Wavelet-based spectrum analysis of sacral skin blood flow response to alternating pressure

Effects of alternating pressure patterns on sacral skin blood flow responses in people with spinal cord injury

Alternating pressure support surface (APSS) is a common support surface for treating pressure injury in individuals with spinal cord injury (SCI). However, conflicting results on the effectiveness of APSS have been reported and may be associated with inappropriate configurations of APSS. The objectives of this study were to compare the different pressure amplitudes (75/5 mmHg [alternating between 75 and 5 mmHg] vs. 65/15 mmHg) and cycle periods (5 min [4 cycles] vs. 2.5 min [8 cycles]) of alternating pressure on sacral skin blood flow responses in 10 individuals with SCI. Sacral skin blood flow during and after loading of four alternating pressure protocols was assessed using laser Doppler flowmetry and was normalised to the value before loading (10-min baseline, 20-min loading and 10-min recovery). The results demonstrated that during the high-pressure phase, there was a significant difference between the 75/5 and 65/15 mmHg protocols (0.3658 ± 0.0688 for 75/5 mmHg and 0.1702 ± 0.0389 for 65/15 mmHg, p < 0.05); and during the low-pressure phase, there was a significant difference between the 75/5 and 65/15 mmHg protocols (1.7184 ± 0.262 for 75/5 mmHg and 0.5916 ± 0.1378 for 65/15 mmHg, p < 0.05). There were no differences between cycle periods in skin blood flow responses. No adverse events were reported. Our finding indicates that the pressure amplitude of alternating pressure is a significant factor affecting sacral skin blood flow responses. An appropriate configuration of alternating pressure is needed to effectively increase skin blood flow and tissue viability in individuals with SCI.

Distribution characteristics of pathogens in different stages of pressure ulcers and the therapeutic effect of linear polarized polychromatic light combined with silver sulfadiazine cream

To investigate the distribution characteristics of pathogens in different stages of pressure ulcers and observe the application of linear polarized polychromatic light (LPPL) combined with silver sulfadiazine cream in treating varying stages of pressure ulcers. This study comprised 88 patients with pressure ulcers who were enrolled in the department of burn and plastic surgery of our hospital from April 2019 to April 2022. The wound exudates from patients were collected, followed by analyzing the distribution of pathogens in different stages of pressure ulcers. Patients were randomly divided into 2 groups. The first group (n = 44) received LPPL combined with silver sulfadiazine. The other group was intervened with LPPL group only for 2 weeks. The clinical efficacy, condition, and pain in the 2 groups, as well as the healing timeframes for patients were measured at different stages. The findings showed that among 88 patients with pressure ulcers, 62 were infected, and the infection rate was 70.45%. The pathogens that were observed in stage II and III to IV pressure ulcers were mainly Gram-negative bacteria. The total effective rate in the combined group was 90.91%, which was much higher than that of LPPL group (70.45%). Compared with LPPL group, the pressure ulcer scale for healing and visual analogue scale scores in the combined group were markedly lower (P < .05). It is important to note that in LPPL group, the healing time of patients in stage II and stage III to IV in the combined arm were 9.76 ± 2.38 days and 13.19 ± 2.54 days, respectively. The corresponding time in the LPPL group was prolonged to 13.20 ± 3.76 and 18.82 ± 4.17 days, respectively. The main pathogens associated with wound infection in patients with pressure ulcers are Gram-negative bacteria. The curative effects of LPPL combined with sulfadiazine silver cream on patients with pressure ulcer is obviously improved, and the recovery and pain relief are faster while the healing time of pressure ulcer is shorter.

Effects of cycle periods and pressure amplitudes of alternating pressure on sacral skin blood flow responses

BACKGROUND

There are no guidelines on selecting alternating pressure (AP) configurations on increasing sacral skin blood flow (SBF).

AIM

The specific aims were to compare different cycle periods and pressure amplitudes of AP on sacral SBF responses in healthy people to establish the efficacy and safety of the protocols.

METHODS

Two studies were tested, including the cycle period study (8 2.5-min vs 4 5-min protocols) and the pressure amplitude study (75/5 vs 65/15 mmHg protocols). Sacral SBF was measured using laser Doppler flowmetry (LDF) in 20 participants. AP loads were randomly applied using an indenter through the rigid LDF probe. Each protocol included a 10-min baseline, 20-min AP and 10-min recovery periods. A 30-min washout period was provided. The SBF response was normalized to the baseline SBF of each condition of each participant.

RESULTS

For the cycle period study, the 4 5-min cycle protocol partially restored more SBF than the 8 2.5-min cycle protocol at the low-pressure phase (0.87 ± 0.04 vs 0.71 ± 0.03, p < 0.05) and at the high-pressure phase (0.25 ± 0.03 vs 0.19 ± 0.03, p < 0.05). For the pressure amplitude study, the 75/5 mmHg protocol partially restored more sacral SBF than the 65/15 mmHg protocol at the low-pressure phase (0.87 ± 0.1 vs 0.25 ± 0.03, p < 0.05) but not at the high-pressure phase (0.23 ± 0.02 vs 0.21 ± 0.02, non-significant).

CONCLUSION

This study demonstrated that 1) a cycle period of 5 min was better than 2.5 min and 2) a pressure amplitude of 75/5 mmHg was better than 65/15 mmHg. The finding provides insights for selecting the AP configurations for increasing SBF.

The attenuating effect of a dynamic cushion on the development of leg edema in wheelchair users with spinal cord injuries

BACKGROUND

Prolonged wheelchair sitting is known to lead to venous stasis and results in leg edema.

OBJECTIVE

To clarify how a dynamic cushion affects leg edema in people with spinal cord injuries (SCI) evoked by wheelchair sitting, we measured the changes in leg volume induced during wheelchair sitting with a dynamic air cushion or a static cushion.

METHODS

Seven wheelchair users with SCI participated in this study. Leg edema during wheelchair sitting was evaluated with strain gauge plethysmography (the gauge was placed 10 cm proximally from the medial malleolus). Following a period of rest, the subjects sat on a reclining wheelchair containing a dynamic cushion for 15 min. Then, the protocol was repeated with a static cushion. The above two procedures were performed in a random order. These data were statistically compared between the two procedures.

RESULTS

The change in leg volume observed during sitting on the dynamic cushion (-0.02 ± 0.21 ml/100 ml) was smaller than that observed during sitting on the static cushion (0.18 ± 0.28 ml/100 ml) (P< 0.05).

CONCLUSIONS

These results suggested that the dynamic air cushion relieved leg edema induced by wheelchair sitting in individuals with SCI.

Nonnegative matrix factorization for the identification of pressure ulcer risks from seating interface pressures in people with spinal cord injury

The purpose of this study was to predict and visualize pressure ulcer risks by using a novel approach of extracting computational features from seating interface pressures in people with spinal cord injury (SCI). In conventional clinical practice, seating interface pressure assessments rely on descriptive statistics of pressure magnitude. In this study, rank-2 nonnegative matrix factorization (NMF) was applied to the seating interface pressure maps during loading and pressure-relieving conditions in 16 people with SCI. The NMF basis images were used for visual interpretation and computational prediction of pressure ulcer risks. The two NMF basis images encapsulated pressure concentration and pressure dispersion, respectively. The first basis converged on the ischial tuberosity under both seating conditions, whereas the second basis converged anterior to the ischial tuberosity during loading and converged on the coccyx during unloading. The classification yielded 81.25% overall accuracy. In general, higher ulceration risk was associated with higher and lower activations of the first and second bases, respectively. The NMF pipeline yielded promising performance. Basis visualization affirmed the importance of lower ischial pressure and higher distribution dispersion while also revealing that clinical practice may currently be underestimating the importance of coccygeal pressure in response to pressure-relieving activities. Graphical abstract.

Optical probe pressure effects on cutaneous blood flow

The variation of blood flow characteristics caused by the probe pressure during noninvasive studies is of particular interest within the context of fundamental and applied research. It has been shown previously that the weak local pressure induces vasodilation, whereas the increased pressure is able to stop the blood flow in the compressed area, as well as to significantly change optical signals.The blood flow oscillations measured by laser Doppler flowmetry (LDF) characterize the functional state of the microvascular system and can be used for noninvasive diagnostics of its abnormality. This study was intended to identify the patterns of the relationship between the oscillating components of blood flow registered by the LDF method under different levels of pressure applied to an optical fiber probe.For this purpose, we have developed an original optical probe capable of regulating the applied pressure. The developed protocol included six sequential records of the blood perfusion at a pressure within the 0 to 200 mmHg range with unloading at the last stage.Using wavelet analyses, we traced the variation of energy of oscillations for these records in five frequency bands associated with different vascular tone regulation mechanisms. Six young volunteers of the same age (three males and three females) were included in this preliminary study and the protocol was repeated five times in each volunteer. Accordingly, 30 LDF records were available for the analyses. As expected, the LDF signal increases at weak pressure (30 mmHg) and decreases at increased pressure. The statistically stable amplification of endothelial associated blood flow oscillations under the 90 mmHg pressure allowed us to put forward a hypothesis that the endothelial activity increases. The possible causes of this phenomenon are discussed.

The effect of caffeine on cutaneous postocclusive reactive hyperaemia

Background

Caffeine is reported to be the most widely used pharmacologically active substance. It causes mental stimulation and increases blood pressure. Acute systolic and diastolic blood pressure response to caffeine attenuates in the course of regular caffeine use; tolerance to cardiovascular responses develops in some people. For some hypertension-prone people coffee ingestion may be harmful, and for others it may be beneficial. The aim of our work was to evaluate the effect of caffeine on postocclusive reactive hyperaemia (PORH), a test of microvascular function, and at the same time to monitor the central effects of caffeine on blood pressure and heart rate.

Methods

Heart rate, arterial pressure, and cutaneous laser-Doppler (LD) flux were monitored in 32 healthy volunteers (aged 25.2 ± 4.3 years) before and after they ingested 200 mg of caffeine. LD flux was measured on a finger at rest and after the release of an 8-minute occlusion of digital arteries above the place of LD flux measurement. All parameters obtained after the ingestion of caffeine were compared to the values obtained before caffeine and to the values obtained after a placebo.

Results

We found slightly increased arterial pressure as well as decreased heart rate and resting LD flux (Dunnett’s test, p<0.05) after the ingestion of caffeine. Caffeine significantly reduced the PORH response (Dunnett’s test, p<0.01). The power of the low-frequency oscillations (0.06–0.15 Hz) of LD flux, representing vascular myogenic activity, increased significantly after the ingestion of caffeine at rest and during the PORH response. A correlation was found between the number of cups of coffee regularly consumed and resting LD flux values (R = 0.492, p = 0.00422), peak LD flux values during PORH (R = 0.458, p = 0.00847), and the PORH area (R = 0.506, p = 0.00313) after caffeine consumption.

Conclusions

From the results, we can conclude that caffeine affects cutaneous microvascular function during rest and during a PORH response, and that it increases blood pressure and decreases heart rate.

The effect of pressure and shear on tissue viability of human skin in relation to the development of pressure ulcers: a systematic review

Pressure ulcers are a significant problem in health care, due to high costs and large impact on patients' life. In general, pressure ulcers develop as tissue viability decreases due to prolonged mechanical loading. The relation between load and tissue viability is highly influenced by individual characteristics. It is proposed that measurements of skin blood flow regulation could provide good assessment of the risk for pressure ulcer development, as skin blood flow is essential for tissue viability. . Therefore, the aim of this systematic review is to gain insight in the relation between mechanical load and the response of the skin and underlying tissue to this loading measured in-vivo with non-invasive techniques. A systematic literature search was performed to identify articles analysing the relation between mechanical load (pressure and/or shear) and tissue viability measured in-vivo. Two independent reviewers scored the methodological quality of the 22 included studies. Methodological information as well as tissue viability parameters during load application and after load removal were extracted from the included articles and used in a meta-analysis. Pressure results in a decrease in skin blood flow parameters, compared to baseline; showing a larger decrease with higher magnitudes of load. The steepness of the decrease is mostly dependent on the anatomical location. After load removal the magnitude of the post-reactive hyperaemic peak is related to the magnitude of pressure. Lastly, shear in addition to pressure, shows an additional negative effect, but the effect is less apparent than pressure on skin viability.

Effects of conventional and alternating cushion weight-shifting in persons with spinal cord injury

A repeated-measures study of 13 adult full-time wheelchair users with spinal cord injury (SCI) was carried out to determine whether alternating-pressure air cushion (APAC) use compared with independent pressure relief (IPR) provides reliable, effective pressure relief for individuals with SCI. Bilateral mean ischial interface pressure (IP), transcutaneous oxygen tension (TcPO2), and unilateral laser Doppler blood flow were evaluated. Blood flow component contributions were determined using short-time Fourier transform (STFT)-based spectral analysis. IPR assessment was carried out at recruitment. Study participants then used an APAC for 2 wk every 3 mo for 18 mo. IPR weight-shifting decreased mean ischial IP (p < 0.05) and increased mean TcPO2 (p < 0.05). All variables rapidly returned to preintervention levels following weight-shifting except for the cardiac component of blood flow. APAC-induced weight-shifting decreased mean ischial IP (p < 0.05). Mean TcPO2 increased and was higher than for IPR. STFT analysis indicated that quiet sitting following APAC-induced weight-shifting produced a higher neurogenic component of blood flow than following IPR (p = 0.02). Thus, IPR positively affects multiple aspects of tissue health but produces transient improvements and must be repeated regularly. APAC activation dynamically and continuously alters IP distribution with more sustained positive tissue health effects.

Comparison of changes in heart rate variability and sacral skin perfusion in response to postural changes in people with spinal cord injury

The current clinical practice has established guidelines to assess influences of severity of autonomic injury on the control of heart and blood pressure following spinal cord injury (SCI). However, the influences of SCI-induced autonomic impairment on microvascular dysfunction have not yet been established. Heart rate variability (HRV) has been shown to be a potential tool for quantifying residual sympathovagal regulation of the cardiovascular system following SCI and may be used to assess the effect of autonomic injury on skin microvascular dysfunction. A total of 26 people were recruited into the study, including 12 people with SCI and 14 nondisabled controls. HRV and sacral skin intervals and sacral skin perfusion were continually recorded during 10 min upright and 10 min prone postures. The sympathovagal balance was defined as the ratio of the power of the low frequency to the high frequency of HRV. The results showed that postural changes of nondisabled people produced significant changes in the sympathovagal balance; lower sympathovagal balance was associated with higher skin perfusion (p < 0.05). People with SCI did not show a significant change of HRV and skin perfusion in response to postural changes. In this study, we have demonstrated that the sympathovagal balance assessed by HRV was associated with the skin vasoconstrictive response to postural changes.

Effect of local cooling on pro-inflammatory cytokines and blood flow of the skin under surface pressure in rats: feasibility study

The primary purpose of this feasibility study was to establish a correlation between pro-inflammatory cytokine accumulation and severity of tissue damage during local pressure with various temperatures. The secondary purpose was to compare skin blood flow patterns for assessing the efficacy of local cooling on reducing skin ischemia under surface pressure. Eight Sprague-Dawley rats were assigned to two protocols, including pressure with local cooling (Δt = -10 °C) and pressure with local heating (Δt = 10 °C). Pressure of 700 mmHg was applied to the right trochanter area of rats for 3 h. Skin perfusion quantified by laser Doppler flowmetry and TNF-∗ and IL-1β levels were measured. Our results showed that TNF-α concentrations were increased more significantly with local heating than with local cooling under pressure whereas IL-1β did not change. Our results support the notion that weight bearing soft tissue damage may be reduced through temperature modulation and that non-invasive perfusion measurements using laser Doppler flowmetry may be capable of assessing viability. Furthermore, these results show that perfusion response to loading pressure may be correlated with changes in local pro-inflammatory cytokines. These relationships may be relevant for the development of cooling technologies for reducing risk of pressure ulcers.

Assessing complexity of skin blood flow oscillations in response to locally applied heating and pressure in rats: implications for pressure ulcer risk

The objective of this study was to investigate the effects of local heating on complexity of skin blood flow oscillations (BFO) under prolonged surface pressure in rats. Eleven Sprague-Dawley rats were studied: 7 rats underwent surface pressure with local heating (Δt = 10 °C) and 4 rats underwent pressure without heating. A pressure of 700 mmHg was applied to the right trochanter area of rats for 3 h. Skin blood flow was measured using laser Doppler flowmetry. The loading period was divided into nonoverlapping 30 min epochs. For each epoch, multifractal detrended fluctuation analysis (MDFA) was utilized to compute DFA coefficients and complexity of endothelia related metabolic, neurogenic, and myogenic frequencies of BFO. The results showed that under surface pressure, local heating led to a significant decrease in DFA coefficients of myogenic frequency during the initial epoch of loading period, a sustained decrease in complexity of myogenic frequency, and a significantly higher degree of complexity of metabolic frequency during the later phase of loading period. Surrogate tests showed that the reduction in complexity of myogenic frequency was associated with a loss of nonlinearity whereas increased complexity of metabolic frequency was associated with enhanced nonlinearity. Our results indicate that increased metabolic activity and decreased myogenic response due to local heating manifest themselves not only in magnitudes of metabolic and myogenic frequencies but also in their structural complexity. This study demonstrates the feasibility of using complexity analysis of BFO to monitor the ischemic status of weight-bearing skin and risk of pressure ulcers.

Skin blood flow response to locally applied mechanical and thermal stresses in the diabetic foot

Diabetic foot ulcers are one of the most common complications in diabetics, causing significant disabilities and decreasing the quality of life. Impaired microvascular reactivity contributes to the development of diabetic foot ulcers. However, underlying physiological mechanisms responsible for the impaired microvascular reactivity in response to extrinsic causative factors of foot ulcers such as mechanical and thermal stresses have not been well investigated. A total of 26 participants were recruited into this study, including 18 type 2 diabetics with peripheral neuropathy and 8 healthy controls. Laser Doppler flowmetry was used to measure skin blood flow at the first metatarsal head in response to a mechanical stress at 300mmHg and a fast thermal stress at 42°C. Wavelet analysis of skin blood flow oscillations was used to assess metabolic, neurogenic and myogenic controls. Our results indicated that diabetics have significantly decreased metabolic, neurogenic and myogenic responses to thermal stress, especially in the neurogenic and myogenic controls during the first vasodilatory response and in the metabolic control during the second vasodilatory response. Diabetics have a significantly decreased myogenic response to mechanical stress during reactive hyperemia. Our findings demonstrate that locally applied mechanical and thermal stresses can be used to assess microvascular reactivity and risk of diabetic foot ulcers.

Skin blood flow dynamics and its role in pressure ulcers

Pressure ulcers are a significant healthcare problem affecting the quality of life in wheelchair bounded or bed-ridden people and are a major cost to the healthcare system. Various assessment tools such as the Braden scale have been developed to quantify the risk level of pressure ulcers. These tools have provided an initial guideline on preventing pressure ulcers while additional assessments are needed to improve the outcomes of pressure ulcer prevention. Skin blood flow function that determines the ability of the skin in response to ischemic stress has been proposed to be a good indicator for identifying people at risk of pressure ulcers. Wavelet spectral and nonlinear complexity analyses have been performed to investigate the influences of the metabolic, neurogenic and myogenic activities on microvascular regulation in people with various pathological conditions. These findings have contributed to the understanding of the role of ischemia and viability on the development of pressure ulcers. The purpose of the present review is to provide an introduction of the basic concepts and approaches for the analysis of skin blood flow oscillations, and present an overview of the research results obtained so far. We hope this information may contribute to the development of better clinical guidelines for the prevention of pressure ulcers.

Comparison of muscle and skin perfusion over the ischial tuberosities in response to wheelchair tilt-in-space and recline angles in people with spinal cord injury

OBJECTIVE

To compare the efficacy of wheelchair tilt-in-space and recline on enhancing muscle and skin perfusion over the ischial tuberosities in people with spinal cord injury (SCI).

DESIGN

Repeated-measures and before-after trial design.

SETTING

University research laboratory.

PARTICIPANTS

Power wheelchair users with SCI (N=20).

INTERVENTIONS

Six combinations of wheelchair tilt-in-space and recline angles were presented to participants in a random order. The testing protocol consisted of a baseline 5 minutes sitting with no tilt/recline and 5 minutes positioned in a tilted and reclined position at each of 6 conditions, including: (1) 15° tilt-in-space and 100° recline, (2) 25° tilt-in-space and 100° recline, (3) 35° tilt-in-space and 100° recline, (4) 15° tilt-in-space and 120° recline, (5) 25° tilt-in-space and 120° recline, and (6) 35° tilt-in-space and 120° recline.

MAIN OUTCOME MEASURES

Muscle and skin perfusion were assessed by near-infrared spectroscopy and laser Doppler flowmetry, respectively.

RESULTS

Muscle perfusion was significantly increased at 25° and 35° tilt-in-space when combined with 120° recline, and skin perfusion was significantly increased at 3 tilt-in-space angles (15°, 25°, 35°) when combined with 120° recline and at 35° tilt-in-space when combined with 100° recline (P<.05). Even in the positions of increased muscle perfusion and skin perfusion (25° and 35° of tilt-in-space combined with 120° of recline), the amount of muscle perfusion change was significantly lower than the amount of skin perfusion change (P<.05).

CONCLUSIONS

Our results indicate that a larger angle of tilt-in-space and recline is needed to improve muscle perfusion compared with skin perfusion. A position of 25° tilt-in-space combined with 120° recline is effective in enhancing muscle and skin perfusion of weight-bearing soft tissues at the ischial tuberosities.

Effect of durations of wheelchair tilt-in-space and recline on skin perfusion over the ischial tuberosity in people with spinal cord injury

OBJECTIVE

To compare the efficacy of various durations of wheelchair tilt-in-space and recline on enhancing skin perfusion over the ischial tuberosity in people with spinal cord injury (SCI).

DESIGN

Repeated-measures, intervention and outcomes measure design.

SETTING

University research laboratory.

PARTICIPANTS

Power wheelchair users with SCI (N=9).

INTERVENTIONS

Three protocols of various durations (3min, 1min, and 0min) of wheelchair tilt-in-space and recline were randomly assigned to the participants. Each protocol consisted of a baseline 15-minute sitting, a duration of 0- to 3-minute reclined and tilted, a second 15-minute sitting, and a 5-minute recovery. The position at the baseline and the second sitting was no tilt/recline of the participant and at the reclined and tilted and recovery was at 35° tilt-in-space and 120° recline.

MAIN OUTCOME MEASURES

Skin perfusion response to tilt and recline was assessed by laser Doppler and was normalized to mean skin perfusion at the baseline sitting.

RESULTS

The results showed that mean skin perfusion during recovery at the 3-minute duration was significantly higher than that at the 1-minute duration (P<.017) and mean skin perfusion was not significantly different between the 1-minute and 0-minute durations (not significant). Skin perfusion during the second sitting was significantly higher at the 3-minute duration than at the 1-minute and 0-minute durations (P<.017).

CONCLUSIONS

Our findings suggest that performing the 3-minute duration of wheelchair tilt-in-space and recline is more effective than the 1-minute duration in enhancing skin perfusion of weight-bearing soft tissues.

Local cooling reduces skin ischemia under surface pressure in rats: an assessment by wavelet analysis of laser Doppler blood flow oscillations

The objectives of this study were to investigate the effects of local cooling on skin blood flow response to prolonged surface pressure and to identify associated physiological controls mediating these responses using the wavelet analysis of blood flow oscillations in rats. Twelve Sprague-Dawley rats were randomly assigned to three protocols, including pressure with local cooling (Δt = -10 °C), pressure with local heating (Δt = 10 °C) and pressure without temperature changes. Pressure of 700 mmHg was applied to the right trochanter area of rats for 3 h. Skin blood flow was measured using laser Doppler flowmetry. The 3 h loading period was divided into non-overlapping 30 min epochs for the analysis of the changes of skin blood flow oscillations using wavelet spectral analysis. The wavelet amplitudes and powers of three frequencies (metabolic, neurogenic and myogenic) of skin blood flow oscillations were calculated. The results showed that after an initial loading period of 30 min, skin blood flow continually decreased under the conditions of pressure with heating and of pressure without temperature changes, but maintained stable under the condition of pressure with cooling. Wavelet analysis revealed that stable skin blood flow under pressure with cooling was attributed to changes in the metabolic and myogenic frequencies. This study demonstrates that local cooling may be useful for reducing ischemia of weight-bearing soft tissues that prevents pressure ulcers.

Enhanced phase synchronization of blood flow oscillations between heated and adjacent non-heated sacral skin

The study of skin microcirculation may be used to assess risk for pressure ulcers. It is observed that local heating causes an increase in blood flow of not only the heated skin, but also in the adjacent non-heated skin. The underlying physiological mechanism of this indirect vasodilation of the non-heated skin remains unclear. We hypothesized that blood flow oscillations (BFO) in the adjacent non-heated skin area synchronize with BFO in the heated skin, thus inducing a vasodilatory response. We investigated BFO in the heated and adjacent non-heated skin (12.1 ± 1.2-cm distance) on the sacrum in 12 healthy participants. The ensemble empirical mode decomposition (EEMD) was used to decompose blood flow signals into a set of intrinsic mode functions (IMFs), and the IMFs with power spectra over the frequency range of 0.0095-0.02, 0.02-0.05, and 0.05-0.15 Hz were chosen as the characteristic components corresponding to metabolic, neurogenic, and myogenic regulations, respectively. Then, the instantaneous phase of the characteristic components was calculated using the Hilbert transform. From the time series of phase difference between a pair of characteristic components, the epochs of phase synchronization were detected. The results showed that myogenic and neurogenic BFO exhibited self-phase synchronization during the slower vasodilation of the heated skin. In the non-heated skin, the degree of synchronization of BFO is associated with the changes in blood flow.

The influence of autonomic dysfunction associated with aging and type 2 diabetes on daily life activities

Type 2 diabetes (T2D) and ageing have well documented effects on every organ in the body. In T2D the autonomic nervous system is impaired due to damage to neurons, sensory receptors, synapses and the blood vessels. This paper will concentrate on how autonomic impairment alters normal daily activities. Impairments include the response of the blood vessels to heat, sweating, heat transfer, whole body heating, orthostatic intolerance, balance, and gait. Because diabetes is more prevalent in older individuals, the effects of ageing will be examined. Beginning with endothelial dysfunction, blood vessels have impairment in their ability to vasodilate. With this and synaptic damage, the autonomic nervous system cannot compensate for effectors such as pressure on and heating of the skin. This and reduced ability of the heart to respond to stress, reduces autonomic orthostatic compensation. Diminished sweating causes the skin and core temperature to be high during whole body heating. Impaired orthostatic tolerance, impaired vision and vestibular sensing, causes poor balance and impaired gait. Overall, people with T2D must be made aware and counseled relative to the potential consequence of these impairments.

New concepts in the prevention of pressure sores

Pressure sores are a serious, and costly, complication for many patients with reduced mobility and sensation. Some populations, such as those with spinal cord injury (SCI), remain at high risk throughout their lifetime. Prevention is highly preferable and while the concept is readily definable, it is much more challenging to develop valid preventative measures. Subjective and objective approaches to risk factor assessment before pressure sores develop are reviewed, including risk status scales and emerging techniques to assess deep tissue injury. Devices to prevent pressure sores have traditionally focused on pressure-relieving cushions and mattresses. Technological advances being applied in the development of new pressure sore prevention devices are presented. Clinical evidence-based practice is integral to pressure sore prevention. Comprehensive assessment must include evaluation of systemic diseases, anatomical and physiological factors, together with environmental and psychosocial factors, which can all contribute to pressure sore development. Extrinsic factors need to be considered in conjunction with intrinsic tissue health factors and are reviewed together with an evaluation of currently available clinical practice guidelines. This chapter presents the broad diversity of factors associated with pressure sore development and highlights the need for an interdisciplinary team approach in order to maximize successful prevention of pressure sores.

Using recurrence network approach to quantify nonlinear dynamics of skin blood flow in response to loading pressure

This paper presents a recurrence network approach to quantify dynamic complexity of skin blood flow oscillations (BFO) in response to loading pressure. This approach consists of three processes, including 1) phase space reconstruction by means of time delay embedding, 2) construction of a recurrence matrix that represents neighboring states in phase space, and 3) consideration of the recurrence matrix as an adjacency matrix representing links in a network and the use of clustering coefficients to characterize phase space properties. By using the Lorenz system and real data, we demonstrate that the global clustering coefficient is robust to the embedding parameters. We applied this approach to study skin BFO at baseline and during loading pressure, a causative factor of skin breakdown. The results showed that global clustering coefficients of BFO significantly decreased in response to loading ( &#60;0.05). Moreover, surrogate tests indicated that such a decrease was associated with a loss of nonlinearity of BFO. Our results suggest that the recurrence network approach can practically quantify the nonlinear dynamics of BFO.

The effect of type-2-diabetes-related vascular endothelial dysfunction on skin physiology and activities of daily living

A common factor contributing to organ damage in type 2 diabetes mellitus (T2DM) is impaired tissue blood flow caused by damage to vascular endothelial cells (VECs). Damage can occur even before the clinical diagnosis of diabetes. It can be caused by both a high average blood glucose concentration and/or large daily spikes in blood glucose. While much of the present literature focuses on the damage to VECs and organs from these large glucose excursions, this review will focus on the consequence of this damage, that is, how endothelial cell damage in diabetes affects normal daily activities (e.g., exercise, reaction to typical stimuli) and various treatment modalities (e.g.. contrast baths and electrical stimulation therapy). It is important to understand the effects of VEC damage such as poor skin blood flow, compromised thermoregulation, and altered response to skin pressure in designing diabetes technologies as simple as heating pads and as complex as continuous glucose monitors. At the simplest level, people with diabetes have poor circulation to the skin and other organs. In the skin, even the blood flow response to locally applied pressure, such as during standing, is different than for people who do not have T2DM. Simple weight bearing on the foot can occlude the skin circulation. This makes the skin more susceptible to damage. In addition, endothelial damage has far-reaching effects on the whole body during normal activities of daily living, including an impaired response to local heat, such as hot packs and contrast baths, and higher body temperatures during whole body heating due to impaired blood flow and a reduced ability to sweat. Finally, because of multiple organ damage, people with T2DM have poor balance and gait and impaired exercise performance.

Multifractal analysis of nonlinear complexity of sacral skin blood flow oscillations in older adults

The objective of this study was to investigate the relationship between cutaneous vasodilatory function and nonlinear complexity of blood flow oscillations (BFO) in older people. A non-painful fast local heating protocol was applied to the sacral skin in 20 older subjects with various vasodilatory functions. Laser Doppler flowmetry was used to measure skin blood oscillations. The complexity of the characteristic frequencies (i.e., metabolic (0.0095-0.02 Hz), neurogenic (0.02-0.05 Hz), myogenic (0.05-0.15 Hz), respiratory (0.15-0.4 Hz), and cardiac (0.4-2 Hz)) of BFO was quantified using the multifractal detrended fluctuation analysis. Compared with the 65-75 years group, the complexity of metabolic BFO in the 75-85 years group was significantly lower at the baseline (P < 0.05) and the second peak (P < 0.001). Compared with baseline BFO, subjects in the 65-75 years group had a significant increase in the complexity of metabolic BFO (P < 0.01) in response to local heating; while subjects in the 75-85 years group did not. Our findings support the use of multifractal analysis to assess aging-related microvascular dysfunction.

Synchronization of sacral skin blood flow oscillations in response to local heating

Local heating causes an increase in skin blood flow by activating sensory axon reflex and metabolic nitric oxide controls. It has been observed that the remote skin area without temperature changes also shows a slightly increase in blood flow. The responsible mechanism of this indirect vasodilation remains unclear. We hypothesized that the remote skin area will have enhanced synchronization of blood flow oscillations (BFO), thus inducing a vasodilatory response. We studied BFO in two sites separated 10 cm of the sacral skin in 12 healthy people. Ensemble empirical mode decomposition method was used to decompose blood flow signals into a set of intrinsic mode functions (IMFs), and an IMF was selected to quantify each of myogenic, neurogenic, and metabolic modes of BFO. Then the instantaneous phase of the mode was calculated using the Hilbert transform. From the time series of phase difference between a pair of characteristic modes, we detected the epochs of phase synchronization and estimated the level of statistical significance using surrogate time series. The results showed that phase synchronization between neurogenic BFO was significantly higher in the period of the maximal vasodilation. We also observed a weak synchronization between myogenic BFO of the two skin sites. Our results suggested that synchronization of BFO may be associated with the changes in skin blood flow at the non-heated site.

Effect of wheelchair tilt-in-space and recline angles on skin perfusion over the ischial tuberosity in people with spinal cord injury

OBJECTIVE

To investigate the efficacy of wheelchair tilt-in-space and recline on enhancing skin perfusion over the ischial tuberosity in wheelchair users with spinal cord injury (SCI).

DESIGN

Repeated-measures, intervention, and outcomes-measure design.

SETTING

A university research laboratory.

PARTICIPANTS

Wheelchair users with SCI (N=11; 9 men, 2 women; mean ± SD age, 37.7±14.2y; body mass index, 24.7±2.6kg/m(2); duration of injury, 8.1±7.5y).

INTERVENTIONS

Protocols (N=6) of various wheelchair tilt-in-space and recline angles were randomly assigned to participants. Each protocol consisted of a 5-minute sitting-induced ischemic period and a 5-minute wheelchair tilt-in-space and recline pressure-relieving period. Participants sat in a position without tilt or recline for 5 minutes and then sat in 1 of 6 wheelchair tilted and reclined positions, including (1) 15° tilt-in-space and 100° recline, (2) 25° tilt-in-space and 100° recline, (3) 35° tilt-in-space and 100° recline, (4) 15° tilt-in-space and 120° recline, (5) 25° tilt-in-space and 120° recline, and (6) 35° tilt-in-space and 120° recline. A 5-minute washout period (at 35° tilt-in-space and 120° recline) was allowed between protocols.

MAIN OUTCOME MEASURES

Laser Doppler flowmetry was used to measure skin perfusion over the ischial tuberosity in response to changes in body positions caused by performing wheelchair tilt-in-space and recline. Skin perfusion response to wheelchair tilt-in-space and recline was normalized to skin perfusion of the upright seated position (no tilt/recline).

RESULTS

Combined with 100° recline, wheelchair tilt-in-space at 35° resulted in a significant increase in skin perfusion compared with the upright seated position (no tilt/recline; P<.05), whereas there was no significant increase in skin perfusion at 15° and 25° tilt-in-space (not significant). Combined with 120° recline, wheelchair tilt-in-space at 15°, 25°, and 35° showed a significant increase in skin perfusion compared with the upright seated position (P<.05).

CONCLUSIONS

Our results indicate that wheelchair tilt-in-space should be at least 35° for enhancing skin perfusion over the ischial tuberosity when combined with recline at 100° and should be at least 25° when combined with recline at 120°. Although smaller angles of wheelchair tilt-in-space and recline are preferred by wheelchair users for functional purposes, wheelchair tilt-in-space less than 25° and recline less than 100° may not be sufficient for effective pressure reduction for enhancing skin perfusion over the ischial tuberosity in people with SCI.

Evaluation of the usefulness of skin blood flow measurements by laser speckle flowgraphy in pressure-induced ischemic wounds in rats

Assessment of blood circulation in pressure ulcers can be beneficial for predicting the severity of tissue damage and making the prognosis. Here, we evaluated the usefulness of laser speckle flowgraphy (LSFG) for assessing skin blood flow in pressure-induced ischemic wounds in rats in comparison with skin temperature measurements by thermography, which is commonly used in clinical settings. The blood flow was assessed in 3 groups (control, 1 kg loading, and 10 kg loading for 3 hours), before, immediately after, and on days 1, 2, and 3 after loading. The 10 kg loading induced more severe tissue damage but did not show any distinguishable gross manifestations immediately after releasing the indenter. LSFG detected a significantly reduced blood flow velocity after 10 kg loading compared with 1 kg loading, whereas thermography did not. These results indicate the usefulness of LSFG measurements for assessing tissue circulation in an early phase after tissue damage onset.

The effects of polarized light therapy in pressure ulcer healing

Background/Aim. Neglecting polarized light as an adjuvant therapy for pressure ulcers and methodology distinctions in the trials engaging polarized light are the reasons for many dilemmas and contradictions. The aim of this study was to establish the effects of polarized light therapy in pressure ulcer healing. Methods. This prospective randomized single-blind study involved 40 patients with stage I-III of pressure ulcer. The patients in the experimental group (E) were subjected, besides polarized light therapy, to standard wound cleaning and dressing. Standard wound cleaning and dressing were the only treatment used in the control group (C). A polarized light source was a Bioptron lamp. Polarized light therapy was applied for six min daily, five times a week, four weeks. The Pressure Ulcer Scale for Healing (PUSH) was used in the assessment of outcome. Statistic analysis included Mann Whitney Test, Fisher Exact Test, Wilcoxon Signed Rank test. Results. There were significant differences between the groups at the end of the treatment regarding the surface of pressure ulcer (E: 10.80?19.18; C: 22,97?25,47; p = 0.0005), rank of pressure ulcer (E: 5.90?2.48; C: 8.6?1.05; p = 0.0005) and total PUSH score (E: 7.35?3.17; C: 11.85?2.35; p = 0,0003). The patients in the experimental group had significantly better values of the parameters monitored than the patients in the control group. Conclusion. After a four-week polarized light therapy 20 patients with stage I-III ulcer had significant improvement in pressure ulcer healing, so it could be useful to apply polarized light in the treatment of pressure ulcers.