Skin Blood Flow Response Signal Using Time and Frequency Domain Features for Pressure Ulcer Evaluation

Pressure Ulcer (PU) is an area of the skin in which cutaneous tissue is compromised and there is progressive damage on the underlying tissue caused by blood flow obstruction due to prolonged external direct pressure. Research has shown that ischemic stress response can be evaluated using skin blood flow response (SBFR) signal features which are useful for pressure ulcer evaluation. Trends of peak reactive hyperemia (RH) were observed for three repetitive loading-unloading cycles in previous animal study to investigate tissue recovery.  However, tissue recovery and tissue damage cannot be discriminated by the trends of peak RH for short recovery time. The trends of alternative time-domain SBFR features such i.e total hyperemic response as well as frequency-domain features using Fast Fourier Transform (FFT) and Short Time Fourier Transform (STFT) i.e total power spectrum are further investigated to indicate tissue recovery. The results show that total hyperaemic response outperforms peak RH at detecting insufficient tissue recovery with 72% of samples with increasing trend in the short recovery time group compared to 57% of samples for peak RH. Total hyperemic response is effective at discriminating insufficient recovery time while other investigated features are only effective at detecting sufficient recovery time

Effectiveness of local cooling on enhancing tissue ischemia tolerance in people with spinal cord injury

People with spinal cord injury (SCI) are at risk of pressure ulcer development due to impaired mobility, sensation or changes in tissue properties. Increased skin temperature is one of the least explored risk factors for pressure ulcers. Since people with SCI also encounter thermoregulation deficits, investigation of the effectiveness of local skin cooling in this population is particularly important. Three groups of subjects were recruited: 1) 14 subjects with SCI at T6 and above, 2) 8 subjects with SCI below T6, and 3) 14 healthy controls. Reactive hyperemic response was the main study outcome and was measured after three different combinations of stimuli: 1) pressure only, 2) pressure with fast cooling (-4°C/min) and 3) pressure with slow cooling (-0.33°C/min). Spectral density of the skin blood flow (SBF) was used to investigate the underlying microcirculatory control mechanisms. Five of the subjects did not have reactive hyperemia in all test sessions and were excluded from statistical analysis. In the control group, the normalized peak SBF and perfusion area were close to significantly greater in pressure only as compared to fast cooling (p=0.023 and p=0.023, respectively) and slow cooling (p=0.033 and p=0.016, respectively). Although this phenomenon was not significant when analyzing subjects with SCI alone, significant changes were observed in the signal attributed to the metabolic control mechanism and were observed in this population with pressure only (p=0.019) and pressure with slow cooling (p=0.041). Since the reactive hyperemic response is mediated by different control mechanisms, the less obvious changes in reactive hyperemia in people with SCI may be due to alterations in microcirculation after injury. Results from this study suggest that local skin cooling is beneficial to ischemic tissue by decreasing the metabolic demand, and this is generally consistent with previous animal studies and our pilot study. Findings from this study also suggest that investigating time domain parameters and time-dependent spectral analysis of the SBF signal is helpful in understanding circulatory control in people with different levels of neurological deficits. This study contributes toward justification for the development of support surfaces with microclimate controls to enhance tissue integrity

Hybrid Equation/Agent-Based Model of Ischemia-Induced Hyperemia and Pressure Ulcer Formation Predicts Greater Propensity to Ulcerate in Subjects with Spinal Cord Injury

Pressure ulcers are costly and life-threatening complications for people with spinal cord injury (SCI). People with SCI also exhibit differential blood flow properties in non-ulcerated skin. We hypothesized that a computer simulation of the pressure ulcer formation process, informed by data regarding skin blood flow and reactive hyperemia in response to pressure, could provide insights into the pathogenesis and effective treatment of post-SCI pressure ulcers. Agent-Based Models (ABM) are useful in settings such as pressure ulcers, in which spatial realism is important. Ordinary Differential Equation-based (ODE) models are useful when modeling physiological phenomena such as reactive hyperemia. Accordingly, we constructed a hybrid model that combines ODEs related to blood flow along with an ABM of skin injury, inflammation, and ulcer formation. The relationship between pressure and the course of ulcer formation, as well as several other important characteristic patterns of pressure ulcer formation, was demonstrated in this model. The ODE portion of this model was calibrated to data related to blood flow following experimental pressure responses in non-injured human subjects or to data from people with SCI. This model predicted a higher propensity to form ulcers in response to pressure in people with SCI vs. non-injured control subjects, and thus may serve as novel diagnostic platform for post-SCI ulcer formation. © 2013 Solovyev et al

Multimodal optical diagnostics of the microhaemodynamics in upper and lower limbs

The introduction of optical non-invasive diagnostic methods into clinical practice can substantially advance in the detection of early microcirculatory disorders in patients with different diseases. This paper is devoted to the development and application of the optical non-invasive diagnostic approach for the detection and evaluation of the severity of microcirculatory and metabolic disorders in rheumatic diseases and diabetes mellitus. The proposed methods include the joint use of laser Doppler flowmetry, absorption spectroscopy and fluorescence spectroscopy in combination with functional tests. This technique showed the high diagnostic importance for the detection of disturbances in peripheral microhaemodynamics. These methods have been successfully tested as additional diagnostic techniques in the field of rheumatology and endocrinology. The sensitivity and specificity of the proposed diagnostic procedures have been evaluated.<br/

Comparison of laser Doppler and laser speckle contrast imaging using a concurrent processing system

Full field laser Doppler imaging (LDI) and single exposure laser speckle contrast imaging (LSCI) are directly compared using a novel instrument which can concurrently image blood flow using both LDI and LSCI signal processing. Incorporating a commercial CMOS camera chip and a field programmable gate array (FPGA) the flow images of LDI and the contrast maps of LSCI are simultaneously processed by utilizing the same detected optical signals. The comparison was carried out by imaging a rotating diffuser. LDI has a linear response to the velocity. In contrast, LSCI is exposure time dependent and does not provide a linear response in the presence of static speckle. It is also demonstrated that the relationship between LDI and LSCI can be related through a power law which depends on the exposure time of LSCI

Oleuropein effects on rat and human microcirculation

The aim of the present study was to investigate oleuropein effects on microvascular responses. First, we investigated the in vivo effects of oleuropein on rat pial microcirculation submitted to hypoperfusion-reperfusion injury. Therefore, we studied acute microvascular responses such as arteriolar vasodilation, permeability increase, leukocyte adhesion and capillary perfusion, by fluorescence microscopy. The working hypothesis was that this polyphenol may induce nitric oxide (NO) release from endothelial cells and consequently protect cerebral blood flow distribution and cerebral tissue. Rat cerebral cortical eNOS protein levels were evaluated as well as the impact of oxidative stress induced by hypopefusion and reperfusion on brain tissue, utilizing DCFH-DA. The second part of the study was aimed to evaluate oleuropein effects on skin microvascular blood flow oscillations of hyperlipidemic obese patients, by laser Doppler flowmetry (LDF). Therefore, hyperlipidemic obese females were administered with a hypocaloric and hypolipidic diet plus oleuropein for three months. These data were compared with the response of hyperlipidemic obese patients administered with hypocaloric and hypolipidic diet. Under baseline conditions and at the end of the study, nutritional status and lipid profile were evaluated as well as skin blood flow oscillations and reactive hyperemia by LDF. The results of the experimental study in rats indicate that oleuropein significantly improved in vivo microvascular responses after hypoperfusion-reperfusion injury. In particular, 20 mg/Kg b.w. of oleuropein induced a dilation by 28 ±2% of baseline (p < 0.01 vs. hypoperfused group) in order 3 arterioles and significantly reduced microvascular leakage (NGL: 0.13 ± 0.03; p < 0.01 vs. hypoperfused group) as well as leukocyte adhesion on venular walls (2.0 ± 0.5/100 µm v.l./30 sec; p < 0.01 vs. hypoperfused group), at the end of reperfusion. Moreover, this polyphenol was able to preserve capillary perfusion at the end of reperfusion (-26.0±4.5% of baseline; p<0.01 vs. hypoperfused group). These responses were associated to the increased eNOS expression in cortex and in striatum of treated animals. Oleuropein was also able to reduce neuronal damage and ROS production at the end of reperfusion, compared with hypoperfused animals. On the other hand, the results of the clinical study revealed that three months of hypocaloric and hypolipidic diet associated to oleuropein significantly improved nutritional status and lipid profile of hyperlipidemic obese patients. Total and LDL cholesterol, indeed, decreased by 15.0±1.2 and 16.5±1.3%, respectively, in patients treated with diet (OD group), and by 21.3±1.5 and 21.2±1.4%, respectively, in subjects treated with diet plus oleuropein (OL group). Moreover, laser Doppler measurements showed an increase in skin perfusion, compared to baseline conditions and control group (+25.6±1.4% of baseline), while the spectral analysis of skin blood flow oscillations revealed an increase in the NO-dependent and myogenic-related frequency components. Furthermore, PORH response improved in oleuropein-treated group, compared to controls. In conclusion, oleuropein appeared able to protect rat pial microcirculation from hypoperfusion-reperfusion injury increasing nitric oxide release from endothelial cells, reducing oxidative stress and, consequently, preserving pial blood flow distribution. Interestingly, this polyphenol showed beneficial effects also in humans; three months of hypocaloric and hypolipidic diet plus oleuropein increased smooth muscle cell functions and microvascular responses in hyperlipidemic obese patients, improving tissue perfusion

Effects of local cooling on skin perfusion response to pressure: implications to pressure ulcer prevention

Pressure ulcers have long been an important healthcare issue in both acute and long-term care settings. Temperature is one of the extrinsic causative factors for this multi-factorial disease not yet fully explored. Previous animal studies revealed that skin cooling reduced the severity of ulceration compared to non-cooling. Cooling is also used widely in plastic surgery and organ transplants for tissue preservation. However, the underlying protective mechanism of local cooling remains unclear. Our study's objective was to measure the effect of cooling on tissue's response to pressure using skin perfusion response on human subjects. Reactive hyperemia is a normal protective physiological response occurring after vessel occlusion. Laser Doppler flowmetrey was used to measure cutaneous perfusion. We hypothesized that local cooling would reduce a rigid indenter induced post-ischemic reactive hyperemic response. Ten young healthy non-smokers were recruited into the study. A repeated measures design was used where all subjects were subjected to pressure with cooling to 25°C and pressure without cooling test sessions. Each test session contained five levels of pressure control: light contact (10 minutes), 60 mmHg (30 minutes), light contact (20 minutes), 150 mmHg (3 minutes), light contact (10 minutes). The cooling intervention was performed during the period of 60mmHg contact pressure. Our results showed a significantly attenuated peak perfusion response after 60mmHg (p=0.019) but not after 150mmHg (p=0.241) of pressure for the cooling session compared to the non-cooling. This study suggests that local cooling may protect skin from the harmful effects of prolonged pressure in this young healthy population. The study protocol would be modified to investigate populations at risk of pressure ulcers

Analysis of the Relationship between Sacral Skin Blood Flow and Transcutaneous Oxygenation in Response to Causative Factors of Pressure Ulcers in Healthy Subjects

Pressure ulcers significantly contribute to the diminished quality of life and substantial disability in people with spinal cord injury (SCI). A broad consensus among clinicians and researchers has been reached that the best approach to reducing this burden is to implement an effective preventive treatment that would greatly reduce the incidence. The preventative intervention should eliminate/diminish causative factors and pathways involved with pressure ulcer development. The objective of this thesis is to explore the relationship between sacral skin blood flow and transcutaneous oxygenation in response to causative factors of pressure ulcers (i.e. thermal stress, mechanical stress, and sympathetic modulations) in five neurologically intact subjects.Two tests were performed to analyze the relationship between sacral skin blood flow and transcutaneous oxygenation. In test 1, skin blood flow and transcutaneous oxygenation were measured while subjects underwent orthostatic stimulation. Results from test 1 showed that both the level of heat used and the location of testing effects how skin blood flow and transcutaneous oxygenation respond to orthostatic stimulation. In test 2, skin blood flow and transcutaneous oxygenation were measured while external pressure was applied. Results from test 2 showed that a significant increase in peak skin blood flow and TcPO2 (p<0.05) occurred on average 588 and 298 seconds, respectively, following removal of occluding pressure when the skin is heated to 44 degrees C; however, at 37 degrees C, skin blood flow and transcutaneous oxygenation showed a significant peak increase (p<0.05) following removal of occluding pressure at 28 and 404 seconds, respectively

Quantifying the Relationship of Bilateral Blood Flow in Glabrous Skin at Rest and During Sympathetic Perturbations

Sympathetic nervous system regulation of blood flow within glabrous skin occurs through control of vasoconstrictor tone, with vasodilation being a passive process. As bursts of sympathetic vasoconstrictor activity occur simultaneously at separate sites of the body, blood flow patterns should also be closely matched due to the direct connection between sympathetic nerves and peripheral microvessels. With sympathetic activity difficult and invasive to measure directly, the possibility of using blood conductance as an indirect measure seems promising. We investigated the relationship of bilateral blood conductance recordings of both middle fingers in ten (7M, 3F) healthy participants, while at rest and in response to perturbations known to elicit sympathetic activity. Cutaneous vascular conductance was measured from both middle fingers via laser Doppler flowmetry, while at rest in a thermoneutral room for 20 minutes and in response to 4 randomized sympathetic perturbations (2 breath holds and 2 cold stimuli) while centrally vasodilated via heating of the back. Correlation coefficients while at thermoneutral rest were high (0.80 ± 0.22) demonstrating a strong temporal relationship for blood conductance in both fingers. During the sympathetic perturbations, blood conductance in both fingers were more related during (0.93 ± 0.11) and post (0.87 ± 0.11) administration of the sympathetic perturbation than prior (0.67 ± 0.25) to the administration (p = 0.002). Taken together, these findings indicate that blood conductance patterns at separate sites of the body are significantly more related during vasoconstrictor activity and that blood conductance may have potential as a non-invasive measure of sympathetic activity