Relationship between bronchial andarterial diameters innormal humanlungs

Inorder tofind anobjective methodformeasuring narrowing ofsmall airways, eight lungs fromfourpeople without lungdisease were inflated andfixed at25cm ofwater pressure.Eight tonineblocks weretaken atrandomfromeachofsixparasaggital slices from eachlung, sectioned, andstained. Thesize ofthebronchioles (airways without cartilage) in relation totheir accompanying arteries was determined. Theinternal bronchiolar diameter was compared withthree different arterial diameters (the internal, external medial, andexternal adventitial). Theratio oftheinternal bronchiolar diameter totheexternal adventitial arterial diameter was constant between lungs (0'62±0 02)andindependent ofthemethodofinflation or theposition within thelungs. Thisratio may provide a useful indexofbronchiolar narrowing in disease. Inrecent years muchinterest hascentred onthe importance ofpathological changes insmallair- waysasacauseofthelungfunction changes re- cordedinchronic bronchitis and emphysema (Hoggetal,1968; Martin etal,1970; Macklemet al,1971;Zameletal,1976). Smallairways are defined inphysiological termsasconducting air- wayswithaninternal diameter ofless than2mm, whichincludes bronchioles aswellassomesmall bronchi. Several morphometric methods havebeen usedtoassess narrowing ofsmallairways, but noneofthemhasallowed thesizeofindividual small airways tobeassessed. Oneapproach hasbeentoplotthesize distri- bution ofsmall airway diameters orcross-sectional areasandcompare themwithnormal distributions (Bignon etal,1970; Linhartova' etal,1971, 1973; Depierre etal,1972;MatsubaandThurlbeck, 1972). Ifanexcess ofairways ofaparticular size rangeisfoundwitha deficit ina larger range presumably narrowing ofthelarger airways has occurred. Similarly, an overall reduction ofthe cross-sectional areaofsmallairways hasbeen interpreted asnarrowing. Anotherapproach has beentomeasuretheratio oftheinternal toexter- nalbronchial diameters (Martin etal,1968, 1970). Thisratio, however, isinfluenced bothbychanges inwallthickness andchanges inluminal diameter.