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BASIC RESEARCH
Year : 2011  |  Volume : 56  |  Issue : 1  |  Page : 19-24
Effect of age on the biomechanical and microcirculatory properties of the skin in healthy individuals and during venous ulceration


College of Applied Medical Sciences, Department of Radiologic Sciences, King Saud University, Riyadh, Saudi Arabia

Date of Web Publication10-Mar-2011

Correspondence Address:
Essam H Mattar
Department of Radiologic Sciences, College of Applied Medical Sciences, King Saud University, P.O. Box 10219, Riyadh 11433
Saudi Arabia
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DOI: 10.4103/0019-5154.77545

PMID: 21572785

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   Abstract 

Background: With aging there is alteration of elastic properties of the skin and skin-blood flow. Aim: The purpose of this study was to compare age-related changes in selected biomechanical parameters of the skin (skin hardness, skin extensibility, relaxation time constant, τ) and subcutaneous microcirculatory quality (SMQ) in individuals with and without venous diseases. Materials and Methods: Two groups were studied: the first group was of asymptomatic healthy individuals and the second group included patients with chronic venous insufficiency (CVI) and venous ulceration, without edema. Both groups were subdivided to three age categories (21-40, 41-60 and 61-90 years old). Skin hardness was measured by durometer, extensibility and τ were measured using extensometer and SQM was assessed via postural vasoconstrictive response (LDF). Results: Results showed that skin hardness, extensibility, and τ-values were increased, whereas LDF was decreased in the older groups as compared with younger groups. These changes are attributed to alterations in the skin structure and reduced capillaries density networks. Similar behavior was found in the biomechanical and microcirculatory changes in patients with venous ulceration and CVI, but these changes were more increased further in older patients with venous ulceration as compared with older patients with CVI and that can be attribute to more intense response against tissue injury. Conclusions: Since aging elevated skin hardness and extensibility, but lowered vasoconstrictive response in individuals, with and without, venous diseases, we conclude that aging process is likely to cause an accumulation of damaged skin tissues and that could induce an apparent antigen-driven response that altered skin structure and the subsequent biomechanical properties obtained in this study.


Keywords: Aging, chronic venous insufficiency, cutaneous blood flow, durometer, extensometer, oedema, skin hardness


How to cite this article:
Mattar EH. Effect of age on the biomechanical and microcirculatory properties of the skin in healthy individuals and during venous ulceration. Indian J Dermatol 2011;56:19-24

How to cite this URL:
Mattar EH. Effect of age on the biomechanical and microcirculatory properties of the skin in healthy individuals and during venous ulceration. Indian J Dermatol [serial online] 2011 [cited 2014 Jul 23];56:19-24. Available from: http://www.e-ijd.org/text.asp?2011/56/1/19/77545



   Introduction Top


Biological aging is cumulative changes in the body organ system, tissue, or cell, which leads to a decrease in functional capacity. The integumentary system, i.e., skin, is consisted of epidermal, dermal, and subcutaneous layers, accounting for 16% of body weight and covering about 2 m 2 surface area. Knowledge of the mechanical properties of the human skin is very important for geriatric and clinical research. Clearly, the atrophy of the human skin that occurs with aging affect its biomechanical properties; however, comparing these age-related changes with patients diagnosed with venous ulceration is poorly understood.

Age-related changes in the human skin are diverse because they are accompanied by a decrease in elasticity and more profound changes that involve a loss of organization within the elastic collagen network, increase of melanin content and advanced glycation end products (AGEs) of the epidermis and dermal layers. With aging the stratum corneum becomes thinner because the rate of keratinocytes death exceeds the rate of their replacement and that alter elastic properties of the skin. Although epidermis cells are not on proximity with blood vessels, they depend on diffusion to obtain their nutrient and oxygen supply. Furthermore, it had been established that with aging, skin-blood flow is reduced because of a decrease in the total number of the blood vessels. [5],[16] Several age-related changes occur in vein including thickenings in the lumen and increase in fibers in the middle layer and venous valves, [4] resulting in venous insufficiency. Furthermore, chronic venous insufficiency induces thickness of the basement membrane [9] surrounding blood vessels, which leads to edema, eczema, lipodermatosclerosis, and ulceration. It was also reported that 80%-95% of leg ulcers are vascular in origin [7],[8],[9] These vascular pathological changes, in parts, contribute to the formations of fibrin and scar tissue, insufficient tissue repair, cellular death, and insufficient cellular replacement compensatory mechanisms. Clearly, venous insufficiency is one of the major risk factors for the development of varicose veins and ulceration resulting in variety of pathological changes in the epidermal, dermal and subcutaneous layers of the skin. It appears that the efficacy of venous system determines the quality of the biomechanical properties of the skin with aging.

In view of the brief review presented above, it is clear that the study of changes of the biomechanical properties of the skin is becoming more important with the increasing life span in modern societies. It becomes also reasonable to hypothesize that age-related ulceration in the peripheral circulation relate to the pathological alterations in skin structure that in turn affect its biomechanical properties. The purpose of this study was to quantify and compare age-related changes in the skin biomechanical parameters (skin hardness, extensibility, relaxation-time constant), and subcutaneous microcirculatory quality in individuals with and without venous diseases.


   Materials and Methods Top


Experimental design

Two groups were studied; the first group comprised of 54 asymptomatic healthy individuals. The exclusion criteria were skin disorder, pregnancy, diabetes, chronic venous insufficiency (CVI), heart diseases, cancer and other terminal illness. For the purpose of analysis and comparisons, this group was assigned to three age groups (21-40 years, 41-60 years and 61-90 years old). A matched venous ulceration group of 43 patients (30 with CVI and 14 with venous ulcer) were also divided into three age groups (21-40 years, 41-60 years, and 61-90 years old). This design produced six groups for data analysis.

Skin-hardness measurement

Durometer (Model 1600, Type 00, Rex Gauge, IL, USA) was used for the measurement of skin hardness. Skin hardness was conducted on the forearm and the gaiter regions of the ankle. Subjects were laying in supine position with the shoulder in 45Ί. The extremity under examination was supported in position using a pillow made of polystyrene beads. The laboratory temperature was maintained at 21-24ΊC, and normally ventilated and free of noise. Three sites in the gaiter region were chosen for hardness measurements, 5 and 10 cm superior to the medial malleolus and midway between the medial malleolus of the ankle and the medial condyles of the tibia. The forearm measurements were made at three sites, 5 and 10 cm inferior to the antecubital fossa, and midway between the antecubital fossa of the wrist joint. These sites were chosen because they were not over bony prominence and were easily standardized. Every effort was done to place the durometer on the skin without exerting any pressure in order to avoid any external force. Force and recovery times were measured to estimate skin stiffness, according to the following linear regression model: Force (N) = 0.23 + 0.00908H00, where H00 is the hardness reading obtained using Durometer type 00.

Reliability of the durometer measurement


Five durometer readings for each site were obtained from seven healthy subjects, on five separate days at the same time of days. Analysis of variance (ANOVA), with repeated measurements design, was conducted in order to reveal the statistical significance of within site variability, for the same site on all the seven subjects, which was not significant (P > 0.05). That means consistent readings were obtained for the same site, on five separate days (Haffor and Nail, 1988). An intraclass correlation coefficient was calculated (Fleiss, 1986; Haffor and Nail, 1988;) to estimate reliability for 1 day (ICC-R1) measurements and for 5 days measurements (ICC-R5), based on ratio of the true variance (σ2 true) to the total variance (σ2 true + σ2 error), then converted to percentage by multiplying by 100, as follows:

R = (σ2 true)/(σ2 true + σ2 error)Χ100.

Calculation of skin hardness indices

Skin hardness measured values (in Newton) were converted to three indices; Index 1, Index 2, and Index 3. Each index was obtained by dividing measured value for the three leg sites by the corresponding sites in the arm. As there were three sites on the arms and on the legs, this yields three indices; namely Index 1, Index 2, and Index 3.

Measurement of Cutaneous tissue extensibility and relaxation time constant (τ)

A Cutech extensor was used to apply a uniform extension to the skin in vivo. One of the exonsometer arms was fixed and the other movable, where driven by means of a motor-lead screw at a controlled rate of 37% in 8 s. This instrument was specific, reliable, and valid in the assessment of cutaneous tissue extensibility and relaxation-time constant.

Statistical analysis

The changes in cutaneous hardness with location were examined using Freedman test. Mann−Whitney test was used to examine the difference in hardness indices between male and females. Kruskal−Wallis and Mann−Whitney tests were used to examine the influence of age on the same parameters.


   Results Top


Analysis of variance with repeated measurements [Table 1] showed that intradays variations (s2day ) was not significant (P > 0.05), which means that the durometer measurements were highly reliable and reproducible at all selected six sites on seven individuals over 5 days in different occasions.
Table 1: ANOVA Summary for mean squares and intraclass correlation for 1 days (ICC-R1) mean of 5 days (ICC-R5)

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The intraclass correlation for 1 day selected at random (ICC-R1), produced reliability values ranged from 51.85% to 91.57 % for the selected six sites repeated on 5 days. When analysis was replicated based on the mean value for 5 days (ICC-R5), reliability values ranged from 84.33%-98.17% for the selected six sites repeated on 5 days [Table 1].

Friedman test results [Table 2] showed that the differences in the skin hardness median values at the corresponding sites were significantly (P < 0.01) lower on upper extremities, as compared with the lower extremities. Results also showed that higher median skin hardness of the leg, as compared with the median hardness of the forearm. However, there was tendency for the skin hardness to increase towards the distal region of the elbow joint, in the forearm, whereas there was tendency to decline toward the proximal region of the ankle joint, in the leg.

Comparison among males and females healthy subjects showed a significant (P < 0.05) higher median values in skin hardness for indices 2 and 3 in female healthy, as compared to their male counterpart healthy subjects [Table 3]. It was noted that median index 1 of skin hardness for females was greater than male counterparts, but the difference was not significant (P > 0.05). It appears that differences in body composition and relative thickness of female skin tissues are possible factors that influence hardness values.
Table 2: Friedman test: summary results for regional variation in skin hardness (Newton) in the same extremity and between extremities in healthy subjects


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Table 3: Summary results of Mann−Whitney for the difference between two median in skin hardness indices among extremities (arm versus leg) in healthy male and female subjects


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Examination of the effect of age on skin hardness showed a significant (P < 0.001) progressive increase skin hardness indices 1 and 2, with increasing age [Table 4]. Although the age differences for index 1 was not significant (P > 0.01), but there was an observed similar behavior for index 1 to indices 2 and 3, that is greater median value was also obtained with aging for index 1. Altogether as age increases, skin hardness increases. The combined effects of age and sex showed that female had significantly (P < 0.05) greater median values, for indices 1 and 2, than their male counterpart at all age categories [Table 5].
Table 4: Mann−Whitney skin hardness indices among ages in healthy subjects


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Table 5: Kruskal-Wallis test for the combined effects of age and sex on skin hardness indices in healthy males and females


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When comparing patients in venous ulcer group with control, results showed that skin hardness, for indices 1 and 2 were significantly (P < 0.03; P < 0.089, respectively) increased [Table 6]. In addition, patients with CVI had higher skin hardness for index 1, as compared with control group. It was also noted that skin hardness for index 1 was elevated in patients with venous ulcer, as compared with patient with CVI.
Table 6: Mann - Whitney test results for control, CVI, and venous ulcer groups


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Cross elderly examination for control, CVI, and venous ulcer groups showed that the median skin hardness for index 1 was significantly (P < 0.01) greater in both patients groups, as compared with control [Table 7]. That is, patients, with venous ulceration had elevated skin hardness in terms of index 1.
Table 7: Mann-Whitney test results in elderly control, CVI, and venous ulcer groups


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   Discussion Top


The results of this study showed that the durometer measurements are reliable and consistent for the measurements of skin hardness in healthy individuals, as tested by intraclass correlation coefficient. Furthermore, the study of Cheatle TR et al.[13] showed that, in fact, durometer measurements are reliable measurements for venous ulceration and are not affected by edema where skin ulceration is more affected by lipodermatosclerosis (LDS). Still further Doppler flow studies [39],[20] showed high correlation between durometer readings and the degree of hardness of LDS patients. In these studies, investigators were able to show a consistent increase in skin hardness in area proximal to the ulcer edge.

The first major finding of this study, female subjects, showed higher skin hardness, as compared with their age counterpart male age group. Most studies have shown that CVI is more prevalent in women than in men, although in recent studies the sex difference was not marked; the female to male ratio was recently estimated at 6:4 [26] and the prevalence of varicose veins was actually higher in men than women. [19],[29]

The second major finding of this study was skin hardness was higher on lower extremities, as compared with the upper extremities. Herein the findings of this study also showed an increase in the skin hardness distal to the elbow joint in the forearm, as compared with a reduction proximal to the ankle joint, in the leg. One possible explanation for these regional differences was attributed to the differences in tissue structural differences. A second possible explanation was attributed to the differences in local homodynamic variables among upper and lower extremities. Homans in 1930 demonstrated the direct relationship between venous hypertension in the legs and increased capillary intraluminal pressures [38] It follows that arteriovenous fistulas in the skin of the lower extremities cause hypoxia, resulting in changes to the skin and tissues structures, but tissue hypoxia hypothesis was challenged by compensation in capillary growth and shunting mechanisms. Furthermore, studies of skin oxygenation suggest that hypoxia is not a major cause of skin changes [12],[14],[41] Thus, hypoxia results seem to be odd, however, the study of Burnand et al. [9] seems to favor the fibrin cuff hypothesis, which describes the primary problem as venous hypertension in the lower extremities causing leakage of plasma proteins, particularly fibrinogen. A fibrin cuff encircles affected capillaries, decreasing oxygen diffusion to surrounding tissues leading to migration and elevated numbers of macrophages, T-lymphocytes and mast cells in skin.

The third major finding of this study was elderly patients, with and without venous ulcer, had elevated skin hardness in terms of Index 1. Most studies have shown that the prevalence of CVI and venous valve closure problems, increases with age. [10],[16],[32],[35] Herein was also found that young patient diagnosed with CVI showed elevated skin hardness, as compared with healthy individuals. A possible explanation for these findings can be justified based on age-induced skin circulatory impairment. Dermal vessels deliver useful materials to the skin cells and carry away biologically useful manufactured substances, such as vitamin D, which can be used by other cells throughout body to regulate many homodynamic processes. Besides their functions to supply oxygen and nutrients and remove wastes and radicals molecules as other blood vessels, dermal vessels deliver antioxidants molecules, white blood cells (WBC) and antibodies in response to antigenic activation signal. Many studies have used WBC trapping theory in order to explain the CVI in the elderly patients, which hypothesizes that venous hypertension and resultant increased capillary pressures trap WBC in the capillaries, where they become activated and damage capillary beds and that allow an elevated capillary permeability which in turn allows seepage of plasma proteins and fibrinogen into the interstitium [27],[28],[34],[36],[37] where a fibrin cuff forms, thus decreasing oxygen diffusion to surrounding tissues, hence hypoxia occurs. [38] Although, estimates of oxygen transport suggest that fibrin cuffs are unlikely to impair diffusion of oxygen significantly [33] with aging the skin immune function is crippled, death of Langerhans cells and the formulation of endothelial adhesion molecules all increases in response to age related hypoxemia and reduced peripheral blood supply. [1],[24],[17]

Although the intravascular plasma proteins and fibrinogen was not measured in this study, it is possible that results herein support fibrin cuff hypothesis because it showed reduced vasoconstrictive response of cutaneous microcirculation in healthy elderly and in patients with CVI and venous ulceration in whom antigenic and infectious agents are likely to spread out in their lower extremities. It is also possible to postulate that age-induced accumulation of dead tissue and cell apoptosis should had enhanced leukocyte responses to activation signals (i.e., cytokines). These activation signals molecules are secreted at early phase and prior to the induction of fibrin cuff formulation and endothelial adhesion molecules. Based on the results of this study, it is possible to recommend an ongoing studies assessing the levels of skin hardness, subcutaneous LDF, free radicals, antioxidants, selected cytokines (i.e., interleukin (IL)-1, (IL)-6), selected cluster of differentiation molecules (i.e., CD3, CD69, CD11b), cell adhesion molecules (i.e., ICAM-1), tumor necrosis factor (TNF)-α, macrophage inflammatory protein [MIP]-2) and fibrin in the peripheral blood of young and old subjects with and without CVI will help to clarify the mechanisms related to age-induced changes in the biomechanical properties of the skin.


   Acknowledgment Top


The author thanks Dr. Al-Said A. Haffor, Department of Radiological Sciences, College of Applied Medical Sciences, - Al-Kharj University, Al-Kharj Saudi Arabia, for data analysis, reviewing this manuscript and making useful revisions.

 
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]



 

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