Effect of compression stockings on cutaneous microcirculation: Evaluation based on measurements of the skin thermal conductivity

Introduction

In Europe, chronic venous disease (CVD) is a frequent cause of medical consultation. Fortunately, the majority of those patients do not experience the late stages of the disease. According to the Bonn Vein study, ¹ around 10% of the monitored population show no signs at all of CVD (C0) while two-thirds of them are concerned by the early stages C1/C2 from the CEAP classification. ² The visible signs announcing venous disorders are related to telangiectases and reticular veins. Compression therapy is an effective solution to face the symptoms and clinical signs of CVD. ³ Numerous medical studies have reported the relationship between compression with elastic compression stockings (ECS) and the effects on veins located in lower limbs; some studies investigated the phenomenon at a macro scale (i.e., the deformation of the vein wall under compression,^4–6 other authors reported global physiological global outcomes. ⁷ However, we need to keep in mind, that before reaching the small veins, the blood flow coming from the arterial side must cross the capillaries where bio exchanges occur at micro scale. Few publications report microcirculation aspects in CVD.^8,9 Only a small number of investigators have been interested in studying the skin’s microcirculatory parameters subsequent to effects of compression.^10,11

According to Abu-Own et al., ¹² skin microcirculatory activities are altered from an interface pressure of 50 mmHg. This statement aligns with the observations of H. Partsch, where within a greater scale, a complete vein occlusion is obtained by external compression around 70 mmHg. ¹³ However, compression therapy protocols do not require such a degree of pressure when using ECS. If it is obvious that ischemia occurs when under excessive pressure, we are interested in learning about the microcirculation subsequent to moderate compression by ECS.

Many non-invasive means exist to evaluate the cutaneous microcirculation activities, which are based on the Laser Doppler Principle.^9,11,14–16 The laser Doppler flowmeter (LDF) is the most widely used instrument for clinical examinations in dermatology, pharmacology, neurosurgery, or anesthesia. ¹⁷ Others options from this technique are available such as laser Doppler imaging (LDI for perfusion evaluation), or more recently, the laser speckle imaging (LSI). ¹⁸ The two last techniques enable linear response signals to the cutaneous blood flow. These optical tools are extremely useful to evaluate the Raynaud’s phenomenon ¹⁹ and also the chronic venous insufficiency (CVI). ²⁰ LDI and LSI provide qualitative and quantitative contactless measurement of skin microcirculatory activities; the results, often artifact dependent, are expressed in arbitrary units.^21,22 The major inconvenience regarding our needs is that these optical instruments cannot perform any measurements through the ECS fabric.

The protocol of our study requires two mandatory conditions: first, the evaluation through the ECS fabric, and then, the investigation within a skin area of a few cm². For these reasons, we decided to involve an instrument, the Hematron, which operates based on a principle of monitoring the effective thermal conductivity of biological tissues. This parameter is considered as a reliable indicator of the metabolic and microcirculatory activities.^23,24,25 The correlation between LDF and Hematron figures was evaluated at r²= 0.86. ²⁶

A preliminary screening campaign was previously conducted on eight volunteers wearing ECS and three ranges of compression (10–15, 15–20, and 20–36 mmHg). ²⁷ The evaluations, performed at the calf area, showed an increase of microcirculation due to the effect of compression by ECS. ²⁷ From those interesting findings, we organized a clinical study aiming to consolidate the hypothesis of the link between microcirculatory skin response and external pressure by ECS.

Materials and methods

Operating principle of Hematron device

The initial hypothesis considers that blood flow, irrigating an area of the skin, reflects the metabolic exchanges related to the amount of nutrients supplied to the cells. These exchanges occur on a microscopic scale as the associated phenomena occur at the cellular level and define the microcirculatory activity.

The measuring principle of the Hematron device is based on a thermal clearance technique, which consists of the creation of a constant thermal field under the probe. It consists of a disc 25 mm in diameter and 4 mm thick. Hematron is a non-invasive measuring device. The sensor surface which is in contact with the epidermis is composed of a heating element in the center and thermocouples measuring the temperature difference between the center of the sensor and its periphery (Figure 1). A specific housing was designed to avoid excessive pressure induced by the sensor when compressed by stockings (Figure 2). OPEN IN VIEWER

Figure 1.

Hematron probe for measuring skin effective thermal conductivity.

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Figure 2.

Specific housing designed to avoid excessive pressure induced by the sensor when used with medical stockings.

A proportional integral regulator controls the electrical power required to maintain a constant temperature difference of 2℃, thereby generating the thermal field. The effective thermal conductivity of the tissues is proportionate to the electrical power supplied to the heater element. The thermal conductivity is expressed in mWcm⁻¹·℃⁻¹ where values are between 2 and 10 mWcm⁻¹·℃⁻¹ for biological tissues. ²³ The geometrical properties of the sensor are designed to ensure that generated thermal field spreads mainly through the capillary network of the skin. ²⁸

The measurement is related to dimensional characteristics of the capillaries, and more specifically, their ability to dissipate heat. Indeed, capillaries are perfect heat exchangers, due to their very small diameter, very thin walls, and high surface density. Thus, the heat generated by the Hematron probe will be proportional to the microcirculatory activity. In other words, when the microcirculatory activity increases, blood flowing through the capillaries draws and decreases heat energy from the thermal field under the heater. Therefore, the temperature difference between the center and the periphery of the sensor decreases. It is then necessary to compensate this thermal dissipation by increasing the temperature control of the heating element to restore the temperature gradient. Variations in electrical power controlling the heating element reflect the microcirculatory activity in the capillary network.

Measurements of the skin microcirculatory activity by Hematron were performed with and without elastic stockings. Relative difference Δ ( P ) % was also calculated for each subject for supine position phase by the relation:

Δ ( P ) % = ( Δ P ) with - ( Δ P ) without ( Δ P ) without × 100

where Δ ( P ) with is the skin effective thermal conductivity measured with the elastic stockings and Δ ( P ) without corresponds to the value measured without compression. Statistical analysis was performed using XLstat software. The difference was calculated with a Wilcoxon signed-rank test for matched pairs (where p < 0.05 is statistically significant).

The volunteers recruitment

Inclusion criteria were: healthy people giving informed consent being able to completely comply the protocol. Female between 25 and 55 years classified C0 or C1 with the presence of venous symptoms, with no compression therapy or veno-active drugs.

The non-inclusion criteria were: pregnant women, skin pathology on measuring area, vaso active drugs, any vascular disease (in particular arteriopathy of the lower limbs), no surgery during the last month, excessive sun exposure during the last month, participation to any other clinical study within the same period.

Among the 32 recruited volunteers (11 C0s and 21 C1s), only 30 have completed this study.

The details are displayed in Table 1.

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Table 1.

Cohort criteria.

Cohort	Clinical study
Number of subjects
Total	30
Female	30
Male	0
Age
Mean (SD)	42 (2)
Range	25–55
Weight (kg)
Mean (SD)	62.1 (13.0)
Range	44–107
Height (cm)
Mean (SD)	161.6 (6.7)
Range	151–175
CEAP
C0s	11
C1s	19
Level of compression at points B and C	Stockings (13 mmHg)

This study was conducted by the laboratory Dermscan (Villeurbanne, France), specialist in clinical investigations in Dermatology. On the recruiting date, each volunteer signed a consent form where they were informed about all of the details of the investigation protocol. This clinical report is referenced #13E0829 – 2013 in Dermscan records.

Results

The resulting value of the conductivity was the average measurement recorded during a period of 5 min (Figure 3). OPEN IN VIEWER

The data obtained from this clinical study highlight a significant improvement of cutaneous microcirculatory activity in 83% of the investigated subjects. Considering the entire population, the overall mean value Δ ( p ) % of the relative increase of cutaneous thermal conductivity in lying position, is 7.6% ± 1.8 (p < 0.0001).

Discussion

The main limitation of this experiment is the lack of measurement of the blood pressure which could affect the results: it will be verified in the next clinical study.

The results from this investigation show a positive and significant influence of the compression by ECS on cutaneous microcirculatory activities. This improvement could be explained by neurophysiological considerations. A light contact pressure against the skin creates a protective physiological reaction to face potential ischemia. This phenomenon is known as pressure induced vasodilation (PIV) mentioned by Fromy et al. ²⁹ ; the authors reported that the skin blood flow is improved by moderate contact pressure (∼30 mmHg) but decreases with higher pressure. The neuronal mechanism is described as follows: the interface pressure against the skin stimulates the nociceptor of capsaicin-sensitive nerve fibers. Those receptors release neuropeptides at cutaneous level inducing relaxation of smooth muscles providing vasodilation as consequences. In our investigations, the ECS exert a pressure amount within the range of the reported PIV.

Conclusion

These results suggest new areas of compression benefits. This microcirculatory response to external elastic textile compression could not be explained by the traditional theory in mechanics of fluids; the neuronal considerations highlight new areas of work in compression therapy. It is usually accepted to consider the level of pressure, as the right dosage of compression therapy and recommendations are available for the selection of pressure range according to the degree of pathology. It was also reported that light compression (10–15 mmHg) is sufficient enough to reduce evening edema ³⁰ or to improve CVI symptoms.^31,32 The physiological benefits of this level of compression, with no rational explanation from vein mechanical deformation at a macro scale, may find some preliminary answer from the micro scale through this microcirculatory approach.