Diurnal variations of blood pressure in shift workers during day and night shifts.

The dependence of blood pressure upon internal rhythms and the short-term effects of shift rota on the blood pressure were investigated in shift workers. Blood pressure was measured every 30 min using automatic records for 24h in 17 physically working men in a chemical factory during their morning and night shifts. There were no differences of the mean blood pressure between the respective sleeping phases or between the working periods. The amplitudes of circadian blood pressure variations were equal. There was a phase difference of 8h corresponding to the lag between the working periods. At this 8-h lag the hourly means of the 24-h blood pressure were closely correlated (r=0.69). Comparisons of 24-h blood pressure profiles during the first and last days of night shift week showed that the effects of night work on the blood pressure were already fully developed within the first 24h (r=0.86). Thus the diurnal variations of the blood pressure are determined by the working and sleeping periods and largely independent of endogenous rhythm. There is no short-term alteration of the mean 24-h blood pressure after shift rota.