Effect of the elastic compression stockings on the calf veins and tissues during a simulated orthostatic test (LBNP).

UNLABELLED: The objective of the present study was to quantify the effects of elastic compression stockings (ECS) on the leg hemodynamics, the venous return (flow and distensibility) and on the leg superficial tissue thickness. MATERIAL & METHODS: 10 healthy women were submitted to LBNP (Lower Body Negative Pressure) tests without then with ECS (French pressure class 1, 2 and 3). The subject was instrumented with Doppler and echographic probes for assessing the femoral artery, the external saphenous and the gastrocnemian vein. RESULTS: 1) At -40 mmHg the heart rate and blood pressure didn't change significantly with or without ECS. 2) The lower limb vascular resistance increased by 20 to 25% (p<0.01) from the initial values (i.e. without depressure) without or with class 1 or 2 ECS, while it increased less (13%, p<0.01) with class 3 ECS. 3) With ECS, the gastrocnemian vein area was reduced by 10 to 15% (p<0.01) from the initial values, in proportion to the ECS class. 4) The maximal distension (cross section) of this vein at -40 mmHg remained similar with or without ECS, but the percent change in vein distension was significantly higher with ECS than without. 5) Only without ECS, the distance between the external saphenous vein and the skin increased by 13% at -40 mmHg (p<0.01) from the initial values (increase of the calf peripheral area by 11% p<0.01). With ECS, there was no increase in distance nor area during LBNP. CONCLUSION: ECS had no effect on the main arterial hemodynamics and venous cross section area, while it prevented liquid stowage into the superficial tissue.

Human muscle fatigue and elastic compressive stockings.

The present study was performed to test if elastic compressive stockings (ECSs) increase muscle fatigability during sustained muscle contraction or if it improves the recovery after fatigue. Surface electromyograms (EMGs) were recorded on 4 leg and thigh muscles, and static ankle dorsal flexion force levels were measured in the right limb of 15 healthy subjects. The subjects maintained a 50% maximum ankle dorsal flexion force (MVF) for as long as possible without and, after a 30 min rest, with a European class I ECS. Finally, after another 30 mn rest, the pressure exerted by the ECS on the skin was measured at standard points on the limb, using a Salzmann apparatus. During the first 10 min of both rest periods, the subjects performed brief static maximum ankle dorsal flexions every 30 s. ECS exerted a 14.3 mm Hg mean pressure at tibial level C. Linear relationships, whose slopes were not influenced by ECS, existed between the maintenance time and both the mean power frequency and the logarithm of the total power of the tibialis anterior and gastrocnemius lateralis EMGs. The endurance times, the force recovery times after fatigue and the linear relationships between the logarithm of the time elapsing after exhaustion and the MVF reached during the recovery period were also independent of ECS. The results show that class I ECSs are not responsible for greater muscle fatigability; but they do not improve force recovery during rest following static fatiguing voluntary contractions.

Intramuscular pressure and surface EMG in voluntary ankle dorsal flexion: Influence of elastic compressive stockings.

Intramuscular pressure (IMP) is of major importance in blood flow and is often taken as a good estimate of muscular tension. However, its measurement remains invasive. The aims of the present work were: (1) to re-examine the possibility of evaluating IMP and muscular tension changes by means of surface electromyographic recordings, and (2) to clarify the influence of elastic compressive stockings (ECS). Surface EMG of muscles tibialis anterior (TA), soleus, gastrocnemius, and IMP from the anterior tibial compartment (ATC), deep posterior compartment (DPC), superficial posterior compartment (SPC) of the right leg, were simultaneously recorded in nine healthy subjects. Subjects performed series of voluntary concentric TA contractions (right ankle dorsal flexions) and TA isometric contractions, with or without elastic ECS, in a decubitus posture. Rest IMP mean values, measured over 60 s, ranged between 12.3 and 26.6 mmHg, i.e. in the range or slightly higher than those reported in the literature. When ECS were applied, mean IMP increase was 6.4 mmHg in ATC, 8.7 mmHg in DPC and 21.0 mmHg in SPC, while the corresponding EMG amplitude decreased. In ankle dorsal flexion movements, instantaneous values of TA-EMG amplitudes were linearly correlated to ATC-IMP instantaneous values, over the whole of the EMG rising part of every movement. When ECS were applied, the relationships between TA-EMG amplitude and ATC-IMP amplitude remained linear but where shifted towards higher IMP, in agreement with the increase in rest IMP. Because of antagonist co-contractions, IMP from DPC and SPC were also linearly correlated with ATC-IMP but with low coefficients of proportionality. As in TA concentric contractions, TA-EMG amplitudes were linearly correlated to ATC-IMP instantaneous values in isometric contractions, but the slopes of the latter were always greater. This result is explained by the relationship between muscle tension and shortening velocity. Al the results showed that: (1) instantaneous changes in surface EMG amplitude may provide a good estimate of IMP changes during the rising part of isometric, but also of concentric voluntary contractions; (2) elastic compressive stockings do not impair subjects relaxation capacity but actually increase the ratio IMP/muscle activation. As a consequence, ECS may actually increase the venous return during voluntary contractions.

[Effects of elastic stockings on venous flow during simple movements and muscular contractions of lower limb in healthy volunteers. Pilot study]. / Effets de la contention elastique sur le flux veineux au cours de mouvements simples et de contractions musculaires du membre inférieur chez le volontaire sain. Etude pilote.

AIM: To study common femoral vein flow during simple movements and voluntary contractions of muscles of lower limbs in healthy volunteers and to evaluate the effects of elastic stocking on venous flow. METHODOLOGY: Experimental study. Ten subjects, aged 21 to 25 years, underwent duplex ultrasound to examine venous flow, the lower limb being fitted with sensors to characterize kinematics and of muscle activity. MOVEMENTS STUDIED: In supine position: thigh muscles contraction. forefoot dorsal flexion. Standing on both feet: thigh muscles contraction, tip-toe, front load transfer, extension of the leg on the knee, loading on one limb, forefoot back flexion. Data were recorded with a computerised system for secondary analysis. A mean venous velocity was calculated after elimination of parasite signals. Venous velocity was correlated with muscle signals. The procedure was repeated with the patient wearing a thigh-length class II elastic stockings (Varisma Innothera Ltd). RESULTS, CONCLUSION: All movements increased venous flow. Wearing elastic stockings increased the venous flush due to movements or muscle contractions. The level of muscle activity during the same movement or the same muscle contraction varied from one subject to the other.

The venous return simulator: an effective tool for investigating the effects of external compression on the venous hemodynamics--first results after thigh compression.

BACKGROUND: To present a virtual model, the venous return simulator (VRS), designed to compute venous hemodynamic variations when compression is applied to the leg. METHODS: The VRS defines a numerical network of the lower extremity and computes the dynamic variables (flow rate, venous diameter and internal pressure) for a defined external pressure. The VRS was based on physiological data from the literature and clinical studies on healthy subjects. Clinical correlations were required to confirm its validity; for this purpose, we carried out experiments simulating the conditions of a clinical trial, in which the diameter of superficial and deep veins was measured while increasing pressures (20, 40 and 60 mmHg.) were applied to the thighs of patients enduring deep valvular insufficiency and venous ulcers. The diameters and flow rates calculated using our VRS model were compared with the experimental data obtained at the same thigh compression levels. RESULTS: The numerical results of VRS are in good agreement with the clinical data obtained by Duplex, (R2 = 0.96). In accordance with the in vivo measurement the computed results show that only a pressure greater than 40 mmHg is able to reduce the venous diameter at thigh-level, both in the great saphenous vein and in the femoral vein. CONCLUSION: The venous return simulator computes lower limb hemodynamic parameters under static conditions. The good correlation existing between the VRS and the data obtained in a previous clinical study shows that this numerical approach could provide a useful means of predicting the hemodynamic consequences of compression therapy.