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Newcastle upon Tyne, United Kingdom

Allen J.,Microvascular Diagnostics | Howell K.,Institute of Immunity and Transplantation
Physiological Measurement | Year: 2014

The microvasculature presents a particular challenge in physiological measurement because the vessel structure is spatially inhomogeneous and perfusion can exhibit high variability over time. This review describes, with a clinical focus, the wide variety of methods now available for imaging of the microvasculature and their key applications. Laser Doppler perfusion imaging and laser speckle contrast imaging are established, commercially-available techniques for determining microvascular perfusion, with proven clinical utility for applications such as burn-depth assessment. Nailfold capillaroscopy is also commercially available, with significant published literature that supports its use for detecting microangiopathy secondary to specific connective tissue diseases in patients with Raynaud's phenomenon. Infrared thermography measures skin temperature and not perfusion directly, and it has only gained acceptance for some surgical and peripheral microvascular applications. Other emerging technologies including imaging photoplethysmography, optical coherence tomography, photoacoustic tomography, hyperspectral imaging, and tissue viability imaging are also described to show their potential as techniques that could become established tools for clinical microvascular assessment. Growing interest in the microcirculation has helped drive the rapid development in perfusion imaging of the microvessels, bringing exciting opportunities in microvascular research. © 2014 Institute of Physics and Engineering in Medicine.

Di Maria C.,Microvascular Diagnostics | Di Maria C.,Northumbria University | Allen J.,Microvascular Diagnostics | Allen J.,Northumbria University | And 3 more authors.
Journal of Clinical Endocrinology and Metabolism | Year: 2014

Context: The disease phase in thyroid eye disease (TED) is commonly assessed by clinical investigation of cardinal signs of inflammation and using the clinical activity score (CAS). Although CAS is the current gold standard, the clinical assessment would benefit if a more objective tool were available. Objective: The aim of this work was to explore the clinical value of a novel thermal imaging analysis technique to objectively quantify the thermal characteristics of the eye and peri-orbital region and determine the disease phase in TED. Design: This was a cross-sectional study comparing consecutive patients with active TED (CAS ≥3/7) attending a tertiary center, with a group of consecutive patients with inactive TED (CAS <3). Patients: Thermal images were acquired from 30 TED patients, 17 with active disease and 13 with inactive disease. Interventions: Patients underwent standard ophthalmological clinical assessments and thermal imaging. Main Outcome Measures: Five novel thermal eye parameters (TEP) were developed to quantify the thermal characteristics of the eyes in terms of the highest level of inflammation (TEP1), overall level of inflammation (TEP2), right-left asymmetry in the level of inflammation (TEP3), maximum temperature variability across the eyes (TEP4), and right-left asymmetry in the temperature variability (TEP5). Results: All five TEP were increased in active TED. TEP1 gave the largest accuracy (77%) at separating the two groups, with 65% sensitivity and 92% specificity. A statistical model combining all five parameters increased the overall accuracy, compared to using only one parameter, to 93% (94% sensitivity and 92% specificity). All five of the parameters were also found to be increased in patients with chemosis compared to those without. Conclusions: The potential diagnostic value of this novel thermal imaging analysis technique has been demonstrated. Further investigation on a larger group of patients is necessary to confirm these results. Copyright © 2014 by the Endocrine Society.

Anderson K.N.,Royal Infirmary | Di Maria C.,Microvascular Diagnostics | Allen J.,Microvascular Diagnostics
Journal of Sleep Research | Year: 2013

Many patients with restless legs syndrome (Willis-Ekbom disease) complain of burning sensations in their feet associated with the desire to move, such that they seek cooler environments. This pilot study aimed to characterise the microvascular skin changes in 12 patients with restless legs syndrome compared with 12 age- and sex-matched controls. Patients with moderate or severe restless legs syndrome and controls underwent detailed thermovascular assessment in a controlled temperature room at three different stages (normothermic phase 23 °C, hot phase 30 °C, cold phase 18 °C). Microvascular activity was recorded during all phases by bilateral great toe laser-Doppler flowmetry and also by whole-body thermography. Patient and control measurements were compared. The study protocol was well tolerated. Parameters extracted from the laser-Doppler flowmetry measurements were used to model a logistic function using binary logistic regression. This demonstrated a statistically significant difference between patients with restless legs syndrome and healthy controls (P < 0.001). Visual inspection of the body thermography image sequences showed increased lower limb movement in patients with restless legs syndrome patients compared with controls. Thermography analysis also showed significant differences between foot temperatures in patients with restless legs syndrome compared with controls during the hot phase (P = 0.011). Notably, patients with restless legs syndrome had more uniform foot temperatures, whereas controls had a wider variability in surface temperature across the feet. This novel study demonstrates impaired microvascular circulation in patients with restless legs syndrome in comparison to matched controls and a potential mechanism for the sensation of burning feet. The protocol also provides an experimental paradigm to test therapeutic interventions for the future. © 2013 European Sleep Research Society.

Allen J.,Microvascular Diagnostics | Murray A.,Microvascular Diagnostics | Di Maria C.,Microvascular Diagnostics | Newton J.L.,Northumbria University
Physiological Measurement | Year: 2012

Autonomic nervous system dysfunction is frequently reported in chronic fatigue syndrome (CFS) with orthostatic intolerance, a common symptom that can be objectively assessed. The frequent finding of autonomic dysfunction and symptoms on standing has the potential to provide a diagnostic biomarker in chronic fatigue. In this study we explored the clinical value of non-invasive optical multi-site photoplethysmography (PPG) technology to assess cardiovascular responses to standing. Multi-site PPG pulses were collected from tissue pads of the ears, fingers and toes of 14 patients with CFS and 14 age-matched sedentary subjects using a measurement protocol of a 10 min baseline (subject supine) followed by 3 min of tilting on a tilt table (head-up to 70°). Percentage change in pulse timing (pulse transit time, PTTf) and pulse amplitude (AMP) at each site were calculated using beat-to-beat pulse wave analysis. A significant reduction in the overall pulse timing response to controlled standing was found for the CFS group (using summed absolute percentage change in PTTf for ear, finger and toe sites, median change of 26% for CFS and 37% for control with p = 0.002). There were no significant differences between subject groups for the AMP measure at any site. Changes in AMP with tilt were, however, weakly significantly and negatively correlated with fatigue severity (p < 0.05). Receiver operating characteristic (ROC) analysis of timing measures produced an area under the curve of 0.81. Experimental linear discriminant classification analysis comparing both timing and amplitude measures produced an overall diagnostic accuracy of 82%. Pulse wave abnormalities have been observed in CFS and represent a potential objective measure to help differentiate between CFS patients and healthy controls. © 2012 Institute of Physics and Engineering in Medicine.

Allen J.,Microvascular Diagnostics | Di Maria C.,Microvascular Diagnostics | Mizeva I.,RAS Institute of Continuous Media Mechanics | Podtaev S.,RAS Institute of Continuous Media Mechanics
Physiological Measurement | Year: 2013

The physiological changes following a deep inspiratory gasp (DIG) manoeuvre have been described in the literature. However, the lack of a reliable signal processing technique to visualize and quantify these physiological changes has so far limited the applicability of the test to the clinical setting. The main aim of this study was to assess the feasibility of using wavelet analysis to quantify the pulse arrival time (PAT) and its changes during the DIG manoeuvre. Vascular responses were extracted from cardiac (electrocardiogram, ECG) and peripheral pulse (photoplethysmography, PPG) waveforms. Wavelet analysis characterized their cardiovascular responses in healthy adult subjects in the time-frequency space, and for the ECG-PPG inter-relationship in terms of the PAT. PAT showed a characteristic biphasic response to gasp, with an increase of 59 ± 59 ms (p = 0.001) compared to the maximum value reached during quiet breathing, and a decrease of -38 ± 55 ms (p < 0.01) compared to the minimum value during quiet breathing. The response measures were repeatable. This pilot study has successfully shown the feasibility of using wavelet analysis to characterize the cardiovascular waveforms and quantify their changes with DIG. © 2013 Institute of Physics and Engineering in Medicine.

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