Caveats Concerning the Informative Value of Studies

American฀states฀ [52] .฀This฀primarily฀questionnaire-based฀study฀in฀smokers฀and฀non-smok- ers฀ with฀ a฀ medical฀ diagnosis฀ of฀ asthma฀ came฀ up฀ with฀ various฀ conclusions:฀ males฀ and฀ females฀had฀equal฀prevalence฀rates฀for฀asthma,฀but฀females฀had฀higher฀incidence฀rates฀ [52] .฀Smoking฀prevalence฀was฀high฀and฀the฀diagnosis฀was฀made฀in฀all฀age฀groups฀64.7.฀ In฀a฀Finnish฀cohort฀study฀ [168] ,฀the฀prevalence฀of฀diagnosed฀asthma฀was฀higher฀among฀ male฀ smokers฀ than฀ among฀ male฀ non-smokers,฀ whereas฀ no฀ signiicant฀ difference฀ was฀ observed฀ for฀ women.฀ Overall,฀ the฀ association฀ between฀ bronchial฀ asthma฀ and฀ cigarette฀ smoking฀is฀not฀clear-cut฀ [169,฀170] . Bronchial฀responsiveness฀to฀cigarette฀smoke฀was฀studied฀in฀98฀smokers฀by฀means฀of฀ lung฀function฀measurements฀FEV 1 ,฀MEF 75 ,฀FEF {25–75} ฀in฀parallel฀with฀the฀methacholine฀ challenge฀test.฀All฀lung฀function฀indices฀were฀decreased฀after฀just฀12฀cigarette฀smoke฀inha- lations.฀FEV 1 ฀fell฀by฀10฀and฀this฀effect฀correlated฀directly฀with฀vital฀capacity,฀pulmonary฀ status฀asthma,฀bronchitis฀and฀cigarette฀consumption,฀but฀not฀with฀methacholine฀bronchial฀ reactivity฀ [171] .฀It฀is,฀therefore,฀clear฀that฀cigarette฀smoking฀is฀a฀major฀cause฀for฀the฀prog- nosis฀of฀bronchitis,฀bronchial฀asthma฀and฀COPD. The฀comparison฀of฀increased฀bronchial฀responsiveness฀of฀smokers฀with฀that฀of฀non- smokers฀ does฀ not฀ reveal฀ consistent฀ results฀ without฀ a฀ simultaneously฀ altered฀ histamine฀ response.฀Reduced฀pulmonary฀function฀was฀observed฀in฀male฀smokers฀who฀are฀older฀than฀ 21฀years฀of฀age฀ [172] .฀Other฀studies฀have฀also฀yielded฀inconsistent฀results฀ [170,฀173] .฀One฀ study฀conducted฀in฀Boston฀ [174] ฀in฀middle-aged฀and฀elderly฀patients฀revealed฀that฀current฀ smoking฀ status฀ was฀ associated฀ with฀ allergic฀ disposition฀ based฀ on฀ the฀ determination฀ of฀ methacholine฀responsiveness.฀In฀addition,฀raised฀IgE฀levels฀and฀eosinophil฀counts฀have฀ been฀detected฀in฀smokers฀ [175] .฀The฀IgE฀concentration฀did฀not฀decline฀with฀age฀in฀smokers฀ as฀compared฀to฀non-smokers. Despite฀the฀numerous฀studies฀conducted,฀it฀is฀evident฀from฀the฀indings฀reported฀that฀no฀ unequivocal฀association฀can฀yet฀be฀demonstrated฀between฀the฀development฀of฀bronchial฀ asthma฀and฀cigarette฀smoking฀in฀adults฀because฀of฀the฀varied฀potential฀for฀bias.฀In฀children,฀ numerous฀indings฀from฀more฀recent฀studies฀indicate฀that฀the฀risk฀for฀bronchial฀asthma฀is฀ increased฀as฀a฀result฀of฀passive฀smoking.

5.4.3 Bronchial Asthma in Children

More฀ than฀ 50฀ epidemiology฀ studies฀ suggest฀ that฀ children฀ who฀ are฀ exposed฀ to฀ tobacco฀ smoke฀suffer฀increasingly฀from฀respiratory฀tract฀diseases฀ [128] .฀The฀outcome฀variables฀ studied฀in฀these฀children฀include฀respiratory฀tract฀symptoms฀such฀as฀cough฀and฀rhonchi,฀ respiratory฀tract฀infections,฀new฀occurrence฀or฀deterioration฀of฀bronchial฀asthma,฀deterio- ration฀of฀pulmonary฀function,฀bronchial฀responsiveness,฀atopy฀and฀increased฀IgE฀levels.฀ Passive฀smoking฀in฀childhood,฀particularly฀where฀the฀mother฀smokes,฀has฀been฀associated฀ with฀some฀of฀these฀symptoms฀ [154,฀176–179] ฀see฀Figs.฀ 5.5 ฀and฀ 5.6 .฀However,฀the฀pres- ence฀ of฀ external฀ confounders฀ familial,฀ socio-economic฀ and฀ environmental฀ conditions฀ means฀that฀it฀is฀dificult฀to฀establish฀a฀deinite฀causal฀relationship฀ [177] . Passive฀smoking,฀particularly฀where฀both฀parents฀are฀smokers,฀is฀associated฀with฀bron- chitic฀and฀asthmatic฀states฀in฀children฀and฀adolescents฀ [182] .฀Several฀studies฀conirm฀an฀ association฀ between฀ passive฀ smoking฀ and฀ childhood฀ obstructive฀ and฀ non-obstructive฀