Genetic Factors Important Risk Factors for COPD

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฀