Occupational and Environmental Factors

5.4 Cigarette Smoking and Bronchial Asthma

Cigarette฀smoking฀has฀a฀deleterious฀effect฀on฀physical฀performance฀in฀people฀with฀asthma฀ [154] .฀Passive฀exposure฀to฀cigarette฀smoke฀see฀ Chap.฀9 ฀is฀also฀dangerous฀for฀children฀and฀ leads฀to฀increased฀asthma฀morbidity฀ [4] .฀Asthma฀sufferers฀should,฀therefore,฀be฀strongly฀ advised฀not฀to฀start฀smoking฀or฀to฀stop฀smoking฀as฀quickly฀as฀possible.

5.4.1 Caveats Concerning the Informative Value of Studies

Prospective,฀randomised,฀double-blind฀and฀placebo-controlled฀studies฀to฀investigate฀a฀pos- sible฀association฀between฀cigarette฀smoking฀and฀bronchial฀asthma฀are฀not฀acceptable฀on฀ ethical฀grounds;฀consequently,฀only฀cohort฀and฀case-control฀studies฀are฀available.฀For฀the฀ most฀part,฀such฀studies฀use฀extent฀of฀cigarette฀smoking฀as฀a฀parameter,฀but฀the฀information฀ provided฀by฀patients฀frequently฀fails฀to฀relect฀the฀true฀extent฀of฀consumption.฀Urinary฀and฀ serum฀concentrations-of฀cotinine,฀exhaled฀CO฀and฀nicotine฀levels฀have฀also฀been฀used฀as฀ aids฀to฀assessment฀ [155] .฀One฀further฀source฀of฀bias฀is฀that฀asthmatic฀patients฀with฀severe฀ symptoms฀possibly฀smoke฀less฀than฀those฀with฀no฀appreciable฀sense฀of฀being฀unwell.฀This฀ already฀results฀in฀smoker฀selection฀in฀this฀disease฀group฀ [156,฀157] . Even฀the฀clinical฀diagnosis฀of฀bronchial฀asthma฀is฀problematic฀because฀rhonchi฀and฀ wheezing฀may฀anticipate฀the฀diagnosis฀by฀several฀years฀ [158] ฀and฀furthermore,฀there฀is฀ symptom฀overlap฀with฀COPD฀e.g.฀wheezing,฀dyspnoea,฀emphysema.฀Reversible฀or฀irre- versible฀bronchial฀obstruction฀may฀also฀occur฀in฀both฀conditions.฀b 1 -adrenoceptor฀stimu- lants฀are฀neither฀sensitive฀nor฀speciic฀enough฀to฀permit฀discrimination฀of฀the฀two฀diseases฀ [159] .฀Likewise,฀the฀administration฀of฀histamine฀or฀methacholine฀to฀provoke฀a฀bronchial฀ spasm฀is฀not฀speciic฀for฀bronchial฀asthma฀because฀the฀response฀may฀also฀occur฀in฀chronic฀ bronchitis,฀sarcoidosis,฀bronchiectasis฀or฀rhinitis฀ [160,฀161] . While฀an฀allergic฀disposition฀can฀be฀identiied฀in฀asthmatics,฀the฀parameters฀used฀skin฀ testing,฀IgE฀levels฀and฀eosinophil฀count฀are฀not฀reliable฀assessment฀criteria.฀Immediate- type฀skin฀reactions฀are฀linked฀with฀IgE฀antibodies฀ [162] ฀and฀are฀frequently฀positive฀in฀ asthmatics฀ [163] .฀However,฀IgE฀levels฀are฀neither฀sensitive฀nor฀speciic฀for฀the฀diagnosis฀ of฀asthma฀ [160] ,฀even฀if฀associations฀with฀reduced฀pulmonary฀function฀have฀been฀detected฀ speciically฀in฀asthmatics฀ [164] .฀Eosinophils฀possibly฀play฀an฀important฀role฀in฀the฀inlam- matory฀changes฀seen฀in฀asthmatics฀ [165] .

5.4.2 Cigarette Smoking and Bronchial Asthma in Adults

Despite฀various฀studies฀to฀investigate฀the฀possible฀association฀between฀bronchial฀asthma฀ and฀cigarette฀smoking,฀such฀an฀association฀has฀not฀been฀demonstrated฀ [158,฀166,฀167] .฀ The฀ NHANESI฀ Study฀ included฀ patients฀ from฀ 100฀ different฀ communities฀ in฀ 38฀ US฀ 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฀