OBSTRUCTIVE FLOW-VOLUME LOOP CONTOURS AFTER SINGLE-LUNG TRANSPLANTATION

The development of spirometric airflow obstruction may be a diagnostic dilemma in recipients of single lung allografts. The contribution of bronchial anastomotic stenosis to the observed spirometric obstruction may be clinically difficult to distinguish from that of obliterative bronchiolitis. Similarly, differentiating the ''normal'' obstructive d efect after single lung transplantation for emphysema from obliterativ e bronchiolitis may be clinically challenging. We retrospectively revi ewed the maximum inspiratory and expiratory flow-volume loop contours of lung transplant recipients with either obliterative bronchiolitis ( n = 7) or bronchoscopically diagnosed severe bronchial anastomotic ste nosis (n = 3). Five patients underwent single lung transplantation for obstructive native lung diseases and underwent observation before and after development of obliterative bronchiolitis. Bronchial anastomoti c stenosis-maximum inspiratory and expiratory flow-volume loops were a nalyzed both before and after correction of stenosis by niobium: yttri um-aluminum-garnet laser photoresection or endobronchial silicone sten t placement. Measures of airflow derived from maximum inspiratory and expiratory flow-volume loops, such as peak expiratory flow, peak inspi ratory flow, forced expiratory flow at 50% vital capacity, forced insp iratory flow at 50% vital capacity, and forced expiratory volume in 1 second/peak expiratory flow ratio could not differentiate patients wit h bronchial anastomotic stenosis versus obliterative bronchiolitis. Th e most clinically useful index was the maximum inspiratory and expirat ory flow-volume contour, which was characterized by terminal plateaus during exhalation and inhalation in patients with bronchial anastomoti c stenosis. This index was reflected in a lower forced inspiratory flo w at 75% vital capacity and forced inspiratory flow at 75% vital capac ity/peak inspiratory flow ratio in bronchial anastomotic stenosis that increased after elimination of the anastomotic obstruction. Patients who underwent single lung transplantation for chronic obstructive pulm onary disease frequently had spirometric obstruction in the absence of allograft rejection. The maximum inspiratory and expiratory flow-volu me contour, however, was characterized by biphasic expiratory flow wit h decreased terminal flow rates (i.e., forced expiratory flow at 75% v ital capacity). We speculate that the reduced forced expiratory flow a t 75% vital capacity was attributed to prolonged expiratory time const ants of the native obstructed lung. Furthermore, development of oblite rative bronchiolitis produced a disproportionate decrease in midexpira tory flow rates (i.e., forced expiratory flow at 50% vital capacity) a nd a concave contour of the expiratory loop. The maximum inspiratory a nd expiratory flow-volume pattern may, therefore, be of value in diffe rentiating diverse causes of spirometric obstruction after single lung transplantation. Definitive diagnosis, however, still necessitates br onchoscopic evaluation with biopsies.