Reduced vascular reactivity in diabetic children and its relation to diabetic control

The Impact of Disease Duration on Microcirculatory Dysfunction in Young Patients with Uncomplicated Type 1 Diabetes

This study aimed to evaluate the earliest changes in the structure and function of the peripheral microcirculation using capillaroscopy and transcutaneous oxygen pressure measurement in children and adolescents with type 1 diabetes mellitus at baseline and during post-occlusive reactive hyperemia (PORH) in the function of diabetes duration. Sixty-seven patients with type 1 diabetes mellitus (T1D), aged 8 to 18 years, and twenty-eight age- and sex-matched healthy subjects were included in the analysis. Diabetic patients were divided into subgroups based on median disease duration. The subgroups differed in chronological age, lipid levels, and thyroid hormones. Capillaroscopy was performed twice: at baseline and then again after the PORH test. Transcutaneous oxygen pressure also was recorded under baseline conditions during and after the PORH test. Comparison of capillaroscopy and transcutaneous oxygen pressure parameters at rest and after the PORH showed no statistically significant difference between the subgroups. This remained true after adjusting for variables that differentiated the two subgroups. However, in the group of patients with long-standing diabetes, significant negative correlations were observed between the Coverage value after the PORH test and capillary reactivity with TcPO2_zero (biological zero). Significant positive correlations were also found between distance after the PORH test and TcPO2_zero. The results of our study indicate that in patients with a shorter duration of diabetes, the use of multiple tests provides a better characterization of the structure and function of microcirculation because the onset of dysfunction does not occur at the same time in all the tests.

Contribution of nitrergic nerve in canine gingival reactive hyperemia

Reactive hyperemia reflects a compensatory vasodilation response of the local vasculature in ischemic tissue. The purpose of this study is to clarify the mechanism of regulation of this response in gingival circulation by using pharmacological analysis of reactive hyperemia and histochemical analysis of gingival tissue. Application of pressure to the gingiva was used to create temporary ischemia, and gingival blood flow was measured after pressure release. Reactive hyperemia increased in proportion to the duration of pressure. Systemic hemodynamics remained unaffected by the stimulus; therefore, the gingival reactive hyperemia reflected a local adjustment in circulation. Gingival reactive hyperemia was significantly suppressed by nitric oxide (NO) synthase inhibitors, especially the neural NO synthase-selective antagonist 7-nitroindazole, but not by anticholinergic drugs, β-blockers, or antihistaminergic drugs. Moreover, immunohistochemical staining for neural NO synthase and histochemical staining for NADPH diaphorase activity were both positive in the gingival perivascular region. These histochemical and pharmacological analyses show that reactive hyperemia following pressure release is mediated by NO-induced vasodilation. Furthermore, histochemical analysis strongly suggests that NO originates from nitrergic nerves. Therefore, NO may play an important role in the neural regulation of local circulation in gingival tissue ischemia.

Physical activity, sport, and pediatric diabetes

The benefits derived from regular physical activity include improved cardiovascular fitness, increased lean mass, improved blood lipid profile, enhanced psychosocial well-being, and decreased body adiposity. The benefits for children with diabetes may also include blood glucose control and enhanced insulin sensitivity. However, for these children, engagement in vigorous physical activity and sport must be properly controlled through modifications in insulin therapy and nutritional intake so that the benefits of exercise outweigh the risks. The following review describes the various physiological and metabolic factors which occur both during exercise and during sport while describing specific recommendations to control glucose excursions by proper insulin management and diet.

Impaired microvascular function related to poor metabolic control in young patients with diabetes

The purpose of the present study was to identify whether young patients with type 1 diabetes using modern multiple insulin injection therapy (MIT) have signs of microvascular dysfunction and to elucidate possible correlations with various disease parameters. Skin blood flow on the dorsum of the foot was measured with laser Doppler perfusion imaging in 37 patients (age 10-21 years, disease duration 6.0-16 years) and 10 healthy controls. Measurements were performed at rest, after change in posture (the leg was lowered below heart level) and during postocclusive hyperaemia. Following a change in posture blood flow increased instead of decreased in a majority of the study subjects. Patients with acute HbA1c >7.5% (n = 22) had an increase in skin blood flow at rest and a significantly reduced blood flow when the leg was lowered below heart level as compared with patients with HbA1c <7.5% (0.26 V versus 0.17 V, P<0.01 and 0.12 V versus 0.23 V, P<0.05, respectively) and healthy controls. Following occlusion of the macrocirculation for 3 min a small non-significant decrease in the hyperaemic response was seen in the patients. The postocclusive hyperaemic response and the venoarteriolar reflex were not correlated to duration of disease, long-term metabolic control or electrophysiological signs of peripheral nerve dysfunction. It is concluded that signs of microvascular dysfunction related to poor metabolic control are present in young patients with MIT treatment and rather well-controlled diabetes. Low resting blood flow levels are suggested to contribute to the absence of postural vasoconstrictor response.

Age-dependent changes of postischemic reperfusion in rat skin

Ischemia-reperfusion plays a certain role in causing skin damage associated with pressure sores. In this study, changes in cutaneous hemodynamics during reperfusion were investigated in young and older rats. After cessation of 1-hour or 2-hour ischemia, the skin blood flow increased transiently (postischemic hyperemia) and quickly returned to the baseline in young and older rats. After 4-hour ischemia, however, the postischemic hyperemia was reduced in both groups, and the skin blood flow decreased below the baseline for a few hours in older rats. The skin blood flow tolerated well the repeated exposures to 1-hour ischemia in both groups. In 2-hour ischemia experiments, the postischemic hyperemia was preserved after the second ischemic period in young rats but not in older rats. These results suggest that the tolerance of skin microcirculation to ischemia-reperfusion may decrease with increasing age.

Vasodilator responses in the forearm skin of patients with insulin-dependent diabetes mellitus

The integrity of endothelium-dependent vasodilation in the skin of patients with insulin-dependent diabetes mellitus (IDDM) is unclear, especially with respect to the role of nitric oxide. To examine this, forearm skin blood flow by laser Doppler flowmetry and total blood flow by venous occlusion plethysmography was measured in response to brachial artery infusions of an endothelium-dependent (methacholine) and -independent (sodium nitroprusside) vasodilator. Peak hyperemic forearm blood flow, following 5 min of arterial occlusion, was also determined. Responses were compared in 11 control subjects and 16 patients with insulin-dependent diabetes mellitus. In ten normal subjects, co-infusion of NG-monomethyl-L-arginine with methacholine produced a significant reduction in total forearm blood flow response to methacholine (p < 0.002), measured by venous occlusion plethysmography, as well as vascular conductance (p < 0.001), confirming that nitric oxide contributes to this response. In contrast, NG-monomethyl-L-arginine had no significant effect on the methacholine-induced increase in forearm skin blood flow measured by laser Doppler flowmetry indicating that factors other than nitric oxide may be involved. Increases in forearm skin blood flow in response to methacholine, sodium nitroprusside and to an ischemic stimulus were not significantly different between the normal subjects and patients with IDDM. Dose-related increases in total forearm blood flow and vascular conductance were not significantly different between control subjects and diabetic patients during infusions of methacholine. The increases in these parameters during infusions of sodium nitroprusside, however, were significantly less in the diabetic group than in the control group (p < 0.05) as was the peak reactive hyperemic blood flow (p < 0.05). Since skin blood flow was not affected, the reduced vasodilator responses to sodium nitroprusside and an ischemic stimulus in the diabetic group are in forearm skeletal muscle. The reduced muscle blood flow does not reflect a decreased vasodilatory capacity, but rather a functional impairment in response to nitric oxide and ischemia since the methacholine dilation was normal. The normal vasodilator responses in the forearm skin, which is predominantly capillary as opposed to arteriovenous anastomatic blood flow, indicate that the response to nitric oxide and an ischemic stimulus in this vascular bed is intact in patients with IDDM. This is, therefore, an unlikely cause of diabetic skin, complications in these areas.

Vascular reactivity and platelet aggregability during the first five years of insulin-dependent diabetes in children

Skin microvascular reactivity and platelet aggregation in response to collagen and adenosine diphosphate (ADP) was studied prospectively in a population-based cohort of children with newly acquired type 1 diabetes mellitus (IDDM), who have now been followed up longitudinally for 5 years. The skin microvascular vasodilation in response to ischaemia was recorded by means of transcutaneous oximetry at 37 degrees C and compared with that in a control group of 58 healthy children. Platelet aggregation was compared with 42 healthy control children. Sixty months after diagnosis, the same degree of impairment of vasodilatory capacity was noted as previously recorded at 24 months and on admission, on all these occasions being significantly lower than the control value and the results from the 12-month follow-up. A sex difference was noted, diabetic girls both during and after puberty exhibiting a greater impairment of vasodilator capacity as compared with diabetic boys. The same degree of platelet aggregation in response to collagen was noted 60 months after diagnosis as had been recorded previously at 24 and 12 months, all significantly increased as compared with the results from admission, but not different from those in controls. By contrast, the aggregation in response to ADP was now lower than that observed on admission. No statistically significant gender difference was noted. The implication of the impaired skin microvascular vasodilation and of the changing pattern of platelet aggregation for later diabetic angiopathy needs to be evaluated in the coming decade.

Cardiovascular autonomic dysfunction in diabetes mellitus

The aim was to assess cardiovascular autonomic dysfunction in children and adolescents with diabetes mellitus. A total of 110 children and adolescents with type 1 (insulin dependent) diabetes (aged 6 to 18 years) and 130 non-diabetic controls were studied. Resting heart rate, heart rate variation to deep breathing, heart rate response to standing from a lying position, fall in systolic blood pressure on standing, and rise in diastolic blood pressure during sustained handgrip were measured. A reference range of results was obtained in the controls. Diabetic children had significantly increased resting heart rate [92.4 (SEM 2.5) v 84.2 (2.2) beats/min], decreased deep breathing heart rate variation [25.3 (0.9) v 32.8 (0.6) beats/min], and lower standing/lying heart rate ratio [1.23 (0.04) v 1.31 (0.03)] compared with controls. 46 diabetic children (42%) had at least one abnormal autonomic test result. Of these, 20 (15%) had only one abnormal test and 26 (24%) had two or more abnormal tests. Using multiple logistic regression analysis, longer diabetes duration and worse long term metabolic control were independently predictive of cardiovascular autonomic dysfunction as the dependent variable [adjusted OR (95% CI): 2.9 (1.1-5.9) and 3.3 (1.2-6.4), respectively]. Cardiovascular autonomic dysfunction is not rare in children with diabetes. Efforts should be made to maintain the best metabolic control to prevent or delay these complications.

Forearm arterial vascular responsiveness in insulin-dependent diabetic subjects

The vascular reactivity of forearm arterioles was measured in 16 control subjects (C) and 30 insulin-dependent diabetic (IDDM) subjects, 16 of whom were shown to have microvascular and/or neuropathic complications (DC) including 8 with autonomic neuropathy (DCa) and 14 were shown to be free of complications (DNC). Forearm blood flow was measured by strain gauge plethysmography basally, following a cold pressor stress and following a period of arterial occlusion (reactive hyperaemia). The tests were repeated 24 h later following aspirin treatment. Both C and DNC showed a significant reduction in blood flow in the cold pressor test (C 0.64 +/- 0.12, DNC 0.89 +/- 0.22 ml/100 ml forearm tissue/min reduction in flow P < 0.005), while DC showed no significant response. Reactive hyperaemia was significantly greater in C than in DNC or DC (8.37 +/- 1.14, 5.51 +/- 1.27 and 4.95 +/- 0.75 ml/100 ml tissue/min, respectively, P < 0.02). In the DC group, DCa had significantly less response than those without autonomic neuropathy. Aspirin treatment restored the response of DNC but not DC to normal, suggesting that the abnormality in the former group may have been due to overproduction of a vasoconstrictive cyclooxygenase product (such as thromboxane A2). It is concluded that the abnormalities of vasomotor responses in diabetic subjects are complex and are apparently dependent on autonomic neuropathy, humoral and perhaps structural changes.

Impaired cutaneous reactive hyperaemia during hypoglycaemia in young insulin-dependent diabetic patients and healthy controls

The aim of the present study was to compare the cutaneous postischaemic hyperaemic response in young insulin-dependent diabetic patients and healthy subjects during normoglycaemia, acute insulin-induced hypoglycaemia and in the posthypoglycaemic state. After a night of normoglycaemia the cutaneous postischaemic hyperaemic response in the forearm skin, measured by the transcutaneous PO2 method, was the same in both groups. A reduction of the maximal postischaemic vasodilatory response was observed in diabetic patients from 2.4 +/- 0.3 to 2.0 +/- 0.2 kPa (P less than 0.05) and in control subjects from 2.7 +/- 0.3 to 1.8 +/- 0.2 kPa (P less than 0.02) during insulin-induced hypoglycaemia (plasma glucose less than 2 mmol/l). Complete recovery of the vasodilatory response occurred in subjects in the posthypoglycaemic state. We conclude that hypoglycaemia induced a transient reduction of the vasodilatory response, which was rapidly reversed after glucose counter-regulation, in both diabetic patients and healthy controls. Thus, the prevailing blood glucose concentration must be taken into account when the postischaemic vasodilatory response is investigated in diabetic patients.

Impaired microvascular hyperaemic response in children with diabetes mellitus

Clinically detectable microvascular complications of diabetes are uncommon in children with diabetes especially in the prepubertal group. It is unclear whether subtle functional abnormalities of the microcirculation occur in children without evidence of clinical microangiopathy and in particular whether abnormalities can be demonstrated in children before puberty. The maximum hyperaemic response to direct local heating (44 degrees C) of the foot skin was measured by laser Doppler fluximetry in 50 diabetic and 50 non-diabetic children. An impaired hyperaemic response occurred in the diabetic children compared with control children (diabetic 1.25 (95% CI 1.13-1.37) V; control 1.74 (1.60-1.88) V; p less than 0.001) and was significantly related to duration of diabetes but not to long-term blood glucose control. The impaired response was also present in prepubertal diabetic children (diabetic 1.37 (1.16-1.58) V; control 1.89 (1.67-2.12) V; p less than 0.001). Systolic and diastolic blood pressure were significantly raised in the prepubertal diabetic children. These data suggest that a functional abnormality of the microcirculation occurs in children with diabetes in the absence of clinically detectable microangiopathy, and even before puberty.

Glimpses into measurements of the microcirculation in skin

There are instances when chronic disease states manifest as microvascular disturbances of the skin. Objective assessment of these disturbances would permit a better understanding of the causative factors and, in certain circumstances, influence decisions of clinical management. Recent advances in technology that permit such assessment non-invasively are evaluated in this review.

Magnesium and insulin-dependent diabetes mellitus

There is accumulating evidence that the changes which occur in the metabolism of some micronutrients in diabetes mellitus might have a specific role in the pathogenesis and complications of this disease. Magnesium deficiency is the most evident disturbance of metal metabolism in insulin-dependent diabetes mellitus. Hypomagnesemia has been linked both to the acute metabolic and late chronic complication of diabetes. Of particular concern, is the association between hypomagnesemia and ischemic heart disease and severe retinopathy in humans with diabetes mellitus. Appropriate magnesium supplementation might prove beneficial in normalizing the low plasma and tissue magnesium levels and prevent or retard the development of vascular complications in diabetic patients. However, well designed and documented experiments need to be performed before the rationales for such therapy are well established.

Impaired beta-adrenergic mediated cerebral blood flow response in streptozotocin diabetic rats

The influence of intracarotic infusion of isoproterenol on cerebral blood flow, on cerebrovascular CO2-reactivity, and on cerebral glucose metabolism were investigated in streptozotocin diabetic rats. Resting cerebral blood flow in diabetic rats decreased by 26% from a control value of 90 ml/100 g.min. to 66 ml/100 g.min. Intracarotid isoproterenol infusion leads to a significant increase in cerebral blood flow in both groups. The increase in cerebral blood flow in control rats (70%), significantly exceeded that in the streptozotocin diabetic rats (33%). Cerebrovascular reactivity to carbon dioxide was preserved after isoproterenol infusion in both groups and there was no significant difference in the relative cerebral blood flow increase in the two groups. Cerebral glucose metabolism was also unaffected by the isoproterenol infusion. The results indicate that impaired beta-adrenergic mechanisms may play a role for alterations in cerebral blood flow that is seen in diabetes mellitus.

Platelet aggregation during the first year of diabetes in childhood

Platelet aggregability in 24 newly diagnosed diabetic children was investigated on five occasions from onset of the disease until one year after diagnosis. Twenty healthy children of similar age and sex served as controls. The magnitude of the platelet shape change after adenosine diphosphate (ADP) stimulation was decreased in diabetic children on admission (p less than 0.05) in comparison with controls, but normalized during the year of the study. Maximal aggregation and initial rate of aggregation after ADP stimulation did not change significantly during the study year, and did not differ from those in controls. Aggregation by low dose collagen (0.5 and 1.0 mg/l) increased significantly (maximal aggregation, p less than 0.01; aggregation velocity, p less than 0.001) in the diabetics during the first year after admission from seemingly normal to clearly supranormal. Aggregation induced by high-dose collagen (5.5 mg/l) remained unchanged during the observation period and did not differ from that in the control group. No correlations were found between the indicators of platelet aggregation and those of carbohydrate control at any time after diagnosis. Platelet dysfunction is thus present already during the first year of diabetes. The different time course of the ADP-induced platelet shape change and collagen-induced aggregation imply that the mechanisms underlying the abnormalities of these two platelet functions differ.

Vascular reactivity during the first year of diabetes in children

Functional vascular response to hypoxia was studied in 24 children followed up prospectively for one year after diagnosis of type 1 diabetes mellitus. Postocclusive reactive hyperaemia was detected non-invasively in the skin using a transcutaneous PO2 method at 37 degrees C. Repeated experiments under standardized conditions were performed before institution of insulin treatment and 3, 7, 21, 30, 180 and 360 days after diagnosis. Impaired vascular reactivity was noted at the first experiment as compared with control children and slight but significant improvement was then noted up to the experiment at 180 days (p less than 0.01). At 30 and 180 days no significant difference between diabetic and control children was found. A small decrease in mean postocclusive reactive hyperaemia was observed at the experiment performed after 360 days. Fast normalization of urine glucose excretion, blood glucose and haemoglobin A1 occurred during the first three weeks of treatment but these variables showed no significant correlation to vascular reactivity, either at diagnosis or later. Impaired vascular reactivity can thus be diagnosed even before the institution of insulin treatment and improves during the first months of treatment, reaching the range of controls. Other factors than indicators of carbohydrate control have to be studied in the search for explanations of the abnormal vascular function in newly diagnosed diabetic children.