Comparison of Forced and Slow Vital Capacity Maneuvers in Defining Airway Obstruction

Abstract

BACKGROUND: Obstructive lung disease is diagnosed by a decreased ratio of FEV 1 to the vital capacity (VC). Although the most commonly used VC is FVC, American Thoracic Society guidelines suggest alternative VCs, for example, slow VC (SVC), may offer a more-accurate evaluation of breathing capacity. There is recent evidence that using only FEV 1 /FVC underrecognizes obstruction in subjects at high risk and who are symptomatic. Previous studies have indicated that healthy individuals show a minimum difference between FVC and SVC; however, testing of individuals with asthma and who are symptomatic indicates that SVC can be markedly larger than FVC. OBJECTIVE: To evaluate the differences among SVC, FVC, and SVC-based measurements in the diagnosis of symptomatic obstructive lung disease. METHODS: A retrospective analysis was performed of spirometry and plethysmography measurements from studies conducted between 2011 to 2015. We established a pulmonary function database that incorporated predictive equations from the National Health and Nutrition Examination Survey III (NHANES III). The SVC to FVC difference was calculated. FEV 1 /SVC was compared with FEV 1 /FVC by using NHANES III lower limit of normal values. RESULTS: A total of 2,710 studies with 2,244 subjects were reviewed. Spirometric obstruction, as defined by NHANES III, was identified in 26.1% of the studies (707/ 2,710). The mean (؎ SD) difference between SVC and FVC was 375.0 ؎ 623.0 mL and 258.8 ؎ 532.5 mL in those with and those without obstruction, respectively. Subgroup and multivariate analysis demonstrated age, body mass index, and FEV 1 associated contributions to the difference between SVC and FVC. By using FEV 1 /SVC, the prevalence of obstruction increased from 26.1 to 45.0% (1,219/2,710) and identified 566 additional studies of subjects with obstruction. Fifty-four percent of the subjects with newly-identified obstructive lung disease (305/566) had smoking histories, and 67.4% (345/512) received medications for obstructive lung disease. CONCLUSIONS: The isolated use of FVC-based diagnostic algorithms did not recognize individuals with symptomatic obstructive lung disease. Recognizing the difference between SVC and FVC measurements in subjects will improve testing and diagnosis of obstructive lung disease.

Ratio of FEV1/Slow Vital Capacity of < 0.7 Is Associated With Clinical, Functional, and Radiologic Features of Obstructive Lung Disease in Smokers With Preserved Lung Function

“…28 Although SVC and FVC in theory should be the same in a healthy population with normal lungs, SVC usually is larger than FVC, especially in obese people or those with airways disease. 29,30 In individuals with no obstructive lung disease, the difference between SVC and FVC increases with increasing BMI and age. 29,30 Current lung function test interpretation guidelines acknowledge that inspiratory or expiratory SVC may be a better estimate of VC than FVC, but they do not provide specific recommendations regarding whether SVC should be used to calculate the FEV 1 to VC ratio.…”

“…29,30 In individuals with no obstructive lung disease, the difference between SVC and FVC increases with increasing BMI and age. 29,30 Current lung function test interpretation guidelines acknowledge that inspiratory or expiratory SVC may be a better estimate of VC than FVC, but they do not provide specific recommendations regarding whether SVC should be used to calculate the FEV 1 to VC ratio. 6 Nevertheless, professional organizations have proposed the FEV 1 to VC ratio instead of the FEV 1 to FVC ratio as a diagnostic criterion for COPD at certain times.…”

Slow vital capacity

“…Using the FEV1/SVC criteria, the prevalence of obstruction increased from 26.1 to 45% and 566 additional cases of obstruction were diagnosed who otherwise had a preserved FEV1/FVC showing that SVC-based diagnostic criteria can lead to earlier detection of disease with improved clinical outcomes. 16 Saint-Pierre et al studied the PFTs of 13,893 adult patients with a FEV1/FVC and TLC at or above the lower limit of normal. It showed that performing the slow maneuver of SVC was able to uncover the airflow limitation which was missed by FEV1/FVC.…”

“…1 The differences between FVC and SVC are affected by variables like body mass index (BMI), age and gender. 16 Fortis et al studied the effect of BMI on the difference between FVC and SVC by retrospectively reviewing the PFTs of 1805 subjects. The results showed that in the patients with a normal BMI (BMI<25 kg/m 2) with no obstruction, FVC was larger than SVC whereas in overweight and obese patients, the SVC was significantly larger than FVC and the SVC-FVC difference positively correlated with the BMI.…”

Slow Is Better Than Fast?

“…7 Also, obese subjects or those with obstructive disease with a greater degree of emphysema yield SVC larger than FVC. 8 Vital capacity measurements have a flow-dependence more pronounced in subjects with COPD, which results in a truncation of expiratory volume in forced maneuvers. Emphysema may result in expiratory airway collapse, which implies increase in SVC-FVC difference; a larger volume of air can be mobilized by the measurement of vital capacity through an unforced maneuver, because it produces lower intrathoracic pressure.…”