Document Type : Full Research Paper


1 Physical Therapy Department, Tarbiat Modarres University

2 Department of Radiology, Iran University of Medical Sciences

3 Department of Biomedical Engineering, AmirKabir University of Technology

4 Department of Anatomy, Baghiyatollah University of Medical Sciences



Pressure ulcers are areas of tissue necrosis that tend to develop when tissue is compressed between a bony prominence and an external surface. Normal structure and physiological function of tissue viability are recognized but mechanism of tissue breakdown is unknown. In this study, an attempt has been made to recognize the tissue mechanical changes after pressure application using 61 male albino guinea pigs, 4-6 months old, weighing 300-450 g. A computer controlled indentor system was developed to induce pressure sore. This system is capable of monitoring and adjusting the applied pressure, friction and shearing force throughout the experiment. The applied force remained within ±10g of desired target force. The applied pressures were at 291 and 387 mmHg for 1,3 or 5 hours over the trochanter region of animal hind limb. The tissue was removed and blood was taken immediately, 2 and 7 days after pressure release. Uniaxial tensile test was performed using deformation rate of 20 mm/min. In this test, the contralateral site on the experimental animal served as intra-animal control. Full- thickness biopsy was taken and stained with H & E, trichrome and orcein for histological examination. Results of tensile tests showed that the maximum tensile strength (Fmax), stress and the area under load-deformation curve (work) have decreased significantly 7 days after pressure application (P<0.05). Histological study immediately and 2 days after force release, showed an increase in cellularity and inflammatory cells infiltration. Muscle necrosis and reduction of the skin fibers density were observed 7 days after load release. Serum CPK (2 days after) was increased. The amount of lactic acid as well as phosphorus immediately and 2 days after pressure also increased (P<0.05). Finally it was distinguished that pressure changed the biomechanical properties of skin and muscle. Decrease of tissue resistance was consistent with the histological findings as well as elevation of muscle specific enzymes in blood. It was also observed that pressure resulted in the tissue ischemia and breakdown.


Main Subjects

[1]     Kanj LF, Wilkings SV, Philips TJ; Pressure ulcers; J Am Acad Dermatol 1998; 38(4):517-36.
[2]     Alvarez OM, Jarczynski E; Pressure ulcers physical supportive and local aspect of management; Clin in Pediatr Med Surg 1991; 8(4):869- 89.
[3]     Feldman D; New intervention in pressure ulcers treatment: Regenerative skin healing; An annual publication of the Med Rehabil Res Training center in secondary complication in spinal cord injury; UAB; Spain Rehabilitation Center 1994; 1-4.
[4]     Seiler WO, Staehelin HB; Skin oxygen tension as a function of imposed skin pressure implication for decubitus ulcers formation; J Am Geriatr Soc 1979; 27(7):298-301.
[5]     Reddy NP; Interstitial fluid flow as a factor in decubitus ulcer formation; Biomechanics 1981; 14(12):879-81.
[6]     Sacks AH; Theoretical prediction of a time - at - pressure curve for avoiding pressure sores; J Rehabil Res Dev 1989; 26(3):27-34.
[7]     Zhang JD, Mak AF, Huang LD; A large deformation biomechanical model for pressure ulcers; J Biomech Eng 1997; 119:406-8.
[8]     ترکمان گیتی، فلاح علی، شرفی علی اکبر، کاتوزیان حمیدرضا و همکاران؛ طراحی و ساخت دستگاه تولیدکننده نیروهای مکانیکی به منظور ایجاد زخم فشاری کنترل شده در حیوانات آزمایشگاهی؛ دانشور 1378، 24: 59-64.
[9]     غیاثی صدیقه، ترکمان گیتی، حاجی زاده سهراب، شرفی علی اکبر، فقیه زاده سقراط؛ مقایسه اثر امواج پالسی فراصوتی با فرکانس 1 MHz و فنوفورزیس اسید اسکوربیک در درمان زخم فشاری ایجاد شده در خوکچه هندی؛ نهمین کنفرانس مهندسی پزشکی ایران، 1378، 471-475.
[10] Kambic HE, Reyes E, Manning T, Waters KC, Reyes SI; Influence of AC and DC electrical stimulation on wound healing in pigs: A biomechanical analysis; J Invest Surg 1993; 6:535-43.
[11] Daly CH, Odland GF; Age-related changes in the mechanical properties of human skin; J Invest Dermatol 1979; 73:84-7.
[12] Escofier C, Pharm M, Rigal J; Related mechanical properties of human skin: An in vivo study; J Invest Dermatol 1989; 93(3):353-7.
[13] Kroushop TA; A synthesis of the factors that contribute to pressure sore formation; Med Hypotheses 1983; 11:255-67.
[14] Goldstein B, Sanders J; Skin response to repetitive mechanical stress: A new experimental model in pig; Arch phys Med Rehabil 1998; 79:265-72.
[15] Edsberg LE, Mates RE, Baier RE, Lauren M; Mechanical characteristices of human skin subjected to static versus cyclic normal pressures; J Rehabil Res Dev 1999; 36(2): 133-141.
[16] Sanders JE, Goldstein BS, Leotta DF; Skin response to mechanical stress: Adoptation rather than breakdown - A review of the literature; Rehabil Res Dev 1995; 32(3):214-26.
[17] Hyodo A, Reger SI, Negami S, Kambic HE; Evaluation of a pressure sore model using monoplegic pigs; Plast Recontr Surg 1995; 96(2):421-28.
[18] Hagistawa S, Martin RN, Ferguson-Pell M, Palmieri VR, Cochran VB; Pressure sores: A biochemical test for early detection of tissue damage; Arch phys Med Rehabil 1988; 69:668-71.
[19] Polliack A, Taylor R, Bader D; Sweat analysis following pressure ischemia in a group of debilitated subjects; J Rehabil Res Dev 1997; 34(3):303-8.
[20] Vaziri ND, Eltoria E, Gonzales E, Winer RL, Pham H, Bui TD, Said S; Pressure ulcer fibronection and related protein in spinal cord injury patients; Arch Phys Med Rehabil 1992; 73:803-6.
[21] Cullum N, Clark M; Intrinsic factors associated with pressure sores in elderly people; J Adv Nurs 1992; 17:427-31.