Lung volume measurement, functional

Stocks J, Quanjer PH. Reference values for residual volume, functional residual capacity and total lung capacity. ATS Workshop on Lung Volume Measurements. Official statement of the European Respiratory Society. Eur Respir J 1995 492-506. 

Forced expiration is commonly used to assess pulmonary function in both healthy and impaired individuals. Static measures of lung volumes (TLC, Vj, FRC) fail to detect dynamic changes in pulmonary function that are attributable to disease (e.g., asthmatic airway constriction). Obtaining maximum expiratory flow-volume (MEFV) curves (Fig. 5.21) permits derivation of key parameters in detecting changes in lung function. 

Most lung volumes can be measured with a spirometer except total lung capacity (TLC), functional residual capacity (FRC) and residual volume (RV). The FRC can be measured by helium dilution or body plethysmography. 

After 2 h of ozone exposure, there was a significant change (p < 0.05) in Fvc, KMF, and airway resistance (Raw) Several other measures (feVi, Vjq, and V35) were lower after 2 h of exposure, but the statistical significance was borderline. However, after 4 h of exposure, all flow measures were significantly decreased, compared with controls. After 4 h, increased, FVC decreased further, and feV decreased significantly. Residual volume, functional residual capacity, and total lung volume did not change as a result of the ozone exposure. 

Respiratory Lung function Spirometry and pulmonary function testing (measurements of lung volumes and flow rates) peak expiratory flow rate measurements (can be done in field with inexpensive hand-held meters)... 

Fig. 1. Tracings of lung airflow and lung volume changes during spontaneous breathing in a conscious rat. Airflow was measured directly using a head-out plethysmograph chamber. The functional endpoints can be automatically calculated for each breath using a data acquisition and analysis software system.

The most common test of lung function in humans is the forced exhalation test, which evaluates both lung volumes and flow performance. After inhaling maximally, the individual exhales as rapidly and deeply as possible to reach residual volume. The volumes of air exhaled per unit time and the airflow during exhalation are recorded. The forced expiratory volume measured in one second (FEVi), along... 

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... 

All the static lung volumes and capaeities except FRC and RV can be measured directly through use of a simple spirometer (an apparatus traditionally consisting of a cylindrical bell immersed in water and equipped with outlets that a person can breathe into, or inhale from, to measure expiratory or inspiratory volumes). Functional residual capacity and RV are measured indirectly by using several alveolar gas dilution techniques. 

The functional residual capacity (FRC) and the residual volume (RV) are the only lung compartments that cannot be measured with a volume-measuring device. Measuring these requires use of the nitrogen analyzer and application of the dilution method. 

Figure 2 Lung volume recruitment. Flow volume loops. The MIC is maintained (higher expired flow) in a patient with ALS over a period of one year despite complete loss of measurable, spontaneous (lower flow) respiratory muscle function. Abbreviations MIC, maximum insufflation capacity ALS, amyotrophic lateral sclerosis.

The large differences between measures of lung function in healthy individuals has hampered their general use. Lung volumes are related to height, age, sex and race. 

Spirometry A test method used to evaluate lung function that measures volume of exhaled air passing through a tube during a given time. 

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