An in-vacuum x-ray diffraction microscope for use in the 0.7-2.9 keV range.

A dedicated in-vacuum coherent x-ray diffraction microscope was installed at the 2-ID-B beamline of the Advanced Photon Source for use with 0.7-2.9 keV x-rays. The instrument can accommodate three common implementations of diffractive imaging; plane wave illumination; defocused-probe (Fresnel diffractive imaging) and scanning (ptychography) using either a pinhole, focused or defocused probe. The microscope design includes active feedback to limit motion of the optics with respect to the sample. Upper bounds on the relative optics-to-sample displacement have been measured to be 5.8 nm(v) and 4.4 nm(h) rms/h using capacitance micrometry and 27 nm/h using x-ray point projection imaging. The stability of the measurement platform and in-vacuum operation allows for long exposure times, high signal-to-noise and large dynamic range two-dimensional intensity measurements to be acquired. Finally, we illustrate the microscope's stability with a recent experimental result.

Fresnel coherent diffraction tomography.

Tomographic coherent imaging requires the reconstruction of a series of two-dimensional projections of the object. We show that using the solution for the image of one projection as the starting point for the reconstruction of the next projection offers a reliable and rapid approach to the image reconstruction. The method is demonstrated on simulated and experimental data. This technique also simplifies reconstructions using data with curved incident wavefronts.

Use of a complex constraint in coherent diffractive imaging.

We demonstrate use of a complex constraint based on the interaction of x-rays with matter for reconstructing images from coherent X-ray diffraction. We show the complementary information provided by the phase and magnitude of the reconstructed wavefield greatly improves the quality of the resulting estimate of the transmission function of an object without the need for a priori information about the object composition.

Three-dimensional imaging of microstructure in Au nanocrystals.

X-ray diffraction using a coherent beam involves the mutual interference among all the extremities of small crystals. The continuous diffraction pattern so produced can be phased because it can be oversampled. We have thus obtained three-dimensional images of the interiors of Au nanocrystals that show 50 nm wide bands of contrast with [111] orientation that probably arise from internal twinning by dynamic recrystallization during their formation at high temperature.

Reconstruction of the shapes of gold nanocrystals using coherent x-ray diffraction.

Inverse problems arise frequently in physics: The magnitude of the Fourier transform of some function is measurable, but not its phase. The "phase problem" in crystallography arises because the number of discrete measurements (Bragg peak intensities) is only half the number of unknowns (electron density points in space). Sayre first proposed that oversampling of diffraction data should allow a solution, and this has recently been demonstrated. Here we report the successful phasing of an oversampled hard x-ray diffraction pattern measured from a single nanocrystal of gold.

Cardiac responses to insulin-induced hypoglycemia in nondiabetic and intensively treated type 1 diabetic patients.

Insulin-induced hypoglycemia occurs commonly in intensively treated patients with type 1 diabetes, but the cardiovascular consequences of hypoglycemia in these patients are not known. We studied left ventricular systolic [left ventricular ejection fraction (LVEF)] and diastolic [peak filling rate (PFR)] function by equilibrium radionuclide angiography during insulin infusion (12 pmol. kg(-1). min(-1)) under either hypoglycemic (approximately 2.8 mmol/l) or euglycemic (approximately 5 mmol/l) conditions in intensively treated patients with type 1 diabetes and healthy nondiabetic subjects (n = 9 for each). During hypoglycemic hyperinsulinemia, there were significant increases in LVEF (DeltaLVEF = 11 +/- 2%) and PFR [DeltaPFR = 0.88 +/- 0.18 end diastolic volume (EDV)/s] in diabetic subjects as well as in the nondiabetic group (DeltaLVEF = 13 +/- 2%; DeltaPFR = 0.79 +/- 0.17 EDV/s). The increases in LVEF and PFR were comparable overall but occurred earlier in the nondiabetic group. A blunted increase in plasma catecholamine, cortisol, and glucagon concentrations occurred in response to hypoglycemia in the diabetic subjects. During euglycemic hyperinsulinemia, LVEF also increased in both the diabetic (DeltaLVEF = 7 +/- 1%) and nondiabetic (DeltaLVEF = 4 +/- 2%) groups, but PFR increased only in the diabetic group. In the comparison of the responses to hypoglycemic and euglycemic hyperinsulinemia, only the nondiabetic group had greater augmentation of LVEF, PFR, and cardiac output in the hypoglycemic study (P < 0.05 for each). Thus intensively treated type 1 diabetic patients demonstrate delayed augmentation of ventricular function during moderate insulin-induced hypoglycemia. Although diabetic subjects have a more pronounced cardiac response to hyperinsulinemia per se than nondiabetic subjects, their response to hypoglycemia is blunted.

Cardiac sympathetic dysinnervation in diabetes: implications for enhanced cardiovascular risk.

BACKGROUND: Regional cardiac sympathetic hyperactivity predisposes to malignant arrhythmias in nondiabetic cardiac disease. Conversely, however, cardiac sympathetic denervation predicts increased morbidity and mortality in severe diabetic autonomic neuropathy (DAN). To unite these divergent observations, we propose that in diabetes regional cardiac denervation may elsewhere induce regional sympathetic hyperactivity, which may in turn act as a focus for chemical and electrical instability. Therefore, the aim of this study was to explore regional changes in sympathetic neuronal density and tone in diabetic patients with and without DAN. METHODS AND RESULTS: PET using the sympathetic neurotransmitter analogue 11C-labeled hydroxyephedrine ([11C]-HED) was used to characterize left ventricular sympathetic innervation in diabetic patients by assessing regional disturbances in myocardial tracer retention and washout. The subject groups comprised 10 diabetic subjects without DAN, 10 diabetic subjects with mild DAN, 9 diabetic subjects with severe DAN, and 10 healthy subjects. Abnormalities of cardiac [11C]-HED retention were detected in 40% of DAN-free diabetic subjects. In subjects with mild neuropathy, tracer defects were observed only in the distal inferior wall of the left ventricle, whereas with more severe neuropathy, defects extended to involve the distal and proximal anterolateral and inferior walls. Absolute [11C]-HED retention was found to be increased by 33% (P<0.01) in the proximal segments of the severe DAN subjects compared with the same regions in the DAN-free subjects (30%; P<0.01 greater than the proximal segments of the mild DAN subjects). Despite the increased tracer retention, no appreciable washout of tracer was observed in the proximal segments, consistent with normal regional tone but increased sympathetic innervation. Distally, [11C]-HED retention was decreased in severe DAN by 33% (P<0.01) compared with the DAN-free diabetic subjects (21%; P<0.05 lower than the distal segments of the mild DAN subjects). CONCLUSIONS: Diabetes may result in left ventricular sympathetic dysinnervation with proximal hyperinnervation complicating distal denervation. This combination could result in potentially life-threatening myocardial electrical instability and explain the enhanced cardioprotection from beta-blockade in these subjects.

Evaluation of hyperbaric oxygen for diabetic wounds: a prospective study.

The purpose of this study was to prospectively evaluate the effect of hyperbaric oxygen (HBO2) on the healing of diabetic lower extremity wounds. Ten consecutive insulin-dependent diabetic patients with chronic lower extremity wounds were referred for HBO2 treatment. The control group consisted of five patients, two claustrophobic and three rural. The latter refused HBO2 treatments because of logistic reasons. Five patients underwent 30 HBO2 treatments in the problem wound protocol (100% oxygen, 2 atm abs, 2 h/day, 5 days/wk). All patients were evaluated with transcutaneous oxygen measurements and had an initial surgical debridement of the wound. Weekly tracings of the wound surface area were made by a nurse or resident who was blinded to the group assignment. At the end of 7 wk, the mean wound area expressed as a percentage of pretreatment baseline area was compared between groups (analysis of variance, Duncan's post hoc). No significant differences were noted between groups with respect to age, gender, baseline wound area, wound site O2 tension, or presence of osteomyelitis. At the completion of each of the 7-wk treatment periods, a significantly greater reduction in wound surface area was noted in the HBO2 vs. the control group (P < 0.05). HBO2 treatment significantly reduced wound size compared to controls in this small, non-randomized prospective study. These results should serve as a basis for larger multicenter prospective, randomized, double-blind controlled studies to definitively evaluate the effect of HBO2 on the healing of diabetic foot wounds.

Aldose reductase inhibitors: the end of an era or the need for different trial designs?

Despite numerous attempts over 16 years, the results of aldose reductase inhibitor (ARI) trials for the treatment of diabetic neuropathy have not proven efficacy. This paper reviews each of the ARI trials, examines confounding factors, and proposes a future course. The confounding factors considered are pharmacokinetics (ARI penetration of human nerve), length of trial (in terms of the natural history of diabetic neuropathy), trial endpoints (reversibility or slowing of progression), reproducibility of clinical measurements (in terms of power calculations), standardization and quality control of endpoints, and clinically meaningful differences in endpoints. We conclude that ARIs are most likely to have a beneficial effect in the management of diabetic distal symmetrical polyneuropathy and autonomic neuropathy but that the clinical role of ARIs is to slow the progression of diabetic neuropathy rather than to reverse it. Future trials should be designed with adequate statistical power, with consideration of the variability of the endpoint measurements for long enough duration, and with rigorous quality control to definitively confirm the utility of ARIs in the treatment of diabetic distal symmetrical polyneuropathy and autonomic neuropathy.

Clinical trials of diabetic neuropathy: past, present, and future.

This article reviews current knowledge of the etiology of diabetic neuropathy and the outcomes and limitations of previous trials and discusses future directions for the investigation of its prevention and treatment. Proposed mechanisms for the development of diabetic neuropathy have been widely studied. It has been shown that there is improvement of nerve function associated with some short-term clinical trials of treatments that address a number of possible etiologic pathways. Improvement of morphometry has also been demonstrated in some short-term clinical trials. However, with the exception of the Diabetes Control and Complications Trial (DCCT), long-term trials with adequate statistical power to evaluate clinical outcome endpoints have not been conducted. The changes in nerve function are similar in most of the clinical trials. For instance, in four clinical trials directed at separate mechanisms (improved glucose control, high myo-inositol diet, therapy with an aldose reductase inhibitor, and therapy with supplementary gamma-linolenic acid), a similar improvement in peroneal motor velocity of 1-2 m/s is observed. This implies that each of the proposed mechanisms contributes equally to the development of neuropathy or that there is some redundancy to their mechanisms. In addition to an etiologic approach, nonspecific neural stimulants, such as gangliosides and nerve growth factors, have also been investigated for the treatment of diabetic neuropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Components of variance for vibratory and thermal threshold testing in normal and diabetic subjects.

Quantitative sensory testing (QST) is commonly used in the assessment of diabetic neuropathy. However, little data are available on the reliability of tactile and thermal testing devices. Reproducibility of QST measures between centers has not been previously reported. This study was designed to validate QST testing procedures and determine if these devices are suitable for large scale multicenter clinical trials. Finger and toe vibratory (Vf, Vt) and thermal (Tf, Tt) thresholds were determined for ten normal individuals by a two-alternative forced-choice procedure using the Optacon Tactile Tester (OTT) and Thermal Sensitivity Tester (TST). Threshold measurements were reproducible between technologists and had a day-to-day coefficient of variation of Vf 20%, Vt 23%, Tf 41%, and Tt 95%. Thresholds were determined for 140 normal individuals at six centers. Mean threshold values between centers were not significantly different. Center-to-center coefficients of variation (CV) were Vf 44%, Vt 45%, Tf 47%, and Tt 87%. There was no significant difference in threshold measures with regard to sex, side studied, presence of calluses, or skin temperature. Vf thresholds significantly correlated with age (p < 0.01). There was no correlation between either vibratory or thermal thresholds in normal individuals, and nerve conduction velocities (NCV). Thermal and vibratory thresholds were determined for 98 diabetic patients. Diabetic subjects without clinical evidence of neuropathy were not significantly different from normal individuals, but diabetic patients with neuropathy had increased thresholds compared to normals (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

A highly successful and novel model for treatment of chronic painful diabetic peripheral neuropathy.

OBJECTIVE: To investigate why, in spite of a vast variety of treatment agents, the alleviation of pain in patients with diabetic neuropathy is difficult. Previous studies have not used a treatment algorithm based on anatomic site and neuropathophysiological source of the neuropathic pain. RESEARCH DESIGN AND METHODS: A model that categorizes the types of pain into three groups (superficial, deep, and muscular) was applied in 75 diabetic patients with chronic (> 12 mo) painful distal symmetrical polyneuropathy in a controlled case series. Twenty-two patients were untreated and 53 patients were treated with imipramine +/- mexiletine for deep pain, capsaicin for superficial pain, and stretching exercises and metaxalone +/- piroxican for muscular pain. Each type of pain was scored separately on a scale of 0 (none) to 19 (worst), and the total of all three types was used as an index of overall pain. Ability to sleep through the night was scored by a scale of 1 (never) to 5 (always). RESULTS: No significant differences were observed in initial pain scores, sleep scores, demographics, biochemistries, or physical findings between the two groups. After 3 mo a significant improvement in scores was noted in the treated but not the untreated patients. In addition, a significant difference was found in the change of scores between the treated and untreated patients: total pain (-18 +/- 2 vs. 0 +/- 2), deep pain (-7 +/- 1 vs. 0 +/- 1), superficial pain (-5 +/- 1 vs. 0 +/- 1), muscular pain (-6 +/- 1 vs. 0 +/- 1), and sleep (1.2 +/- 0.2 vs. 0.2 +/- 0.2), all P < 0.0001. In treated patients 21% became pain-free (total pain < 2), 66% had improvement (decrease in total pain > 5, but not total elimination of painful symptoms), and 13% were considered treatment failures (a decrease in total pain of < or = 5). This compares with 0 (P < 0.02), 10 (P < 0.0001), and 90% (P < 0.0001), respectively, in the untreated patients. CONCLUSIONS: This study presents a new rationale and hypothesis for the successful treatment of chronic painful diabetic peripheral neuropathy. It uniquely bases the treatment algorithm on the types and sources of the pain.

Risk for cardiovascular autonomic neuropathy is associated with the HLA-DR3/4 phenotype in type I diabetes mellitus.

OBJECTIVE: To identify risk factors for the development of cardiovascular autonomic neuropathy in patients with juvenile-onset type I diabetes mellitus. DESIGN: Cross-sectional examination of an inception cohort 15 to 21 years after the onset of diabetes. SETTING: Outpatient diabetes clinic. PATIENTS: Seventy-nine patients with type I diabetes who experienced onset of disease before 21 years of age and who were followed for 15 to 21 years. MEASUREMENTS: Autonomic nerve function was evaluated in all patients using deep breathing and tilt tests. On the basis of these tests, an index of cardiovascular autonomic neuropathy was derived and patients were classified as having intact, mildly impaired, or significantly impaired autonomic function. RESULTS: The group with significantly impaired function had a higher mean hemoglobin A1 at the time of examination than the group without impairment, yet the groups did not differ regarding glycemic control during the first decade of diabetes. The HLA-DR3/4 phenotype was present in more than 50% of the patients with significant autonomic dysfunction and conferred relative odds of 6.2 (95% CI, 1.7 to 23.3) for the development of autonomic neuropathy when compared with other HLA-DR phenotypes. Sex, percent ideal body weight, and smoking did not have a statistically significant effect on the development of autonomic neuropathy. CONCLUSIONS: The development of cardiovascular autonomic neuropathy in type I diabetes mellitus is strongly associated with the HLA-DR3/4 phenotype. Thus, genetic predisposition may play an important role in the development of this complication.

Cardiovascular autonomic dysfunction: diagnosis and prognosis.

The symptoms of cardiovascular autonomic dysfunction may be subtle and occur late in the course of diabetes. They include abnormal exercise-induced cardiovascular performance, postural hypotension, and cardiac denervation syndrome. Autonomic nervous system testing involves an evaluation of the responses of complex reflex pathways. Some of the most commonly used and validated cardiovascular autonomic tests are RR-variation, the Valsalva manoeuvre, and postural testing. Sinus arrhythmia during breathing is termed RR-variation. In diabetic patients with autonomic neuropathy the magnitude of the RR-variation is decreased. Abnormal exercise-induced cardiovascular performance has been observed in diabetic subjects with abnormal RR-variation due to autonomic neuropathy. The Valsalva manoeuvre consists of forced expiration against a standardized resistance for a specified period of time. The reflex bradycardia that follows the Valsalva period in normal subjects is lacking in diabetic patients with clinical evidence of autonomic neuropathy. Postural hypotension in diabetics may be due to neuropathy or to a variety of secondary causes. An algorithm is presented to facilitate assessment of diabetic patients with postural symptoms. Treatment of postural hypotension should be directed primarily to the correction of secondary causes, in the absence of which the symptoms can be controlled by mechanical measures, plasma volume expansion, and vasoconstriction. Cardiac denervation syndrome may result in denervation supersensitivity and afferent (pain) nerve dysfunction. The RR-variation is a sensitive indicator of impairment of cardiac autonomic innervation and is a simple method for identifying asymptomatic patients at risk for painless ischaemia. Formal cardiovascular stress testing may be prudent before initiating an exercise programme in such individuals.

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.

Diabetic autonomic neuropathy and cardiovascular risk. Pittsburgh Epidemiology of Diabetes Complications Study III.

Diabetic autonomic neuropathy (DAN) has been shown to confer a high risk of mortality. The association between DAN and cardiovascular risk factors was examined in a well-defined cohort of 25- to 34-year-old insulin-dependent diabetes mellitus subjects (n = 168) with and without DAN as evaluated by heart rate response to deep breathing, standing, and the Valsalva maneuver. The autonomic tests were performed using both an office-based procedure and a method employed by the Diabetes Control and Complications Trial with analyses performed by the Diabetes Research and Analysis Association, Lexington, Ky. Good agreement was found between the procedures for the assessment modalities of heart rate response to deep breathing. Modeling potential correlates in logistic analyses, where heart rate response to deep breathing was the dependent variable, revealed hypertension status, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and gender (female) to be independent determinants of DAN. These results suggest that traditional cardiovascular risk factors are important correlates of DAN and may relate to both its cause and poor prognosis. Since these results are from a cross-sectional study, prospective follow-up of this cohort will be needed for confirmation.