Furlan R; Barbic F;
Piazza S; Tinelli M; Seghizzi P;
Malliani A
Centro Ricerche Cardiovascolari,
CNR, University degli Studi
di Milano, Milan, Italy. raffaellof@fisiopat.sacco.unimi.it
BACKGROUND: Shift work is
associated with an increased rate of cardiovascular diseases and accidents.
Discordance between circadian rhythms of stress-related biological variables
and the work-sleep schedule might explain the reduced efficiency of work. It is
not clear whether a shift schedule of work may induce similar discordance in
the 24-hour oscillatory pattern of the cardiac autonomic control in respect to
the work-sleep periods. METHODS AND RESULTS: Twenty-two healthy male
blue-collar shift workers underwent 24-hour ECG recordings during each of the 3
different shifts (first, 6 AM to 2 PM; second, 2 to 10 PM; third, 10 PM to 6
AM). Spectral analysis of heart rate variability over 24 hours provided the
normalized markers of cardiac sympathetic (LF(nu)) and vagal (HF(nu)) modulation of the sinoatrial
node activity and of the sympathovagal balance
(LF/HF). LF(nu) and LF/HF
exhibited 24-hour oscillations with different times of maximum and minimum in
accordance with the working and sleeping periods, respectively. Lower values of
LF(nu) and LF/HF suggestive of a reduced cardiac
sympathetic modulation were present when the job task was performed at night
compared with the values observed when the work was performed during morning
and evening. CONCLUSIONS: Continuous weekly changes of time of maximum and
minimum in the cardiac sympathetic and vagal
autonomic control may play a role in the excessive rate of cardiovascular
diseases in shift workers. The reduced values of the indexes of cardiac
sympathetic modulation during night work might be related to the presence of
sleepiness or diminished alertness, which in turn could facilitate errors and
accidents.