Normal healthy subjects show a reflex rise in precapillary resistance in the skin of the foot when they rise from lying to standing. To investigate the integrity ofthis reflex in patients with diabetes mellitus blood flow in the plantar region of the big toe was measured, using a laser Doppler flowmeter. The responses of diabetic patients with and without peripheral sensory neuropathy and healthy control subjects matched for age and sex were studied, with the foot at heart level and the foot passively lowered to 50 cm below the heart.In normal subjects mean blood flow recorded during the third to fourth minute of dependency fell to 18-1 (SD 11-9)% of the preceding resting flow determined with the foot at heart level. In the diabetic patients without neuropathy blood flow fell to 28.9 (18-6)% ofthe preceding resting flow. In the diabetic patients with neuropathy blood flow fell to 53-5 (23-7)% of the preceding resting flow, which was significantly different from the value achieved by the diabetics without neuropathy (p<0-02) and the healthy controls (p<0002). Six normal subjects were indirectly heated to release sympathetic tone and achieve the same mean skin temperature of the foot as the diabetic patients with neuropathy, and blood flow fell to 38-7 (24-3)% of the preceding resting flow, a value not significantly different from the response seen in the patients with neuropathy.These findings suggest that the postural control of blood flow in the foot is disturbed in patients with diabetic neuropathy, and this disturbance is compatible with a loss of sympathetic vascular tone. The resultant hyperperfusion on dependency may account for the oedema seen in some patients with neuropathy and may also act as a stimulus for the thickening of capillary basement IntroductionThe precapillary resistance in the skin of the foot rises on standing, thereby limiting the rise in capillary pressure resulting from the vertical column of blood between the heart and the foot.' Evidence suggests that this vasoconstriction is mediated by a sympathetic axon reflex.2 We examined this reflex in patients with diabetes for

1. The mechanism of postural vasoconstriction in the skin of the foot was examined in 102 healthy subjects by using laser Doppler flowmetry. 2. In 45 subjects, when one foot was lowered 50 cm below heart level and the other foot kept horizontal, blood flow was progressively reduced in the dependent foot (by 79%) with a concomitant, but less pronounced, reduction in flow in the horizontal foot (by 18%), indicating that a central mechanism is involved. After lumbar sympathetic blockade (in 10 patients with epidural anaesthesia), the flow in the horizontal foot remained virtually constant, indicating that the central component is mainly mediated via efferent sympathetic nerves, whereas the postural fall in flow in the dependent foot, though partially attenuated, was preserved, indicating that a local mechanism is mainly involved. 3. On lowering one foot below heart level in 12 subjects, there was a small but significant reduction in systolic and mean arterial pressures during the first minute of dependency. During the fourth minute, systolic pressure decreased, diastolic pressure and heart rate increased, but the mean arterial pressure was maintained. 4. In 19 subjects postural vasoconstriction was nearly abolished during local nervous blockade (lignocaine 3.7 x 10(-4)-7.4 x 10(-2) mol/l), indicating that the local mechanism mediating the vasoconstriction is mainly neurogenic in nature. However, there was still a small fall (19%) in flow in the dependent foot during blockade, probably indicating a minor contribution of a local myogenic mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Postural vasoconstriction in the foot was examined in 15 women during the menstrual, follicular and luteal phases of the menstrual cycle, and in 13 age-matched men on two separate occasions, in a constant-temperature environment (22 degrees C). 2. Skin blood flow was measured using laser Doppler flowmetry with the subject lying down, first with the foot maintained at heart level, then with the foot lowered passively 50 cm below the heart. In six of the women, at the time of experiment, serum oestradiol and progesterone were determined by radioimmunoassay. In four women and three men, foot swelling rate was also measured in the dependent foot using a strain gauge plethysmograph in addition to the postural changes in flow. At each visit, in all subjects, arterial blood pressure, heart rate, body temperature, foot skin temperature and body weight were also recorded. 3. The men showed no significant changes in all the variables assessed. In contrast, in women during the luteal phase diastolic and mean arterial pressures were significantly reduced, whereas heart rate, body temperature, foot skin temperature and body weight were significantly increased, as compared with the follicular and menstrual phases of the cycle. 4. During the follicular phase, when oestradiol concentration was high, there were significant reductions in dependent flow and foot swelling rate associated with a significantly augmented postural fall in flow, whereas during the luteal phase, when both oestradiol and progesterone levels were high, there were significant increases in dependent flow and foot swelling rate associated with a significantly impaired postural fall in flow.(ABSTRACT TRUNCATED AT 250 WORDS)

We studied the effects of the timing of tourniquet release in 88 patients randomly allocated for release after wound closure and bandaging (group A), or before the quadriceps layer had been closed allowing control of bleeding before suture (group B). The groups were similar in mean age, weight, gender, preoperative knee score, radiographic grading, and prosthesis implanted. Patients in group B had less postoperative pain, achieved earlier straight-leg raising, and had fewer wound complications. Five patients in group A had to return to theatre, three for manipulation under anaesthesia, one for secondary closure of wound dehiscence, and one for drainage of a haematoma. The last patient later developed a deep infection, which was treated by a two-stage revision. There were no significant differences between the two groups in operating time, or the decrease in haemoglobin concentration at 48 hours postoperatively. Some of the adverse effects of the use of a tourniquet for knee surgery can be significantly reduced by early tourniquet release, with haemostasis before the quadriceps mechanism and the wound are closed.

It has been shown in previous studies that skin blood flow in the human foot falls when the extremity is placed below heart level, owing to an increase in precapillary resistance that is probably mediated by a local sympathetic axon reflex or a myogenic response. In order to clarify the influence of the central thermoregulatory mechanisms on this local postural vasoconstrictor response, 12 normal male subjects were studied under standardized conditions, at rest and during heating of the trunk with an electric blanket. Skin blood flow was measured before and during body heating using laser Doppler flowmetry with the foot maintained at heart level and placed passively 50 cm below the heart. Skin blood flow and skin temperature were determined at two sites: the plantar surface of the big toe, an area with a relatively large number of arteriovenous anastomoses, and the dorsum of the same foot, where these anastomoses are few or absent. When the foot was placed in the dependent position, skin blood flow recorded in the dorsum of the foot during indirect heating fell to a level similar to that achieved before heating. In contrast, indirect heating greatly diminished the postural fall in skin blood flow recorded in the plantar surface of the big toe. In conclusion, the partial release of sympathetic vasoconstrictor tone associated with indirect heating appears to over-ride the local postural control of cutaneous vascular tone in areas where arteriovenous anastomoses are relatively numerous.