Initial Comparison of Ginner and Control Groups
Under the constraint of the number of control subjects available to us, it was not possible to match the control subjects to the ginners for all the major variables of sex, ethnicity, age, and cigarette smoke exposure. As a result, there were significant differences between the ginners and control subjects as follows: the mean age of the ginners was older, there being a higher percentage of ginners in the 50 to 65 age range (20.8 percent vs 11.6 percent for the control subjects); the ginners had a higher percentage of smokers than the control subjects; and the ginners who smoked had a greater exposure to smoke (measured by pack-years) than the control subjects who smoked (Table 1). All subjects were men, and there was no significant difference in ethnic composition between the two groups. Pulmonary function of the ginners, as measured by FEVj, FEVj/FVC, and FEF25-75%, was significantly inferior to that of the control subjects (Table 1). The mean exposure of the ginners to cotton dust was 48 months.
Change in Pulmonary Function with Time
All four years of the study were completed by 146 ginners and 91 control subjects; one to four years were completed by 217 ginners and 221 controls. The mean annual change in FE Vx (the difference between the first and last values divided by the number of years) for subjects completing all four years of study was — 27.3 ml in the ginners and — 35.5 ml in the control subjects (p = 0.37). The corresponding figures for the ratio of FEV/FVC were -0.21 percent and -0.23 percent, respectively (p = 0.86). The FEF25-75% declined 0.058 L/s/annum in the ginners vs 0.066 Us/ annum in the control subjects (p = 0.68) (Table 2). The mean annual change in FEVx (calculated from individual regression lines) for subjects completing all four years of study was —30.2 ml for the ginners and — 29.9 ml for the control subjects (p = 0.97) (Table 2).
The mean annual changes in FEV!, FEVj/FVC, FEF25-75% (calculated by finding the difference between the initial and the final values and dividing by the number of years) for all subjects completing at least one lull year of study are shown in Table 3. The annual changes are less in the ginners than in the control subjects, although the differences are not statistically significant. Further, the annual decline in FE V\ in the ginners is less when all ginners completing at least one year of study are compared with those completing all four years.
Comparison of the initial mean spirometric values of ginners who dropped out of the study before four years with those of the ginners who completed all four years is shown in Table 4. The dropouts were not significantly different from those completing the study except for the ratio of FEV/FVC. The ratio was 75.8 percent in the dropouts and 78.2 percent in those ginners completing all four years of the study (p = 0.021). The mean annual changes in spirometry did not differ significantly between the two groups, although the AFEV! was considerably less in the dropout group than in the completers, approaching statistical significance at p = 0.074 (Table 4).
Table 1—Initial Comparison of Ginners and Control Subjects
|Characteristic||Control (n = 268)||Ginners (n = 260)||p Value|
|Mean age, yr*||35.3±11.7||38.1±11.9||0.0071|
|Mean pack-years* (per smoker)||15.7 ±17.1||22.9±23.1||0.0001|
|History of heart or lung disease, %||11.6||12.0||0.8862|
|FVC, % pred*||107.6 ±13.3||105.8± 12.7||0.1419|
|FEV* % pred*||105.4 ±14.0||101.0 ±14.7||0.0005|
|FEV/FVC, %*||79.8 ±7.5||77.1 ±8.3||0.0001|
|FEF25-75%, % pred*||89.0 ±27.9||74.4 ±26.9||0.0001|
Table 2—Anna/ Change in Pulmonary Function for Subjects Completing 4 Years of Study
|Test||Controlst (n = 146)||Ginnerst (n = 91)||p Value|
|FEV,, ml||-35.5 ±5.5||-27.3 ±6.4||0.37|
|FEVj/FVC, %||-0.23 ±0.06||–0.21 ±0.10||0.86|
|FEF25-75%, Us||-0.066 ±0.02||-0.058 ±0.01||0.68|
Table 3—Mean Annual Change in Pulmonary Function for Subjects Completing 1 to 4 Years of Study
|Test||Controlst (n = 217)||Ginnerst (n = 221)||p Value|
|FEV,, ml/yr||-32.5 ±6.3||-13.2 ±8.6||0.07|
|FEV,/FVC, %/yr||-0.31 ±0.09||-0.22 ±0.14||0.60|
|FEF25-75%, L/s/yr||-0.09 ±0.03||-0.06 ±0.02||0.26|
Table 4—Comparison of Pulmonary Function Between the Ginners Completing All 4 Years and the Ginners Completing Less Than 4 Years (Dropouts)
|Test||Dropouts* (n = 114)||Completers* (n = 146)||p Value|
|FEV,, L||3.79±0.08||3.90 ±0.06||0.246|
|FEV,, % pred||99.8± 1.50||102.1 ±1.09||0.223|
|FEV./FVC, %||75.8 ±0.83||78.2 ±0.64||0.021|
|FEF25-75%, L/s||3.53 ±0.14||3.78±0.11||0.146|
|FEF25-75%, % Pred||77.4 ±2.67||81.2±2.09||0.264|
|AFEV„ ml/yrt||+ 15.2 ±22.60||-27.30 ±6.40||0.074|