Venous compression syndromes: clinical features, imaging findings and management

Extrinsic venous compression is caused by compression of the veins in tight anatomic spaces by adjacent structures, and is seen in a number of locations. Venous compression syndromes, including Paget-Schroetter syndrome, Nutcracker syndrome, May-Thurner syndrome and popliteal venous compression will be discussed. These syndromes are usually seen in young, otherwise healthy individuals, and can lead to significant overall morbidity. Aside from clinical findings and physical examination, diagnosis can be made with ultrasound, CT, or MR conventional venography. Symptoms and haemodynamic significance of the compression determine the ideal treatment method.

A Hebbian learning rule gives rise to mirror neurons and links them to control theoretic inverse models

Mirror neurons are neurons whose responses to the observation of a motor act resemble responses measured during production of that act. Computationally, mirror neurons have been viewed as evidence for the existence of internal inverse models. Such models, rooted within control theory, map-desired sensory targets onto the motor commands required to generate those targets. To jointly explore both the formation of mirrored responses and their functional contribution to inverse models, we develop a correlation-based theory of interactions between a sensory and a motor area. We show that a simple eligibility-weighted Hebbian learning rule, operating within a sensorimotor loop during motor explorations and stabilized by heterosynaptic competition, naturally gives rise to mirror neurons as well as control theoretic inverse models encoded in the synaptic weights from sensory to motor neurons. Crucially, we find that the correlational structure or stereotypy of the neural code underlying motor explorations determines the nature of the learned inverse model: random motor codes lead to causal inverses that map sensory activity patterns to their motor causes; such inverses are maximally useful, by allowing the imitation of arbitrary sensory target sequences. By contrast, stereotyped motor codes lead to less useful predictive inverses that map sensory activity to future motor actions. Our theory generalizes previous work on inverse models by showing that such models can be learned in a simple Hebbian framework without the need for error signals or backpropagation, and it makes new conceptual connections between the causal nature of inverse models, the statistical structure of motor variability, and the time-lag between sensory and motor responses of mirror neurons. Applied to bird song learning, our theory can account for puzzling aspects of the song system, including necessity of sensorimotor gating and selectivity of auditory responses to bird's own song (BOS) stimuli.

Improved Thermal Response in Encapsulated Phase Change Materials by Nanotube Attachment on Encapsulating Solid

This paper demonstrates greatly improved specific power (W/g) for encapsulated phase change materials (EPCM) as a result of modified interface morphology. Carbon nanotubes are strongly attached to the interior walls of the graphitic foam encapsulation. Microstructure analysis using scanning electron microscopy (SEM) indicates that the wax infiltrates into the carbon nanotubes (CNT) forest and creates an intimate contact with increased interfacial area between the two phases. Specific power has been calculated by measuring thermal response times of the phase change materials using a custom system. The carbon nanotubes increase the specific power of the encapsulated phase change materials by about 27% during heating and over 146% during the more important stage of latent heat storage. Moreover, SEM images of the interface after repeated thermal cycling indicate that the presence of CNT may also improve durability of the EPCM by preventing interfacial gaps and maintaining improved contact between the graphite and PCM phases.

Hyperlactatemia and concurrent use of antiretroviral therapy among HIV infected patients in Uganda

BACKGROUND

We determined the prevalence and factors associated with hyperlactatemia among HIV patients admitted on the emergency ward of a national hospital in Uganda.

OBJECTIVE

We were specifically interested in knowing whether there was an association between clinically significant hyperlactatemia and concurrent antiretroviral therapy (ART) use.

METHODS

A cross sectional descriptive study enrolled 303 HIV infected patients at a national referral hospital between March and April 2008. We consecutively recruited all eligible HIV infected patients above 18 years admitted on the emergency ward. Data were collected on socio-demographic, clinical and laboratory characteristics. Lactate levels were measured using the Accutrend® portable lactate analyser. Data analysis was performed using Stata 10.0; P-value of < 0.05 was considered to be significant.

RESULTS

Three hundred and three HIV infected patients were recruited. Prevalence of hyperlactatemia (lactate ≥2.5mmol/L) was 252 (83.2%). Clinically significant hyperlactatemia (lactate ≥4mmol/L) was present in 105/303(34.6%) patients. There was no association between use of ART and clinically significant hyperlactatemia. In the multivariate analysis, body weakness 1.91 (1.09-3.35), skin rash 3.18 (1.11-9.10) and tachypnoea 1.04 (1.01-1.07) were independently associated with clinically significant hyperlactatemia.

CONCLUSION

There was a high prevalence of clinically significant hyperlactatemia among HIV infected patients but it was not associated with concurrent antiretroviral use.

Heightened central affective response to visceral sensations of pain and discomfort in IBS

BACKGROUND Typically, conventional functional imaging methods involve repeated exposures to sensory stimulation. In rectal distension (RD) studies that involve multiple distensions, however, it is difficult to disambiguate the central response to RD from pathological alterations in peripheral neural responses associated with relaxation and accommodation of the rectum. METHODS This study addressed potential confounders found in previous imaging studies by collecting functional magnetic resonance imaging studies (fMRI) data during a single slow ramp-tonic distension paradigm and analysing fMRI signal changes using independent component analysis. KEY RESULTS Compared with controls, IBS participants showed increased activation of the anterior cingulate cortices, insula and ventral medial prefrontal regions suggesting heightened affective responses to painful visceral stimuli. In addition, the failure by IBS patients to down-regulate activity within ventral medial prefrontal and the posterior cingulate/precuneus regions was suggestive of reduced sensitivity to somatic changes and delayed shifts away from rest in ;default network' activity patterns. Controls showed heightened activation of the thalamus, striatal regions and dorsolateral prefrontal cortex suggesting greater arousal and salience-driven sustained attention reactions and greater modulation of affective responses to discomfort and pain. CONCLUSION&INFERENCES This work points to alterations in the central response to visceral pain and discomfort in IBS, highlighting diminished modulation and heightened internalization of affective reactions.