Objectives: To define whether a diurnal rhythm of peripheral resistance exists in normotensive and hypertensive subjects, has any relationship with that of blood pressure and differs in dipper and non-dipper hypertensives.
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 intervals, plethysmographic forearm flow was simultaneously measured and forearm resistance calculated. The analysis was performed for the whole 22 h period and for three 4 h truncated periods, two of certain wakefulness 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 higher blood pressure values during waking time, with a trend quite similar to that of the normotensives, whereas the other nine were non-dippers. Resistance was lower during sleep than during waking both in the normotensives and in the dipper hypertensives, whereas in the non-dippers it was higher during sleep.
Conclusions: A sleep/waking rhythm of peripheral resistance with the highest values during daytime and the lowest during night-time does exist in normotensive as well as in the majority of hypertensive subjects resting continuously in bed, and therefore is largely independent of physical activity. Only in a minority of hypertensive patients are higher values of peripheral resistance present during sleep.