Circadian variation of cardiac autonomic nervous profile is affected in Japanese ambulance men with a working system of 24-h shifts.
OBJECTIVE
The purpose of this study was to compare the stress levels of Japanese ambulance men between on-duty and off-duty days, by using the physiological indices of heart rate variability (HRV) and cortisol in urine, measured over each 24-h period.


METHODS
Measurements were made during one on-duty and one off-duty day for each subject. The participants were monitored for 24 h with a Holter recording system and a parameter reflecting overall stress levels was obtained by measuring the cortisol level in urine collected over 24 h.


RESULTS
The circadian variation of cardiac autonomic nervous system activity was affected when the subjects were on duty. The low-frequency/high-frequency power ratio (=low-frequency power/high-frequency power: LF/HF), which is a useful parameter that reflects the balance of cardiac autonomic nervous activity, differed significantly between the waking and sleeping times on the off-duty day (P=0.03), while it did not differ between these two states on the on-duty day (P=0.56). Similarly, the normalized high-frequency power [=high-frequency/(high-frequency+low-frequency) power: HF/(HF+LF)] ratio, which is a useful measure of the activity of the parasympathetic nervous system, differed significantly between these two states on the off-duty day (P=0.04), while there was no significant difference in the ratio between the two states on the on-duty day (P=0.13).


CONCLUSIONS
These results show that the diurnal balance of the cardiac autonomic nervous system is affected on the on-duty day, even though it is possible for ambulance men to sleep regular hours.
Mitani
Satoko
S
Department of Health Promotion and Human Behavior, Graduate School of Public Health, Kyoto University, Yoshidakonoe-cho, Sakyo-ku, Kyoto, 606-8501, Japan. mitani@pbh.med.kyoto-u.ac.jp
Fujita
Masatoshi
M
Shirakawa
Taro
T
D000328:Adult; D001341:Autonomic Nervous System; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory; D004634:Emergency Medical Technicians; D006339:Heart Rate; D049690:History, Ancient; D006801:Humans; D006854:Hydrocortisone / Q000652:urine; D007564:Japan; D008297:Male; D008875:Middle Aged; D013315:Stress, Psychological / Q000503:physiopathology; D014940:Work Schedule Tolerance / Q000502:physiology*
D006854:Hydrocortisone