Longitudinal decline in measured firefighter single-breath diffusing capacity of carbon monoxide values - A respiratory surveillance dilemma

Seattle firefighters participate in a voluntary annual medical surveillance program including measurements of ventilatory capacity (FVC and FEV1) and single-breath diffusing capacity of carbon monoxide (DLCO) From 1989 to 199 6, average % predicted DLCO (Crapo) for all participating firefighters decl ined from 94.4% (95% confidence interval [CI]: 93.4% to 95.5%) to 87.3% (95 % CI: 86.2% to 88.3%), with no significant change in average FVC or FEV1. A random-effects regression model based on data from 812 firefighters with a t least two annual sets of DLCO measurements showed the expected associatio ns between DLCO and age, height, gender, race, ventilatory capacity, and sm oking. In addition, two important temporal changes were observed, including , for an average firefighter, a large mean decline in DLCO of -1.02 ml/min/ mm Hg associated with year of measurement, and a relatively smaller decline of -0.006 ml/min/mm Hg associated with number of fires fought. Although th e stability of ventilatory capacity over time is reassuring, the marked tem poral decline in diffusing capacity among this population of firefighters r aises issues of concern. Interpretation of the observed decline poses a dil emma in terms of the reliability and efficacy of diffusing capacity as a sc reening tool, in whether DLCO is subject to unacceptable technical variabil ity or whether it might provide more sensitive detection of early adverse r espiratory effects of smoke inhalation.