Desynchronization and internal dissociation in aircrew

Continuous records of sleep, sleepiness, urine samples and subjective fatigue ratings were obtained from and continuous monitoring of their temperature and electrocardiogram (ECG) was carried out on 12 B747 cockpit crewmembers during a base-line period of 36 h, 3 days of operating regular passenger flights between Frankfurt' (FRA) and San Francisco (SFO) and 44 h after their return to Germany. This paper deals with the circadian aspects of hormone and electrolyte excretion in addition to those of rectal temperature and ECG. Normal circadian phase relations of these functions were disrupted due to the time zone transitions of 9 h in both directions. Internal dissociation was most pronounced on the second day in SFO, with maximum shifts in acrophases up to 12.5 h for sodium and minimum shifts of about 2 h for 17-hydroxycorticosteroids (17-OHCS) excretion rates. After the return flight, readaptation to local time in Germany also differed among functions, but to a minor degree: the range of internal dissociation was reduced to 3 h, with extreme values observed in the curves of sodium excretion (delay of about 3.75 h) and of heart rate (delay of 0.6 h). The coupling with internal synchronizers varied considerably between the different measured parameters. Some body functions, such as 17-OHCS and temperature, were only slightly influenced by external factors. Others, such as heart rate and sodium excretion rates, were much more affected, e.g. by sleep, activity and food intake. From our findings we conclude that, due to dissociation and desynchronization, irregular work hours for pilots lead to rhythm disturbances, which may impair the well-being and, in some cases, may also affect the performance of aircrew during duty.