Vascular responses in diabetic peripheral neuropathy

Human temperature regulation under heat stress in health, disease, and injury

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.

Autonomic neuropathy and toe circulation. A prospective study

Ankle and toe pressure ratios and toe temperature reactions to cold followed by indirect heating were evaluated in 23 diabetic patients with and without autonomic neuropathy (AN) in a first and in a second follow-up study after 5-7 years. In the first study, despite normal blood pressure ratios, AN patients, all with parasympathetic neuropathy, showed a markedly delayed increase in toe temperature after cooling followed by indirect heating. In the second study, most AN patients showed sympathetic neuropathy and had higher toe temperatures before cooling than those without AN. Parasympathetic neuropathy leads to increased sensitivity to cold in toe vessels and sympathetic neuropathy to vasodilation and increased toe temperatures.

Gangrene localized to the lower limbs in diabetics

Over a period of eight years, 247 unselected patients with more or less widespread areas of obvious cutaneous erythema on the lower legs and/or feet (incipient gangrene) or corresponding areas with cutaneous necrosis (manifest gangrene) were examined at our department. Of these patients, 34% had incipient and 66% manifest gangrene. It was found that 75% had open diabetes; the other were classified as non-open diabetics. In 75% of the 247 patients these lesions accompanied cardiac decompensation with or without edema, edema of other causes or--in some cases--arterial insufficiency. The gangrene developed in most patients a short time after the onset of these precipitating factors. Arterial insufficiency alone or together with other precipitating factors was seen considerably less often. Edema was thus the main precipitating factor for these lesions. Cardiac decompensation as well as edema of the legs due to other causes respond well to treatment. When treating such patients with open or nonopen diabetes, it should be taken into consideration that gangrene is a serious condition.

Influence of autonomic neuropathy on leg circulation and toe temperature in diabetes mellitus

The relationship between neuropathy and peripheral circulation was assessed in 26 patients with a short to moderate duration (less than 20 years, mean 11 years) and in 26 patients with a long duration (greater than 20 years, mean 35 years) of diabetes mellitus. Peripheral nervous function was evaluated from measurements of vibration thresholds and ankle reflexes and autonomic nervous function from deep breathing, Valsalva, and tilt table tests. Peripheral circulatory tests included plethysmography, systolic blood pressure ratios, and thermography. A markedly delayed toe temperature increase after cooling followed by indirect heating occurred in diabetics of short duration with autonomic neuropathy (AN). Judging from blood flows and pressure ratios, functional vasospasm caused abnormal toe temperature reactions in short duration diabetics. No correlation existed between AN and abnormal toe temperature reactions in diabetics of long duration. Macroangiopathy rather than AN seemed to be responsible for abnormal toe temperature reactions in long duration diabetics. Thus, an abnormal toe temperature reaction indicates AN in patients with a short duration and macroangiopathy in patients with a long duration of diabetes.

Peripheral circulation, particularly heat regulation reactions, in patients with amyloidosis and polyneuropathy

As patients with amyloidosis and polyneuropathy often have signs and symptoms of circulatory disturbances in the extremities, especially the legs, we have examined such patients and controls with oscillometry and digital pulse plethysmography in order to estimate the occurrence of any arterial circulatory insufficiency. No signs of significant obliterative arterial changes were found. Skin temperature was also determined in fingers and toes during body-cooling and at subsequent indirect heating. At low environmental temperature the skin temperature was higher in patients than in controls. In a few patients there was almost no decrease in skin temperature, despite a long period of cooling and a low rectal temperature. Indirect heating elicited a marked increase in the skin temperature of the toes and fingers of the controls. In most patients this reaction was completely absent in the toes and absent or reduced in the fingers. These deviations can be explained by nerve damage caused by amyloid deposition in the nerves. Amyloid deposits in the wall of small blood vessels may be an additional factor. Maximum blood flow in the anterior tibial muscle after combined ischemia and exercise, investigated with radioactive xenon, was reduced in half of the patients.

Skeletal lesions of the feet in diabetics and their relationship to cutaneous erythema with or without necrosis on the feet

Seventy patients with cutaneous erythema of the feet with or without necrosis were the subjects of this investigation. Sixty-five of them had open diabetes. The glucose tolerance of the remaining five patients was altered in a diabetic direction. Twenty-seven of the 70 patients had roentgenologically demonstrable destruction in the bones of the feet. These 70 patients were compared with 61 diabetic control patients of corresponding age and duration of diabetes but without these skin lesions of the feet. Only four of the 61 control patients had destruction in the bones of the feet and all these destructions were small. Precipitating factors were identified in general for the skin lesions, the most common being cardiac decompensation. A higher frequency of precipitating factors was seen in patients with skeletal destructions than in those without. The skeletal destructions and cutaneous necrosis are supposed to be equivalent lesions, localized to different tissues in the feet. When patients presenting skin lesions of the feet in the form of distal gangrene were compared with those who had cutaneous erythema and necrosis of the feet, but no distal gangrene, no differences were found with respect to age, duration of diabetes, occurrence of precipitating factors and the occurrence of skeletal destruction. Cutaneous erythema without necrosis is understood to be incipient diabetic gangrene.

The relationship between pressure ulcers and skin blood flow response after a local cold provocation

OBJECTIVE

To study the relationship between an impaired blood flow response after a local cold stimulus, testing nerve regulation of the local blood flow response, and an increased risk of developing pressure ulcers.

DESIGN

An observational, longitudinal, prospective study.

SETTING

Dutch nursing home.

PATIENTS

Eighty-two newly admitted somatic nursing home patients, age 60 years and older.

INTERVENTION

A local cold stimulus (17 degrees C) applied to the trochanter major.

MAIN OUTCOME MEASURES

On admission, blood flow response to a local cold stimulus. As the stimulus was withdrawn, the temperature measured at the skin increased asymptotically toward the final temperature, T(f). The velocity of this rise was characterized by the time constant, tau, of the process. On admission, and weekly during a 4-week follow-up period, the presence or absence of pressure ulcers was verified.

RESULTS

The blood flow response time correlated significantly with the risk of developing pressure ulcers. The patients who developed pressure ulcers during the follow-up period had a significantly longer response time than the patients who did not.

CONCLUSIONS

Malfunction of the nervous regulatory mechanisms of the local blood flow is partially responsible for an increased susceptibility to pressure ulcer formation.

Finger skin blood flow in response to indirect cooling in normal subjects and in patients before and after sympathectomy

Finger skin blood flow was measured in 80 healthy subjects, using laser Doppler imaging during basal vasodilatation at a local temperature of 40 degrees C. The response to cooling of the contralateral hand at 15 degrees C was studied. A vasoconstriction index was calculated in all subjects and a nomogram was constructed, taking age into consideration. Compared with these normal subjects, four patients operated on with transthoracic endoscopic sympathectomy due to hand hyperhidrosis showed clearly attenuated responses. The results indicate that the test can be used to assess disturbances in the sympathetic regulation of the peripheral blood flow.

Cutaneous vasomotor responses in young type I diabetic patients

Abnormal skin temperature reactions have been reported in type I diabetic patients. Whether this is due to a primary vascular disturbance or autonomic neuropathy is unclear. The aim of this study was to clarify this issue by evaluating cutaneous circulatory reactions before and after provocation. Seventeen type I diabetic patients and 17 age-matched controls were studied by recording blood flow (laser Doppler technique) on the dorsum of the hand (before, during, and after arterial occlusion), blood flow and skin temperatures on the dorsum of the foot and on the toe (before and after cooling followed by indirect body heating) and autonomic nerve function (heart rate reaction to deep breathing and to tilting). The results showed that before [4.6 +/- 0.5 perfusion units (PU) versus 6.1 +/- 0.7 PU; p = 0.0356] and after arterial occlusion (17.5 +/- 1.6 PU versus 25.3 +/- 1.7 PU; p = 0.0024), hand skin blood flow was significantly lower in patients than in controls. On the dorsum of the foot, skin temperatures was significantly lower in patients than in controls before cooling (29.2 degrees C +/- 0.3 degrees C versus 30.5 degrees C +/- 0.4 degrees C; p = 0.0107) whereas toe temperature and toe blood flow were similar before and after cooling in patients and controls. After body heating, however, toe temperature (after 30 min: 25.2 degrees C +/- 1.4 degrees C versus 30.9 degrees C +/- 1.2 degrees C; p = 0.0022) and toe blood flow (after 30 min: 10.9 +/- 2.5 degrees C versus 22.9 +/- 4.9 PU; p = 0.0313) were significantly lower in patients than in controls, especially in patients with parasympathetic neuropathy (i.e., patients with abnormal heart rate reactions to deep breathing). In conclusion, type I diabetic patients demonstrated a vascular disturbance in their skin that seemed to be exaggerated by parasympathetic neuropathy.

Pulse oximetry for the assessment of autonomic neuropathy in diabetic patients

Altered vascular responses to various thermal stimuli correlate well with the changes of autonomic neuropathy. These responses were assessed by the use of pulse oximetry. Standard cardiac autonomic function tests were performed in normal subjects (n = 12), diabetic patients without autonomic neuropathy (n = 8), and diabetic patients with autonomic neuropathy (n = 7). Autonomic functions in the same patients then were assessed by estimating the severity of vasospasm in response to cold stimulus with the help of pulse oximetry. Percentage fall in oxygen saturation at 15, 30, 60, 90, and 120 sec of exposure to cold stimulus was recorded on pulse oximeter. Time required for recovery and presence or absence of rebound rise following removal of cold stimulus were noted. In diabetics with autonomic neuropathy, the rate of fall in percentage oxygen saturation was significantly slower (p < 0.0001), less intense (p < 0.0001) and with delayed subsequent recovery (p = 0.013), compared to normal subjects. Rebound rise in oxygen saturation was absent in all the diabetics with autonomic neuropathy, compared to 2 of 12 normal subjects (p < 0.0001). We conclude that pulse oximetry may be a potentially useful, simple, and noninvasive bedside method for assessment of diabetic autonomic neuropathy.

Decreased sympatho-adrenal activity in diabetic patients with autonomic dysfunction following mental stress

The sympathetic nervous system is of major importance in the regulation of numerous physiological functions. While it is clearly established that there is a decreased noradrenergic status in people with autonomic neuropathy, the epinephrine secretion is much more controversial. Basal and mental stress-stimulated plasma catecholamine levels were measured in 42 diabetic patients with and without pathological cardiovascular function tests and in 13 healthy, non-diabetic control subjects. In addition, the excretion of catecholamines was measured in a 24 h urine collection and compared with the stress stimulated plasma levels. During mental stress exposure a diminished epinephrine secretion was found in diabetic patients with autonomic neuropathy compared with diabetic patients without neuropathy and the healthy control group (p < 0.05: respectively). The decreased epinephrine response to mental stress was strongly correlated with a diminished urinary excretion of this "neurotransmitter' (r = 0.46; p < 0.01). Diabetic patients suffering from cardiovascular autonomic neuropathy exhibit a diminished sympatho-adrenal response following mental stress exposure. Both measurement of urinary and mental stress stimulated plasma epinephrine levels following mental stress provide reliable information regarding sympatho-adrenal activity in diabetic patients.

Diabetes-induced changes in the contractility of the aorta and pA2 of nifedipine in the rat

Diabetes-induced changes in the calcium influx and contractile responses of aortic rings to various drugs were investigated in streptozotocin-treated rats. Diabetes is associated with calcium influx into the aortic rings (1.5-and 2.5-fold, respectively, after either KCl or noradrenaline stimulation compared with normal). The maximum KCl-induced contraction of the arorta in diabetic rats was reduced by 38%, but the EC50 of KCl remained unchanged. The pA2 of nifedipine for inhibiting the contractile response of aorta to KCl decreased one order of magnitude in the diabetic rats (8.26 vs 9.03 for non-diabetic rats). It is concluded that diabetes reduces the sensitivity of aortic tissue to nifedipine and may affect the stimulation-contraction coupling of vascular smooth muscle in such a way that a higher influx of calcium results after stimulation and that this may be responsible for diabetes-induced vascular complications.

Asymptomatic peripheral nerve dysfunction and vascular reactivity in IDDM patients with and without microalbuminuria

Abnormal vascular reactivity has been implicated in the aetiology of diabetic microvascular disease and we have previously demonstrated enhanced contractility of hand veins to noradrenaline in insulin-dependent diabetic (IDDM) patients with microalbuminuria. We have now assessed the possible contribution of subclinical peripheral nerve dysfunction to exaggerated vascular reactivity in micro-albuminuric patients. Twenty-five IDDM patients (15 with microalbuminuria), none of whom had symptomatic neuropathy, and 10 control subjects were studied. Vasoconstrictor responses were measured in dorsal hand veins using noradrenaline and phenylephrine. Conduction in median, peroneal and sural nerves was assessed using electrophysiology, and autonomic function using standard cardiovascular reflex tests. The noradrenaline dose causing 50% vasoconstriction was significantly lower in the microalbuminuric diabetic subjects compared with normoalbuminuric (3.6(1.7) mean (SEM) ng/min vs 20.1(6.0) ng/min, p = 0.0002) and non-diabetic subjects (35.1(5.0) ng/min; p < 0.0001). However, reactivity to phenylephrine did not differ between the groups. Median nerve motor conduction velocity was significantly slower in microalbuminuric (48.4(1.4) m/s) than in normoalbuminuric (52.7(1.2) m/s, p = 0.04) and non-diabetic subjects (56.7(0.9) m/s, p = 0.0001). In the diabetic group overall, there was a strongly positive linear correlation between vascular response to noradrenaline and conduction velocity in both the median nerve (r = 0.62, p = 0.0009) and peroneal nerve (r = 0.53, p = 0.006). There was no correlation between phenylephrine-induced responses and motor conduction velocity in either nerve, nor were indices of autonomic function correlated with vascular reactivity to either agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention by insulin treatment of endothelial dysfunction but not enhanced noradrenaline-induced contractility in mesenteric resistance arteries from streptozotocin-induced diabetic rats

1. Streptozotocin-induced diabetic rats (Wistar) were implanted with sustained release insulin pellets (release rate = 4 u day-1) or with placebo pellets (palmitic acid) from the onset of glycosuria. 2. Noradrenaline sensitivity, endothelium-dependent relaxation to acetylcholine and endothelium-independent relaxation to sodium nitroprusside were assessed in mesenteric resistance arteries from the insulin-treated (IT) diabetic animals and compared to placebo-implanted (PI) diabetics and age-matched controls. 3. Arteries from PI-diabetic rats (8-10 weeks) demonstrated an enhanced maximal response to noradrenaline compared to controls, which was not prevented by insulin treatment (control 2.65 +/- 0.17 mN mm-1, n = 18 arteries versus PI-diabetic 3.73 +/- 0.40 mM mm-1, n = 5, P < 0.05; control versus IT-diabetic 4.02 +/- 0.19 mN mm-1, n = 22, P < 0.001). Sensitivity to noradrenaline was similar between the three groups. 4. In the presence of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), IT and PI arteries were more sensitive to noradrenaline than control arteries (pEC50: control 5.75 +/- 0.08, n = 17, versus PI-diabetic 6.14 +/- 0.09, n = 8, P < 0.05; control versus IT-diabetic 6.38 +/- 0.08, n = 20, P < 0.001). 5. The maximum contractile response to depolarizing 125 mM K+ was significantly enhanced in IT-diabetic arteries but not PI-diabetic when compared to control arteries (maximum response: control 3.74 +/- 0.15 mN mm-1, n = 18, versus PI-diabetic 3.61 +/- 0.19 mN mm-1, n = 11, NS; control versus IT-diabetic 4.66 +/- 0.18 mN mm-1, n = 22, P < 0.001). 6. Endothelium-dependent relaxation to acetylcholine was profoundly impaired in the PI-diabetic arteries, but in the IT-diabetic arteries was not significantly different from controls (pEC50: control 7.64 +/- 0.19, n = 17, versus PI-diabetic 6.07 +/- 0.12, n = 8, P < 0.001; control versus IT-diabetic 7.36 +/- 0.09, n = 22, NS). 7. Endothelium-independent relaxation to sodium nitroprusside was slightly but significantly impaired in the PI-diabetic arteries, but was not significantly different in the IT-diabetic arteries compared to controls (pEC50: control 7.78 +/- 0.10, n = 13, versus PI-diabetic 7.31 +/- 0.13, n = 13, P <0.05; control,versus IT-diabetic 7.64 +/- 0.09, n = 16, NS).

The validity and reproducibility of the skin vasomotor test--studies in normal subjects, after spinal anaesthesia, and in diabetes mellitus

Skin sympathetic vasomotor control can be examined in the extremities by the skin vasomotor test. In this test the change in skin blood flow and skin temperature in the hand and foot in response to a cold stimulus is utilized as an index of distal sympathetic nerve fibre integrity. This is of importance in conditions such as diabetes mellitus as peripheral autonomic neuropathy is associated with orthostatic hypotension and diabetic foot complications. The validity and reproducibility of the test as a marker of distal sympathetic nerve function has been studied. The test was performed in nine healthy control subjects and in nine subjects (undergoing minor surgery) after a sympathetic nerve conduction block (L2-L3) was achieved in the lower extremities by spinal analgesia. Changes in skin temperature (p < 0.001) and skin blood flow (p < 0.005) in responses to cooling were significantly larger in the control group than in the group with spinal analgesia. Repeated skin temperature measurements on 42 occasions (test-retest period of 4 weeks) in eight healthy and 34 diabetic subjects indicated a reliability coefficient of 80%. We conclude, therefore, that the skin vasomotor test provides a valid and reproducible quantitative assessment of skin sympathetic nerve function in upper and lower extremities.

Outcome criteria in patients with peripheral arterial disease

To adequately evaluate patients with chronic occlusive arterial disease several factors will need to be taken into account and documented. These include associated diseases such as diabetes mellitus. When surgical or endovascular therapy is applied, analysis of outcome must include the symptomatic status of the patient, the anatomic evidence of patency of the procedure and of the proximal and distal disease, the hemodynamic result, limb preservation, and mortality. All of these factors will provide a better global picture of the disease and information on how it can be best treated.

Altered cardiac adrenergic neurotransmission in streptozotocin-induced diabetic rats

1. Functional alterations of the sympathetic neuroeffector junction of the left atria were studied in rats with streptozotocin-induced diabetes. 2. Eight to 12 weeks of diabetes resulted in a marked decrease in the positive inotropic response of left atria to electrical field stimulation (EFS). 3. The overflow of [3H]-noradrenaline from diabetic left atria caused by EFS was much less than that from control preparations. 4. The concentration-response curves showed no change in sensitivities of the left atria to exogenous noradrenaline and tyramine in diabetic rats. The maximum positive inotropic response to these agents were similar in diabetic and control animals. 5. The left atrial content of noradrenaline was not significantly changed in diabetic rats. The cocaine-sensitive uptake of [3H]-noradrenaline was also unaltered. 6. Atropine enhanced the positive inotropic response and [3H]-noradrenaline overflow induced by EFS in control left atria. Similarly, yohimbine caused an enhancement of EFS-evoked inotropic response in control atria. However, these effects of the antagonists were not observed in diabetic left atria. 7. It is concluded that the decrease in the positive inotropic response of the left atria to EFS in diabetic rats is caused by an impairment of noradrenaline release from the sympathetic nerve terminals through a calcium-dependent exocytotic mechanism. The present results also indicate that presynaptic alpha 2-adrenoceptors and muscarinic receptors that are linked to inhibition of the noradrenaline release during nerve stimulation may be functionally impaired in diabetic animals.

The effect of insulin infusion on capillary blood flow in the diabetic neuropathic foot

The effect of a short-term improvement in glycaemic control induced by insulin infusion on foot skin capillary blood flow was previously unknown. In seven Type 2 (non-insulin-dependent) diabetic subjects with neuropathy capillary blood flow was measured in the great toe nailfold by television microscopy. An estimate of arteriovenous shunt flow was obtained simultaneously in the pulp of the great toe by laser Doppler flowmetry. After omission of oral hypoglycaemic therapy for 24 h mean blood glucose was 15.7 +/- 0.7 (SEM) mmol l-1. A priming infusion of 0.1 U kg-1 of insulin was given intravenously over 15 min, followed by a variable rate insulin infusion adjusted to steadily reduce blood glucose avoiding hypoglycaemia. At the end of the study blood glucose was reduced to 6.9 +/- 0.7 mmol l-1 (p less than 0.001). During the insulin infusion, capillary blood velocity increased by 28.8% (p less than 0.05), and the diameter of the capillary erythrocyte column increased from 7.6 +/- 0.2 to 9.2 +/- 0.3 micron (p less than 0.01). Thus during the insulin infusion, the calculated capillary flow increased to 226 +/- 36% above basal values (p less than 0.01). Laser Doppler flow did not change significantly, suggesting that during insulin infusion skin blood flow is redistributed with an increase in capillary flow relative to arteriovenous shunt flow.

Profound vasoconstrictive effect of cigarette smoking in diabetics with autonomic neuropathy

Changes in leg skin temperature during and after cigarette smoking were examined in 25 diabetics with autonomic neuropathy (au-neuropathy) (mean age 52 +/- 2 years) and 23 without (mean age 49 +/- 2 years), and 15 normal controls (mean age 49 +/- 2 years) using a Thermoviewer JTG 3300. All subjects were habitual smokers. Japanese Seven Star cigarettes (each containing 1.2 mg nicotine) were used for the test. Tender brand cigarettes (0.3 mg) were used additionally to compare the effect of nicotine content on the results. The smoking-stimulated thermographic pattern in the control group was rather flat, with a slight decrease in temperature followed by a slight increase before returning to the baseline level 15-20 min after smoking. The frequency of the typical temperature decreasing pattern, characterized by a profound decrease and gradual return to the baseline level in about 1 h, was significantly higher in the diabetic group than in the control group (33/48 vs 1/15; P less than 0.005). A comparison of the two diabetic subgroups revealed that the frequency was considerably higher in the subgroup with au-neuropathy (23/25 vs 10/23). These results suggest that au-neuropathy affects smoking-induced vasoconstriction in diabetic subjects. The maximum temperature decreases recorded were 1.5 +/- 2.0 and 2.69 +/- 0.24 degrees C in the controls and diabetics with au-neuropathy, respectively. The effect of Tender cigarettes with a low nicotine content was much weaker than that of Seven Star, which further suggests that smoking-induced vasoconstriction was also nicotine-dependent.

Aetiology of diabetic foot ulceration: a role for the microcirculation?

Neuropathy, mechanical stress, and macrovascular disease are involved in the pathogenesis of diabetic foot ulceration. Implicit in the development of gangrene and ulceration is the recognition that these factors interact with the microcirculation, resulting in the failure of skin capillary flow to meet nutritive requirements. There is little evidence to associate structural microangiopathy with foot microcirculatory failure. Significant functional abnormalities of the microcirculation have been defined. In accord with the haemodynamic hypothesis early hyperaemia and capillary hypertension promote more sinister late functional abnormalities with increasing duration of diabetes. These late functional abnormalities include loss of autoregulation and reduced hyperaemic responses which interact with loss of neurogenic flow regulation, disturbed endothelial function, and abnormal rheology to produce the familiar clinical picture of the diabetic foot. Ischaemia secondary to multi-segment arterial disease induces additional abnormalities of microcirculatory function which are superimposed on the pre-existing diabetic microvascular structural and functional microangiopathy.

Quantitation of skin vasomotor control in normal subjects and in diabetic patients with autonomic neuropathy

Peripheral autonomic neuropathy in diabetes has been difficult to evaluate. We have developed a test to quantitate sympathetic skin vasomotor function in the extremities. Skin vasomotor reflexes were investigated after warming and cooling the left arm and recording changes in skin temperature as a measure of skin blood flow in the right hand and both feet. Twenty-three diabetic patients with cardiac autonomic neuropathy and 28 healthy control subjects were examined. In contrast to the healthy subjects, the diabetic patients showed reduced or even absent responses in skin temperature to both warming and cooling. The rate of skin temperature decrease for the hand and feet during cooling, which was used as the actual parameter to quantitate skin vasomotor control, was significantly reduced in the diabetic group as compared with the healthy control subjects. We conclude that this technique provides a simple non-invasive method for quantitating skin vasomotor function in the extremities of diabetic patients.

Use of Doppler flow velocity waveform analysis in detection of initial diabetic microangiopathy

Doppler flow velocity waveform analysis (FVWFA), recorded from the dorsalis pedis artery (DPA) and the radial artery (RA), was performed on 36 women in attempting to detect an initial diabetic microangiopathy (DM). The study comprised two groups of women affected by non-insulin-dependent diabetes mellitus, 6 patients (pts) of reproductive age (1), 12 pts in menopause (II), and two groups of age-matched healthy controls (C) (III and IV). Clinical signs of initial DM were present in group I. All the examined pts were nonsmokers and normotensive and without cardiopathy, signs of diabetic macroangiopathy, collagen vascular disease and/or Raynaud's phenomenon, and renal failure. Four waveform dimensions capable of separating different degrees of peripheral obstructive arteriolar disease were determined on velocity tracing and the results used in a single best discriminant equation. The resultant discriminant score (DS), derived by FVWFA on DPA, showed a highly accurate rate of separating the young pts with DM from both C and the pts in menopause without DM. Furthermore, the resultant DS was statistically not different in groups II, III, and IV. In conclusion, FVWFA on DPA, in this experience, has proved to be an accurate and sensitive method in the detection of initial DM.

The effect of an aldose reductase inhibitor on cardiovascular performance in patients with diabetes mellitus

Because some aldose reductase inhibitor studies have demonstrated clinical improvement in scored neurological signs and symptoms of diabetic neuropathy, a prospective study of the effect on cardiovascular performance of sorbinil 250 mg/day for 12 months was conducted on patients with diabetic autonomic neuropathy who were free of atherosclerotic coronary artery disease and/or cardiomyopathy. After 1 year of treatment, the study group (n = 14) demonstrated significant improvement in both the resting cardiac output (P = 0.02), and the maximal cardiac output (P = 0.03). This observation suggests that the use of an aldose reductase inhibitor may be useful in treating suboptimal cardiovascular performance in patients with diabetic cardiac autonomic neuropathy.

Plasma adrenaline kinetics in type 1 (insulin-dependent) diabetic patients with and without autonomic neuropathy

Plasma adrenaline kinetics (clearance, extraction across the forearm, initial plasma disappearance rate, mean sojourn time, volume of distribution) were studied in sixteen Type 1 (insulin-dependent) diabetic patients during constant i.v. infusion of tritium labelled adrenaline. In patients with (n = 8) and without (n = 8) neuropathy forearm venous plasma noradrenaline and adrenaline concentrations as well as plasma clearance of adrenaline based on arterial sampling (1.7 vs 2.1 l/min) were not significantly different. The initial disappearance time (T 1/2) after the infusion of the tritium labelled adrenaline had been stopped was significantly prolonged in Type 1 diabetic patients with neuropathy compared to those without (after 20 min infusion 2.7 vs 2.2 min, p less than 0.02, after 75 min infusion 3.7 vs 2.9 min, p less than 0.05). The corresponding values for the mean sojourn time of adrenaline in plasma were 6.5 vs 4.7 min (p less than 0.05) after 20 min infusion and 18 vs 10 min (p less than 0.05) after 75 min of infusion. The unchanged plasma clearance and the prolonged initial halftime and mean sojourn time of adrenaline in plasma suggest that adrenaline is distributed in a larger volume in Type 1 diabetic patients with neuropathy as compared to patients without neuropathy (estimated space of distribution 29 vs 20 l). Our results suggest that patients with diabetic neuropathy do not adjust the plasma adrenaline concentration to changes in adrenaline infusion rate as rapidly as those without neuropathy, i.e. the effect of an elevated adrenaline secretion rate may be prolonged in patients with diabetic autonomic neuropathy.

Altered tail-skin temperature responsiveness in streptozotocin-induced diabetic rats

We evaluated the tail-skin temperature response to administration of several doses of isoproterenol in streptozotocin-induced diabetic rats after 48 h and after 4 weeks of diabetes. Blood glucose concentrations were significantly increased over controls 48 hours after administration of streptozotocin (65 mg/kg, i.v.) and remained elevated to a similar degree in the 4-week group. Basal rectal temperature and tail-skin temperature (TST) were not different between controls and the diabetic groups and were not affected by administration of saline. However, administration of isoproterenol (25 micrograms/kg, s.c.) caused a significant rise in TST in the control group, but not in the rats diabetic for 4 weeks. A similar but exaggerated response was observed in the controls after subcutaneous administration of 40 micrograms/kg and 100 micrograms/kg of isoproterenol. The TST response in the 4-week diabetic rats still remained negligible with the two higher doses of isoproterenol. When the data were summarized as area under the TST curve, a dose-dependent increase was observed in the control groups and a significant absence of response was observed in the 4-week group. The rats studied 48 h after streptozotocin injection had a similar TST response to the control group after administration of 40 micrograms/kg of isoproterenol. Colonic temperatures did not significantly change between the two groups in any of the studies, although the colonic temperatures tended to rise in the control groups following administration of isoproterenol. We conclude from this study that the absence of a tail-skin temperature response in rats diabetic for 4 weeks results from either a reduced beta-adrenergic receptor mediated response or an altered neural thermoregulatory reflex response, or both. These changes are probably not due to streptozotocin treatment or increases in blood glucose.

Metabolic and cardiovascular responses to epinephrine in diabetic autonomic neuropathy

Norepinephrine-induced vasoconstriction, which is mediated by alpha-adrenergic receptors, is accentuated in patients with autonomic neuropathy. In contrast, responses mediated by beta-adrenergic receptors, including vasodilatation and metabolic changes, have not been evaluated in these patients. To study these responses, we administered epinephrine in a graded intravenous infusion (0.5 to 5 micrograms per minute) to seven diabetic patients without neuropathy, seven diabetic patients with autonomic neuropathy, and seven normal subjects. Mean arterial pressure decreased significantly in the patients with autonomic neuropathy (P less than 0.01) but was unchanged in the other groups. Since cardiac output increased to a similar extent in the three groups, the decrease in blood pressure was due to a significantly larger decrease (P less than 0.01) in total peripheral vascular resistance in the patients with autonomic neuropathy. The heart rate increased significantly more during the infusions in the patients with neuropathy than in those without neuropathy. Epinephrine produced a greater increase in blood glucose, the glucose-appearance rate, lactate, glycerol, and free fatty acids in the patients with autonomic neuropathy than in the other groups (P less than 0.05). These findings indicate that several beta-receptor-mediated responses to epinephrine are enhanced in patients with diabetic autonomic neuropathy. The underlying mechanism remains to be elucidated.

A contrasting effect of the diabetic state upon the contractile responses of aortic preparations from the rat and rabbit

Diabetes was induced in rats by a single intraperitoneal injection of streptozotocin (65 mg kg-1). Rabbits were rendered diabetic by injecting alloxan (100 mg kg-1) into the lateral ear vein. Diabetes was confirmed by a significant elevation of serum glucose in both species 8 weeks after injection. The maximum contraction to noradrenaline (NA), 5-hydroxytryptamine (5-HT) and KCl was markedly diminished in thoracic aortic rings (AR) from diabetic rats with no change in the EC50 of the agonists. There were no differences in the contractile properties of AR from diabetic rabbits to NA, 5-HT or KCl. Diabetes did not alter the responsiveness of AR from the rat to angiotensin II (AII). However, AR from diabetic rabbits displayed a decreased maximal contraction and an increased EC50 to AII. The magnitude of the acetylcholine-induced relaxation to precontracted AR was not different between diabetic and control rats and rabbits. The contractile responses of AR to NA, 5-HT and KCl were depressed in diabetic rats, regardless of the control tissue to which they were compared. The decrease in maximal contraction to NA, 5-HT and KCl seen in diabetic animals was prevented by insulin replacement. The results demonstrated that while both rats and rabbits exhibited a similar degree of hyperglycemia after treatment with a diabetogenic agent, aortic preparations from the rabbit are not affected in the same way as the aorta from the diabetic rat when exposed to NA, 5-HT and KCl. This feature may be related to the marked differences between the extent of sympathetic innervation of the aorta in the rabbit and rat. Furthermore, the decrease in maximal contraction in rat aorta was non-specific with respect to agonists since it could also be demonstrated with KCl. Therefore, it follows that the diabetic state may affect processes responsible for contraction beyond the level of receptor activation.

Disorders of the autonomic nervous system: Part 1. Pathophysiology and clinical features

Autonomic dysfunction may result from diseases that affect primarily either the central nervous system or the peripheral autonomic nervous system. The most common pathogenesis of disturbed autonomic function in central nervous system diseases is degeneration of the intermediolateral cell columns (progressive autonomic failure) or disease or damage to descending pathways that synapse on the intermediolateral column cells (spinal cord lesions, cerebrovascular disease, brainstem tumors, multiple sclerosis). The peripheral autonomic nervous system may be damaged in isolation in the acute and subacute autonomic neuropathies or in association with a generalized peripheral neuropathy. The peripheral neuropathies most likely to cause severe autonomic disturbance are those in which small myelinated and unmyelinated fibers are damaged in the baroreflex afferents, the vagal efferents to the heart, and the sympathetic efferent pathways to the mesenteric vascular bed. Acute demyelination of the sympathetic and parasympathetic nerves in the Guillain-Barré syndrome may also cause acute autonomic dysfunction. Although autonomic disturbances may occur in other types of peripheral neuropathy, they are rarely clinically important.

Abnormal cerebrovascular carbon dioxide reactivity in people with diabetes

Cerebral blood flow was measured both under conditions of normocapnia and hypercapnia in 22 diabetic patients and 20 normal control subjects, using either the intravenous 133Xe method or the closely comparable 133Xe inhalation method. While 19 out of 20 control subjects responded appropriately to hypercapnia with an increase in flow, eight of the diabetic patients failed to respond normally, this difference being significant (p = 0.03). Those manifesting an abnormal response included young, insulin-dependent patients with a short duration of diabetes and no clinical evidence of complications.

The diabetic foot: pathophysiology and treatment

The diabetic foot can be classified into the neuropathic foot, characterized by the neuropathic ulcer, the Charcot joint and neuropathic oedema associated with a good circulation, in which neuropathy predominates, and the ischaemic foot in which atherosclerosis is the dominant factor leading to a reduction in blood flow with absent pulses. In the neuropathic foot, blood flow is increased, the vessels are still and dilated as a result of medial wall calcification and there is evidence for arteriovenous shunting. The neuropathic ulcer characteristically develops on the plantar surface following inflammatory autolysis and haematoma formation under neglected callosities. Chiropody is therefore the mainstay of treatment and recurrence is prevented by redistribution of weight bearing forces by moulded insoles in special footwear. Charcot osteoarthropathy is often preceded by fracture which is a further complication of diabetic neuropathy and which precipitates the rapid bone and joint destruction of the Charcot joint. Neuropathic oedema responds to ephedrine with a reduction in peripheral flow and an increase in urinary sodium excretion. The ischaemic foot is characterized by rest pain, ulceration and gangrene. Medical management can be successful in up to 72%, the remainder needing arteriography to assess suitability for arterial reconstruction or angioplasty. In the diabetic leg, atherosclerosis is predominant in the branches of the popliteal artery making arterial reconstruction difficult. Optimum care of the diabetic foot is provided in a diabetic foot clinic where the skills of chiropodist, shoe-fitter and nurse receive full support from physician and surgeon. Many lesions of the diabetic foot are avoidable and thus patient education is the cornerstone of prevention.

Diabetic autonomic neuropathy

The incidence of autonomic dysfunction as a complication of diabetes mellitus is reported to be as high as 20% to 40%. Symptoms of diabetic autonomic neuropathy (DAN) are often vague, and signs difficult to detect on routine physical examination. The early diagnosis of DAN is possible by utilizing several simple noninvasive tests, which may also be helpful in localizing the lesion(s) to specific autonomic pathways. DAN may affect multiple organ systems, to include cardiovascular, gastrointestinal, genitourinary and/or neuroendocrine, and may, in fact, be life-threatening. The same metabolic disturbances of somatic peripheral nerve may also be responsible for DAN. Like somatosensory neuropathy, definitive therapy for DAN is not yet satisfactory, although multiple chemotherapeutic agents have been tried and warrant further investigation.

A new index of autonomic neuropathy in diabetes mellitus: heat stimulated thermographic patterns

Autonomic neuropathy, especially sympathicopathy, a life-threatening complication of diabetes mellitus, has been difficult to evaluate, and remains undetermined. We studied the thermographic patterns of 62 patients (50-69 years old), revealing the vasodilated activities of one leg by immersing the other leg in a warm water bath, for the detection of sympathetic neuropathy, using Thermoviewer MDJTG-MD. The normal pattern shows an increase in skin temperature, while the flat pattern shows no rise or even a paradoxical decrease. The latter had a significantly longer duration of diabetes and poor blood sugar control. The thermographic pattern is closely related to microangiopathy, R-R interval variation and motor nerve conduction velocity. However, R-R interval variation is often abnormal in patients with normal thermographic patterns, showing vasosympathetic abnormalities appearing far later in the development of diabetic neuropathy. The flat pattern develops slowly after at least several years of poor blood sugar control. Change in the pattern is also gradual and slow. The reproducibility of the pattern is excellent and requires relatively simple and noninvasive techniques. Thermography is one of the most reliable, reproducible and noninvasive indexes for finding and following diabetic sympathetic abnormalities.

Selection of patients for lumbar sympathectomy

We successfully predicted that patients presenting with critical ischemia of a limb and Doppler ratios greater than or equal to 0.3 would benefit from lumbar sympathectomy alone. However, we found that the procedure failed in 14 per cent of limbs whose ratios were greater than or equal to 0.3. In retrospect, all these patients were found to have deep infection. Had we known this fact prospectively, our predictions for success would have been close to 100 per cent. We were less than 50 per cent successful in predicting failure of the procedure, but the number of patients in this group is too small to draw reliable conclusions. We believe that patients with arm-ankle Doppler ratios greater than or equal to 0.3 whose manifestations of ischemia are limited to the skin will have a greater than 95 per cent chance of receiving a good result from lumbar sympathectomy alone and that this result will be maintained for many years.

Impaired autoregulation of blood flow in skeletal muscle and subcutaneous tissue in long-term Type 1 (insulin-dependent) diabetic patients with microangiopathy

Autoregulation of blood flow was studied in skeletal muscle and subcutaneous tissue in seven Type 1 (insulin-dependent) diabetic patients (median age: 36 years) with nephropathy and retinopathy and in eight normal subjects of the same age. Blood flow was measured by the local 133Xe washout technique. Reduction in arterial perfusion pressure was produced by elevating the limb 20 and 40 cm above heart level. Blood flow remained within 10% of control values when the limb was elevated in normal subjects. In five of the seven diabetic subjects blood flow fell significantly in both tissues when the limb was elevated 40 cm indicating impaired autoregulation. The results suggest that intrinsic vascular (arteriolar) mechanisms (myogenic and/or metabolic) underlying the normal autoregulatory response are defective in some diabetic patients with microangiopathy.

Digital gangrene caused by finger pricks made to obtain blood for blood glucose monitoring

We report the case of a 57-year-old man with diabetes in whom severe Raynaud's phenomenon and digital infarction were precipitated by finger pricks made to obtain blood for blood glucose monitoring. We discuss the possible mechanisms involved.

Noradrenergic innervation of the penis in control and streptozotocin-diabetic rats: evidence of autonomic neuropathy

The noradrenergic sympathetic innervation of the penis of control and 4-month streptozotocin-diabetic rats was examined with the glyoxylic acid histofluorescence method. Noradrenergic varicosities were found in the corpora cavernosa in a dense subtunical plexus and in the perisinusoidal and trabecular regions of the erectile tissue, in the corpus spongiosum in perisinusoidal tissue, around large arteries and veins, and around small tortuous arterioles and small draining veins of the corpora cavernosa and spongiosum. Noradrenergic varicosities were diminished in number and fluorescent intensity in all regions of the penis of diabetic rats compared with controls. The subtunical plexus was absent, perisinusoidal and trabecular varicosities were sparse, and only occasional intermittent, discontinuous, dull fluorescent fibers or plexuses were found around the vessels. Quantitation with high-performance liquid chromatography revealed a significant reduction of norepinephrine in the penis of diabetic rats compared with controls. The present study suggests that long-term streptozotocin diabetes in the rat is accompanied by sympathetic autonomic neuropathy of the penis that seems to parallel changes in the noradrenergic content of penile corpora of men with diabetes and erectile impotence. The streptozotocin-diabetic rat merits further study to explore the relationship between noradrenergic innervation of the penis and erectile tissue.

Ephedrine: a new treatment for diabetic neuropathic oedema

Peripheral oedema secondary to diabetic neuropathy is poorly understood and difficult to treat. Ephedrine markedly reduced neuropathic oedema in four insulin-dependent diabetics. Mean weight-loss (p less than 0 . 05) after 7 days' treatment was 7 . 43 +/- 4 . 51(SD) kg. The oedema returned (mean weight increase 6 . 33 +/- 1 . 73 kg; p less than 0 . 01) when ephedrine was withdrawn but resolved (weight-loss 4 . 85 +/- 1 . 57 kg; p less than 0 . 01) when ephedrine treatment was repeated. In one patient mean 24 h sodium excretion increased from 177 +/- 5 . 20 mmol before ephedrine to 502 +/- 78 mmol on ephedrine therapy (p=0 . 028). Ephedrine also reduced excessive peripheral blood flow produced by the neuropathy; both arterial diastolic flow and arteriovenous shunting as demonstrated by Doppler blood velocity profiles were reduced and the pulsatility index increased from 2 . 50 +/- 0 . 61 to 4 . 75 +/- 1 . 76 (p less than 0 . 001). Ephedrine continues (12-15 months) to be an effective treatment for neuropathic oedema in these four patients.

Adrenergic mechanisms and blood pressure regulation in diabetes mellitus

Changes in blood pressure (BP) and plasma norepinephrine (NE) following various stimuli of the sympathetic, nervous system were studied in six healthy subjects and in 17 diabetic patients. The latter were subdivided in three groups: (1) six patients with neither peripheral neuropathy nor autonomic dysregulation, (2) six patients with severe peripheral neuropathy without autonomic dysregulation, and (3) five patients with autonomic dysregulation, three of whom suffered also from peripheral neuropathy. The following procedures were performed: (1) cold pressor test (2 min), (2) mechanical irritation of the skin by suction (0.75 kg/cm2, 10 min), (3) orthostasis (10 min), and (4) i.v. infusion of NE (50, 100, 200 ng kg-1 min-1 for 15 min each). Both the stimulated endogenous plasma NE levels and BP response to exogenous NE were the same in normal subjects, in diabetic controls and in diabetics with peripheral neuropathy without autonomic dysregulation. In contrast, diabetics with postural hypotension showed a less pronounced release of NE to standing (P less than 0.05), but not to cold pressor test and mechanical skin irritation. Furthermore, they showed increased vasoreactivity to the highest dose (P less than 0.05), but not to the lower doses of exogenous NE. Thus NE release and adrenergic BP regulation seem to be altered only in diabetics with clinical signs of autonomic dysregulation. These alterations can only be evaluated when patients are exposed to stimuli of higher intensity, such as orthostasis or infusion of a high NE dose.

Endothelial factors, toe temperature and leg circulation in diabetics with and without autonomic neuropathy

A low plasminogen activator response to venous occlusion is frequently found in diabetes. The aims of this investigation were to study any relationships between plasminogen activator activity and autonomic neuropathy (AN), and between abnormal toe temperature reactions and AN. Asymptomatic AN is frequently found in insulin dependent diabetics. The results might be an abnormal balance between the parasympathetic and sympathetic innervation of the vessels, which in turn will lead to a change of the reaction to cooling of the feet followed by indirect heating. In this study 52 insulin dependent diabetics were examined with a combination of tests for AN and blood flow measurements as well as plasminogen activator activities of the blood and vascular walls. In patients with a short duration of diabetes (mean 11 years) the prevalence of AN was high in those with abnormally slow increase in toe temperature after cooling followed by indirect heating. The mechanism behind appeared to be a functional vasospasm. In diabetics of short as well as of long duration (mean 35 years), an abnormally low plasminogen activator activity of the blood during venous occlusion was found in those without AN, while those with AN showed a normal activity. Thus, AN might influence the deterioration of the circulation in diabetes.

Sympathetic reflex latencies and conduction velocities in patients with polyneuropathy

(1) Micro-electrode recordings of multi-unit sympathetic activity were attempted in skin or muscle branches of the peroneal nerve at the fibular head and the median nerve at the elbow in 41 patients with polyneuropathy of different causes. An indirect measure of sympathetic conduction velocity was obtained by determining the latency of either of two sympathetic reflexes. For skin nerve sympathetic activity (SSA) reflex responses to electrical skin stimuli were used and for muscle nerve sympathetic activity (MSA) reflex inhibition caused by the arterial pulse wave. The skin sympathetic function was also evaluated by measuring changes in skin resistance and finger/toe pulse plethysmograms. Motor conduction velocities were measured with surface electrodes. (2) In muscle (but not in skin) nerve fascicles afferent mass activity in myelinated fibres was often weak or absent. (3) There was a significant relationship between symptoms of autonomic impairment and impaired skin resistance and/or plethysmographic responses. There was also a relationship between impairment of these responses and failure to detect SSA. (4) Failure to find sympathetic activity occurred in 60% of diabetic patients but only in 27% of the whole material. When found, sympathetic activity had normal appearance and sympathetic reflex latencies were normal irrespective of degree of slowing of motor conduction velocity. (5) The results suggest that in polyneuropathy conduction velocities of post-ganglionic sympathetic fibres are normal as long as the fibres conduct. Degeneration of sympathetic fibres may be especially common in diabetic neuropathy.