Skin Surface Pressure Research Articles

The Effect of Surface Observations on Enhancing the GIIRS Thermodynamic Profile Retrieval

Understanding boundary-layer atmospheric temperature and moisture is essential for advancing our knowledge of the Earth system. This study adopts a one-dimensional variational (1DVAR)-based technique to integrate spaceborne measurement and ground-based observations for improving the retrieval of low-level atmospheric profiles. The performance of the algorithm under different atmospheric and observational scenarios, such as surface-air and skin temperature differences (∆T), surface pressure (Ps), and satellite zenith angle, respectively, has been systematically evaluated using the Geosynchronous Interferometric Infrared Sounder (GIIRS) on board the Fengyun-4A satellite as an example. Through theoretical information analysis, using both simulated and actual data experiments, this study demonstrates that incorporating ground-based temperature and moisture observations significantly enhances retrieval accuracy with 1DVAR, particularly over elevated terrain. The new algorithm is more effective in low-level temperature retrievals when air temperatures are colder relative to surface-skin temperatures, and it also shows greater benefit for water-vapor retrievals when the temperature difference between the air and the skin is minimal. However, as the zenith angle increases to 55°, the accuracy of temperature retrievals deteriorates, although this is mitigated by the combination of surface-air temperature observations. Notably, the positive impact of surface observations extends to approximately 100–200 hPa above the surface, underscoring the importance of accurate ground-based measurements in conjunction with spaceborne data for atmospheric profiling.

Boundary sources of velocity gradient tensor and its invariants

The present work elucidates the boundary behaviors of the velocity gradient tensor (A≡∇u) and its principal invariants (P, Q, R) for compressible flow interacting with a stationary rigid wall. First, it is found that the boundary value of A exhibits an inherent physical structure being compatible with the normal-nilpotent decomposition, where both the strain-rate and rotation-rate tensors contain the physical contributions from the spin component of the vorticity. Second, we derive the kinematic and dynamical forms of the boundary A flux from which the known boundary fluxes can be recovered by applying the symmetric–antisymmetric decomposition. Then, we obtain the explicit expression of the boundary Q flux as a result of the competition among the boundary fluxes of squared dilatation, enstrophy and squared strain-rate. Importantly, we find that both the coupling between the spin and surface pressure gradient, and the spin-curvature quadratic interaction (sw·K·sw), are not responsible for the generation of the boundary Q flux, although they contribute to both the boundary fluxes of enstrophy and squared strain-rate. Moreover, we prove that the boundary R flux must vanish on a stationary rigid wall. Finally, the boundary fluxes of the principal invariants of the strain-rate and rotation-rate tensors are also discussed. It is revealed that the boundary flux of the third invariant of the strain-rate tensor is proportional to the wall-normal derivative of the vortex stretching term (ω·D·ω), which serves as a source term accounting for the spatiotemporal evolution rate of the wall-normal enstrophy flux. As an example, several relevant surface quantities to the surface curvature are calculated based on global skin friction and surface pressure measurements in a flow over a National Advisory Committee for Aeronautics Fundamental Aeronautics Investigates The Hill model. These theoretical results provide a unified description of boundary vorticity and vortex dynamics, which could be valuable in understanding the formation mechanisms of complex near-wall coherent structures and the boundary sources of flow noise.

A clinical comparison of a digital versus conventional design methodology for transtibial prosthetic interfaces

A transtibial prosthetic interface typically comprises a compliant liner and an outer rigid socket. The preponderance of today’s conventional liners are mass produced in standard sizes, and conventional socket design is labor-intensive and artisanal, lacking clear scientific rationale. This work tests the clinical efficacy of a novel, physics-based digital design framework to create custom prosthetic liner-socket interfaces. In this investigation, we hypothesize that the novel digital approach will improve comfort outcomes compared to a conventional method of liner-socket design. The digital design framework generates custom transtibial prosthetic interfaces starting from MRI or CT image scans of the residual limb. The interface design employs FEA to simulate limb deformation under load. Interfaces are fabricated for 9 limbs from 8 amputees (1 bilateral). Testing compares novel and conventional interfaces across four assessments: 5-min walking trial, thermal imaging, 90-s standing pressure trial, and an evaluation questionnaire. Outcome measures include antalgic gait criterion, skin surface pressures, skin temperature changes, and direct questionnaire feedback. Antalgic gait is compared via a repeated measures linear mixed model while the other assessments are compared via a non-parametric Wilcoxon sign-rank test. A statistically significant (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P=0.032$$\\end{document}) decrease in pain is demonstrated when walking on the novel interfaces compared to the conventional. Standing pressure data show a significant decrease in pressure on novel interfaces at the anterior distal tibia (\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P = 0.012$$\\end{document}), with no significant difference at other measured locations. Thermal results show no statistically significant difference related to skin temperature. Questionnaire feedback shows improved comfort on novel interfaces on posterior and medial sides while standing and the medial side while walking. Study results support the hypothesis that the novel digital approach improves comfort outcomes compared to the evaluated conventional method. The digital interface design methodology also has the potential to provide benefits in design time, repeatability, and cost.

The Pressure Is on: Dorsal Versus Volar Univalves for Long-arm Casts.

Fiberglass casts are routinely used to treat fractures of the upper extremity. When posttraumatic edema is anticipated, the cast is often valved to hopefully prevent potential complications, especially compartment syndrome. Due to volar forearm compartments being most involved with upper extremity compartment syndrome, volar skin surface pressures (SSP) are paramount. Despite past literature showing that a univalved cast will retain a 3-point mold better than a bivalved cast, there is a paucity of information analyzing the effects of univalving on the volar SSP. We hypothesized that a volar univalve technique would have a greater decrease in the volar skin surface pressures compared to a dorsal univalve in long-arm casts. A 100-mL saline bag attached to an arterial line pressure transducer was placed between a long-arm cast and the skin along the volar forearm of a single adult volunteer. Fourteen casts were applied by a single certified orthopaedic technologist with 30 years of experience and assigned randomly to receive either a volar or dorsal univalve. We calculated the change in volar forearm SSP on each cast in 4 stages: isolated univalve, with a 3-mm cast spacer, with a 6-mm spacer, and with bivalve. Statistical analysis of the data was performed using a Mann-Whitney U test. When comparing volar versus dorsal univalve, volar SSP significantly dropped by a mean of 32.00 versus 20.43mmHg (P value=0.001) in stage I, 45.14 versus 38.00mmHg in stage II (P value=0.026), and 56.53 versus 49mmHg in stage III (P value=0.001). There was no significant difference between the 2 groups after a bivalve was performed at stage IV (P value=0.318). Our findings support that a volar univalve with a 6-mm spacer will provide the greatest reduction of skin surface pressure while theoretically maintaining the cast's structural integrity and biomechanical properties when compared to a bivalved cast. Level II, prospective comparative study.

Lie derivatives of fundamental surface quantities in incompressible viscous flows

Lie derivative is an important concept in differential geometry. From the perspective of theoretical fluid dynamics, the present paper evaluates and interprets the Lie derivatives of the fundamental surface physical quantities (including skin friction, surface vorticity, and surface pressure) with respect to a characteristic velocity field in near-wall incompressible viscous flows. It is found that the Lie derivatives are directly associated with the boundary enstrophy flux, an orthogonal pair of skin friction and surface vorticity, and an orthogonal pair of surface enstrophy gradient and its conjugate vector, while components of the Lie derivatives in skin-friction-surface-vorticity orthogonal frame are related to four on-wall coupling scalar quantities (associated with the skin friction divergence and the surface vorticity divergence). The derived theoretical results are first evaluated in a laminar oblique Hiemenz flow and a turbulent channel flow. Then, features of the Lie derivatives are explored in a typical skin friction structure generated by a complex separated flow over a hill model. The present exposition provides a unique perspective of the Lie derivatives to the boundary vorticity dynamics and near-wall flow physics.

Exact relations between Laplacian of near-wall scalar fields and surface quantities in incompressible viscous flow

In this short paper, we derive the on-wall values and the wall-normal derivatives of the Laplacians of pressure and kinetic energy density at the wall for incompressible viscous flow past a stationary wall. The theoretical results reveal some interesting on-wall coupling pairs that are composed of the fundamental surface physical quantities (including skin friction, surface vorticity and surface pressure) and surface curvature. The exact results are valid for flow past any stationary curved wall, which are valuable for understanding the near-wall viscous flow very close to the wall.

Lamb dilatation and its hydrodynamic viscous flux in near-wall incompressible flows

In this paper, we introduce a new physical concept referred to as the wall-normal Lamb dilatation flux (WNLDF), which is defined as the wall-normal derivative of the Lamb dilatation (namely, the divergence of the Lamb vector) multiplied by the dynamic viscosity for incompressible viscous flows. It is proved that the boundary Lamb dilatation flux (BLDF, namely the wall-normal Lamb dilatation flux at the wall) is determined by the boundary enstrophy flux (BEF) and the surface curvature-induced contribution. As the first step to explore this new concept, the present study only considers flow past a stationary no-slip flat wall without curvature-fluid dynamic coupling effects. It is found that the temporal–spatial evolution rate of the WNLDF is contributed by four source terms, which can be explicitly expressed by using the fundamental surface quantities including skin friction (or surface vorticity) and surface pressure. Therefore, the instantaneous near-wall flow structures are directly related to the WNLDF in both laminar and turbulent flows. As an example, for the turbulent channel flow at Reτ=180, the intensification of the temporal–spatial evolution rate of the WNLDF is caused by the strong wall-normal velocity event (SWNVE) associated with quasi-streamwise vortices and high intermittency of the viscous sublayer. In addition, near the SWNVE, this evolution rate is mainly contributed by the dot product of skin friction and surface enstrophy gradient, as well as the coupling between the skin friction divergence and the boundary enstrophy. The exact results presented in this paper could provide new physical insights into complex near-wall flows.

Intelligent Prophylaxis of Diabetic Foot Ulcer

A high skin surface pressure at the feet over a longer period of time can cause foot ulcers. It can occur due to insufficient relief of tissue and a lack of alarm signals from the nervous system, especially for patients with Diabetic Polyneuropathia. A healthy person would move and relieve the foot after a while.

Anterior Ankle Skin Surface Pressures in Lower Extremity Splints: Minimizing Insult after Injury

Category:Ankle; Trauma; OtherIntroduction/Purpose:Though ubiquitously utilized in orthopaedic trauma, lower extremity splints are not without their associated iatrogenic risk of morbidity. In fact, improper splinting not only necessitates replacement, but splint-related soft tissue complications are the second most common iatrogenic cause for referral to plastic surgery. Improper splinting techniques include inadequate molding of plaster/fiberglass splints, inadequate padding over bony prominences, excessive compressive forces from elastic bandages applied too aggressively, and/or pressure areas created by applying padding and casting material in varying joint positions. While clinicians commonly pad bony prominences to minimize skin pressure, the effect of joint position on skin pressure and, more specifically, changing joint position, is understudied. The purpose of this study is to evaluate anterior ankle skin pressure secondary to joint position change during splinting.Methods:Following ethics approval by our institutional review board, various constructs of lower extremity, short-leg splints were applied to two healthy subjects (2 limbs total in this preliminary data set) with an underlying pressure transducer (Tekscan I- Scan system (Tekscan Inc, South Boston, MA, USA) on the skin surface centered on the anterior ankle on the tibialis anterior tendon. All subjects underwent anterior ankle surface pressure assessment when padding was applied in maximum plantar flexion and neutral position for conventional short leg splints application. Percent change from initial contact pressure centered on the tibialis anterior with either Webril (Covidien/Medtronic, Dublin, Ireland), or Specialist Cotton Blend Cast Padding (BSN Medical, Charlotte, NC, USA) were calculated. Neutral position of the foot/ankle will be confirmed with goniometer.Results:There were 2 limbs total that were analyzed for the presentation of pilot data for this study. The percent change in anterior ankle contact pressure when padding was applied in maximum plantarflexion (PF) and then placed in neutral was increased at least two-fold without the addition of plaster and subsequently with the addition of plaster in lower extremity short leg splints (Figure 1).Conclusion:In this pilot data, we report significant increases in anterior ankle contact pressures when splint padding is applied in plantar-flexion and re-positioned into neutral during splint application which may precipitate iatrogenic pressure ulcers in patients sustaining foot/ankle trauma. This data, though preliminary, underscores the importance in proper splinting techniques for all clinicians that manage lower extremity trauma (eg, orthopaedic surgery, emergency medicine, urgent care, etc).

Features of surface physical quantities and temporal-spatial evolution of wall-normal enstrophy flux in wall-bounded flows

This paper presents a concise derivation of the temporal-spatial evolution equation of the wall-normal enstrophy flux on a no-slip flat wall. Each contribution to the evolution is explicitly expressed using the two fundamental surface quantities: skin friction (or equivalently surface vorticity) and surface pressure which are coupled through the boundary enstrophy flux (BEF). The newly derived relation is then used to explore, in a preliminary manner, the physical features of surface quantities and their dynamical roles in wall-bounded laminar and turbulent flows. It is confirmed that the BEF usually changes its sign near the separation and attachment lines in the skin friction field. For the simulated incompressible turbulent channel flow at Reτ=180, violent variations of different terms in the derived formulation are observed in the regions below the strong wall-normal velocity events (SWNVEs) when compared to other common regions. Near the SWNVEs, the evolution of the wall-normal enstrophy flux is found to be dominated by the wall-normal diffusion of the vortex stretching term which is relatively weak or negligible for laminar flows. Combined with our previous research results, it is conjectured that the strong interaction between the quasi-streamwise vortex and the channel wall intensifies the temporal-spatial evolution of the wall-normal enstrophy flux on the wall, which accounts for the highly intermittent feature of the viscous sublayer.

Skin Friction Extracted from Surface Pressure in Incident Shock-Wave/Boundary-Layer Interaction

High-resolution skin-friction fields are extracted from pressure-sensitive paint (PSP) data obtained in shock-wave/boundary-layer interaction (SWBLI). The method of extracting skin friction from surface pressure is described, including the fundamental relation between skin friction and surface pressure, the variational method, error analysis, and an approximate iterative method. The proposed method is based on a coupling relation between skin friction and surface pressure, where the boundary enstrophy flux is suitably modeled or approximated. This method is applied to unsteady PSP data obtained in incident SWBLIs at Mach 2.5 for different Reynolds numbers, revealing the skin-friction structures of the flows: particularly, the separation bubble induced by the incident shock wave. The extracted results are in good agreement with the data obtained by the surface-stress-sensitive film.

Effects of Upper Extremity Elevation on Intra-Cast Pressure and Digital Perfusion in a Fiberglass Short-Arm Cast Model.

The goal of this study was to determine the relationship of digital artery pressure to arm position and forearm skin surface pressure using a short-arm cast experimental setup, to ascertain the safest position for the injured casted upper extremity. A total of 27 volunteers were placed in bilateral short-arm fiber-glass casts with an empty 50-mL bladder bag under the cast and attached to a pressure transducer. Digital systolic pressure (Pdig), and skin surface pressure under the cast (Pskin) were assessed in 4 positions. Measurements were taken with and without 50 mL air in the bladder bag. A total of 54 forearms were evaluated. Both arm position and Pskin had a significant effect on Pdig (P<.001 for both), with increasing elevation leading to a decrease in Pdig (r=-0.50). The effect size of position on Pdig was large, whereas that of Pskin was small (partial eta-squared=0.371 and 0.028, respectively). Linear regression analysis of Pskin and Pdig with air in the neutral position yielded a moderate negative relationship with body mass index (r=-0.64, P<.001 for Pskin; r=0.49, P<.001 for Pdig) and wrist circumference (r=-0.66, P<.001 for Pskin; r=0.52, P<.001 for Pdig), without significant association with forearm length. For volunteers with short-arm fiberglass casts, increasing arm elevation had a large effect size on digital arterial pressure, whereas 50 mL simulated swelling had only a small effect size. Decreasing body mass index and forearm circumference correlated with increased skin surface pressure and decreased digital arterial pressure. These findings show that aggressive elevation of the injured limb may not be as desirable as previously believed. [Orthopedics. 2021;44(4):e487-e492.].

Near-wall flow structures and related surface quantities in wall-bounded turbulence

By applying the Taylor-series expansion solution of the Navier–Stokes equations, an analysis is given to elucidate the relationships between near-wall flow structures and the fundamental surface quantities (skin friction and surface pressure). The derived results are used to understand the physical features of near-wall flow structures around a typical strong wall-normal velocity event (SWNVE) in a turbulent channel flow based on the direct numerical simulation data at Reτ=180. The simulation is carefully done using a multiple-relaxation-time lattice Boltzmann method combined with an improved on-wall bounce-back implementation. It is found that both the skin friction divergence and the Laplacian of surface pressure have good correspondence with sweep and ejection motions induced by the quasi-streamwise vortex above the viscous sublayer. Interestingly, the surface pressure variation induced by a quasi-streamwise vortex tends to attenuate the wall-normal velocity magnitude in both the sweep and ejection sides through the Laplacian of surface pressure. Similar physical effects of surface-pressure-related terms are also observed for the near-wall Reynolds stress. The concentrated enstrophy and dissipation are associated with the SWNVE and high skin friction magnitude. It is found that the SWNVE is dynamically important in generating the boundary enstrophy flux, greatly enhancing the intermittency of turbulence inside the viscous sublayer. In addition, by applying the methods of differential geometry, the near-wall Taylor-series expansions are generalized for a stationary curved surface in a general curvilinear coordinate system. The generalized results could be useful in evaluating the curvature effect in the near-wall region for complex flows.

Study on Inflatable Deployment Characteristics of Flexible Film Wing

The inflation deployment process directly affects the forming and bearing deformation characteristics of the flexible wing. In order to optimize the structural design of the flexible inflatable wing, the inflation deployment process was studied with the finite element simulation calculation for the distribution characteristics of pressure and displacement when the wing is not inflated and after inflation molding. The results show that the inflation process is: for the first stage, when the inflation pressure is lower than the critical forming pressure, due to the effect of gravity, the flexible film wing downward bending, and the skin surface pressure is quite small, while the wing is inflated, the overall deformation and displacement is quite large. for the second stage of inflation molding, the flexible wing has a bearing stiffness, but due to aerodynamic loading upward warping occurred, the pressure of the wing root is large, but the displacement of the wing tip is large, which could provide a valid reference method to study the precision and stability of the flexible wing inflation process.

Pain Tolerance: The Influence of Cold or Heat Therapy

ObjectivesResources of heat or cold therapies have been widely used for their low cost, analgesic action and for assisting the rehabilitation of acute or chronic injuries. The objective of this study was to search for associations between skin surface temperature and pressure pain tolerance thresholds (PPTs) of healthy individuals undergoing cryotherapy and thermotherapy. MethodsThis is an experimental clinical trial with 22 healthy university students aged between 18 and 35 years. Volunteers underwent thermography and algometry assessments at 6 points in both knees before, immediately after, and 20 minutes after the application of frozen (cryotherapy) or heated (thermotherapy) gel bags in the right knee for 20 minutes. Data were analyzed by 1-way analysis of variance, Student's t test, and Pearson or Spearman correlation tests. ResultsThere was a significant change in skin surface temperature after cryotherapy and thermotherapy, which was maintained after 20 minutes of withdrawal (P < .001). After the intervention, no significant differences were observed regarding the PPT compared to the baseline measurements, nor between the experimental and control knees. ConclusionCryotherapy and thermotherapy produced significant changes in the temperature of the evaluated points after their application. Despite this, no differences in pain tolerance were observed, and there was little association between skin surface temperature and PPT in the knees of healthy women after application of the resources.

Relations between skin friction and other surface quantities in viscous flows

This paper presents the derivations of the exact relations between skin friction and other important dynamical and kinematical quantities on a stationary curved surface in a viscous flow by applying the standard methods of differential geometry to the governing partial differential equations in fluid mechanics. In particular, the mathematical structures of the effects of the surface curvature are explicitly expressed, which extend the previous results on a flat surface. These relations reveal that skin friction is intrinsically coupled with surface pressure, temperature, and scalar concentration through the boundary enstrophy flux, heat flux, and mass flux, respectively. As an example, the relation between skin friction and surface pressure is examined in the Oseen flow over a sphere to elucidate the significant effect of the surface curvature at a very small Reynolds number. Two other validation examples are a gravity-driven creeping liquid film flow over a wavy surface and the Falkner-Skan flow over a wedge. Furthermore, the relation is applied to a simulated turbulent channel flow to explore the local near-wall coherent structure and understand its dynamical roles in turbulence production.

Structures of Skin Friction, Surface Pressure, and Boundary Enstrophy Flux in Attachment-Line Flow

Abstract The on-wall structures in an attachment-line flow are discussed based on an exact solution of the Navier–Stokes (NS) equations, focusing on distinct features of skin friction, surface pressure, and boundary enstrophy flux (BEF) and intrinsic connections between them.

Associations Between Skin Surface Temperature and Pressure Pain Tolerance Thresholds of Asymptomatic Individuals Exposed to Cryotherapy and Thermotherapy

ObjectiveThe purpose of this study was to evaluate associations between skin surface temperature and pressure pain tolerance thresholds (PPTs) of asymptomatic individuals exposed to cryotherapy and thermotherapy. MethodsTwenty-two asymptomatic female university students aged between 18 and 35 years underwent thermography and algometry assessments at 6 points in both knees before, immediately after, and 20 minutes after the application of frozen (cryotherapy) or heated (thermotherapy) gel bags in the right knee for 20 minutes. Data were analyzed by 1-way analysis of variance, Student t test, and Pearson or Spearman correlation tests. ResultsThere was a significant change in skin surface temperature after cryotherapy and thermotherapy, which was maintained after 20 minutes of withdrawal (P < .001). After the intervention, no significant differences were observed regarding PPT compared with the baseline measurements, nor between the experimental and control knees. ConclusionCryotherapy and thermotherapy produced significant changes in the temperature of the evaluated points after their application. No differences in pain tolerance were observed in these asymptomatic participants. There was little association between skin surface temperature and PPT in the knees of healthy women after application of the resources.

Personalized modeling for real-time pressure ulcer prevention in sitting posture

Ischial pressure ulcer is an important risk for every paraplegic person and a major public health issue. Pressure ulcers appear following excessive compression of buttock's soft tissues by bony structures, and particularly in ischial and sacral bones. Current prevention techniques are mainly based on daily skin inspection to spot red patches or injuries. Nevertheless, most pressure ulcers occur internally and are difficult to detect early. Estimating internal strains within soft tissues could help to evaluate the risk of pressure ulcer. A subject-specific biomechanical model could be used to assess internal strains from measured skin surface pressures. However, a realistic 3D non-linear Finite Element buttock model, with different layers of tissue materials for skin, fat and muscles, requires somewhere between minutes and hours to compute, therefore forbidding its use in a real-time daily prevention context. In this article, we propose to optimize these computations by using a reduced order modeling technique (ROM) based on proper orthogonal decompositions of the pressure and strain fields coupled with a machine learning method. ROM allows strains to be evaluated inside the model interactively (i.e. in less than a second) for any pressure field measured below the buttocks. In our case, with only 19 modes of variation of pressure patterns, an error divergence of one percent is observed compared to the full scale simulation for evaluating the strain field. This reduced model could therefore be the first step towards interactive pressure ulcer prevention in a daily set-up.

Skin stiffness determined from occlusion of a horizontally running microvessel in response to skin surface pressure: a finite element study of sacral pressure ulcers.

Pressure ulcers occur following sustained occlusion of microvessels at bony prominences under skin surface pressure (SSP). However, the mechanical conditions of the surrounding soft tissue leading to microvascular occlusion are not fully understood. This study determined the stiffness of homogenized skin with microvasculature at the sacrum that occludes microvessels at an SSP of 10kPa (consistent with a standard mattress) and recovers from occlusion at 5kPa (consistent with a pressure-redistribution mattress). We conducted two-dimensional finite element analyses under plane stress and plane strain conditions to determine the stiffness of the skin. The results for plane stress conditions show that the microvessel was occluded with a Young's modulus of 23kPa in response to an SSP of 10kPa at the center of the sacrum and that the circulation recovered following a reduction in the SSP to 5kPa. The resulting Young's modulus is consistent with reported data. Our study indicates that the critical value of the SSP for microvascular occlusion is determined not only by the stiffness of homogenized skin with microvasculature but also by the intraluminal pressure, microvascular wall stiffness, and body support conditions.