EFFECTS OF 10-H TIME ZONE CHANGES ON FEMALE FLIGHT ATTENDANTS CIRCADIAN-RHYTHMS OF BODY-TEMPERATURE, ALERTNESS, AND VISUAL-SEARCH

The aim of the study was to analyse the effects of rapid time zone cha nges on the circadian rhythms of flight attendants. The mean age of th e 40 female subjects was 30.0 (SD=6-9) years. Measurements of oral tem perature, alertness, and visual search were performed at two hour inte rvals two days before the flight from Helsinki to Los Angeles, during the second and the fourth day in the USA and during the second and fou rth day after the return flight to Finland. The body temperature desyn chronized and the phases of the alertness and visual search rhythms sh ifted rapidly in the USA. After the return flight, the acrophases of t he circadian rhythms delayed during the second and fourth day in Finla nd. During the fourth day the acrophase of alertness was 35 min and th e acrophases of body temperature and visual search were 2 h 2 min and 3 h 8 min delayed, respectively. The mathematical model based on the C -, S- and W-process theory of alertness explained 25-96% of the variat ion of observed mean alertness of the subjects in different conditions . It is concluded that the duration of the de- and resynchronization p rocess of the flight attendants' circadian rhythms is on the average l onger than 9 days during and after round flights over ten time zones. The mean alertness of the subject can be predicted with considerable a ccuracy using the mathematical model.