Flow-volume loops obstructive disease

Spirometry is the most widely available and useful PFT. It takes only 15 to 20 minutes, carries no risks, and provides information about obstructive and restrictive disease. Spirometry allows for the measurement of aU lung volumes and capacities except RV, FRC, and TLC and allows assessment of FEVi and FEF25%-7s%. Spirometry measurements can be reported in two different formats—standard spirometry (Eig. 25-2) and the flow-volume loop (Fig. 25-3). In standard spirometry, the volumes are recorded on the vertical (y) axis and the time on the horizontal (x) axis. In flow-volume loops, volume is plotted on the horizontal (x) axis, and flow (derived from volume/time) is plotted on the vertical (y) axis. The shape of the flow-volume loop can be helpful in differentiating obstructive and restrictive defects and in the diagnosis of upper airway obstruction (Fig. 25 ). This curve gives a visual representation of obstruction because the expiratory descent becomes more concave with worsening obstruction. 

FIGURE 25-4. A. Flow-volume loop depicting mild obstruction characterized by decrease flow at low lung volumes. B. Moderate airflow obstruction characterized by a more concave curve. C. Variable intrathoracic obstruction in which peak flow is decreased at higher lung volumes with normalization of curve at lower lung volumes. D. Restrictive lung disease with a curve that is decreased in width but with a normal shape. 

FIGURE 7.7 Typical flow-volume loops, (a) Normal flow-volume loop, (b) Flow-volume loop of patient with obstructive lung disease. 

Three anatomic patterns of TBA exist, each with distinct pulmonary function test characteristics (i) proximal trachea, ii) mainstem bronchi, and (Hi) distal airways. Proximal disease limits expiratory airflows, producing flow-volume loop changes consistent with extrathoracic upper airway obstruction. Mainstem bronchial disease affects large airways flow, decreasing FEVl/FWC ratio. In contrast, distal airway involvement results in decreased small airway or FEF 25 to 75 flows (56). Bronchoscopically, TBA appears as submucosal plaques or diffuse infiltration in 44% cases, nodular disease in 28%, and circumferential lesions in 28% (58). 

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