PHYSIOLOGICAL DEFINITIONS OF OBLITERATIVE BRONCHIOLITIS IN HEART-LUNGAND DOUBLE-LUNG TRANSPLANTATION - A COMPARISON OF THE FORCED EXPIRATORY FLOW BETWEEN 25-PERCENT AND 75-PERCENT OF THE FORCED VITAL CAPACITYAND FORCED EXPIRATORY VOLUME IN ONE SECOND

Background and methods: A comparison of the forced expiratory flow bet ween 25% and 75% of the forced vital capacity (FEF(25-75)) and forced expiratory volume in 1 second (FEV(1)) was conducted for the detection of obstructive airway disease as an early manifestation of obliterati ve bronchiolitis. Pulmonary function tests performed on heart-lung and double lung transplant recipients between March 1981 and March 1993 w ere reviewed. Thirty patients were identified who showed progressive d eterioration in pulmonary function after transplantation. Ratios deter mining proportionate decreases were calculated from measurements of ab solute values for the FEF(25-75) and FEV(1) at the point when the FEF( 25-75) reached < 70% and less than or equal to 30% of predicted, divid ed by baseline values obtained before the decline in function. Similar ratios were obtained for FEV(1) and FEF(25-75) at the point the FEV(1 ) declined greater than or equal to 20% from its baseline value. Resul ts: Comparison of the ratios for the FEF(25-75) and FEV(1) at FEF(25-7 5) values < 70% and less than or equal to 30% of predicted and a simil ar comparison when the FEV(1) declined greater than or equal to 20% fr om baseline showed a greater proportional decrease in FEF(25-75) than FEV(1) (p < 0.01). With the use of the FEF(25-75), declines in airway function were detected earlier. After transplantation a decline in FEF (25-75) to < 70% of predicted occurred approximately 112 days before a 20% decline in FEF1. Conclusion: The FEF(25-75) is more sensitive tha n the FEV(1) for the early detection of obliterative bronchiolitis. A presumptive diagnosis of obliterative bronchiolitis can be made with p hysiologic criteria, providing infection or acute rejection has been r uled out. When conducting epidemiologic studies or for vital statistic s we propose that a decline in FEF(25-75) to < 70% be used to define t he onset of obliterative bronchiolitis.