7578409637

1254

THE NEW ENCLAND JOURNAL OK MKDICINF.

May 3. 1990

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Iłuman circadian paccmakcr was untgucly inscn$itivc to liglit and tlial il instcad rclicd oii “social con-t:icts“ to acliicvc syuclirony witli tlić ‘il-bour day.**

dcmonstratcd tliai tlić liglit-dark cyclc bas a dircci syncliroui/.ing cf-fcct on tlić humnn circadian pacc-n»akcr.^7?-^7a Furchcrmorc, wc havc rcccntly discovcrcd tłiat propcrły timcd cxposurc to bright light and darkncss can rcscl thc paccmakcr by as much as 12 hours within two to thrcc days.⁷⁹ Wc found that thc paccmakeris rcsctting responsc to bright light dcpcnds on thc timing of thc avcragc midpoint of thc to-tal daily exposure to light, after wcighting for brightncss.⁷⁹ Thcrc-forc, thc bright light to which night-timc workcrs arc oftcn cxposcd during thc day (c.g., during thc return home from work) may prcvcnt them from adapting co night work.

On thc basis of thesc rcsults, wede-signed a pattern of cxpo$ure to bright light and darkncss in thc work and homc cnvironmcnts by which thc phasc of thc paccmakcr can bc reset rapidly and cfTcctivcly in persons who work at night, even if they arc cxposcd to natural light on thc way homc from work each moming.

Howcvcr, wc liavc

Contro* Study

II

-1.2 hr

Ttcatmonl Study

T*me oł O-ły (hr)

I - I

-9.2 hr

No SZgńfcara Adaplauon

Comptetc Adaptaliofl

Figurę 1. OveraII Siudy Protocol (Mtddlc PanelsJ and Changes in Temperaturę Re-corded during the First and Sixth Night Shifts (Upper and Lowcr Panets) in One Mart

during a Contro! Study and a Treatment Study. .

Solid bars indicate daily slcep episodes. open bars constant routines. and drded x's thc rnitiaJ and Finał endogenous circadian temperaturę nadirs as derived from the temperaturę dala (ver1ical dashed fines) measured during the constant routine. During the second (hrough Irtth nights of woik {midnight to 08:00 hours). the men were exposed either to ordinary indoor light (approwmately 150 lux; stippled box) in the contro! studics or to bright Hght (7000 to 12.000 lux; solar symbol in the open box) in the treatment studies. To fadiitate visual compahsoos. segmcnts of the temperaturę

data have been doubte-plotled.

Women’s Hospital. Wricten informed conscnt was obuinod Grom cadi man bcforc pa ni ci pa li oo in thc study.

Overatl Study Design

Subjects

Ten iwo-wcck studics werc carricd out in eight hcaJthy men, 22.to 29 ycars old. The subjects had no mcdical, psychiatrie, or slćcp disorders as detcnmined from their mcdical historics, physical oc-aminations, chcst radiographs. cJcctrocardiograms, biochetntcal scrccning tests, and psychological scrccning ąuestionnaires (thc Minnesota Multiphasic Pcrsonality Invcntory). Nonc had worited rcgularly at night on a permanem or rotating shift within thc pre-ccding year, and nonc had travcled to another timc zonc during the prcv»ous six wcefcs. They were not taking any medications and werc instructcd to absuin from the use of alcohol, rccrcational drugs, and products containing caffeine for the duratioo of thc study. Uri-nary toxicologic scrccning was uscd to vcrify that they were drug-free at thc timc of thc study.

The first two subjects participatcd in the control study and then in the treatment study, after an intcrval of three to fivc wccks during which they livcd at Iłomc and mainiained a Schedule of regular daytimc act»viiy and noctumal sleep. To (adlitate reoruitmem thc remainiug six mcii were asked (o panicipatc in only one study; cach was randomly assigncd to either the contro! study or thc treatment study after thc succcssful complction of an initiaf evaluation of his circadian phasc.

AU ihc studies were carricd out in (lic summer, to avnid scasonal variation in caposurc to outdoor liglit during thc w cek of night work. The cupcrimcntal procedurę* and the procedurę for ohuiuiitg informed consetit were approved by thc Committcc for thc Protec-tion of Humań Subjcct* from Rcseardt Risks of ttrigham and

Five control and fivc treatment studies werc performed; each consistcd of one weck of ambulatory recording of basc-linc temperaturę, physical a cii vi ty, and hcart ratę, followcd by a weck of night-shift work. The men łivcd at home throughout cach study, rcpocting for “work" in thc laboratory each night of thc second weck. To cvaluate the eactent of physiologic adaptation to nighttimc work, thc output of the circadian paccmakcr was eyaluated” during thc first and Stach coasecuiwc night shifts. On" those nights, and during cach of thc immediatcly prcccding days; thc actirity of thc subjects was restrictcd to the enforeed semirccumbcrit wakefulness of a laboratory constant routine as dcscribcd bclow. Ooth thc control and thc treatment protocols are shown in Figurę 1.

During the wcckof basc-linc recording, thc men maintained regular bed limes and waking ci mes (within a rangeof i I hour). Their subjeciiveslecp-waVc łogs were verificd for accuracy bycomparison with the rcsults of continuous ambulatory monitoring of wrist activ-ity, hcart ratę, and body temperaturę (PMS-8 Recordcr, Vitalog, Rcdwood City, Calif.) throughout both wceks of thc study. In lite casc of two men (one control and one treatment subject) whosc bchavior during thc study did not conform to the protocol, thc rcsults werc cxeludcd before thc outeome of their CKperimental tri-als was determined.

On the second (hrough thc fifih nights of work, thc men rc|>oric<l to thc laboratory at 23:43 hours and s|>cm thc cight hours lietwecn midnight and 08:00 scatcd at a desk. On tlmsc four nights, the men ie» thc trcatineut studies were exf>o*cd to bright light (7000 to 12.000 <ux, an imcmity comparable to that of natural suulight just after dawn) betwcen 00:15 and 07:45 hours, whcrcas those in the contro! studies werc cxj>osed to ordinary* room light (approxiiita(cly 150 lux). Ali subjects complcted cognitivc-|K:rf<»rtitaiice tatks l»ourly