Assessing the acute effect of compression socks on improving arterial compliance in young volunteers

Abstract

Background: Wearing compression socks increases mean deep venous velocity, reduces venous blood retention, and improves venous return. However, no existing studies reported their effect on arteries. Thus, we aimed to determine whether wearing compression socks decreases brachial-ankle pulse wave velocity (ba-PWV).

Methods: We compared ba-PWV measurements in 106 participants (40 men and 66 women) under three conditions: bare feet, wearing normal socks, and wearing compression socks for 10 min. Mean arterial blood pressures (MAPs) were measured at the upper arms and ankles on both sides. Sensor cuffs were attached over socks to estimate pressures exerted on arterial walls by the socks in the condition of wearing socks.

Results: Tukey's honestly significant difference test showed that PWVs for the compression sock condition were significantly lower than those for bare feet (95 % confidence intervals: 0.3051-0.9478 [right], 0.3454-0.9889 [left], p < 0.0001 on both sides) and normal sock conditions (0.0126-0.6552, 0.0656-0.7092, p < 0.04 on both sides). The mean ba-PWV of the right side decreased from 10.57 m/s (bare feet) to 9.94 m/s (compression socks) [absolute difference: 0.63 m/s; relative difference: 5.96 %]. The left-sided mean ba-PWV decreased from 10.79 m/s (bare feet) to 10.11 m/s (compression socks) [absolute difference: 0.67 m/s; relative difference: 6.21 %]. We observed no significant differences in PWVs between bare feet and normal sock conditions on either side. In the compression sock condition, the difference between upper-arm and ankle MAPs while wearing socks indicated the pressure exerted on the arterial wall by the compression socks. We found significant negative correlations between ba-PWV and the estimated pressure exerted on the arterial wall at both ankles (regression analysis, F(1, 104) = 10.55, p < 0.02) [right], F(1, 104) = 12.92, p < 0.0005 [left]).

Conclusions: Wearing compression socks reduced ba-PWV, indicating increased arterial compliance in lower limb arteries by applying external pressure to the arterial wall.

Keywords: Brachial-ankle pulse wave velocity; Compression socks; Lower limb arteries.

Fig. 1

Experimental workflow of socks affecting peripheral arterial volume distensibility. A. Peripheral arterial volume distensibility among three groups (bare feet, normal socks, and compression socks) was measured for ba-PWV using a blood pressure pulse wave device. Socks were worn bilaterally during measurements, and ankle cuffs for measurements were wrapped over the socks. B. Wrap blood pressure-measuring cuffs around the extremities (both upper arms and ankles). The time difference between the rise of the volume pulse wave at the distance from the aortic valve opening to the upper arm (L_b) and the distance from the aortic valve opening to the ankle (L_a) is ΔT. ba-PWV was calculated by dividing the brachial-to-ankle distance by ΔT. C. Three pressures are described. The first (red thick arrow) is the pressure exerted on the arterial wall from the inside, corresponding to the blood pressure. The second (black thick arrow) is the pressure on the skin surface of the lower leg where the socks (normal or compression) are worn. The third (grey thick arrow) is the pressure transmitted from the socks through the skin as well as the biological tissue of the lower leg to the outer vascular wall. The ankle blood pressure when wearing socks was measured with a cuff set over the socks, so that the mean blood pressure of the measured ankle blood pressure was equal to the true mean blood pressure minus the pressure applied to the arterial wall by the sock. The mean blood pressure at the upper arm minus the mean ankle blood pressure over the sock is defined as the external pressure applied to the arterial wall by the sock through the skin layer and the tissue. This made it possible to analyse the effect of the pressure applied by the sock to the outer wall of the vessel.

Fig. 2

Environment during PWV measurement. The cuff for measuring blood pressure in the upper limb is worn on the upper arm, and the cuff for measuring blood pressure in the lower limb is worn on the ankle. To ensure that PWV values are not affected by the environment, measurements are performed in a controlled space with regulated room temperature and maintained sound insulation.

Fig. 3

Measurement of sock pressure. The dark grey areas of the compression socks are designed to exert higher pressure than the lighter areas on the front. The diagram on the right shows the positions of the mannequins and sensors from which the pressures were measured. Mannequins wore normal socks and compression socks, and the pressure at each location was measured. Measurements were taken at a total of six points on the mannequin: three on the anterior surface of the lower leg and three on the posterior surface of the lower leg.

Fig. 4

Statistical comparison for the three conditions. Box plot diagrams showing the comparison of three conditions (bare feet, normal socks, and compression socks). The notches on the box plots indicate the 95 % confidence intervals of the median calculated as median plus ±1.5 × IQR/(n), with IQR being the difference between the third and first quartiles. (A) Comparison of mean blood pressure in the upper arm among the three groups; (B) comparison of mean pulse pressure in the upper arm among the three groups; (C) comparison of pulse pressure in the ankle among the three groups; (D) for each participant, the result of the upper-arm MAP minus the ankle MAP was compared among the three groups; and (E) comparison of ba-PWVs among the three groups. A p value less than 0.05 was considered statistically significant. ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.005.

Fig. 5

Relationship between ba-PWV and differences in MAPs between upper arm and ankle when wearing compression socks. The horizontal axis shows the differences in MAPs between the upper arm and ankle after 10 min of wearing compression socks. The vertical axis shows the ba-PWV. Both right and left sides illustrate a similar negative relationship, with a larger difference in MAPs between upper arm and ankle resulting in a lower ba-PWV.

Fig. 6

Improvement value of ba-PWV. (A) Results of a random forest to explore dependent variables closely related to improved ba-PWV. There were seven independent variables, but only DIA was closely associated with ba-PWV. (B) The bifurcation and scatterplots of the analysis. The Random Forest analysis resulted in a bifurcation of the right ankle DIA values at 70.6 mmHg. There was a statistically significant difference in improved ba-PWV between the groups with ankle DIA less than 70.6 mmHg and those with ankle DIA greater than 70.6 mmHg (p < 0.005).

Fig. 7

Relationships among external cuff pressure, arterial volume distensibility, and pulse wave velocity in the upper extremity. In the case of external cuff pressures on the horizontal axis and arterial volume distensibility on the vertical axis, the mechanical characteristics are as shown by the black line. As the external cuff pressures increase, arterial volume distensibility increases. In addition, external cuff pressure increases, and pulse wave velocity decreases (adapted from Zheng et al. [27]).