The differential effect of the level of spinal cord stimulation on patients with advanced peripheral vascular disease in the lower limbs

Percutaneous spinal cord stimulation (SCS) (Medtronic model 3487A PISCES-Quad lead) was carried out in 10 patients with rest pain from advanced peripheral vascular disease of the lower limb, who were unsuitable for conventional treatment. Trial stimulation ranged from 1-20 weeks and was associated with pain relief in nine of the patients. Claudication distance was improved in six patients. Trophic lesions improved in one patient with small artery disease. Spinal cord stimulation did not reverse the course of acute gangrenous lesions. The distal arterial pressure measured by Doppler Ankle/Brachial Pressure Index, (ABPI), showed no change. The capillary blood flow and skin temperature of both feet, measured, respectively, by Laser Doppler flowmetry and skin thermistor, showed a tendency to decrease when the stimulation was at the higher level, above T10, compared with an increase when the stimulation was at the lower level T12. Transcutaneous oxygen tension monitoring of the symptomatic foot showed an increase in four out of five patients. Pain relief was not dependent on circulatory changes, but it was more significant when the circulatory changes showed an impressive increase in the blood flow. The mechanism of these circulatory changes is probably by modulation of the sympathetic nervous system. Recognition of the optimal sitting of SCS may be critical in the clinical use of this technique, which seems to be a valuable option in the treatment of patients with advanced peripheral vascular disease (PVD).     

The Effect of Implementation of Guidelines for the Management of Severe Head Injury on Patient Treatment and Outcome

The authors retrospectively analysed two groups of consecutive patients who were similarly matched for brain injury severity. From a total of 39 severe head injury patients, 23 were treated according to the Guidelines for the Management of Severe Head Injury with intracranial pressure (ICP) monitoring ("Guidelines group"). Such an approach allowed the maintenance of ICP within normal values, especially in patients with intraventricular ICP monitoring allowing the release of cerebrospinal fluid (CSF) from the ventricular system. In the Guidelines group only two patients were administered barbiturates, after all other means of ICP lowering had been exhausted. The second group consisted of 16 patients who were not monitored for ICP ("non-Guidelines group"). In this group, management consisted of the prophylactic administration of barbiturates, high dose osmotic diuretics and hyperventilation usually at levels below 25 mm Hg. In the Guidelines group the mortality rate was 30% compared to 44% in the non-Guidelines group. Almost twice as many patients achieved a "favourable" (good recovery and moderate disability) outcome (49%) compared to the non-Guidelines treated patients (25%). Furthermore, there was a 32% decrease in severe neurological disabilities in those patients in the Guidelines group. It seems that the implementation of "Guidelines" in the treatment of severe head injury, based on the result of our clinical study, reduces death and disability rates in patients with severe head injury. The administration of therapy based on the "Guidelines principles" and monitoring of ICP, can minimise the application of those therapeutic modalities (barbiturate coma and prolonged hyperventilation) which, in addition to favourable effects, may also have harmful effects on patients with severe head injury.     

The effects of matrix stiffness and RhoA on the phenotypic plasticity of smooth muscle cells in a 3-D biosynthetic hydrogel system

Studies using 2-D cultures have shown that the mechanical properties of the extracellular matrix (ECM) influence cell migration, spreading, proliferation, and differentiation; however, cellular mechanosensing in 3-D remains under-explored. To investigate this topic, a unique biomaterial system based on poly(ethylene glycol)-conjugated fibrinogen was adapted to study phenotypic plasticity in smooth muscle cells (SMCs) as a function of ECM mechanics in 3-D. Tuning the compressive modulus between 448 and 5804 Pa modestly regulated SMC cytoskeletal assembly in 3-D, with spread cells in stiff matrices having a slightly higher degree of F-actin bundling after prolonged culture. However, vinculin expression in all 3-D conditions was qualitatively low and was not assembled into the classic focal adhesions typically seen in 2-D cultures. Given the evidence that RhoA-mediated cytoskeletal contractility represents a critical node in mechanosensing, we molecularly upregulated contractility by inducing SMCs to express constitutively active RhoA. In these cells, F-actin bundling and total vinculin expression increased, and focal adhesion-like structures began to emerge, consistent with RhoA's mechanism of action in cells cultured on 2-D substrates. Furthermore, SMC proliferation in 3-D did not depend significantly on matrix stiffness, and was reduced by constitutive activation of RhoA irrespective of ECM mechanical properties. Conversely, the expression of contractile markers globally increased with constitutive RhoA activation and depended on 3-D matrix stiffness only in cells with heightened RhoA activity. Combined, these data suggest that the synergistic effects of ECM mechanics and RhoA activity on SMC phenotype in 3-D are distinct from those in 2-D, and highlight the importance of studying the mechanical role of cell-matrix interactions in tunable 3-D environments.     

Prevascularization of a fibrin-based tissue construct accelerates the formation of functional anastomosis with host vasculature

One critical obstacle facing tissue engineering is the formation of functional vascular networks that can support tissue survival in vivo. We hypothesized that prevascularizing a tissue construct with networks of well-formed capillaries would accelerate functional anastomosis with the host upon implantation. Fibrin-based tissues were prevascularized with capillary networks by coculturing human umbilical vein endothelial cells (HUVECs) and fibroblasts in fibrin gels for 1 week. The prevascularized tissue and nonprevascularized controls were implanted subcutaneously onto the dorsal surface of immune-deficient mice and retrieved at days 3, 5, 7 and 14. HUVEC-lined vessels containing red blood cells were evident in the prevascularized tissue by day 5, significantly earlier than nonprevascularized tissues (14 days). Analysis of the HUVEC-lined vessels demonstrated that the number and area of perfused lumens in the prevascularized tissue were significantly larger compared to controls. In addition, collagen deposition and a larger number of proliferating cells were evident in the prevascularized tissue at day 14. Our results demonstrate that prevascularizing a fibrin-based tissue with well-formed capillaries accelerates anastomosis with the host vasculature, and promotes cellular activity consistent with tissue remodeling. Our prevascularization strategy may be useful to design large three-dimensional engineered tissues.     

Human glial cell production of lipoxygenase-generated eicosanoids: a potential role in the pathophysiology of vascular changes following traumatic brain injury

Acute cerebrovascular changes which occur following traumatic brain injury represent a highly complex, multifactorial pathophysiologic process which is poorly understood. It is now recognized that, under normal conditions, the brain is a source of a variety of arachidonic acid metabolites which are synthesized by both cyclooxygenase and lipoxygenase. The specific cellular source of these highly vasoactive substances remains controversial. Recent work has demonstrated that lipoxygenase products were detected by immunosensitive assay in whole brain samples from a gerbil concussive injury model, yet the production of leukotrienes could not be accounted for by cerebral vessels and their contents alone. It has been theorized that the probable source for these metabolites is the cortical neuron. We sought to elucidate whether cultured human glial cells, obtained from specimens removed at the time of surgery, are a significant source of lipoxygenase products as measured by high performance liquid chromatography (HPLC). We observed that these cells consistently produced 5, 12, and 15-HETE class eicosanoids despite failure to produce significant cyclooxygenase products. These preliminary findings are of considerable interest because these lipoxygenase products are known to be highly vasoactive as well as potent mediators of increased vascular permeability. Since it is known that mechanical perturbation of cell membranes stimulates the release of arachidonic acid from membrane phospholipids, it is conceivable that the production of these eicosanoids following traumatic brain injury could account for local cerebrovascular changes including both vasospasm and interstitial edema formation.     

Extent of microstructural white matter injury in postconcussive syndrome correlates with impaired cognitive reaction time: a 3T diffusion tensor imaging study of mild traumatic brain injury

BACKGROUND AND PURPOSE: Diffusion tensor imaging (DTI) may be a useful index of microstructural changes implicated in diffuse axonal injury (DAI) linked to persistent postconcussive symptoms, especially in mild traumatic brain injury (TBI), for which conventional MR imaging techniques may lack sensitivity. We hypothesized that for mild TBI, DTI measures of DAI would correlate with impairments in reaction time, whereas the number of focal lesions on conventional 3T MR imaging would not.MATERIALS AND METHODS: Thirty-four adult patients with mild TBI with persistent symptoms were assessed for DAI by quantifying traumatic microhemorrhages detected on a conventional set of T2*-weighted gradient-echo images and by DTI measures of fractional anisotropy (FA) within a set of a priori regions of interest. FA values 2.5 SDs below the region average, based on a group of 26 healthy control adults, were coded as exhibiting DAI.RESULTS: DTI measures revealed several predominant regions of damage including the anterior corona radiata (41% of the patients), uncinate fasciculus (29%), genu of the corpus callosum (21%), inferior longitudinal fasciculus (21%), and cingulum bundle (18%). The number of damaged white matter structures as quantified by DTI was significantly correlated with mean reaction time on a simple cognitive task (r = 0.49, P = .012). In contradistinction, the number of traumatic microhemorrhages was uncorrelated with reaction time (r = −0.08, P = .71).CONCLUSION: Microstructural white matter lesions detected by DTI correlate with persistent cognitive deficits in mild TBI, even in populations in which conventional measures do not. DTI measures may thus contribute additional diagnostic information related to DAI.

Traumatic brain injury (TBI) is the leading cause of death and disability in young people, with 1.4 million annually reported cases in the United States and an estimated 57 million people worldwide hospitalized with 1 or more TBIs.¹ Furthermore, approximately 80% of the hospital-reported patients with TBI are categorized as having mild TBI on the basis of a Glasgow Coma Scale score between 13 and 15. Although those patients with mild TBI with normal CT findings and no post-traumatic amnesia usually have complete resolution of post-traumatic symptoms within 1 month, approximately 30% of patients with mild TBI with posttraumatic amnesia have persistent posttraumatic symptoms, and a significant number at 1-year postinjury have decreased functional outcome.^2,3Structural imaging studies of acute TBI demonstrate that MR imaging is more sensitive than CT in the number of traumatic lesions visualized.⁴ However, the relationship between focal structural lesions detected by conventional MR imaging and long-term patient outcome is controversial.^3,5-7 Nevertheless, patients with TBI with posttraumatic symptoms often have cognitive impairment, and their cognitive function is a major predictor of poor outcome.^8-12 In particular, attention, working memory, cognitive manipulation of temporal information, and processing speed are vulnerable.^13,14 Sequelae of TBI cause significant disability, which compelled the National Institutes of Health (NIH) to declare mild TBI as a major public health problem.¹⁵Although conventional MR imaging techniques can readily visualize posttraumatic focal structural lesions, they fail to adequately detect diffuse axonal injury (DAI), the key mechanism of damage following TBI.¹⁶ DAI results from unequal rotational or acceleration/deceleration forces that cause multifocal lesions in white matter due to a shear-strain deformation.^17-19 DAI is primarily responsible for transient deficits in cognitive performance in domains such as processing speed, working memory, and attention.^20,21 More recent studies suggest that DAI causes persistent postconcussive symptoms in executive function and memory dysfunction.^8,22-25MR diffusion tensor imaging (DTI) may be used to better assess DAI. In DTI, the characteristics of water diffusion in the brain are used to assess microstructural integrity of white matter pathways.²⁶ In white matter, water diffuses more readily along the orientation of axonal fibers than across the fibers due to hindrance from structural elements such as the axolemma and the myelin sheath. One can calculate the apparent diffusion coefficient (ADC), which is a rotationally invariant measure of the magnitude of diffusion. The degree of directionality of diffusion is termed “anisotropy.” This is the variation in the eigenvalues of the diffusion tensor.²⁷ Fractional anisotropy (FA), a normalized measure of anisotropy, has been shown to be sensitive to microstructural changes in white matter integrity.^28,29 Such measurements quantify the extent of damage following TBI^24,30-32 and are more sensitive than conventional MR imaging to axonal injury in a mouse model of TBI.³³In a group of patients with mild TBI with persistent postconcussive symptoms, we tested the hypothesis that the extent of microstructural white matter injury on DTI would account for deficits in cognitive reaction time, whereas the number of focal lesions on conventional MR imaging would not. The purpose of this study was to determine the predominant areas of damage in mild TBI and whether the spatial extent of white matter injury on DTI can be used as an effective biomarker for global cognitive outcome.     

Mesenchymal stem cells enhance angiogenesis in mechanically viable prevascularized tissues via early matrix metalloproteinase upregulation

Angiogenesis, the sprouting of new blood vessels from existing vasculature, is a complex biological process of interest to both the treatment of numerous pathologies and the creation of thick engineered tissues. In the context of tissue engineering, one potential solution to the diffusion limitation is to create a vascular network in vitro that can subsequently anastomose with the host after implantation, allowing the implantation of thicker, more complex tissues. In this study, the ability of endothelial cells to sprout and form stable vascular networks in 3-dimensional (3D) fibrin matrices was investigated as a function of matrix density in a prevascularized tissue model. The results demonstrate that while increasing matrix density leads to a nearly 7-fold increase in compressive stiffness, vascular sprouting is virtually eliminated in the most dense matrix condition. However, the addition of human mesenchymal stem cells (HMSCs) to the denser matrices reverses this effect, resulting in an up to a 7-fold increase in network formation. Although the matrix metalloproteinases (MMPs) MMP-2, MMP-9, and MT1-MMP are all upregulated early on with the addition of HMSCs, MT1-MMP appears to play a particularly important role in the observed angiogenic response among these proteases. This study provides a means to design stiffer prevascularized tissues utilizing naturally derived substrates, and its results may yield new mechanistic insights into stem cell-based angiogenic therapies.