FORCED MIDEXPIRATORY TIME - REFERENCE VALUES AND THE EFFECT OF CIGARETTE-SMOKING

Background: Forced midexpiratory time (FET(25-75%)), the time required to exhale from 25 to 75% of forced vital capacity (FVC), has been adv ocated as a relatively volume-independent measure of obstruction. Prev ious estimates of normal FET(25-75%) have not systematically studied t he effect of age, height, sex, and smoking history. Methods: We analyz ed flow-volume loops from 369 normal lifetime nonsmokers and smokers, a random sample of the population of Michigan. Linear models including age and/or height were considered, with and without logarithmic trans formation. Results: The best models used age, or age and height, and n o transformation. Age and height contributed much less to the variabil ity of FET(25-75%) than to spirometric flows previously investigated. The Largest r(2) was found in the male smokers, with the largest contr ibution from age, suggesting a smoking effect. Conclusions: As age was the major contributor to the value of FET(25-75%) and that contributi on was small, we suggest the use of simplified age-stratified referenc e values derived from our data.