Chronic leg ulceration is a major cause of morbidity in patients with homozygous sickle cell disease; the ulcers commonly resolve on bed rest. We have therefore compared the cutaneous vascular response to dependency in three groups of eight patients with sickle cell disease (those with an active ulcer, with an ulcer scar and with no history of ulceration) and in eight subjects with normal haemoglobin and no history of leg ulceration. 2. We monitored, with a laser Doppler flowmeter, the change in red cell (erythrocyte) flux induced in the skin of the leg, at two sites proximal to the malleoli, with the leg horizontal and 5 and 10 min after moving the leg to the dependent position. 3. With the leg horizontal, mean cutaneous red cell flux was substantially higher in normal skin of patients with sickle cell disease than in normal subjects and was higher still at the site of the ulcer or scar. On dependency, red cell flux fell not only in normal subjects but also in the patients with sickle cell disease, both in the normal skin and at the site of the ulcer or scar; there was no difference in any group between the 5- and 10-min values. The fall in red cell flux in normal skin of patients with sickle cell disease was smaller than in normal subjects when considered as a percentage of the control values (32%, 36%, 30% and 61% respectively in sickle cell patients with an active ulcer, with an ulcer scar and with no history of ulceration and in normal subjects), but in absolute terms the falls in red cell flux were similar in sickle cell patients and normal subjects. By contrast, the fall in red cell flux at the ulcer or scar site was greater than in normal skin from sickle cell patients whether considered as a percentage of the control value (48% and 49% respectively in those with an active ulcer or ulcer scar) or in absolute terms. 4. We propose that high resting perfusion is important in patients with sickle cell disease to maintain normal integrity of cutaneous tissue and that pronounced vasoconstriction on dependency hinders the healing and encourages recurrence of leg ulcers.
