Leg Versus Forearm Flow

A circadian blood pressure rhythm has been demonstrated in the majority of subjects, even if inactive during daytime. A rhythm of leg blood flow and peripheral resistance, with higher values during sleep than during waking, has also been recently shown in subjects confined to bed. Doubts still persist on whether such a rhythm also exists in the forearm, and whether or not its trend is similar to that found in the leg. In this study, leg and forearm blood flow and resistance were monitored noninvasively every 15 min for 22 h in 14 normotensives and 14 agematched hypertensives confined to bed. A significant blood pressure fall (normotensives, 24.8%/26.1%; hypertensives, 27.1%/26.3%; all P <.0001), heart rate decrease (214.9 in the former, 210% in the latter; both P <.0001) and leg flow increase (normotensives, 147.4%, hypertensives, 136.1%; both P <.0001) were found during sleep in all subjects, because of a blood redistribution probably attributable to activation of the cholinergic system. Forearm flow was significantly higher during sleep (126.1%, P <.0001) in the normotensives, whereas in the hypertensives a slight nocturnal decrease (21.9%) was found. In conclusion, the hypertensives had lower leg and forearm flow than the normotensives during sleep and similar during daytime. Peripheral resistance measured in the leg and in the forearm was greater in the former than in the latter, both during sleep and during waking. Am J Hypertens 1998;11:190–195 © 1998 American Journal of Hypertension, Ltd.