Vital capacity measurements

Forced vital capacity (FVC) quantifies the maximum air volume expired following a maximal inspiration and is one of the basic measures of analyzing flow changes such as reduced airway patency observed in asthma. To measure FVC, an individual inhales maximally and then exhales as rapidly and completely as possible. FVC primarily reflects the elastic properties of the respiratory tract. The gas volume forcibly expired within a given time interval, FEV (where t is typically one second, FEVj q)... 

Respiratory problems are diagnosed using a spirometer. The patient exhales as hard and as fast as possible into the device. The spirometer measures (1) the total volume exhaled, called the forced vital capacity (FVC), with units in liters (2) the forced expired volume measured at 1 second (FEV,), with units in liters per second (3) forced expiratory flow in the middle range of the vital capacity (FEV 25-75%), measured in liters per second and (4) the ratio of the observed FEVj to FVC X 100 (FEVj/FVC%). 

Volume-Time and flow- Volume Curves The characteristics measured by the maximal expiration are forced vital capacity ( o, 1-s forced expiratory volume (FEv,), peak expiratofy flow rate (Vn x)> and flow rates at and 25% of the remaining fvc (Vj . 2 ) for partial and maximal flow-volume curves. These measurements give an easily obtained, relatively reproducible evaluation of overall pulmonary mechanical performance, but provide little information on the mechanisms responsible for an observed change. 

No respiratory effects were associated with exposure to 2,3,7,8-TCDD-contaminated herbicides in a group of Vietnam Air Force veterans involved in Operation Ranch Hand examined more than 10 years after the war (Wolfe et al. 1985). In the 1987 follow-up (USAF 1991), no association was found between the initial or current serum level of 2,3,7,8-TCDD and incidences of asthma, bronchitis, pleurisy, pneumonia, or tuberculosis abnormal spirometric measurements were often associated with CDD blood levels, but according to the authors (USAF 1991), the differences in the mean level between high- and low-exposure subjects were not clinically important. The authors suggested that these findings may have been related to the association between 2,3,7,8-TCDD and body fat because obesity is known to cause a reduction in vital capacity. 

Effects on respiratory function were measured by vital capacity, forced inspiratory volume, and forced expiratory volume immediately after exposure subjective responses were taken at 15-min intervals. No effects on respiratory function were found. Subjects reported irritation of the eyes and throat, objectionable odor, and general discomfort. Non-experts rated their effects as more severe than did the experts. At the highest concentration, none of non-experts stayed in exposure chamber for 2 h all of the experts remained in the chamber. ... 

Forced vital capacity (FVC) measures the maximum volume of air expelled from the lung in a single forced expiration there is no time limit. Forced expiratory volume in one second (FEVi) measures the volume of air which can be expelled from the lung in one second. In a normal individual 80% of the vital capacity can be expired in one second, but patients with obstructive disease have difficulty in emptying the lung and this value is significantly reduced. 

The approach most commonly used to evaluate effects on distal airways in clinical and occupational medicine is the maximum forced expiratory maneuver, which allows measurement of airflows as a function of lung volume from total lung capacity to residual volume. Typically, the forced vital capacity (FVC) and the forced expiratory volume at 1 s (as a % of FVC) (FEVi) are measured. Peak expiratory flow is a frequently used measure since simple portable devices permit self-evaluation by patients with obstructive disease. Decreased airflow rates are seen with emphysema, chronic bronchitis, and following... 

Formaldehyde-induced effects on human pulmonary function variables including forced vital capacity (FVC), forced expiratory volume in 1.0 seconds (FEV, q), peak expiratory flow rate (PEFR), and forced expiratory flowrate between 25 and 75% FVC (FEFRoj,, ), have not been found as consistently as symptoms of eye and nose irritation at acute exposure levels in the range of 0.4-3 ppm. In controlled exposure studies, no statistically significant exposure-related effects on lung function measurements were found in 10 healthy subjects exposed to up to 2 ppm for 3 hours (Kulle et al. 1987 Kulle 1993),... 

The combinations or sums of two or more lung volumes are termed capacities (see Fig. 25-1). Vital capacity (VC) is the maximal amount of air that can be exhaled after a maximal inspiration. It is equal to the sum of the IRV, Vt, and ERV. When measured on a forced expiration, it is called the forced vital capacity (FVC). When measured over an exhalation of at least 30 seconds, it is called the slow vital capacity (SVC, VC). The VC is approximately 75% of the total lung capacity (TLC), and when the SVC is within the normal range, a significant restrictive disorder is unlikely. Normally, the values for SVC and FVC are very similar unless airway obstruction is present. 

FIGURE 25-3. Normal flow-volume loop. Flows are measured on the vertical (y) axis, and lung volumes are measured on the horizontal (x) axis. FVC can be read from the tracing as the maximal horizontal deflection. Instantaneous flow (Vmax) at any point in FVC also can be measured directly. FVC = forced vital capacity. 

In another study, 105 subjects inhaled Cts ranging from 2.4 to 19.6 mg min m-3 (retained doses of 0.1-3.1 pg kg-1). There was a mean erythrocyte cholinesterase inhibition of 30% at a retained dose of 2.2 pg kg-1 and a rough correlation of enzyme inhibition with retained dose. However, although measures of pulmonary function varied widely both above and below baseline, none changed consistently with dose. Measures used included resting tidal volume, exercise tidal volume, maximum breathing capacity and vital capacity (MOD18). 

There are two techniques used to measure diffiision capacity. In one procedure, the subject takes a single vital capacity inspiration of a dilute mixture of CO and holds his breath for 10 seconds. In the second, the subject breathes a low concentration of CO (about 0.1%) for 30 seconds until a steady state has been reached. In both methods, the rate of disappearance of the CO from the alveolar gas is calculated by measuring the concentrations of CO in the inspired and expired air with an infrared analyzer. The larger the diffiising capacity (DlCO), the more CO enters the blood and the lower the amount of CO measured in the expired gas. 

Examination of lung volumes often indicate that total lung capacity is normal but that there is a moderate elevation of residual volume and hence a mild decrease in vital capacity. Compliance and carbon monoxide difiiision capacity (DlCO) measurements are usually normal. 

Several decades ago, investigators attempted to characterize pulmonary impairment caused by exposure to nerve agents by performing pulmonary function studies (such as measurements of vital capacity and maximal breathing capacity) on subjects exposed to small amounts of sarin vapor (the Ct values for sarin ranged up to 19.6 mg min/m3).60 Some observers found increases in airway resistance61 and other changes, while other researchers did not.62... 

When subjects were exposed to CS concentrations of 1 to 13 mg/m3 daily for 10 days, their airway resistances, measured 2 to 4 minutes after the fourth and tenth exposures, were unchanged from the preexposure values.4 Tidal volume, vital capacity, and peak flow in 36 subjects also were unchanged when they were measured immediately and 24 hours after exposure to CS.5... 

FIGURE 7.4.14 Lung function measurements related to body height and age in males. TLC, total lung capacity VC, vital capacity, RV, residnal volume. (From Bartlett, R.G., Respiratory system, in Bioastronautics Data Book, J.F. Parker, Jr. and V.R. West, eds., NASA, Washington, EXT, 1973,489-531.)... 

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