In vivo laser speckle contrast imaging of microvascular blood perfusion using a chip-on-tip camera.

Laser speckle contrast imaging (LSCI) is an important non-invasive capability for real-time imaging for tissue-perfusion assessment. Yet, the size and weight of current clinical standard LSCI instrumentation restricts usage to mainly peripheral skin perfusion. Miniaturization of LSCI could enable hand-held instrumentation to image internal organ/tissue to produce accurate speckle-perfusion maps. We characterized a 1mm2 chip-on-tip camera for LSCI of blood perfusion in vivo and with a flow model. A dedicated optical setup was built to compare chip-on-tip camera to a high specification reference camera (GS3) for LSCI. We compared LSCI performance using a calibration standard and a flow phantom. Subsequently the camera assessed placenta perfusion in a small animal model. Lastly, a human study was conducted on the perfusion in fingertips of 13-volunteers. We demonstrate that the chip-on-tip camera can perform wide-field, in vivo, LSCI of tissue perfusion with the ability to measure physiological blood flow changes comparable with a standard reference camera.

An evaluation of mechanical and biophysical skin parameters at different body locations.

BACKGROUND: Skin is the largest organ in the body, representing an important interface to monitor health and disease. However, there is significant variation in skin properties for different ages, genders and body regions due to the differences in the structure and morphology of the skin tissues. This study aimed to evaluate the use of non-invasive tools to discriminate a range of mechanical and functional skin parameters from different skin sites. MATERIALS AND METHODS: A cohort of 15 healthy volunteers was recruited following appropriate informed consent. Four well-established CE-marked non-invasive techniques were used to measure four anatomical regions: palm, forearm, sole and lower lumbar L3, using a repeated measures design. Skin parameters included trans-epidermal water loss (TEWL), pH (acidity), erythema, stratum corneum hydration and stiffness and elasticity using Myoton Pro (skin and muscle probe). Differences between body locations for each parameter and the intra-rater reliability between days were evaluated by the same operator. RESULTS: The results indicate that parameters differed significantly between skin sites. For the Myoton skin probe, the sole recorded the highest stiffness value of 1006 N/m (SD ± 179), while the lower lumbar recorded the least value of 484 N/m (SD ± 160). The muscle indenter Myoton probe revealed the palm's highest value of 754 N/m (± 108), and the lower lumbar recorded the least value of 208 N/m (SD ± 44). TEWL values were lowest on the forearm, averaging 11 g/m2/h, and highest on the palm, averaging 41 g/m2/h. Similar skin hydration levels were recorded in three of the four sites, with the main difference being observed in the sole averaging 13 arbitrary units. Erythema values were characterised by a high degree of inter-subject variation, and no significant differences between sites or sides were observed. The Myoton Pro Skin showed excellent reliability (intra-class correlation coefficients > 0.70) for all sites with exception of one site right lower back; the Myoton pro muscle probes showed good to poor reliability (0.90-017), the corneometer showed excellent reliability (>0.75) among all the sites tested, and the TEWL showed Good to poor reliability (0.74-0.4) among sites. CONCLUSION: The study revealed that using non-invasive methods, the biophysical properties of skin can be mapped, and significant differences in the mechanical and functional properties of skin were observed. These parameters were reliably recorded between days, providing a basis for their use in assessing and monitoring changes in the skin during health and disease.

Vascular endothelial function is improved after active mattress use.

OBJECTIVE: Active mattresses are used to prevent, treat and relieve pressure ulcers (PU) by intermittent contact pressure/relief. However, no studies have directly assessed the vascular endothelial response to long-term active mattress use. This study investigated the hypothesis that eight weeks use of an active mattress would lead to improvements in vascular endothelial function in healthy participants. METHODS: Physiological parameters of baseline skin temperature (BskT), resting blood flow (RBF) and endothelial function as measured using post-occlusive reactive hyperaemia (PORH), were assessed at baseline (week 0); following eight weeks of sleeping on an active mattress, and after an eight week washout period (at week 16). RESULTS: We recruited 10 healthy participants (four male, age 52.7±8.5 years, six female age 51.8±17.5 years). Following active mattress use RBF, PORH and BskT at the hallux pulp increased by 336%, 197% and 3.5ºC, respectively. Mean values increased from 24.3±38.3 perfusion units to 106.0±100.3 perfusion units (p=0.021) and from 13,456±10,225 to 40,252±23,995 perfusion units x seconds (p=0.003) and from 22.9±2.5ºC to 26.4±1.9ºC (p<0.001), respectively. CONCLUSION: Active mattress use for eight weeks leads to significant improvements in RBF, PORH, and BskT. These results suggest that active mattress use can improve endothelial function. Future research is required to explore the potential of active mattress use in the treatment and management of diseases and conditions that would benefit from an improved endothelial function.

Intraoperative Tissue Perfusion Measurement by Laser Speckle Imaging: A Potential Aid for Reducing Postoperative Complications in Free Flap Breast Reconstruction.

Adequate tissue perfusion is essential to minimize postoperative complications following microsurgery. Intraoperative knowledge of tissue perfusion could aid surgical decision-making and result in reduced complications. Laser speckle imaging is a new, noninvasive technique for mapping tissue perfusion. This article discusses the feasibility of using laser speckle imaging during free flap breast reconstruction and its potential to identify areas of inadequate perfusion, thus reducing surgical complications. Adult patients scheduled to undergo free flap breast reconstruction were recruited into the study. Laser speckle images were obtained from the abdominal and breast areas at different stages intraoperatively. Zonal perfusion was compared with the Holm classification and clinical observations. Twenty patients scheduled to undergo free flap breast reconstruction were recruited (23 reconstructed breasts) (mean age, 50 years; range, 32 to 68 years). Flap zonal perfusion was 238 (187 to 313), 222 (120 to 265), 206 (120 to 265), and 125 (102 to 220) perfusion units for zones I, II, III, and IV, respectively (analysis of variance, p < 0.0001). Zonal area with perfusion below an arbitrary perfusion threshold were 20 (0.3 to 75), 41 (3 to 99), 49 (9 to 97), and 99 (25 to 100) percent, respectively (analysis of variance, p < 0.0001). One example is presented to illustrate potential intraoperative uses for laser speckle imaging. This study shows that laser speckle imaging is a feasible, noninvasive technique for intraoperative mapping of tissue perfusion during free flap breast reconstruction. Zonal tissue perfusion was reduced across the Holm classification. Observations indicated the potential for laser speckle imaging to provide additional information to augment surgical decision-making by detection of inadequate tissue perfusion. This highlights the opportunity for surgeons to consider additional aids for intraoperative tissue perfusion assessment to help reduce perfusion-related complications. CLINICAL QUESTION/LEVEL OF EVIDENCE:: Diagnostic, IV.

Time-Dependent Behavior of Microvascular Blood Flow and Oxygenation: A Predictor of Functional Outcomes.

OBJECTIVE: This study investigates the time-dependent behaviour and algorithmic complexity of low-frequency periodic oscillations in blood flux (BF) and oxygenation signals from the microvasculature. METHODS: Microvascular BF and oxygenation (OXY: oxyHb, deoxyHb, totalHb, and SO2%) was recorded from 15 healthy young adult males using combined laser Doppler fluximetry and white light spectroscopy with local skin temperature clamped to 33  °C and during local thermal hyperaemia (LTH) at 43 °C. Power spectral density of the BF and OXY signals was evaluated within the frequency range (0.0095-1.6 Hz). Signal complexity was determined using the Lempel-Ziv (LZ) algorithm. RESULTS: Fold increase in BF during LTH was 15.6 (10.3, 22.8) and in OxyHb 4.8 (3.5, 5.9) (median, range). All BF and OXY signals exhibited multiple oscillatory components with clear differences in signal power distribution across frequency bands at 33 and 43 °C. Significant reduction in the intrinsic variability and complexity of the microvascular signals during LTH was found, with mean LZ complexity of BF and OxyHb falling by 25% and 49%, respectively ( ). CONCLUSION: These results provide corroboration that in human skin microvascular blood flow and oxygenation are influenced by multiple time-varying oscillators that adapt to local influences and become more predictable during increased haemodynamic flow. SIGNIFICANCE: Recent evidence strongly suggests that the inability of microvascular networks to adapt to an imposed stressor is symptomatic of disease risk which might be assessed via BF and OXY via the combination signal analysis techniques described here.

Dynamics of microvascular blood flow and oxygenation measured simultaneously in human skin.

OBJECTIVE: To evaluate the dynamics of skin microvascular blood flow (BF) and tissue oxygenation parameters (OXY) measured simultaneously at the same site using a combined non-invasive BF+OXY+temperature probe. METHODS: Skin BF, oxygenated (oxyHb) and deoxygenated (deoxyHb) haemoglobin and mean oxygen saturation (SO2 ) were measured in 50 healthy volunteers at rest and during perturbation of local blood flow by post-occlusive reactive hyperaemia, sympathetic nervous system-mediated vasoconstriction (deep inspiratory breath-hold) and local skin warming. Signals were analysed in time and frequency domains. RESULTS: The relationship between BF and SO2 over the range of flows investigated was described by a non-linear equation with an asymptote for SO2 of 84% at BF >50 PU. SO2 was independently associated with BF, skin temperature, BMI and age, which together identified 59% of the variance in SO2 (p<0.0001). Fourier analysis revealed periodic low frequency fluctuations in both BF and SO2 , attributable to endothelial (~0.01 Hz), neurogenic (~0.04 Hz) and myogenic (~0.1 Hz) flow motion activity. The frequency coherence between the BF and SO2 signals was greatest in the endothelial and neurogenic frequency bands. CONCLUSIONS: The simultaneous evaluation of microvascular blood flow and oxygenation kinetics in healthy skin provides a platform from which to investigate microvascular impairment in the skin and more generally the pathogenesis of microvascular disease.

Evaluation of a new high power, wide separation laser Doppler probe: potential measurement of deeper tissue blood flow.

OBJECTIVE: To compare the output from a novel high power, wide separation laser Doppler flow probe (DP1-V2-HP, 4 mm, with IRLD20) with that of a standard flow probe (DP1-V2, 0.5 mm, with DRT4) (Moor UK) and to explore its potential for use in the noninvasive measurement of blood flow in deeper tissues in humans. METHODS: Monte Carlo modeling was used to predict depths of light scattering in skin with each probe, geometry. Experimentally, forearm blood flow was measured at rest and during local warming of the skin surface and post occlusion reactive hyperaemia (PORH). Laser Doppler blood flux (LDF) and the power spectral density of its component frequency intervals, were compared. RESULTS: Monte Carlo modeling indicated that while the majority of wide probe LD signal derives from deeper tissue, a significant portion is from superficial (dermal) tissue (and vice versa for standard probe). Perturbation of local blood flow differentially increased LDF and spectral power as measured by the two probes, with the standard skin probe showing a significantly greater response to local skin warming (p<0.01). CONCLUSIONS: These differences support our hypothesis that the wide probe is recording predominantly blood flux within the vasculature of sub-dermal tissue. This is in agreement with Monte Carlo simulation.

Comparison of red and green laser doppler imaging of blood flow.

BACKGROUND AND OBJECTIVES: Laser Doppler imaging (LDI) of perfusion has been performed with a novel green wavelength (532 nm) for comparison with a HeNe laser (633 nm), the aim being validation of the green laser wavelength as a research tool. STUDY DESIGN/MATERIALS AND METHODS: The effect of wavelength and power on images was investigated and perfusion response following both finger occlusion and local heating of the dorsum were examined as reproducible stimuli for clinical studies. RESULTS: The most striking difference between red and green LDI is the absence of veins on green LDI, which are seen with red LDI. Differences have been quantified using vein LDI profiles. Differences were found between blood flow responses imaged by red and green LDI (3 and 5 mW, respectively) for occlusion and heat stimuli. Results are discussed in the context of light penetration. CONCLUSIONS: Red and green wavelengths appear to image different components of the microcirculation.

The influence of probe fiber distance on laser Doppler perfusion monitoring measurements.

Laser Doppler perfusion monitoring (LDPM) is a noninvasive technique for monitoring skin microcirculation. The aim of this article was to investigate the influence of fiber separation on clinical LDPM measurements. A dual-channel LDPM system was used in combination with a probe that consists of two sets of detection fibers, at 0.2 and 1.0 mm from the illuminating fiber. Measurements were performed at the big toe of 8 healthy subjects and 11 subjects who had vascular disorders. In most cases, fluxes detected at both fiber distances showed very similar fluctuations. For each fiber separation, flux values of healthy subjects and patients were not significantly different. Furthermore, skin temperature (range: 22-34 degrees C) influenced the toe's pulp microcirculation markedly, increasing similarly at both probe separations, with a higher flux at a separation of 1.0 mm than at 0.2 mm. The flux ratio signal, obtained by dividing the flux at 0.2 mm by the flux at 1.0 mm, was significantly different between the two groups (p &< 0.05). In conclusion, the flux detected in vivo by means of LDPM, is influenced by the distance between the optical fibers. Use of the flux ratio with a multiseparation probe deserves attention as it is a possible marker for discriminating normal tissue perfusion from pathological skin tissue perfusion, independently from tissue temperature.