Flow Volume Loops in Diagnosis
Gelb and associates have described the physiologic characteristics of malignant unilateral mainstem bronchial obstruction in patients treated with laser therapy. In their most recent series, eight patients without a prior history of COPD had a restrictive pattern on flow volume loops, four with associated air flow obstruction. After treatment, all patients had an increase in FVC with a parallel rightward shift in MEFV curve. We recently evaluated a patient who had a flow volume loop configuration which is potentially diagnostic for mainstem bronchial obstruction.
This patient was a 76-year-old man who presented with a six- month history of intermittent hemoptysis. Fiberoptic bronchoscopy revealed a polypoid tumor (poorly differentiated carcinoma) located 3 cm from the carina, causing complete obstruction of the bronchus during expiration. Spirometric testing revealed a mixed ventilatory defect with FVC of 2.56 L (63 percent of predicted) and FEV, of 1.09 L (35 percent of predicted). FEV, increased 17 percent post- bronchodilator therapy. There was no difference between FVC and SVC in this patient. Lung volume measurements revealed a normal FRC by both helium dilution and body box methods and a normal TLC. Diffusion capacity was 88 percent of predicted. Flow volume loop revealed a normal upstroke to the peak flow and then a rapid linear fall to an inflection point at approximately 43 percent of forced vital capacity. From this point to residual volume, flow was very low and approached zero (Fig).
This patients pulmonary (unction test results indicated that he had a mixed ventilatory defect on spirometry but normal total lung capacity. The flow volume loop suggested that the nonobstructed side of the lung empties rapidly, and the obstructed side empties slowly throughout the forced vital capacity maneuver. Consequently, the expiratory portion of the flow volume loop demonstrates both a restrictive pattern and a severe obstructive pattern in series and is unlike any of the patterns reported by Gelb et al. This pattern is not the airway collapse pattern described by Healy et al and Jayamanne et al. Patients with severe COPD may have the airway collapse pattern in which there is an abrupt decrease in flow from peak to an inflection point less than 50 percent of peak flow which occurs during the first 25 percent of expired vital capacity. These patients typically have very severe obstructive ventilatory defects with low diffusion capacities (mean FEV, 24 percent of predicted, mean Deo 41 percent of predicted in Healy et al. This pattern reflects dynamic compression of the tracheobronchial tree early in expiration and probably develops secondary to reduced central airway support, reduced lung recoil, increased peripheral resistance, and increased intrapleural pressures during forced expiration.
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Figure. Flow volume loop redrawn from original tracing using a Macintosh computer. This study was done with the Gould 2450 system (dry seal spirometer and Epson printer).
In our patient, the inflection point occurred near mid-vital capacity and the patient had no physiologic evidence of emphysema, at least based on diffusion capacity. In summary, we suggest that this flow volume loop pattern observed in our patient is diagnostic of mainstem endobronchial tumors which cause nearly complete obstruction during forced exhalation maneuvers. This case is similar to one reported by Dull and coworkers.