24H RHYTHM OF BLOOD-PRESSURE AND FOREARM PERIPHERAL RESISTANCE IN NORMOTENSIVE AND HYPERTENSIVE SUBJECTS CONFINED TO BED

Objectives To define whether a diurnal rhythm of peripheral resistance exists in normotensive and hypertensive subjects, has any relationshi p with that of blood pressure and differs in dipper and non-dipper hyp ertensives. Design and methods Forty-three subjects (13 normotensives and 30 mild-to-moderate essential hypertensives) confined for 24 h to bed were included. Blood pressure was recorded for 22 h at 15 min inte rvals, plethysmographic forearm flow was simultaneously measured and f orearm resistance calculated, The analysis was performed for the whole 22 h period and for three 4 h truncated periods, two of certain wakef ulness and one of certain sleep. Results A circadian rhythm of forearm resistance was shown in the normotensives, paralleling that: of blood pressure. All the normotensives were dippers, with a nocturnal blood pressure dip (systolic/diastolic) of -4.5/-6.0%, In the hypertensives, the day/night blood pressure trends were not homogeneous: 21 showed h igher blood pressure values during waking time, with a trend quite sim ilar to that of the normotensives, whereas the other nine were non-dip pers, Resistance was lower during sleep than during waking both in the normotensives and in the dipper hypertensives, whereas in the non-dip pers it was higher during sleep. Conclusions A sleep/waking rhythm of peripheral resistance with the highest values during daytime and the l owest during night-time does exist in normotensive as well as in the m ajority of hypertensive subjects resting continuously in bed, and ther efore is largely independent of physical activity. Only in a minority of hypertensive patients are higher values of peripheral resistance pr esent during sleep.