Circulatory and mechanical response of skin to loading

Abstract

We investigated the tolerance of skin to mechanical loading over the tibia and over the tibialis anterior muscle in 12 normal volunteers. Surface load, subcutaneous tissue pressure, skin deformation under load, and transcutaneous partial pressure of oxygen (TcPO2) were simultaneously monitored. The skin over bone showed a significantly stiffer load deformation relationship than the skin over muscle (p less than 0.001). The displacement required to reduce TcPO2 to 0 over bone, 1.1 +/- 0.3 mm (mean +/- standard deviation), was significantly less than that required over tibialis anterior muscle, 5.4 +/- 1.1 mm (p less than 0.001). The applied pressure required to reduce TcPO2 to 0 was significantly greater for skin over muscle (71 +/- 16 mm Hg) than for skin over bone (42 +/- 8 mm Hg) (p less than 0.001). However, the subcutaneous pressure required to reduce TcPO2 to 0 was not significantly different for skin over muscle (36 +/- 11 mm Hg) than for skin over bone (28 +/- 10 mm Hg) (p greater than 0.05). Our results indicate that skin over muscle tolerates greater locally applied loads and deformations because the pressure is lower within the tissue than when similar loads and deformation are applied to skin over bone. Cutaneous perfusion, as indicated by TcPO2, seems to be linked more closely to the subcutaneous tissue pressure than to the surface load or deformations. These results provide some data for predicting mechanical and physiologic response to locally applied loads such as those that may be encountered in prosthetic wear.

Assessing evidence supporting redistribution of pressure for pressure ulcer prevention: A review

“…Loading at the sac rum did not resu lt in the same relationship with blood pressure. Sangeorzan et al de termined that 71 mmHg was need ed to occl ude flow over the tibialis anterior (a "soft" site) but only 42 mmHg occluded flow over the tibia (a "hard" site ) [9]. Bennett et al measured occlusion pressure at the thenar eminences of nondisabled subjects and found that 100 to 120 mmHg was necessary to occlude v essels in "low shear" conditions and 60 to 80 mmHg was needed in the pre sence of "high shear" conditions [10].…”

Patient repositioning and pressure ulcer risk�Monitoring interface pressures of at-risk patients

“…Healthy capillary pressures typically range from 10 to 30 mm Hg [14]; however, capillary pressures may be lower for individuals in poor health [15][16]. Studies on blood flow in response to loading vary in the amount of pressure required to stop or reduce blood flow and oxygen delivery as well as by anatomical location or tissue type [17][18][19][20][21]. Therefore, no widely accepted value exists that will ultimately lead to pressure ulceration [5,22].…”

Analysis of a below-knee patellar tendon-bearing prosthesis: A finite element study

“…stresses were seen in the distal anterior portion of the socket (Figure 4 and Figure 5). Many nomal stresses were in excess of values reported (2) to occlude arteriolar blood flow in the thenar eminence (13-16, and 8-11 KPa under low and high shear conditions, respecfvely), and those reported (15) to cause transcutaneous oxygen partial pressures to drop to zero (5.6, and 9.5 KPa over the tibia, and tibialis anterior, respectively). Higher norrnal stresses can be tolerated, if peak durations are not too long, and have ample time between them.…”

“…These higher strains resulted in higher elastic moduli, which resulted in higher spring constant values, leading to higher calculated normal stress values. While measured at normal stresses too low for application to this analysis, Sangeorzan et al (15), reported stiffness of soft tissue over the tibia to be 2.5 to 7 times greater than the stifhess of soft tissue over the tibialis anterior. The tissue stiffness on the subcubneous border of the tibia resulting from our selection of tissue thickness is 6 times greater than over the tibialis anterior ( Table 2).…”