Association between cardiovascular risk profile and impaired microvascular function in a Swedish middle-aged cohort (the SCAPIS study).

AIM: The aim was to investigate the relationship between microvascular function, cardiovascular risk profile, and subclinical atherosclerotic burden. METHODS: The study enrolled 3809 individuals, 50-65 years old, participating in the population-based observational cross-sectional Swedish CArdioPulmonary bioImage Study (SCAPIS). Microvascular function was assessed in forearm skin using an arterial occlusion and release protocol determining peak blood oxygen saturation (OxyP). Cardiovascular risk was calculated using the updated Systematic Coronary Risk Evaluation (SCORE2; 10-year risk of fatal and non-fatal CVD events). OxyP was compared with Coronary Artery Calcification Score (CACS) and to plaques in the carotid arteries. RESULTS: Individuals with OxyP values in the lowest quartile (Q1; impaired microvascular function), had a mean SCORE2 of 5.8% compared to 3.8% in those with the highest values of OxyP (Q4), a relative risk increase of 53%. The risk of having a SCORE2 > 10% was 5 times higher for those in Q1 (OR: 4.96 95% CI: 2.76-8.93) vs. Q4 when adjusting for BMI and hsCRP. OxyP was lower in individuals with CACS > 0, and in those with both carotid plaques and CACS >0, =compared with individuals without subclinical atherosclerotic burdens (87.5 ± 5.6% and 86.9 ± 6.0%, vs 88.6 ± 5.8%, p < 0.01). CONCLUSION: In a population without cardiovascular disease or diabetes mellitus, impaired microvascular function is associated with cardiovascular risk profiles such as higher SCORE2 risk and CACS. We suggest that OxyP may serve as a microcirculatory functional marker of subclinical atherosclerosis and CVD risk, that is not detected by structural assessments.

Impaired microvascular function was associated with higher cardiovascular risk profile SCORE2 and subclinical atherosclerotic burden defined by carotid plaque and coronary artery calcification (CACS).­ Individuals with impaired microvascular function (peak oxygen saturation in forearm skin, OxyP, after a prolonged arterial occlusion provocation), had a moderate risk level of SCORE2 compared to low risk level in those with the highest values of OxyP.­ OxyP was lower in individuals with CACS > 0, and in those with both carotid plaques and CACS >0, =compared with individuals with carotid plaque only and in individuals without subclinical atherosclerotic burdens.

Microvascular dysfunction in women with a history of hypertensive disorders of pregnancy: A population-based retrospective cohort study.

OBJECTIVE: To evaluate microvascular function in women with previous hypertensive disorders of pregnancy (HDP). DESIGN: Retrospective population-based cohort study. SETTING: Linköping, Sweden. POPULATION: Women aged 50-65 years, participating in the Swedish CArdioPulmonary bioImage Study (SCAPIS) at one site (Linköping) 2016-18, who underwent microcirculatory assessment (N = 1222). METHODS: Forearm skin comprehensive microcirculatory assessment was performed with a PeriFlux PF6000 EPOS (Enhanced Perfusion and Oxygen Saturation) system measuring oxygen saturation and total speed resolved perfusion. Obstetric records were reviewed to identify women with previous HDP. Data on cardiovascular risk factors, comorbidities, medication, lifestyle, anthropometric data, and biochemical analyses were obtained from SCAPIS. The microcirculatory data were compared between women with and without previous HDP. MAIN OUTCOME MEASURES: Skin microcirculatory oxygen saturation and total speed resolved perfusion at baseline and post-ischaemic peak. RESULTS: Women with previous pre-eclampsia displayed impaired post-ischaemic peak oxygen saturation compared with women with normotensive pregnancies (88%, interquartile range [IQR] 84-89% vs 91%, IQR 87-94%, p = 0.001) 6-30 years after pregnancy. The difference remained after multivariable adjustment (ß -2.69, 95% CI -4.93 to -0.45). CONCLUSIONS: The findings reveal microvascular dysfunction at long-term follow up in women with previous pre-eclampsia and strengthen the possible role of endothelial dysfunction as a link to the increased risk of cardiovascular disease in women with HDP.

Absorption and reduced scattering coefficients in epidermis and dermis from a Swedish cohort study.

Significance: Knowledge of optical properties is important to accurately model light propagation in tissue, but in vivo reference data are sparse. Aim: The aim of our study was to present in vivo skin optical properties from a large Swedish cohort including 3809 subjects using a three-layered skin model and spatially resolved diffuse reflectance spectroscopy (Periflux PF6000 EPOS). Approach: Diffuse reflectance spectra (475 to 850 nm) at 0.4 and 1.2 mm source-detector separations were analyzed using an inverse Monte Carlo method. The model had one epidermis layer with variable thicknesses and melanin-related absorptions and two dermis layers with varying hemoglobin concentrations and equal oxygen saturations. The reduced scattering coefficient was equal across all layers. Results: Median absorption coefficients (mm-1) in the upper dermis ranged from 0.094 at 475 nm to 0.0048 at 850 nm and similarly in the lower dermis from 0.059 to 0.0035. The reduced scattering coefficient (mm-1) ranged from 3.22 to 1.20, and the sampling depth (mm) ranged from 0.23 to 0.38 (0.4 mm separation) and from 0.49 to 0.68 (1.2 mm separation). There were differences in optical properties across sex, age groups, and BMI categories. Conclusions: Reference material for skin optical properties is presented.

Nurses' strategies to enable continuous positive airway pressure therapy in a general medical ward context: A qualitative study.

BACKGROUND: Continuous positive airway pressure is a non-invasive therapy beneficial for patients with acute respiratory failure. The need for this therapy outside intensive care units is growing, but nurses face many challenges to enable this therapy in general medical wards. AIMS AND OBJECTIVES: The aim of the study was to explore nurses' strategies for enabling continuous positive airway pressure therapy in a general medical ward context. METHOD: An explorative qualitative design was used including semi-structured interviews with 15 Swedish nurses. Data were analysed using a conventional content analysis. RESULTS: The nurses' strategies included a non-hierarchical approach when utilising an intra- and interprofessional collaboration. Inexperience was compensated for by collaboration. Nurses' strategies involved advanced patient-centred care using interventions to manage and ease the patient's treatment and discomfort. The creation of an alliance with the patient was crucial to prevent treatment failure. The strategies were interrelated and considered as parts of a whole. CONCLUSION: Nurses described the strategy of a dynamic team that could be enlarged or decreased in tandem with other professionals, depending on the situation and the nurses' needs. Nurses need to have an attentive response to the patients' physical, psychosocial and relational needs and to maintain trust for a positive therapy outcome.

Post-ischemic skin peak oxygen saturation is associated with cardiovascular risk factors: a Swedish cohort study.

The objective of this study was to explore the associations between skin microcirculatory function and established cardiovascular risk factors in a large Swedish cohort. As part of the Swedish CArdioPulmonary bioImage Study (SCAPIS), microcirculatory data were acquired at Linköping University hospital, Linköping, Sweden during 2016-2017. The subjects, aged 50-64 years, were randomly selected from the national population register. Microcirculatory reactivity was assessed using a 5-min arterial occlusion-release protocol. Comprehensive skin microcirculatory data were continuously acquired by using a fiberoptic probe placed on the lower right arm. After exclusion of missing data (208), 1557 subjects were remaining. Among the parameters, skin microcirculatory peak oxygen saturation after occlusion release, had the strongest relationship to the cardiovascular risk factors. The linear associations between peak oxygen saturation and cardiovascular risk factors were analyzed adjusted for age and sex. We found a negative association with peak oxygen saturation (standardized regression coefficient) for blood pressure (systolic -0.05 (95% CI: -0.10;-0.003) and diastolic -0.05 (-0.10; -0.003)), BMI -0.18 (-0.23; -0.13), waist circumference (males -0.20 (-0.32; -0.16), females -0.18 (-0.25; -0.11)), prevalent diabetes -0.31 (-0.49; -0.12), hypertension -0.30 (-0.42; -0.18), dyslipidemia -0.24 (-0.40; -0.09), fasting glucose level -0.06 (-0.12; -0.01), HbA1c -0.07 (-0.12; -0.02), triglyceride level -0.09 (-0.14; -0.04), hsCRP -0.12 (-0.17; -0.07), and current smoker versus never smoked -0.50 (-0.67; -0.34). A positive association with peak oxygen saturation was found for cholesterol level 0.05 (0.005; 0.11) and HDL 0.11 (0.06; 0.17). This is the first study showing that post-ischemic skin microvascular peak oxygen saturation is associated with virtually all established cardiovascular risk factors in a population-based middle-aged cohort.

Normative data and the influence of age and sex on microcirculatory function in a middle-aged cohort: results from the SCAPIS study.

The objective of this study was to assess normative values for comprehensive forearm skin microcirculatory function: oxygen saturation, tissue fraction of red blood cells (RBCs), and speed-resolved perfusion. Furthermore, to examine the influence of age and sex on microcirculatory function. Measurements were performed using a noninvasive probe-based system, including diffuse reflectance spectroscopy and laser-Doppler flowmetry, yielding output data in absolute units. The study was conducted within the Swedish CArdioPulmonary BioImage Study (SCAPIS) and included 1,765 men and women aged 50-65 yr from the Linköping general population. Normative values are given at baseline, at the end of a 5-min occlusion of the brachial artery and during hyperemia after occlusion release. We found a consistent age distribution, in which the oldest individuals had the lowest peak oxygen saturation (P < 0.001) and the highest baseline low-speed perfusion (P < 0.001). Women had higher peak oxygen saturation (P < 0.001), lower RBC tissue fraction, in general (P < 0.001), lower baseline perfusion in all speed regions (P = 0.01), and lower peak high-speed perfusion at hyperemia (P < 0.001). The normative data can be used as reference values in future studies of disease-specific populations. The results show that age and sex are important aspects to consider in studies of microvascular function. Women and younger age were factors associated with higher peak oxygen saturation after ischemia. This is a novel parameter that reflects overall microcirculatory function associated with vascular dilation capacity.NEW & NOTEWORTHY This study expands experimental microcirculatory research to clinical use by providing normative values on microcirculatory function in a large population-based cohort. Women and younger age were factors associated with higher peak oxygen saturation after ischemia, which implies that age and sex are important aspects to consider in studies of microvascular function. This study is the first step toward using microcirculatory assessment as a tool to improve diagnosis, prognosis, and treatment in disease-specific populations.

Assessment of oxygenation with polarized light spectroscopy enables new means for detecting vascular events in the skin.

INTRODUCTION: Impaired oxygenation in the skin may occur in disease states and after reconstructive surgery. We used tissue viability imaging (TiVi) to measure changes in oxygenation and deoxygenation of haemoglobin in an in vitro model and in the dermal microcirculation of healthy individuals. MATERIALS AND METHODS: Oxygenation was measured in human whole blood with different levels of oxygenation. In healthy subjects, changes in red blood cell concentration (CRBC,TiVi), oxygenation (ΔCOH,TiVi) and deoxygenation (ΔCDOH,TiVi) of haemoglobin were measured during and after arterial and venous occlusion using TiVi and were compared with measurements from the enhanced perfusion and oxygen saturation system (EPOS). RESULTS: During arterial occlusion, CRBC,TiVi remained unchanged while ΔCOH,TiVi decreased to -44.2 (10.4) AU (p = 0.04), as compared to baseline. After release, CRBC,TiVi increased to 39.2 (18.8) AU (p < 0.001), ΔCOH,TiVi increased to 38.5. During venous occlusion, CRBC,TiVi increased to 28.9 (11.2) AU (p < 0.001), ΔCOH,TiVi decreased to -52.2 (46.1) AU (p < 0.001) compared to baseline after 5 min of venous occlusion. There was a significant correlation between the TiVi Oxygen Mapper and EPOS, for arterial (r = 0.92, p < 0.001) and venous occlusion (r = 0.87, p < 0.001), respectively. CONCLUSION: This study shows that TiVi can measure trends in oxygenation and deoxygenation of haemoglobin during arterial and venous stasis in healthy individuals.

Long-term effectiveness of arthrocentesis with and without hyaluronic acid injection for treatment of temporomandibular joint osteoarthritis.

This study evaluated the long-term effectiveness of intra-articular temporomandibular joint arthrocentesis for patients with osteoarthritis and compared arthrocentesis/lavage alone with arthrocentesis/lavage and injected hyaluronic acid. Forty patients met the inclusion criteria, and 37 completed long-term follow-up (approximately 4 years). The patients were randomly allocated to two groups: arthrocentesis with lavage alone (A-group, n = 17) or combined with hyaluronic acid treatment (AS-group, n = 20). Standard two-needle arthrocentesis was performed. Pain and joint sounds were measured at baseline and approximately 4 years after treatment. Reported pain, as indicated by visual analogue scale (VAS) score, significantly decreased from baseline to the final follow-up examination in both groups. Mean VAS score decreased from 64 to 16 (P < 0.001) in the A-group and from 63 to 25 (P < 0.001) in the AS-group. Average maximum incisor opening increased significantly in both groups but did not significantly differ between groups (P = 0.223). Joint sounds did not significantly improve within groups (A-group, P = 0.495; AS-group, P = 0.236). Both methods resulted in significant long-term improvements in pain and jaw function.

In vivo characterization of light scattering properties of human skin in the 475- to 850-nm wavelength range in a Swedish cohort.

We have determined in vivo optical scattering properties of normal human skin in 1734 subjects, mostly with fair skin type, within the Swedish CArdioPulmonary bioImage Study. The measurements were performed with a noninvasive system, integrating spatially resolved diffuse reflectance spectroscopy and laser Doppler flowmetry. Data were analyzed with an inverse Monte Carlo algorithm, accounting for both scattering, geometrical, and absorbing properties of the tissue. The reduced scattering coefficient was found to decrease from 3.16 ± 0.72 to 1.13 ± 0.27 mm-1 (mean ± SD) in the 475- to 850-nm wavelength range. There was a negative correlation between the reduced scattering coefficient and age, and a significant difference between men and women in the reduced scattering coefficient as well as in the fraction of small scattering particles. This large study on tissue scattering with mean values and normal variation can serve as a reference when designing diagnostic techniques or when evaluating the effect of therapeutic optical systems.

The relationship between forearm skin speed-resolved perfusion and oxygen saturation, and finger arterial pulsation amplitudes, as indirect measures of endothelial function.

OBJECTIVE: Endothelial function is important for regulating peripheral blood flow to meet varying metabolic demands and can be measured indirectly during vascular provocations. In this study, we compared the PAT finger response (EndoPAT) after a 5-minutes arterial occlusion to that from forearm skin comprehensive microcirculation analysis (EPOS). METHODS: Measurements in 16 subjects with varying cardiovascular risk factors were carried out concurrently with both methods during arterial occlusion, while forearm skin was also evaluated during local heating. RESULTS: Peak values for EPOS skin Perfconv and speed-resolved total perfusion after the release of the occlusion were significantly correlated to the EndoPAT RHI (ρ = .68, P = .007 and ρ = .60, P = .025, respectively), mainly due to high-speed blood flow. During local heating, EPOS skin oxygen saturation, SO2, was significantly correlated to RHI (ρ = .62, P = .043). This indicates that SO2 may have diagnostic value regarding endothelial function. CONCLUSIONS: We have demonstrated for the first time a significant relationship between forearm skin microcirculatory perfusion and oxygen saturation and finger PAT. Both local heating and reactive hyperemia are useful skin provocations. Further studies are needed to understand the precise regulation mechanisms of blood flow and oxygenation during these tests.

Skin microvascular endothelial dysfunction is associated with type 2 diabetes independently of microalbuminuria and arterial stiffness.

Skin and kidney microvascular functions may be affected independently in diabetes mellitus. We investigated skin microcirculatory function in 79 subjects with diabetes type 2, where 41 had microalbuminuria and 38 not, and in 41 age-matched controls. The oxygen saturation, fraction of red blood cells and speed-resolved microcirculatory perfusion (% red blood cells × mm/s) divided into three speed regions: 0-1, 1-10 and above 10 mm/s, were assessed during baseline and after local heating of the foot with a new device integrating diffuse reflectance spectroscopy and laser Doppler flowmetry. Arterial stiffness was assessed as carotid-femoral pulse wave velocity. Subjects with diabetes and microalbuminuria had significantly higher carotid-femoral pulse wave velocity compared to subjects without microalbuminuria and to controls. The perfusion for speeds 0-1 mm/s and red blood cell tissue fraction were reduced in subjects with diabetes at baseline and after heating, independent of microalbuminuria. These parameters were correlated to HbA1c. In conclusion, the reduced nutritive perfusion and red blood cell tissue fraction in type 2 diabetes were related to long-term glucose control but independent of microvascular changes in the kidneys and large-vessel stiffness. This may be due to different pathogenic pathways in the development of nephropathy, large-vessel stiffness and cutaneous microvascular impairment.

Temporal and spatiotemporal variability in comprehensive forearm skin microcirculation assessment during occlusion protocols.

Forearm skin hyperemia during release after brachial occlusion has been proposed for evaluating peripheral arterial disease and endothelial dysfunction. We used a novel fiberoptic system integrating Laser Doppler Flowmetry and Diffuse Reflectance Spectroscopy for a comprehensive pointwise model based microcirculation characterization. The aim was to evaluate and compare the temporal and the spatiotemporal variabilities in forearm skin microcirculation parameters (speed resolved perfusion; low speed <1mm/s, PerfSR, <1; mid-speed 1-10mm/s, high speed >10mm/s, and total perfusion (PerfSR, tot); the concentration and oxygenation of red blood cells, CRBC and SO2). Ten healthy subjects underwent arterial and venous forearm occlusions (AO, VO), repeated within one week. The repeatability was calculated as the coefficient of variation (CV) and the agreement as the intra-class correlation coefficient (ICC). The temporal CVs for conventional perfusion, Perfconv, PerfSR, tot, CRBC and SO2 were 14%, 12%, 9% and 9%, respectively, while the ICC were >0.75 (excellent). The perfusion measures generally had a higher spatiotemporal than temporal variability, which was not the case for SO2 and CRBC. The corresponding spatiotemporal CVs were 33%, 32%, 18% and 15%, respectively. During VO, CRBC had a CV<35% and ICC>0.40 (fair-good), and after release this was the case for CRBC (AO and VO), SO2 (VO) and PerfSR, <1 (VO). In conclusion, the skin microcirculation parameters showed excellent temporal repeatability, while the spatiotemporal repeatability especially for perfusion was poorer. The parameters with acceptable repeatability and fair-good agreement were: CRBC during and after release of VO, the PerfSR, <1 after release of VO, the SO2 and the CRBC after release of AO. However, the value of these parameters in discriminating endothelial function remains to be studied.

Blood flow responses over sacrum in nursing home residents during one hour bed rest.

OBJECTIVES: To describe individual BF responses in a nursing home resident population for one-hour periods of bed rest. METHODS: BF was measured for one hour over the sacrum in 0° supine position and 30° supine tilt position in 25 individuals aged 65 y or older while lying on a pressure-redistributing mattress. Measurements were made at three tissue depths (1, 2, and 10 mm) using the noninvasive optical techniques, LDF and PPG. RESULTS: Eleven participants had a PIV response at 1 mm depth in both positions and seven participants had a lack of this response at this depth and positions. The BF response at 1 mm depth appeared immediately and remained over, or below, baseline for the entire 60 min of loading in both positions. These BF patterns were also seen in deeper tissue layers. CONCLUSIONS: The cutaneous BF response among the nursing home residents was distinct, appeared early, and remained during the one hour of loading.

Nursing staff induced repositionings and immobile patients' spontaneous movements in nursing care.

The aim of this study was to investigate nursing staff induced repositionings and the patients' spontaneous movements during the day and night among older immobile patients in nursing care. Furthermore, the aim was to identify factors associated with the nursing staff induced repositionings and the patients' spontaneous movement frequency. An observational cross-sectional design was used. Spontaneous movements among patients (n = 52) were registered continuously using the MovinSense monitoring system. The nursing staff documented each time they repositioned the patient. Patients spontaneous movements were compared with nursing staff induced repositionings. There were large variations in the patients' spontaneous repositioning frequency during both days and nights, which shows that, although immobilised, some patients frequently reposition themselves. Analgesics were positively related to the movement frequency and psycholeptics were negatively related. The nursing staff more often repositioned the patients who were assessed as high risk than those assessed as low risk, but the patients' spontaneous movement frequency was not correlated to the risk score. This may be important when planning repositioning schedules. A monitoring system may be useful in decision making with regard to planning repositioning and positions used in the prevention of pressure ulcers among elderly immobile patients.

The effects of different lying positions on interface pressure, skin temperature, and tissue blood flow in nursing home residents.

BACKGROUND: Although repositioning is considered an important intervention to prevent pressure ulcers, tissue response during loading in different lying positions has not been adequately explored. AIM: To compare the effects of different lying positions on interface pressure, skin temperature, and tissue blood flow in nursing home residents. METHOD: From May 2011 to August 2012, interface pressure, skin temperature, and blood flow at three tissue depths were measured for 1 hr over the sacrum in 30° supine tilt and 0° supine positions and over the trochanter major in 30° lateral and 90° lateral positions in 25 residents aged 65 years or older. Measurement of interface pressure was accomplished using a pneumatic pressure transmitter connected to a digital manometer, skin temperature using a temperature sensor, and blood flow using photoplethysmography and laser Doppler flowmetry. RESULTS: Interface pressure was significantly higher in the 0° supine and 90° lateral positions than in 30° supine tilt and 30° lateral positions. The mean skin temperature increased from baseline in all positions. Blood flow was significantly higher in the 30° supine tilt position compared to the other positions. A hyperemic response in the post pressure period was seen at almost all tissue depths and positions. CONCLUSION: The 30° supine tilt position generated less interface pressure and allowed greater tissue perfusion, suggesting that this position is the most beneficial.

Pressure-induced vasodilation and reactive hyperemia at different depths in sacral tissue under clinically relevant conditions.

OBJECTIVE: To characterize PIV and RH at different sacral tissue depths in different populations under clinically relevant pressure exposure. METHODS: Forty-two subjects (<65 years), 38 subjects (≥65 years), and 35 patients (≥65 years) participated. Interface pressure, skin temperature, and blood flow at tissue depths of 1, 2, and 10 mm (using LDF and PPG) were measured in the sacral tissue before, during, and after load in a supine position. RESULTS: Pressure-induced vasodilation and RH were observed at three tissue depths. At 10 mm depth, the proportion of subjects with a lack of PIV was higher compared to superficial depths. The patients had higher interface pressure during load than the healthy individuals, but there were no significant differences in blood flow. Twenty-nine subjects in all three study groups were identified with a lack of PIV and RH. CONCLUSIONS: Pressure-induced vasodilation and RH can be observed at different tissue depths. A lack of these responses was found in healthy individuals as well as in patients indicating an innate susceptibility in some individuals, and are potential important factors to evaluate in order to better understand the etiology of pressure ulcers.

Different lying positions and their effects on tissue blood flow and skin temperature in older adult patients.

AIM: To report a study to compare the effects of different lying positions on tissue blood flow and skin temperature in older adult patients. This article reports the evaluation of study design and procedures. BACKGROUND: To reduce risk of pressure ulcers, repositioning of immobile patients is a standard nursing practice; however, research into how different lying positions effect tissue microcirculation is limited. DESIGN: Descriptive comparative design. METHODS: From March-October 2010, 20 inpatients, aged 65 years or older, were included in the study. Tissue blood flow and skin temperature were measured over bony prominences and in gluteus muscle in four supine and two lateral positions. RESULTS: The blood flow over the bony prominence areas was most influenced in the superficial skin and especially in the 30° lateral position, where the blood flow decreased significantly in comparison with the supine positions. There were significant individual differences in blood flow responses, but no common trend was identified among the patients considered at risk for pressure ulcer development. The study procedure worked well and was feasible to perform in an inpatient population. CONCLUSION: The lying positions seem to influence the tissue blood flow over the bony prominences in different ways in older adult inpatients, but further study is needed to confirm the results and to make recommendations to clinical practice. The study procedure worked well, although some minor adjustments with regard to heat accumulation will be made in future studies.

Existence of tissue blood flow in response to external pressure in the sacral region of elderly individuals--using an optical probe prototype.

OBJECTIVE: The aim was to investigate the existence of sacral tissue blood flow at different depths in response to external pressure and compression in elderly individuals using a newly developed optical probe prototype. METHODS: The tissue blood flow and tissue thickness in the sacral area were measured during load in 17 individuals using laser Doppler flowmetry and photoplethysmography in a combined probe, and digital ultrasound. RESULTS: The mean age was 68.6 +/- 7.0 years. While loading, the mean compression was 60.3 +/- 11.9%. The number of participants with existing blood flow while loading increased with increased measurement depth. None had enclosed blood flow deep in the tissue and at the same time an existing more superficial blood flow. Correlation between tissue thickness and BMI in unloaded and loaded sacral tissue was shown: r = 0.68 (P = 0.003) and r = 0.68 (P = 0.003). CONCLUSIONS: Sacral tissue is highly compressed by external load. There seems to be a difference in responses to load in the different tissue layers, as occluded blood flow in deeper tissue layers do not occur unless the blood flow in the superficial tissue layers is occluded.

Blood flow measurements at different depths using photoplethysmography and laser Doppler techniques.

BACKGROUND/PURPOSE: This study has evaluated a multi-parametric system combining laser Doppler flowmetry and photoplethysmography in a single probe for the simultaneous measurement of blood flow at different depths in the tissue. This system will be used to facilitate the understanding of pressure ulcer formation and in the evaluation of pressure ulcer mattresses. METHODS: The blood flow in the tissue over the sacrum was measured before, during and after loading with 37.5 mmHg, respectively, 50.0 mmHg. The evaluation of the system consisted of one clinical part, and the other part focusing on the technicalities of the probe prototype. RESULTS: An increase in blood flow while loading was the most common response, but when the blood flow decreased during loading it was most affected at the skin surface and the blood flow responses may be different due to depths of measurement. Reactive hyperaemia may occur more frequently in the superficial layers of the tissue. CONCLUSION: The study showed that the new system is satisfactory for measuring tissue blood flow at different depths. The laser Doppler complements the photoplethysmography, and further development of the system into a thin flexible probe with the ability to measure a larger area is required.