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<br />AMERICAN JOURNAL OF RESPIRATORY AND CWTICAL CARE MEDICINE VOL to 1997
<br />marUuaoa use (15) to undergo repeat lung function testing on
<br />up to six additional occasions at Intervals of at least I The
<br />we also fitted A second random<ffccts model in which tobacco and
<br />me"j'"
<br />yr.
<br />Present report presents the results of the analysis of this longitu-
<br />nes status were constant ewvariabla, rather than t6nc-depesedent,
<br />For this analysis, each subject was classified as a never or continuing
<br />dinal study of lung function.
<br />smoker oreaa substance uparstely, based on whether the subject was
<br />either A nonsmoker or a smoker or that substance at each and every
<br />Lino, respectively. Otherwise, subjects were classified as inlerrrjuent
<br />METHODS
<br />smokers for that substance
<br />The initial sample consisted of healthy volunteers 25 to 49 yr of age,
<br />including 144 heavy, habitual smokers of marijuana alone (MS), 133
<br />regular smokers or both marijuana and tobacco (MTS), 70 smokers or
<br />tobacco only (TS), and 97 nonsmokers (NS) of any substance (11). Sub-
<br />jects were Initially recruited from the general Los Angeles area through
<br />newspaper and radio announcemenis from 19831hrough 1985. Criteria
<br />for study entry have been pnwiou* reported (I5). Specifically excluded
<br />were persons who reported current or previous intravenous drug use or
<br />smoking of other illicit substances (eg.. crack cocaine, phencyclidine,
<br />methamphetamine, heroin, and opium) more than 12 times In thdr Ilves
<br />or within the previous 6 mo. Persons with significant occupational ex-
<br />posures to substances potentially hazardous to rapbatory health, or with
<br />a history of Chronic respiratory Illness, were also excluded.
<br />Eligible subjects completed a detailed respiratory and drug use ques-
<br />tionnaire adapted from the American Thoracic Society/National Han,
<br />Lung and Blood Institute (ATS/NHLBI) questionnaire (20) and the Na.
<br />bona) Institute on Drug Abuse (NIDA) nationwide survey on drug abuse
<br />(21). An extensive battery of pulmonary function testa was also per.
<br />formed. Details of the testing procedures, methods of Calculation, And
<br />comparison with expected reference values used in the study haw been
<br />described previously (15). A subsd of these participants (36 MS, 42 MTS,
<br />267%and 40 NS) also underwent f4booptic broncbascopy, bronchoal-
<br />veolar lavage (RAL), and bronchial mucosal biopsies at variable times
<br />following pulmonary function testing. Results of the broachoscopic
<br />studies have been reported previously (17, 18, 22. 23).
<br />Since 1985, extensive efforts haw been made to reeootad at least
<br />annually, by mall and telephone, all 446 participants who had under-
<br />gone Initial testing in 1923 through 1985. Mail was scot under a US.
<br />Postal Service arrangement that pronleled the tender with Identification
<br />of the address to which the mail was delivered. Participants who were
<br />lost to follow-up (cit-, unddivered mail with no forwarding address) were
<br />traced through work telephone numbers, contacts with Individuals Iden -
<br />ti fled by the subject as Likely to know his or be whereabouts, Stale depart-
<br />ment of motor vehicle rosters, voter registration fila, the U.S. Social
<br />Security forwarding syuem, and commercial credit seambes. A field visit
<br />to the last known residence of a participant was utilind it necessary.
<br />The National Death Index (NDI) was used to identify deaths In the study
<br />group NDI searches were run eaeb year for individuals not known to
<br />be alive at the end of that year. For deaths of study subjects identified
<br />by the NDI, death eoreineatu and hospital and pathology records were
<br />requested to determine the mum of death.
<br />Recontacted particiPeats were Invited to undergo subsequent rounds
<br />or examinations at periods of 3 I yr, Including an interval respiratory
<br />and drug use interview and at least forced expiratory spirometry. Tro
<br />experienced technicians who were sou -trained In the study procedures
<br />Performed the Initial And follow-up pulmonary function tats. The same
<br />pulmonary function equipment and testing procedures were used through-
<br />out the study (I5). Questionnaires were administered by trained later -
<br />viewers.
<br />Data Analysis
<br />For FEV„ random-erfects modeling was used to estimate the rate of
<br />decline In lung function with age in relation to snacking status fm mariju.
<br />ana or tobacco at any point In time, with smoking staters as a time -
<br />dependent covariable (24, 23). Other potential covar(ables were height
<br />(constant) and intensity of use of marijuana (joints/day) and tobacco
<br />(cigarettes/day), the tobaao-marijwna interaction, and former smok-
<br />ing of each substance, which were all assessed at each survey (time.
<br />dependent). The model Also included data from subjects with only one
<br />measurement These single observations contribute to the estimate of
<br />the Intercept but do not affect the slope csdmatt The advantage of this
<br />model is that it allows for one or more changes in smoking status ower
<br />flue. Analyses were performed rot men and women scpamtdy.
<br />RESULTS
<br />Of the 446 eligible subjects Initially enrolled in the study, 394
<br />underwent measurements of lung function. Demographic char-
<br />acteristics, smoking status, and FEV, of the 394 study participants
<br />with evaluable lung function are shown in Table I by smoking
<br />category at the lime of study entry (Visit 1). The tobacco -only
<br />smokers were slightly older than subjects in the other smoking
<br />categories (P <0.05). The marijuana smokers were heavy daily
<br />smokers (mean of more than 3.5 joints/d), w ^ as the tobacco
<br />smokers smoked an average of nearly I to 1.5 packs of cigarettes
<br />Per day. The combined smokers of marijuana plus tobacco
<br />smoked less tobacco than did the tobacco -only smokers (p <
<br />0.03), whereas the current intensity and lifetime amount of
<br />marijuana smoking was not significantly different between the
<br />dual and maiijuaaa-only smokers. The mean age and tobacco
<br />consumption of the female subjects in each smoking category
<br />were similar to those of the male subjects in the same category.
<br />Baseline % predicted FEV, did not differ across smoking cate-
<br />gonm
<br />Table 2 shows the number of longitudinal assessments by gen-
<br />der. The mean interval between consecutive visits was 1.7 d: 1.1
<br />(SD) yr, with minimum and maximum intervals of approximately
<br />I and 8 yr, respectively. The mean interval between the first and
<br />last visit for each subject was 4.9 t 2.0 yr. Nearly two-thirds
<br />of the cohort (255/394) were festal on two or more occasions.
<br />Nearly all of those not retested bad moved out of the area or
<br />were otherwise lost to follow -u0. The proportion of male and
<br />female subjects who underwent morethan one set of lung func-
<br />tion tests was similar, and the proportion of subjects who were
<br />tested more than once (MS 66.7%; MTS 56.391s; TS 64.65o; NS
<br />73.3%) did not differ significantly from those who did not un.
<br />dergo follow-up testing by baseline smoking category (p> 0.09;
<br />chi-square analysis). Moreover, within each smoking category,
<br />no significant differences were found in the age, baseline smok-
<br />ing characteristics, or baseline FEV, of the subjects who were
<br />studied only once and those with multiple tests, except that MTS
<br />in the follow-up group were slightly lighter tobacco smokers (16.0
<br />cigarettes/d) than MTS who were studied only once (21.7 ciga.
<br />rettes/d) (p < 0.05).
<br />Fourteen participants were known to have died during the
<br />follow-up period, including 8 MTS, 2 MS, 3T& and 1 NS. Known
<br />causes of death included acquired immune deficiency syndrome
<br />(AIDS) (1 MS, 1 MTS, and 2 TS); violence (3 MTS); suicide (1
<br />MTS); drug overdose (1 MTS); breast cancer (1 MTS and I NS);
<br />and asphyxiation from aspirated food (1 TS).
<br />The number of subjects in each smoking category who re.
<br />mained "continuing smokers" of each substance or temporarlly
<br />quit (or started) smoking a particular substance during the follow-
<br />up period Cintermittent smokers") is shown in Table 3. More
<br />than 80% of smokers of marijuana with or without tobacco con-
<br />tinued to smoke marijuana throughout the follow-up period, and
<br />RPPmsxjmately 90% of (obacco-ordy smokers continued to smoke,
<br />Whereas; 75% of dual smokers of tobacco and mar))uana Con.
<br />tinued to smoke tobacco. Relatively few subjects in any smoking
<br />category began smoking either tobacco or marijuana during
<br />follow-up. Although most smokers of marijuana (nitially (587e
<br />of MS and 67% of MTS), including those who quit smoking
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