research
Definition and Measurement of Timed Vital Capacity (TVC)
- The timed vital capacity (TVC) is not explicitly defined in the provided studies, but we can infer information about vital capacity and its relation to other pulmonary function measurements.
- Vital capacity (VC) is mentioned as one of the spirometric measurements of highest clinical value, along with forced expiratory volume in one second (FEV1) 2.
- Forced vital capacity (FVC) is defined as the volume of air that can be forcibly exhaled after a maximal inspiration 3, 4, 5.
Relation to Other Pulmonary Function Measurements
- The ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) is used as a diagnostic criterion for airflow obstruction, with a ratio < 70% indicating obstruction 3, 5.
- The use of post-bronchodilator FEV1/FVC ratio of 0.7 is supported by health-related quality of life measurements for diagnosing chronic obstructive pulmonary disease (COPD) 3.
- FVC is also used to evaluate the reversibility of COPD, with an increase in FVC of 12% or 200 ml or more indicating a positive response to bronchodilators 4.
Clinical Significance
- Pulmonary function testing, including measurements of VC and FVC, has an important role in diagnosing and staging COPD, as well as assessing disease severity and monitoring treatment effects 5, 2.
- The American Thoracic Society (ATS) and European Respiratory Society (ERS) have published standards for pulmonary function testing, including definitions, equipment, and patient-related procedures 2.