Introduction: The wake-sleep cycle is regulated by the Circadian (C) and Homeostatic (S) processes.
The C process controls endogenous markers such as Core Body Temperature (CBT). On
the other hand, the S process induces sleep to compensate for the time spent awake.
CBT exhibits a circadian rhythm (1), often related to performance (2), and changes
under sleep deprivation conditions (3). CBT reaches its nadir during the early morning,
a time of greater sleep propensity and reduced alertness and attention. Conversely,
during the acrophase, it is the time of highest attention, alertness, and quick response
to stimuli (2,4,5). Thus, CBT can serve as an indicator of performance (6) in sleep
deprivation situations where direct testing and evaluations are not feasible, such
as for military firefighters during incident responses. The objective of this study
was to compare the CBT of Military Firefighter cadets after a typical night of sleep
and during a 36-hour sleep deprivation protocol.
Methods: The sample consisted of 37 volunteers, including 31 men and 6 women, with an average
age of 30.7 years, members of the Military Firefighters Academy of the CBMMG, who
underwent 36 hours of sleep deprivation. CBT was measured from gastrointestinal temperature
by swallowing a capsule and using a telemetric system (CorTemp® EliteTM Data Recorder).
The swallowed capsule transmits low-frequency radio waves that vary in wavelength
depending on body temperature. These radio waves are received and converted into a
digital format by a data recorder (CorTemp® EliteTM Data Recorder). Volunteers were
evaluated every two hours starting from day 1 (08hD1), totaling 19 evaluations by
the end of day 2 (20hD2)
Results: The CBT from the first seven evaluations (08hD1, 10hD1, 12hD1, 14hD1, 16hD1, 18hD1,
20hD1) was compared with the CBT from the last seven evaluations (08hD2, 10hD2, 12hD2,
14hD2, 16hD2, 18hD2, 20hD2), which occurred chronologically at the same time, using
a paired sample t-test. No statistically significant differences were found in six comparisons, while
the CBT at 20h on day 1 was significantly different from 20h on day 2 (p < 0.01).
Conclusion: CBT displayed a circadian pattern (Process C) throughout the 36 hours of sleep deprivation,
showing no significant differences between day 1 (post-typical sleep) and day 2 (during
sleep deprivation), but with a potential homeostatic effect (Process S) after 36 hours
of sleep deprivation, consistent with existing literature. The measurement of CBT
can be used as an indicator of performance in Military Firefighter cadets of the CBMMG
during sleep deprivation situations where direct assessments and measurements cannot
be conducted. Support: UFMG, FEPE, CEPE, CEMSA, CAPES, CBMMG, CNPQ.
