Longitudinal Decline in Measured Firefighter Single-Breath Diffusing Capacity of Carbon Monoxide Values

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Abstract
Seattle firefighters participate in a voluntary annual medical surveillance program including measure- ments of ventilatory capacity (FVC and FEV 1 ) and single-breath diffusing capacity of carbon monox- ide (D LCO ). From 1989 to 1996, average % predicted D LCO (Crapo) for all participating firefighters de- clined 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 FEV 1 . A random-effects regression model based on data from 812 firefighters with at least two annual sets of D LCO measurements showed the ex- pected associations between D LCO and age, height, gender, race, ventilatory capacity, and smoking. In addition, two important temporal changes were observed, including, for an average firefighter, a large mean decline in D LCO of 2 1.02 ml/min/mm Hg associated with year of measurement, and a rel- atively smaller decline of 2 0.006 ml/min/mm Hg associated with number of fires fought. Although the stability of ventilatory capacity over time is reassuring, the marked temporal decline in diffusing capacity among this population of firefighters raises issues of concern. Interpretation of the observed decline poses a dilemma in terms of the reliability and efficacy of diffusing capacity as a screening tool, in whether D LCO is subject to unacceptable technical variability or whether it might provide more sensitive detection of early adverse respiratory effects of smoke inhalation. Burgess JL, Brod- kin CA, Daniell WE, Pappas GP, Keifer MC, Stover BD, Edland SD, Barnhart S. Longitudinal decline in measured firefighter single-breath diffusing capacity of carbon monoxide values: a respiratory surveillance dilemma. AM J RESPIR CRIT CARE MED 1999;159:119-124.