Modulation of Structural, Electronic, and Optical Properties of Titanium Nitride Thin Films by Regulated In Situ Oxidation

Epitaxial titanium nitride (TiN) and titanium oxynitride (TiON) thin films have been grown on sapphire substrates using a pulsed laser deposition (PLD) method in high-vacuum conditions (base pressure <3 × 10^-6 T). This vacuum contains enough residual oxygen to allow a time-independent gas phase oxidation of the ablated species as well as a time-dependent regulated surface oxidation of TiN to TiON films. The time-dependent surface oxidation is controlled by means of film deposition time that, in turn, is controlled by changing the number of laser pulses impinging on the polycrystalline TiN target at a constant repetition rate. By changing the number of laser pulses from 150 to 5000, unoxidized (or negligibly oxidized) and oxidized TiN films have been obtained with the thickness in the range of four unit cells to 70 unit cells of TiN/TiON. X-ray photoelectron spectroscopy (XPS) investigations reveal higher oxygen content in TiON films prepared with a larger number of laser pulses. The oxidation of TiN films is achieved by precisely controlling the time of deposition, which affects the surface diffusion of oxygen to the TiN film lattice. The lattice constants of the TiON films obtained by x-ray diffraction (XRD) increase with the oxygen content in the film, as predicted by molecular dynamics (MD) simulations. The lattice constant increase is explained based on a larger electrostatic repulsive force due to unbalanced local charges in the vicinity of Ti vacancies and substitutional O. The bandgap of TiN and TiON films, measured using UV-visible spectroscopy, has an asymmetric V-shaped variation as a function of the number of pulses. The bandgap variation following the lower number of laser pulses (150-750) of the V-shaped curve is explained using the quantum confinement effect, while the bandgap variation following the higher number of laser pulses (1000-5000) is associated with the modification in the band structure due to hybridization of O_2p and N_2p energy levels.

Forming Anisotropic Crystal Composites: Assessing the Mechanical Translation of Gel Network Anisotropy to Calcite Crystal Form

The promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. Here, we demonstrate that anisotropic agarose gel networks can mechanically "mold" calcite crystal growth, yielding anisotropically structured, single-crystal composites. Drying and rehydration of agarose gel films result in the affine deformation of their fibrous networks to yield fiber alignment parallel to the drying plane. Precipitation of calcium carbonate within these anisotropic networks results in the formation of calcite crystal composite disks oriented parallel to the fibers. The morphology of the disks, revealed by nanocomputed tomography imaging, evolves with time and can be described by linear-elastic fracture mechanics theory, which depends on the ratio between the length of the crystal and the elastoadhesive length of the gel. Precipitation of calcite in uniaxially deformed agarose gel cylinders results in the formation of rice-grain-shaped crystals, suggesting the broad applicability of the approach. These results demonstrate how the anisotropy of compliant networks can translate into the desired crystal composite morphologies. This work highlights the important role organic matrices can play in mechanically "molding" biominerals and provides an exciting platform for fabricating crystal composites with direction-specific and emergent functional properties.

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.

Phase-diverse coherent diffractive imaging: high sensitivity with low dose

This Letter demonstrates that coherent diffractive imaging (CDI), in combination with phase-diversity methods, provides reliable and artefact free high-resolution images. Here, using x rays, experimental results show a threefold improvement in the available image contrast. Furthermore, in conditions requiring low imaging dose, it is demonstrated that phase-diverse CDI provides a factor of 2 improvement in comparison to previous CDI techniques.

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.

High-resolution X-ray imaging of Plasmodium falciparum-infected red blood cells

Methods for imaging cellular architecture and ultimately macromolecular complexes and individual proteins, within a cellular environment, are an important goal for cell and molecular biology. Coherent diffractive imaging (CDI) is a method of lensless imaging that can be applied to any individual finite object. A diffraction pattern from a single biological structure is recorded and an iterative Fourier transform between real space and reciprocal space is used to reconstruct information about the architecture of the sample to high resolution. As a test system for cellular imaging, we have applied CDI to an important human pathogen, the malaria parasite, Plasmodium falciparum. We have employed a novel CDI approach, known as Fresnel CDI, which uses illumination with a curved incident wavefront, to image red blood cells infected with malaria parasites. We have examined the intrinsic X-ray absorption contrast of these cells and compared them with cells contrasted with heavy metal stains or immunogold labeling. We compare CDI images with data obtained from the same cells using scanning electron microscopy, light microscopy, and scanning X-ray fluorescence microscopy. We show that CDI can offer new information both within and at the surface of complex biological specimens at a spatial resolution of better than 40 nm. and we demonstrate an imaging modality that conveniently combines scanning X-ray fluorescence microscopy with CDI. The data provide independent confirmation of the validity of the coherent diffractive image and demonstrate that CDI offers the potential to become an important and reliable new high-resolution imaging modality for cell biology. CDI can detect features at high resolution within unsectioned cells.

Three-dimensional mapping of a deformation field inside a nanocrystal

Coherent X-ray diffraction imaging is a rapidly advancing form of microscopy: diffraction patterns, measured using the latest third-generation synchrotron radiation sources, can be inverted to obtain full three-dimensional images of the interior density within nanocrystals. Diffraction from an ideal crystal lattice results in an identical copy of this continuous diffraction pattern at every Bragg peak. This symmetry is broken by the presence of strain fields, which arise from the epitaxial contact forces that are inevitable whenever nanocrystals are prepared on a substrate. When strain is present, the diffraction copies at different Bragg peaks are no longer identical and contain additional information, appearing as broken local inversion symmetry about each Bragg point. Here we show that one such pattern can nevertheless be inverted to obtain a 'complex' crystal density, whose phase encodes a projection of the lattice deformation. A lead nanocrystal was crystallized in ultrahigh vacuum from a droplet on a silica substrate and equilibrated close to its melting point. A three-dimensional image of the density, obtained by inversion of the coherent X-ray diffraction, shows the expected facetted morphology, but in addition reveals a real-space phase that is consistent with the three-dimensional evolution of a deformation field arising from interfacial contact forces. Quantitative three-dimensional imaging of lattice strain on the nanometre scale will have profound consequences for our fundamental understanding of grain interactions and defects in crystalline materials. Our method of measuring and inverting diffraction patterns from nanocrystals represents a vital step towards the ultimate goal of atomic resolution single-molecule imaging that is a prominent justification for development of X-ray free-electron lasers.

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.

Diabetic neuropathy

Diabetic neuropathy, the most common peripheral neuropathy in the Western world, is responsible for most limb amputations and considerable morbidity in diabetic patients. Although it is a sequela to insulin deficiency and/or hyperglycemia, its exact pathogenetic mechanism remains unclear. Therapy is directed at early diagnosis, exclusion of other neuropathic disorders, prudent glucose control, and avoidance of secondary complications of neuropathy such as foot ulceration by aggressive foot care, hygiene, and patient education.

Autonomic influence on cardiovascular performance in diabetic subjects

PURPOSE

Cardiomyopathy, coronary artery atherosclerosis, or autonomic neuropathy may affect the cardiovascular performance of the diabetic patient. To evaluate the role of parasympathetic nervous system activity on cardiovascular performance, 25 diabetic subjects who lacked symptoms, signs, or objective measurements of ischemia or cardiomyopathy were studied.

PATIENTS AND METHODS

Diabetic subjects were classified according to their RR variation, an index of cardiac parasympathetic nervous system activity. Fourteen diabetic subjects had a normal RR variation of greater than 30 (D-NOR), and 11 diabetic patients had an abnormal RR variation of less than 20 (D-ABN). Fifteen age- and weight-matched, healthy, nondiabetic subjects (NOR) constituted the control group. All subjects had oxygen consumption, multigated acquisition determination of cardiac output, and work product measured before and during supine bicycle maximum exercise testing.

RESULTS

There was no difference in the resting cardiac output among the groups. Resting work product, however, was greatest in the D-ABN group when compared with performance in the other two groups (D-ABN: 11,500 +/- 800; D-NOR: 9,000 +/- 600; NOR: 8,700 +/- 400; p less than 0.0025). This was due to an increase in both heart rate (p less than 0.025) and systolic blood pressure (p less than 0.015). In the diabetic subjects, there was an inverse relationship between the RR variation and resting work product (r = 0.47, n = 25, p less than 0.005). In response to exercise, the percent increase in cardiac output at matched percent maximum oxygen uptake was greatest in the NOR, D-NOR, and D-ABN groups, respectively (analysis of variance, p less than 0.01). In the diabetic subjects, there was a significant relationship between the RR variation and the maximum percent change in cardiac output (r = 0.41, n = 25, p less than 0.02). Compared with the NOR group, the maximum increase in work product was impaired in diabetic subjects (p less than 0.002) and not different between the D-NOR and D-ABN groups.

CONCLUSIONS

The increase in resting work product and the poor cardiac output responses to exercise in the D-ABN group are due to a decrease in cardiac parasympathetic nervous system activity and can be suggested by an abnormal RR variation. This index of parasympathetic nervous system activity can help the physician identify that subset of diabetic patients that may need special consideration when exercise training is prescribed.

The inotropic action of tolbutamide and glyburide

The effect of glyburide on myocardial function in human beings is not known. We divided 37 normal male volunteers into five groups. Each group received either intravenous saline solution; 10 mg propranolol by intravenous push followed by 0.1 mg/min; 5 micrograms/kg/min dobutamine; 1000 mg or 1250 mg oral tolbutamide; or 5 mg glyburide. Comparable therapeutic blood levels were obtained. Myocardial function was assessed by measurement of work product (WP, systolic pressure times heart rate) and ejection fraction (EF) by means of radionucleotide ventriculography. There was no change in EF or WP after administration of saline solution and tolbutamide; propranolol decreased EF and WP; dobutamine and glyburide increased EF and WP. In summary, tolbutamide had no effect on myocardial contractility, whereas glyburide increased myocardial contractility as measured by ejection fraction.

Depression in obese men

Using the Beck depression inventory (BDI), we studied depression in young, healthy, male subjects who represented a wide range of body weight. Body mass index (BMI), defined as the weight (in kilograms) divided by the square of height (in meters), was used to classify subjects as obese (BMI greater than 31.1, n = 27), overweight (BMI = 27.8-31.1, n = 10) or acceptable weight (BMI less than 27.8, n = 26). BDI scores of 0-9 indicated no depression; scores of 10-15 indicated mild depression. BDI scores from 16 to 63 indicated increasing depression. No group of subjects (obese, overweight or acceptable weight subjects), had mean BDI scores suggesting depression. The mean BDI score for the obese subjects was 5.6 +/- 0.8 (mean +/- s.e.m.), which was significantly higher than the mean BDI scores for both the overweight subjects (2.5 +/- 1.1; P less than 0.04) and the acceptable weight subjects (1.5 +/- 0.3; P less than 0.001). There was a weak positive correlation of BDI with BMI (n = 63, r = 0.404, P less than 0.001). In addition, the obese subjects did form a heterogeneous group with four obese subjects (14.8 percent) having BDI score of 10 or greater. The overweight subjects had one subject (10 percent) with a BDI score of 12. None of the acceptable weight subjects had a BDI score of greater than 5. There was no correlation between waist/hip ratios and BDI scores (n = 37, r = 0.262, P = 0.118). We conclude that mild depression is present in some obese persons even when medically healthy.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetic autonomic neuropathy--Part I. Autonomic nervous system data analysis by a computerized central unit in a multicenter trial

To determine the feasibility of utilizing a central, computerized unit to analyze autonomic nervous system function tests for a 10-year, multicenter, clinical trial, the Autonomic Nervous System Reading Center was established. The Reading Center selected and standardized testing methods, designed the testing protocol, developed testing equipment, computerized data analysis, and instituted measures to monitor data quality. Three cardiovascular testing methods, RR-variation, Valsalva maneuver, and postural testing, were selected because each is a simple, non-invasive, quantitative, sensitive, and reproducible test. Furthermore, a hierarchy of sensitivity has been established with these cardiovascular autonomic nervous system measurements: RR-variation, Valsalva maneuver, and finally postural testing. Confounding variables were minimized by prescribing eligibility criteria. Testing equipment, designed to record time between RR intervals in a form easily read into a computer, has been in 21 clinics for three years and a total of 54 technicians have been trained. Over 85 percent of the autonomic nervous system tests performed have been usable at initial testing. A central reading center is an efficient and necessary means of collecting and analyzing data for a multicenter clinical trial.

Diabetic autonomic neuropathy--Part II. Coefficient of variation of RR-variation and Valsalva maneuver tests

To confirm the reliability and validity of cardiovascular autonomic nervous system tests, RR-variation and Valsalva maneuver, coefficient of variation for triplicate tests was calculated. The testing data were collected from patients participating in the Statil Neuropathy Trial. Triplicate testing was done within a three-week period at three different time points: baseline, 12 months, and 18 months. BMDP Statistical Software was used in the analysis. There is no significant difference between the coefficients of variation between clinics for either RR-variation or Valsalva maneuver tests. The coefficient of variation of pooled data was not significantly different from the coefficient of variation of individual clinics. Furthermore, there was no evidence that there was a significant worsening of coefficient of variation with time. Thus, RR-variation and Valsalva maneuver provide reliable and reproducible results that do not vary in consistency over time.

Peripheral diabetic neuropathy

Diabetic neuropathy is a common complication of diabetes mellitus with significant morbidity and mortality. Hyperglycemia with its secondary metabolic, vascular, and enzymatic consequences is most likely to be the predominant cause. The clinical manifestations includes a wide range of somatic and autonomic syndromes. Painful diabetic neuropathy may require symptomatic treatment. The precise role of therapies such as continuous subcutaneous insulin therapy and aldose reductase inhibitors remains to be clarified.

RR-variation: the autonomic test of choice in diabetes

RR-variation is a sensitive, reproducible, and noninvasive autonomic test. It is simple to perform and easy for both the operator and the subject. Furthermore, RR-variation correlates to known physiologic function. It therefore fulfills many of the characteristics of a practical diagnostic test. Many of the confounding factors are known, and with proper standardization the test may not only have diagnostic capabilities but also predictive value. RR-variation should be included in clinical research trials of diabetic neuropathy and should be considered in routine clinical management of the diabetic patient.

Body fat and the activity of the autonomic nervous system

The cause of most cases of human obesity is unknown. Specific alterations in the activity of the autonomic nervous system may mediate and perhaps cause obesity in animal models. We therefore looked for alterations in autonomic activity in human obesity. Fifty-six healthy men with various percentages of body fat underwent autonomic testing while at rest. Significant correlations were found between the percentage of body fat and the variation in the R-R interval after beta-adrenergic blockade (r = -0.30, P less than 0.03), the heart rate (r = 0.30, P less than 0.03), the plasma norepinephrine concentration (r = -0.30, P less than 0.05), the plasma epinephrine concentration (r = -0.49, P less than 0.001), and the pupillary latency period (r = 0.39, P less than 0.01). Each of these variables reflects the activity of the sympathetic nervous system or parasympathetic nervous system or both. Depressions in sympathetic and parasympathetic activity were significantly but weakly associated with increasing percentages of body fat. These associations indicate that in obese persons, autonomic changes, though not necessarily causal, involve several organ systems. We suggest that autonomic alterations are important in human obesity, as they are in animal obesity. A disordered homeostatic mechanism may promote excessive storage of energy by decreasing sympathetic activity, while defending against weight gain by decreasing parasympathetic activity. The use of autonomic profiles holds promise for classifying human obesity and identifying obese patients at increased risk for various disorders.

Sensitivity of R-R variation and Valsalva ratio in assessment of cardiovascular diabetic autonomic neuropathy

R-R variation and the Valsalva ratio are commonly used to quantitatively assess diabetic autonomic neuropathy (DAN). To assess the sensitivity of these two measures to parasympathetic ablation, 12 nondiabetic subjects were tested before and after graded doses (0.3-4.0 mg i.v.) of atropine. R-R variation was significantly reduced at 0.7 mg, whereas Valsalva ratio was not significantly smaller until the 2.0-mg dose of atropine. R-R variation continued to become progressively smaller during the 0.85-, 1.0-, and 2.0-mg doses. Valsalva ratio, but not R-R variation, was further reduced by the 4.0-mg dose. To further compare these two measures, two groups of diabetic subjects were compared with a group of nondiabetic subjects (n = 22). One group of diabetic subjects had symptoms of DAN (n = 22), and the other diabetic group had no symptoms of DAN (n = 19). In DAN subjects, both R-R variation (nondiabetic 33.2 +/- 4.3 vs. DAN 9.8 +/- 1.2, P less than .001) and the Valsalva ratio (nondiabetic 1.98 +/- 0.07 vs. DAN 1.55 +/- 0.07, P less than .001) were reduced. However, in asymptomatic subjects, R-R variation (23.2 +/- 3.9, P less than .05), but not Valsalva ratio (1.94 +/- 0.13, NS), was less than nondiabetic subjects. Even after beta-blockade, R-R variation was still less in both groups of diabetic subjects (nondiabetic 34.4 +/- 4.2 vs. DAN 7.4 +/- 1.3, P less than .001; asymptomatic 21.8 +/- 3.3, P less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha-adrenergic blockade improves glucose-potentiated insulin secretion in non-insulin-dependent diabetes mellitus

The impairment of glucose-potentiated insulin secretion present in non-insulin-dependent diabetes mellitus (NIDDM) can be approximated in normal subjects by an epinephrine infusion. Therefore, we sought to determine the role of the endogenous sympathetic nervous system in glucose-potentiated insulin secretion in both NIDDM (n = 6) and normal (n = 6) subjects. Glucose-potentiated insulin secretion was calculated as the slope of the curve relating increasing ambient glucose levels to the acute insulin response to an intravenous pulse of 5 g of L-arginine. Glucose-potentiated insulin secretion was determined on separate days during alpha-, beta-, and combined alpha- plus beta-adrenergic blockade and compared with a saline control. In normal subjects, there was no effect of alpha-, beta-, or alpha- plus beta-blockade on the slope of glucose potentiation. In NIDDM, the initially decreased slope of glucose potentiation (0.25 +/- 0.06 microU X ml-1 X mg-1 X dl, mean +/- SE; P less than .01) was not affected by beta-blockade but increased during alpha-blockade (0.91 +/- 0.22 microU X ml-1 X mg-1 X dl; P less than .05). However, this improvement was abolished by combined alpha- plus beta-blockade (0.32 +/- 0.07 microU X ml-1 X mg-1 X dl). Plasma norepinephrine was increased above basal levels in both normal (+260 +/- 89 pg/ml) and NIDDM (+438 +/- 162 pg/ml) subjects during alpha-blockade (P less than .05 for both). This increase in plasma norepinephrine strongly suggests that there is an increase in synaptic cleft norepinephrine concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

The hemodynamic effects of sympathetic stimulation combined with parasympathetic blockade in man

To define the effects of circulating norepinephrine and epinephrine on cardiac function and to determine whether left ventricular function is influenced by parasympathetic mechanisms during catecholamine stimulation, hemodynamic changes were investigated in healthy young human subjects who were supine and awake during infusion of intravenous norepinephrine alone (125 ng/kg/min) (n = 6), norepinephrine (125 ng/kg/min) plus epinephrine (50 ng/kg/min) (n = 6), and norepinephrine plus epinephrine plus parasympathetic blockade induced by atropine (2 mg intravenously) (n = 5). Ejection fraction and changes in cardiac volumes were measured by radionuclide ventriculography. During the infusion of norepinephrine plus epinephrine, plasma norepinephrine increased from 358 +/- 35 to 1782 +/- 123 pg/ml (mean +/- SE) and plasma epinephrine increased from 31 +/- 5 to 355 +/- 90 pg/ml (both p less than .01 vs baseline). These increases in plasma catecholamines were associated with increases in the heart rate (58 +/- 3 to 67 +/- 2 beats/min, p = NS), systolic blood pressure (113 +/- 3 to 140 +/- 6 mm Hg, p less than .01), ejection fraction (0.64 +/- 0.02 to 0.72 +/- 0.02 ejection fraction units, p less than .01), stroke volume (+41 +/- 5%, p less than .01), and cardiac output (+54 +/- 8%, p less than .01), and a decrease in systemic vascular resistance (-31 +/- 3%, p less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetic peripheral neuropathy. Part II. Autonomic neuropathies (continuing education credit)

Diabetic autonomic neuropathies (DAN) are clinical syndromes resulting from impairments of the autonomic nervous system in patients with diabetes mellitus. Since the autonomic nervous system innervates most body organs, any or all of those organs may be affected by DAN. A high index of suspicion is the best diagnostic tool. Proper management, with patient and family education in its center, improves the quality of life of persons with DAN. Undiagnosed and ignored, DAN could cause severe disability and even death.

Development of a method to determine autonomic nervous system function in the rat

A noninvasive method to evaluate autonomic nervous system (ANS) function in animals is needed for studies of diabetic autonomic neuropathy. These studies modified the RR-variation test, used to test diabetic ANS function in humans, and applied it to rats. Permanent wire electrodes were implanted in the chest wall of a rat. ECG complexes were obtained by connecting the electrodes to leads going to an impedence pneumograph and high gain coupler. This information was then converted into square waves by a trigger unit and recorded on magnetic tape for subsequent analysis by computer. Recordings were at least 60 seconds long, of which 30 seconds was used for analysis. In order to establish autonomic influence, RR-variation was measured before and after application of pharmacologic agents. Directly decreasing parasympathetic tone with atropine (20 mg/kg, n = 6) increased heart rate (P less than 0.001) and decreased RR-variation (P less than 0.05). Directly decreasing beta adrenergic tone with propranolol (10 mg/kg, n = 7) decreased heart rate (P less than 0.01) but had no effect on RR-variation (NS). Stimulation of the beta adrenergic receptors (isoproterenol, 0.1 mg/kg, n = 5) increased heart rate (P less than 0.01) but decreased RR-variation (P less than 0.01). Increasing parasympathetic tone reflexly with alpha-1 adrenergic receptor stimulation (phenylephrine, 1 mg/kg, n = 7) decreased heart rate (P less than 0.05) and increased RR-variation (P less than 0.025). The responses to phenylephrine could be blocked by parasympathetic blockade. Phentolamine (0.1 mg/kg, n = 7) caused an increase in heart rate (P less than 0.001) and a decrease in RR-variation (P less than 0.01). The responses to phentolamine could be blocked by beta adrenergic receptor blockade.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetic peripheral neuropathy. Part I. Sensorimotor neuropathy (continuing education credit)

Diabetic neuropathy, defined as objective evidence of neural im pairment accompanied by discern ible symptoms, is a common complication of diabetes. Pathologically it is considered a "dying back " neuropathy in which the distal portions of the neurons are first and more severely affected. Both vascular and metabolic hypotheses have been advanced for its patho genesis. Diabetic sensorimotor neuropathy has two subclasses: focal and distal symmetrical polyneuropathy. Signs and symp toms, complications, and guide lines for treatment are listed for the different syndromes. Current research includes investigations of the possible preventive and therapeutic roles of glycemic control and specific therapeutic agents.

Development of a predictive model for symptomatic neuropathy in diabetes

In evaluating therapeutic interventions aimed at preventing diabetic neuropathy, choosing a suitable measure of neural function is difficult, partly because the relation between most available objective measures and the development of symptomatic neuropathy (SN) is unclear. Using data from 67 diabetic patients, we developed a linear logistic regression model to assess the relationship between SN and a set of neural measures, including dark-adapted pupil size; pupillary latency; heart rate; a measure of respiratory sinus arrhythmia (R); the Valsalva ratio; and conduction velocities for the peroneal, median motor, and median sensory nerves. Models allowed for possible effects related to age, sex, duration and type of diabetes, glycosylated hemoglobin, and adiposity. Thirty-two of the patients reported SN (autonomic and/or sensorimotor). The best-fitting model for predicting the presence of any SN included only heart rate, duration of disease, and R. Exclusion of duration (P less than .01), or heart rate (P less than .05), or R (P less than .001) significantly impaired the fit of the model. To evaluate the temporally predictive power of the model, nine of the asymptomatic patients were reinterviewed 2 yr later by the same interviewer, who was unaware of the results of the modeling. Four of five to whom the model had assigned high probability of symptoms had indeed developed SN during the follow-up period, whereas none of the four assigned low probability had developed SN (P less than .05). Thus it seems that a measure of respiratory sinus arrhythmia provides an index of neural function strongly related to SN, and our follow-up data suggest that diminished R can be used to predict the development of SN in diabetes.

Decreased numbers of platelet alpha-adrenergic binding sites in diabetes mellitus

Eleven men with diabetes mellitus were compared with 45 male controls for platelet alpha-adrenergic binding sites by using [3H]dihydroergocryptine (DHE) as the radioligand antagonist. There was no difference between the two for binding affinity, but the number of sites was 430 +/- 30 (means +/- SEM) for diabetic subjects and 574 +/- 29 for controls (P = .005). Decreased sites were related to increased glycosylated hemoglobin levels (P = .002). There was no relationship between the decreased sites and catecholamine levels, duration of disease, body weight, or fasting blood sugar. Hence, binding sites were inversely related to control, but further studies are needed to define the pathophysiologic significance of this.

Clinical trials of sorbinil on nerve function

Three clinical trials to evaluate the efficacy of the aldose reductase inhibitor sorbinil in improving or preventing diabetic neural function have either been completed or are currently in progress. In the first study from Seattle and Chicago, motor and sensory nerve conduction velocities (NCV) were evaluated in 39 insulin- and noninsulin-dependent, glycemic-stable diabetic patients in a randomized, double-blind, crossover trial. During the 9 weeks of treatment with 250 mg/d of sorbinil, there was a faster nerve conduction velocity of all 3 nerves tested when compared with the placebo period: peroneal motor NCV (+0.70 +/- 0.24 m/s; means +/- SEM; P less than 0.008), median motor NCV (+0.66 +/- 0.27 m/s; P less than 0.005), and median sensory NCV (+1.16 +/- 0.50 m/s; P less than 0.035). Conduction velocity for all 3 nerves declined significantly within 3 weeks following cessation of the drug. These effects of sorbinil were unrelated to glycemic control, which was constant during the study. Although the effects of sorbinil in improving nerve conduction velocity were small, the findings suggest that the polyol-pathway activity contributes to slowed nerve conduction velocity in diabetics. The second study is a seven-center, double-blind, randomized, 12-month trial of 210 to 280 diabetic patients with clinical signs, symptoms, and objective measurements of neuropathy. The trial has a common-core protocol with end-point evaluations of scored neural signs, symptoms, and neural measurements. Two unique neural tests were designed and validated for use in this trial: thermal and tactile perception thresholds of the fingers and toes.(ABSTRACT TRUNCATED AT 250 WORDS)

Pentobarbital suppresses basal and reflexive pancreatic polypeptide release in dogs

We sought to determine in overnight-fasted dogs whether basal or 2-deoxy-D-glucose (2-DG)-stimulated levels of pancreatic polypeptide (PP) could be reliably used as an index of cholinergic activity at the pancreas and thereby determine the effect of pentobarbital anesthesia on this cholinergic outflow. At low basal PP levels, either atropine or pentobarbital had a small effect on PP levels; at higher basal levels, both atropine and pentobarbital had a larger effect. Thus both drugs decreased PP in proportion to its initial basal level, suggesting that basal PP levels have a variable cholinergic component. Atropine abolished the PP response to intravenous 2-DG, confirming in our animal model that the PP response to neuroglucopenia is entirely cholinergically mediated. Pentobarbital also abolished the PP response to 2-DG, suggesting that anesthesia either suppresses cholinergic outflow to the pancreas or the response of the pancreatic F-cell to it. To test the latter hypothesis, the acetylcholine analogue bethanechol was administered before and during pentobarbital anesthesia. The PP response to direct cholinergic stimulation was not abolished by pentobarbital, although it was reduced modestly. We conclude that only part of the basal level of PP is under cholinergic control; all of the PP response to 2-DG is cholinergically mediated; pentobarbital anesthesia abolishes the cholinergic input to the pancreas; and if the endogenous cholinergic input influences certain pancreatic endocrine and exocrine responses, then its contribution would be seriously underestimated when studied in pentobarbital-anesthetized animals.

Effects of glycemic control and aldose reductase inhibition on nerve conduction velocity

In two studies of patients with diabetes who did not have neurologic symptoms, nerve conduction velocity was increased either by an improvement in glucose control or by the administration of the aldose reductase inhibitor sorbinil. In a 1981 study by Graf et al, glycemic control and motor and sensory nerve conduction velocities were evaluated in 18 patients with non-insulin-dependent diabetes before and after one, three, six, and 12 months of antihyperglycemic therapy. There was an improvement in motor nerve conduction velocity (median motor, p less than 0.01; peroneal motor, p less than 0.05; and tibial motor, p less than 0.05), which was associated with the improvement in fasting plasma glucose levels after three months for some motor nerves (median motor: r = -0.62, p less than 0.01; peroneal motor: r = -0.50, p less than 0.05). A direct linear relationship between the change in fasting glucose and glycosylated hemoglobin levels and the change in median motor nerve conduction velocity after 12 months of antihyperglycemic therapy was also found. Thus, there was a tendency for those patients who had the greatest improvement in glycemic control to have the greatest improvement in motor nerve conduction velocity. The findings in the first study are consistent with the hypothesis that hyperglycemia contributes to slowed nerve conduction velocity. In a 1983 randomized, double-blind, crossover study by Judzewitsch et al, motor and sensory nerve conduction velocities were evaluated in 39 patients with insulin-dependent or non-insulin-dependent diabetes in whom glycemic control was stable. During nine weeks of treatment with 250 mg per day of sorbinil, nerve conduction velocity was faster in the three tested nerves when compared with the velocities during the placebo period (peroneal motor nerve conduction velocity: +0.70 +/- 0.24 m per second, mean +/- SEM, p less than 0.008; median motor nerve conduction velocity: +0.66 +/- 0.27 m per second, p less than 0.005; median sensory nerve conduction velocity: +1.16 +/- 0.50 m per second, p less than 0.035). Although the effect of an improvement in glycemic control and administration of sorbinil in increasing nerve conduction velocity in two groups of neurologically asymptomatic patients with diabetes was small, the findings are consistent with the hypothesis that polyol pathway activity contributes to slowed large-fiber nerve conduction velocity in these patients.

Correlations among autonomic, sensory, and motor neural function tests in untreated non-insulin-dependent diabetic individuals

A well-defined group of untreated non-insulin-dependent (NIDD) subjects were evaluated to determine whether involvement of neural function measurements is generalized and symmetrical and to compare the autonomic, sensory, and motor neural measurements. After age adjustment, the sensory and motor neural function measurements were significantly slower in the diabetic group than in normal subjects (P less than 0.01). Similarly, the autonomic nervous system function measurements were also abnormal in the NIDD group (P less than 0.01). Further analysis revealed that each of the specific measurements--median motor nerve conduction velocity (NCV,P less than 0.005), peroneal motor NCV (P less than 0.005), median sensory NCV (P less than 0.005), dark-adapted pupil size after muscarinic blockade (P less than 0.02), pupillary latency time (P less than 0.02), and RR-variation after beta adrenergic blockade (P less than 0.001)--was significantly less by analysis of covariance after age adjustment in the NIDD group than in normal subjects. Thus, there was evidence of motor and sensory neural impairment in the upper and lower extremities as well as evidence of impairment of the reflex arcs involving the parasympathetic nerves to the heart and eye and the sympathetic nerves to the iris. Further analysis revealed that right and left NCV were correlated (P less than 0.01), as were the median motor and median sensory NCV (P less than 0.01), the median motor and peroneal motor NCV (P less than 0.001), and the peroneal motor and median sensory NCV (P less than 0.001). Thus, there was evidence of symmetrical upper and lower limb, as well as motor and sensory proportional involvement of large nerve fiber NCV in this group of NIDD subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucose regulation in non-insulin-dependent diabetes mellitus. Interaction between pancreatic islets and the liver

The degree of fasting hyperglycemia in patients with non-insulin-dependent diabetes mellitus is dependent on the rate of hepatic glucose production. The basal rate of hepatic glucose production is increased in patients with non-insulin-dependent diabetes mellitus, and there is a positive correlation between hepatic glucose production and fasting glucose levels. Diminished secretion of insulin, impaired hepatic sensitivity to insulin's effects, or a combination of these factors could contribute to the elevated hepatic glucose production in patients with non-insulin-dependent diabetes mellitus. The relationship between insulin secretion and hepatic glucose production is regulated by a closed feedback loop operating between glucose levels and pancreatic beta cells. Although fasting insulin levels are usually comparable between patients with non-insulin-dependent diabetes mellitus and normal subjects, insulin secretion is markedly impaired in non-insulin-dependent diabetes mellitus in relation to the degree of hyperglycemia present. In fact, the degree of fasting hyperglycemia in a given patient with non-insulin-dependent diabetes mellitus is closely related to the degree of impaired pancreatic beta-cell responsiveness to glucose. Such findings suggest that impaired insulin secretion leads to increased hepatic glucose production, which raises the plasma glucose level. The resulting hyperglycemia helps to maintain relatively normal basal insulin output. Chronic sulfonylurea drug therapy of patients with non-insulin-dependent diabetes mellitus enhances pancreatic islet sensitivity to glucose, leading to increased insulin secretion, suppression of hepatic glucose production, and a decline in the steady-state fasting glucose level.

Hemodynamic effects of epinephrine: concentration-effect study in humans

The hemodynamic effects of three different infusion rates of epinephrine (25, 50, or 100 ng X kg-1 X min-1 for 14 min) were examined in 10 normal human subjects. Ejection fraction and changes in cardiac volumes were assessed by radionuclide ventriculography. Plasma epinephrine was increased to levels that spanned the normal physiological range (178 +/- 15, 259 +/- 24, and 484 +/- 69 pg/ml, respectively). Epinephrine infusions resulted in dose-dependent increases in heart rate (8 +/- 3, 12 +/- 2, and 17 +/- 1 beats/min, mean +/- SE) and systolic pressure (8 +/- 1, 18 +/- 2, and 30 +/- 6 mmHg). Although epinephrine infusions had minimal effects on end-diastolic volume, there were significant increases in stroke volume (+26 +/- 2, 31 +/- 4, and 40 +/- 4%), ejection fraction (+0.10 +/- 0.01, 0.14 +/- 0.02 and 0.16 +/- 0.03 ejection fraction units), and cardiac output (+41 +/- 4, 58 +/- 5, and 74 +/- 1%). These increases in left ventricular performance were associated with a decreased systemic vascular resistance (-31 +/- 3, -42 +/- 2, and -48 +/- 8%). Supine bicycle exercise resulted in similar plasma epinephrine levels (417 +/- 109 pg/ml) and similar changes in stroke volume, ejection fraction, and systemic vascular resistance but greater increases in heart rate and systolic blood pressure. Since infusion-associated hemodynamic changes occurred at plasma epinephrine levels commonly achieved during many types of physical and emotional stress, epinephrine release may have an important role in regulating systemic vascular resistance, stroke volume, and ejection fraction responses to stress in man.