# Interface pressure and microcirculation at bony prominences Body and sleep A pressure map is not a blood flow measurement Pressure measuring mats show forces at the contact surface. They neither measure the blood flow of individual capillaries nor the load on all deep tissue layers. Particularly at the heel, sacrum and greater trochanter, pressure, shear, anatomy and individual vascular reaction can interact in different ways. The central conclusion is therefore: lower surface pressure is a helpful mechanical finding, but not sufficient evidence of better tissue perfusion. This research explains suitable measurement methods and shows why a universal capillary closure value is unsuitable for mattress consultation. ## From external load to internal tissue loading The contact force is distributed over a limited area. Where bony structures have little soft tissue over them, different deformations occur than in well-padded regions. Additionally, tangential forces can shift tissues against each other. A pressure map does not fully reflect this internal deformation. Two surfaces with similar peak values can therefore create different biomechanical conditions. Loading duration is also decisive. A short peak during turning over is to be assessed differently than a load maintained over a long period. Furthermore, the person reacts through movement, local vascular response and altered posture. The investigation must therefore record chronological developments and anatomical locations. The simplification to a single red spot on a colour map is not suitable as proof of compromised blood flow. ## Laser Doppler, photoplethysmography and oxygen measurement Laser Doppler techniques record movement-dependent light signals as a measure of microvascular perfusion in the volume under investigation. Photoplethysmography describes optical changes related to blood volume or pulsation. Transcutaneous oxygen measurement investigates a further level of local supply. None of these methods corresponds to a direct count of blood flow in every single capillary. An investigation of sacral tissue combined laser Doppler measurement and photoplethysmography at different depths with pressure and temperature measurement. Pressure-induced vasodilation and reactive hyperaemia after unloading were also decisive. The surface with the lowest pressure values did not automatically show the most favourable vascular response. [1] This finding contradicts a simple conversion of pressure maps into blood flow quality. ## Heel and sacrum react differently A study with 25 healthy volunteers compared several hospital mattresses with a hard surface. Blood flow and haemoglobin parameters were recorded at the heel and sacrum. The results differed according to body region; at the heel, maintaining blood flow proved to be particularly challenging. [2] No direct recommendation of a specific domestic mattress type follows from this, but there is a need for regional testing. The sacrum rests differently in a supine position than the greater trochanter in a lateral position. A surface that creates a large contact area for one position can have unfavourable local loads in another position. In consultations, the sleep positions actually used should therefore be considered. In the case of people requiring care, mobility, skin condition and clinical risks are added; the material label does not replace this assessment. ## Why a single threshold value is misleading A historical capillary pressure value is frequently used as a general safety limit for contact pressure. This equivalence overlooks differences between vessels, body regions, measurement setups, and individuals. In a trial with 16 healthy volunteers, oxygen tension and laser-Doppler signals changed at different external pressure levels. [3] Thus, a specific threshold for one measurement variable was not automatically the threshold for all other variables. Automatic traffic light systems that derive a medical diagnosis immediately from a colour change are particularly problematic. The colour scale can often be changed, and an individual sensor can create a different contact state than tissue without a measurement mat. For a professional presentation, scale, calibration, resolution, measurement duration, and uncertainty must remain visible. The statement should then be "higher contact pressure was measured here," not "blood supply is being cut off here." ## Practical limitations of pressure measurement systems Sensor resolution, wrinkles in the cover, drift, and the stiffness of the measurement mat influence the results. Particularly small contact areas can lie between sensors or be spatially averaged. More contact area can reduce the average pressure, even though a locally relevant peak area remains. Therefore, the mean value, high percentiles, contact area, and temporal progression must be considered together. For product development, a pressure map is a useful tool when combined with posture, subjective comfort, and, if applicable, physiological measurements. For clinical pressure ulcer prevention, risk assessment, skin inspection, and individual pressure-relieving measures are also required. A high-quality mattress can be part of a care concept but does not automatically take over all tasks of this concept. ## Heel toppers and local perfusion measurement The heel has a small weight-bearing surface over a prominent bony protrusion. A softer surface can increase the contact area, while internal tissue deformation and shear remain relevant. A lower surface pressure is therefore not a complete statement regarding capillary flow. For the specific question of toppers, material thickness, underlying support, and actual load must be documented. The heel must not be viewed in isolation if positioning also places load on the Achilles tendon or calf. Laser Doppler methods capture local microvascular signals within a limited measurement volume; transcutaneous oxygen measurement and other perfusion methods answer supplementary questions. The measurement probe itself can alter contact and pressure. Baseline blood flow, temperature, vascular disease, and measurement duration are important influencing variables. A dedicated trial combines a pressure map and perfusion measurement with a standardized unloading section. A blanket capillary occlusion limit is not used as a safety value valid for all persons. In cases of compromised skin, clinical pressure injury prevention is the deciding factor, not a brief sales demonstration. ## Why average values can mask local risks A low mean pressure can arise because the contact area increases. A small, heavily loaded area can nevertheless persist. Conversely, a single high sensor value can be caused by a wrinkle or measurement artifact. Interpretation therefore requires spatial context and repeated measurement. Mean blood flow values can also mask different individual reactions. Some individuals show compensatory hyperaemia, others do not. If these patterns are averaged, a seemingly unremarkable group result can emerge. For practical application, it is therefore sensible to consider reaction profiles and anatomical regions separately. The scientific question is not only which support achieves the most favourable average, but also in whom it acts unfavourably and how reliably such differences can be detected. ## Hypothetical case of an impressive pressure map A demonstration shows many red areas on mattress A and almost exclusively blue on mattress B. Without an identical colour scale, the same position, and the same measurement duration, no robust comparison is possible. Even with correct representation, the map initially only shows the measured contact load. Proper consultation explains the scale and repeats the measurement in a comparable position. Afterwards, comfort, posture, and movement are considered. If mattress B provides lower pressure values but makes turning significantly more difficult, the decision is not final. In cases of medical risk, further professional criteria are added. The map is a tool for discussion and not an automatic proof of better capillary blood flow. ## Units and apparent safety limits Pressure can be expressed in pascals, kilopascals, or millimetres of mercury. Different units do not change the underlying quantity, but can make a comparison confusing. Measurement reports should therefore state the unit clearly and remain traceable during conversions. A number line with "safe" below and "dangerous" above a single value is too coarse for individual tissue loading. Duration, shear, temperature, and vascular response are missing from this. A responsible report describes the measured conditions and limits the conclusion to these. The decision regarding clinical pressure relief follows a more comprehensive risk assessment. Pressure measuring mat | Contact force per area | No direct evidence of blood flow Laser Doppler | Local perfusion change | Probe position and measurement volume relevant Photoplethysmography | Optical blood volume change | Movement and depth influence signal Transcutaneous oxygen | Local oxygen supply | Not identical to interface pressure Pressure distribution | Calibrated mat and fixed scale | Document anatomical region Perfusion reaction | Before, during and after loading | Individual reaction instead of just group averages Temperature | Measure simultaneously near the skin | Influences vascular reaction Shear and position | Additional biomechanical recording | Missing in pure pressure images A separate laboratory comparison should examine the heel, sacrum and lateral hip area separately. The procedure includes a resting baseline, a defined loading phase and unloading, each with synchronised pressure and perfusion signals. Mattress order and measurement side are controlled; probes must not generate additional local pressure. The sample should include different age groups and clearly described health conditions. For vulnerable persons, medical supervision is necessary. A primary endpoint could be a predefined perfusion reaction; pressure peaks remain supplementary mechanical endpoints. A pressure map alone does not fulfil this study objective. STOLL should explain pressure measurements as a comparative aid and not derive a blood flow diagnosis from them. In customer consultations, comfort, body position and mobility must be linked to the map. In cases of limited mobility or existing skin damage, the selection must be coordinated with the treating professional or nursing staff. An inspection report is particularly valuable if it names specific body regions, loading duration and measurement methods. Statements about 'capillary-friendly lying' require physiological evidence in the relevant system. ## Lower pressure A larger contact area can reduce local loading. The vascular response must be checked separately. ## Red pressure mark Red means a value on the selected scale. Without a scale and reference, no medical interpretation is possible. ## Heel loading Small contact area and anatomy deserve special attention. A favourable sacrum measurement cannot be transferred to the heel. [1] Bergstrand und Kollegen Microcirculatory responses of sacral tissue 2015 https://pubmed.ncbi.nlm.nih.gov/26562377/ Primary study with pressure and perfusion at multiple depths. [2] A quantitative analysis of microcirculation in sore prone pressure areas 2014 https://pubmed.ncbi.nlm.nih.gov/24950658/ Comparative study on 25 healthy volunteers. [3] Influence of external pressure on transcutaneous oxygen tension and laser Doppler flowmetry 1996 https://pubmed.ncbi.nlm.nih.gov/8867777/ Experiment with 16 volunteers; reaction specific to the measured variable. This paper is a targeted narrative research as of 30 September 2026. The starting point is the specific topic question, scientific publications, and, for technical or legal questions, the relevant original sources. The Word documents provided by the client serve as templates for the professional structure and comparative presentation. Their individual statements have not been adopted without verification. This research is not a systematic comprehensive survey, a meta-analysis, or a product certification. The sources were checked via accessible publication sites, bibliographic datasets, and available excerpts. A complete article was not accessible for every source. Where only an abstract or excerpt was available, the description is limited to the information discernible therein. Figures are only mentioned within their study context; missing details are not supplemented. A phrase such as "no reliable evidence identified" describes the result of this targeted research and does not prove that no such work exists worldwide. The source numbers in the text refer to the list at the end. Directly examined findings, mechanistic considerations, and the author's own practical deductions are linguistically separated. Hypothetical cases illustrate the decision-making logic; they are not documented customer experiences. The suggested test plans are original designs. They do not establish a binding standard or a medical treatment process. Statements about a product class are not automatically transferred to individual models. For classification, the primary criterion is whether the source examines the exact question asked. A technically precise material measurement can be highly informative for a material property while saying little about sleep or long-term health. A clinical study may show a relevant benefit, but only for the group of people, construction, and duration of use studied. Proximity to the concrete question is therefore just as important as the study design. Subsequently, comparison conditions, sample size, observation duration, and potential biases are considered. Blinding is often difficult with bedding. Expectations, habituation, and the sequence of tested variants can influence results. In the case of manufacturer funding, transparency and independent replication are particularly helpful; funding alone does not decide for or against the validity of a finding. Small pilot studies are primarily used to formulate a question more precisely and to plan a larger trial. Statistical significance is not the same as practical importance. A small difference can be mathematically detectable without having a tangible benefit for the person in question. Conversely, a relevant individual improvement may remain statistically uncertain in a small group. Therefore, effect size, uncertainty, and everyday relevant endpoints are assessed together. A blanket score would obscure these differences. The interactive companion page consequently does not use fabricated health scores or simulated figures that appear like measured material data. For implementation, a concrete goal is first defined, and then the smallest reasonably testable change is selected. The initial state, construction used, and observation period are documented. Feedback should capture both the desired benefit and possible new disadvantages. If several components are changed simultaneously, the attribution of success remains uncertain. An individual comparison can improve personal selection but does not replace a general efficacy study. A supplier proof should concern the model actually offered and the intended use. Deviations in the cover, topper, base, care, or software can alter the transferability. The consultation openly states such limitations and formulates only the performance covered by data or immediate observation. For medical or legal questions, the relevant professional assessment remains necessary. The practical recommendation of this document is a basis for decision-making and not an individual diagnosis.