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(Circulation. 2000;102:1912.)
© 2000 American Heart Association, Inc.

Clinical Investigation and Reports

Modifications of Cardiac Autonomic Profile Associated With a Shift Schedule of Work

Raffaello Furlan, MD; Franca Barbic, MD; Simona Piazza, MD, PhD; Mauro Tinelli, MD, PhD; Paolo Seghizzi, MD; Alberto Malliani, MD

From Centro Ricerche Cardiovascolari, CNR; Unità Sincopi e Disturbi della Postura, Medicina Interna II, Medicina III, Ospedale L. Sacco; Università degli Studi di Milano, Milan, Italy (R.F., S.P., A.M.); Medicina del Lavoro, Ospedale Maggiore della Carità, Novara, Italy (F.B.); Medicina del Lavoro, Ospedali Riuniti Bergamo, Italy (P.S.); and STMicroelectronics Srl, Agrate Brianza, Milano, Italy (M.T.).

Correspondence to Dr Raffaello Furlan, Unità Sincopi e Disturbi della Postura, Medicina Interna II, Ospedale L. Sacco, Università di Milano, Via GB Grassi 74, 20157 Milano, Italy. E-mail raffaellof{at}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.

Key Words: nervous system, autonomic • circadian rhythm • shift work

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