24-hour leg and forearm haemodynamics in transected spinal cord subjects

Objective: A circadian rhythm of blood pressure has been demonstrated both in subjects who are physically active during the day and in those confined to bed. The study of the circadian rhythm of arterial flow and peripheral r esistance, on the other hand, is limited to pioneer experiments. This paper is aimed at demonstrating that leg peripheral resistance has circadian flu ctuations which are modulated by spinal neural traffic. Methods: Eleven nor mal (able-bodied) human subjects and 11 patients with spinal transection du e to spinal cord injury (SCI) were studied. They were confined to bed for 2 4 h. Blood pressure and heart rate were monitored every 15 min with an auto matic device and leg flow with an automatic strain-gauge plethysmograph syn chronised to the pressurometer. Peripheral resistance was calculated at the same intervals. Results: In able-bodied subjects leg resistance was signif icantly higher during waking hours (when the sympathetic system is more act ivated) than during sleep, while in subjects with spinal cord injury no dif ference was detected between day-time and night-time. Conclusions: The circ adian rhythm is controlled by adrenergic fibres transmitted via the spinal cord. (C) 1999 Elsevier Science B.V. All rights reserved.