Effect of shift work on cardio-vascular function -A comparison between normotensive and hypertensive subjects-

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Aims of this study are to investigate effects of shift work on blood pressure and cardio-vascular function, and to identify whether there are differences in such effects between normotensive and hypertensive subjects. The subjects of this study were 10 normotensive men, 9 hypertensive men without medication, and 9 men under anti-hypertensive medication. Ambulatory blood pressure (ABP) during 24 hours in daytime shift and in nighttime shift was recorded by the non-invasive devise (Nihon-Koden). Also physical activities, heart rates and postures were measured by lightweight portable monitor (GMS, Activetracer AC301).Results; (1) Blood pressures were changed according to activity level in both daytime and nighttime. (2) Among normotensive subjects, the basal blood pressures (the lowest blood pressure during sleeping) were higher in nighttime shift than in daytime shift with statistical significance. (3) The mean blood pressures during work-time weren't different between daytime shift and nighttime shift for normotensive subjects arid hypertensive subjects. (4) Among subjects under anti-hyoertensive medication, the blood pressures immediately after nighttime work were higher than that after daytime work. (5) Among the subjects with hypertension, the standard deviations of blood pressure during working time were larger in nighttime shift than in daytime shift. (6) There are positive linear regression between blood pressure, heart rate and activities measured by accelometer. The heart rates during night shift decreased compared with those during daytime shift.These results suggested that nighttime shift had effects on cardio-vascular function to both normotensive and hypertensiove subjects. Among hypertensive subjects, the effects of extrinsic stimulation seemed to be larger during nighttime shift than daytime shift. Also among normotensive subjects, we found higher blood pressure level during sleep between nighttime shifts than daytime shift.