Role of MRI in investigating the effects of elastic compression stockings on the deformation of the superficial and deep veins in the lower leg

Thigh-length graduated compression stocking cannot increase blood velocity of the common femoral vein in patients awaiting total hip arthroplasty

Objectives

Graduated compression stocking (GCS) is one of the mechanical prophylaxes commonly used for deep vein thrombosis (DVT). The present study was designed to observe the effects of graduated compression stockings on the vein deformation and hemodynamics of lower limbs in patients awaiting total hip arthroplasty (THA).

Methods

The lower extremity veins of 22 patients awaiting THA were examined by ultrasound, when they rested in supine position with or without thigh-length GCS. The deformation parameters we measured included antero-posterior (AP) diameters, latero-medial (LM) diameters, and cross-sectional area (CSA) of great saphenous vein (GSV), posterior tibial vein (PTV), popliteal vein (PV), gastrocnemius vein (GV), and superficial femoral vein (SFV). We measured peak velocity and mean velocity of GSV, common femoral vein (CFV), junction of GSV and CFV to represent for hemodynamics of veins.

Results

Significant compression was observed in almost all measured veins with the use of thigh-length GCS, while it was unable to significantly compress GSV in latero-medial diameter. The mean latero-medial diameter reductions for GSV, PTV, GV, PV and SFV were 19.4, 30.2, 43.2, 29.7 and 20.4%, respectively. GCS significantly compressed antero-posterior diameter of GSV, PTV, GV, PV and SFV by 43.4, 33.3, 42.1, 37.5, and 27.8%, respectively. The mean reduction of cross-section area was 44.8% for GSV, 49.6% for PTV, 60.0% for GV, 57.4% for PV, and 36.2% for FV. No significant changes were observed in the mean blood velocity of GSV, CFV, and junction. GCS was able to significantly reduce peak velocity of CFV (17.6 ± 5.6 cm/s to 16.1 ± 6.0 cm/s) and junction (23.3 ± 9.5 cm/s to 21.3 ± 9.7 cm/s), while it did not change the peak velocity of GSV.

Conclusion

Thigh-length GCS is sufficient to compress lower extremity veins in patients awaiting THA in supine position with the greatest compression in GV, while it was unable to significantly increase blood velocity of common femoral vein or GSV. GCS may prevent DVT through more than simply increasing blood flow. Further studies are needed to determine the specific effects of GCS.

The impact of graduated compression stockings on calf-vein deformation and blood velocity in patients awaiting total knee arthroplasty

Objectives

This study was designed to explore venous deformation of the lower extremities and the changes in venous hemodynamics in supine position before and after wearing graduated elastic stockings in patients awaiting total knee arthroplasty (TKA).

Method

The leg veins of 21 elderly patients awaiting TKA were imaged in the supine position with and without knee-length graduated compression stockings (GCS) according to a fixed protocol. Measured parameters including the lateromedial (LM) diameter, anteroposterior (AP) diameter, and cross-sectional area (CSA) of the great saphenous vein (GSV), gastrocnemius vein (GV), soleus vein (SV), posterior tibial vein (PTV), fibular vein (FV), and anterior tibial vein (ATV). In addition, the mean and maximum velocities of the popliteal vein (PV) and superficial femoral vein (FSV) were measured.

Results

GCS-related compression was observed for all the measured veins. Maximal reduction was observed for the GV and SV, whereas the GSV exhibited the lowest degree of GCS-related compression. The mean cross-sectional area reduction values associated with GCS were 33.1 ± 41.2 % for the GSV, 94.8 ± 11.1 % for the GV, and 85.6 ± 20.3 % for the SV, while the mean reduction of anteroposterior diameter was 18.1 ± 34.5 % for the GSV, 89.0 ± 22.5 % for the GV, and 72.9 ± 35.1 % for the SV, and the mean reduction of the lateromedial diameter was 25.9 ± 36.4 % for the GSV, 89.6 ± 19.6 % for the GV, 78.2 ± 28.3 % for the SV. No significant GCS-related changes in blood velocity in the superficial femoral veins or popliteal veins were detected.

Conclusions

For elderly patients awaiting TKA, knee-length GCS can significantly reduce calf vein dilation while at rest in the supine position, with the greatest reductions being observed for the soleus and gastrocnemius veins. These data might help provide a theoretical basis for the GCS in reducing incidence of deep vein thrombosis in patients undergoing TKA.

Which pressure of adjustable compression wrap system is necessary to reduce deep vein cross section area in post-thrombotic patients? A proof-of-concept study

Objective

The conservative treatment of post-thrombotic syndrome includes application of compression on the affected extremity. However, the type and the level of compression required to manage post-thrombotic syndrome are still unclear. The aim of our proof-of-concept study was to assess the compression required to reduce cross section area of post-thrombotic deep veins in 22 patients with post-thrombotic syndrome.

Methods

The circumference and cross section area of posterior tibial veins and saphenous vein trunk were assessed on mid-calf level using 3T magnetic resonance scanner, at increasing compression (0, 30, 40, and 50 mmHg), provided by a novel adjustable Velcro compression wrap, the CircAid JuxtaLite®.

Results

A significant reduction of baseline vein cross section area in post-thrombotic syndrome patients in the lying position required compression of at least 30 mmHg for posterior tibial veins, and at least 40 mmHg for the saphenous trunk. Apart from morphological changes of the compressed veins, we observed extinction of T2w signal at compression above 40 mmHg, which corresponded to accelerated blood flow in the veins, and therefore may be considered as a hemodynamic marker of compression effectiveness.

Conclusion

CircAid adjusted to compression level ≥40 mmHg accelerates blood flow in affected deep veins, thus it may facilitate post-thrombotic syndrome management.

Two layers of graduated compression stockings can reduce healthy saphenous vein diameters in the standing position

Background

Previous studies reported graduated compression stockings can reduce the calibre of deep veins in the standing subjects. However, the literature has been inconclusive on the effect of graduated compression stockings on superficial veins in standing subjects.

Objectives

To assess the effect of two layers of graduated compression stockings on the diameter of saphenous veins in healthy subjects.

Materials and methods

In 17 legs of nine healthy subjects, we studied the effect of single layering and double layering of graduated compression stockings (23–32 mmHg, Thigh High Belted Sigvaris, Switzerland) on the diameter of the great saphenous vein mid-thigh, great saphenous vein mid-calf and small saphenous vein mid-calf. The measurements were taken using duplex ultrasound (Toshiba Aplio XG 500, 18-7 MHz transducer), through the fabric using a generous amount of ultrasound gel, on subjects both supine or prone and standing.

Results

Two layers of Class II graduated compression stockings reduced the calibre of great saphenous vein mid-thigh from (4.1 mm to 3.3 mm, p < 0.05), great saphenous vein mid-calf (2.8 mm to 2.2 mm, p < 0.01) and small saphenous vein (2.7 mm to 1.9 mm, p < 0.01) in the standing position. In the supine or prone position, great saphenous vein showed narrowing but there was no measurable change in the calibre of the small saphenous vein. The degree of narrowing was measurable, but insufficient to approximate the vein walls.

Conclusion

Superimposition of two Class II graduated compression stockings reduced the calibre of the saphenous veins in the standing position but did not approximate the vein walls. In the supine or prone position, the addition of a second layer of graduated compression stockings did not result in further narrowing of the saphenous veins.

Knee-high compression socks minimize head-up tilt-induced cerebral and cardiovascular responses following dynamic exercise

In healthy individuals during a non-exercised state, knee-high compression socks (CS) may reduce the magnitude of lower limb venous pooling during orthostasis but are not effective at minimizing the incidence of pre-syncopal symptoms. However, exaggerated reductions in cerebral blood flow velocity (CBV) and cardiac stroke volume (SV) occur during passive head-up tilt (HUT) testing following dynamic exercise. It is unknown if CS can minimize post-exercise HUT-induced decrements in CBV and SV in this population. To test the hypothesis that CS will attenuate the reductions in SV and CBV during 60° HUT following 60 minutes of moderate-intensity (60% VO₂ peak) cycling exercise. Ten healthy volunteers (22.6 ± 2.1 years, 24.1 ± 2.5 kg/m² ) completed pre- and post-exercise 15-minute HUT tests during randomized CS and Control (no CS) conditions. Changes in blood pressure (finger plethysmography), SV (Modelflow® method), and CBV (Transcranial Doppler) were measured during HUT and preceding supine rest periods. Pre-exercise HUT-induced similar (all, P > .47) reductions in SV (Control; -23.1 ± 11.5%, CS; -20.5 ± 10.9%) and CBV (Control; -18.1 ± 6.3%, CS; -15.3 ± 9.0%). However, larger post-exercise decreases in SV and CBV during HUT were observed in the Control versus CS condition. Specifically, CS attenuated the drop in SV (Control: -32.9 ± 5.6%, CS: -24.3 ± 11.6%; P = .01) and CBV (Control: -25.1 ± 5.8%, CS: -17.6 ± 7.8%; P = .02) during the post-exercise HUT test. These results indicate that CS attenuated HUT-induced reductions in SV and CBV following moderate-intensity cycling exercise and suggest that CS may be an effective countermeasure to reduce the incidence of post-exercise syncope in vulnerable populations.

Investigating the impact of passive external lower limb compression on central and peripheral hemodynamics during exercise

PURPOSE

The objective of this study was to assess the effectiveness of graduated compression socks (GCS) on enhancing muscle blood flow and oxygenation during exercise and recovery in healthy subjects.

METHODS

Twelve healthy volunteers completed a protocol involving baseline, exercise, and recovery periods with and without GCS. Each test was repeated twice to assess repeatability of the results. The applied sock pressure was measured prior to experimentation using a custom pressure sensing system, and modified as necessary using tensor bandages to control the applied load. During each of the experimental phases, blood velocity in the popliteal artery, calf muscle tissue oxygenation, muscle activity, heart rate, blood pressure, cardiac output, and applied pressure from the sock were measured. Popliteal artery diameter was measured during baseline and recovery periods.

RESULTS

The GCS significantly reduced deoxyhemoglobin (HHb) in the leg during baseline (HHb, p = 0.001) and total blood volume and HHb in the leg during exercise (total hemoglobin, p = 0.01; HHb, p = 0.02). However, there were no differences in leg muscle blood flow velocity or any other variables with and without GCS at baseline, exercise, or recovery. Interestingly, it was found that the local applied sock pressure was very sensitive to the sock application process and, furthermore, the pressure varied considerably during exercise.

CONCLUSIONS

No significant changes were observed in measures reflecting oxygen delivery for healthy subjects using GCS during exercise and recovery. Applied sock pressure was carefully controlled, thus eliminating the sock application process as a variable.

Relationship between medical compression and intramuscular pressure as an explanation of a compression paradox

Background

Using standing magnetic resonance imaging (MRI), we recently showed that medical compression, providing an interface pressure (IP) of 22 mmHg, significantly compressed the deep veins of the leg but not, paradoxically, superficial varicose veins.

Objective

To provide an explanation for this compression paradox by studying the correlation between the IP exerted by medical compression and intramuscular pressure (IMP).

Material and methods

In 10 legs of five healthy subjects, we studied the effects of different IPs on the IMP of the medial gastrocnemius muscle. The IP produced by a cuff manometer was verified by a Picopress® device. The IMP was measured with a 21G needle connected to a manometer. Pressure data were recorded in the prone and standing positions with cuff manometer pressures from 0 to 50 mmHg.

Results

In the prone position, an IP of less than 20 did not significantly change the IMP. On the contrary, a perfect linear correlation with the IMP ( r = 0.99) was observed with an IP from 20 to 50 mmHg. We found the same correlation in the standing position.

Conclusion

We found that an IP of 22 mmHg produced a significant IMP increase from 32 to 54 mmHg, in the standing position. At the same time, the subcutaneous pressure is only provided by the compression device, on healthy subjects. In other words, the subcutaneous pressure plus the IP is only a little higher than 22 mmHg—a pressure which is too low to reduce the caliber of the superficial veins. This is in accordance with our standing MRI 3D anatomical study which showed that, paradoxically, when applying low pressures (IP), the deep veins are compressed while the superficial veins are not.

Dogmas and controversies in compression therapy: report of an International Compression Club (ICC) meeting, Brussels, May 2011

The International Compression Club (ICC) is a partnership between academics, clinicians and industry focused upon understanding the role of compression in the management of different clinical conditions. The ICC meet regularly and from these meetings have produced a series of eight consensus publications upon topics ranging from evidence-based compression to compression trials for arm lymphoedema. All of the current consensus documents can be accessed on the ICC website (http://www.icc-compressionclub.com/index.php). In May 2011, the ICC met in Brussels during the European Wound Management Association (EWMA) annual conference. With almost 50 members in attendance, the day-long ICC meeting challenged a series of dogmas and myths that exist when considering compression therapies. In preparation for a discussion on beliefs surrounding compression, a forum was established on the ICC website where presenters were able to display a summary of their thoughts upon each dogma to be discussed during the meeting. Members of the ICC could then provide comments on each topic thereby widening the discussion to the entire membership of the ICC rather than simply those who were attending the EWMA conference. This article presents an extended report of the issues that were discussed, with each dogma covered in a separate section. The ICC discussed 12 'dogmas' with areas 1 through 7 dedicated to materials and application techniques used to apply compression with the remaining topics (8 through 12) related to the indications for using compression.

Finite element analysis of the deformation of deep veins in the lower limb under external compression

Compression devices applied to the lower limb can help improve venous flow by deforming the muscles and veins. In this study, a two-dimensional finite element model using displacement boundary conditions was employed to simulate the deformations of deep veins in the calf under external compression. Magnetic resonance (MR) scans were performed on four healthy volunteers with and without compression stockings. The displacement boundary condition was extracted from the corresponding deformed (with stocking) and undeformed (without stocking) MR images by using a non-rigid image registration procedure. In the finite element model, soft tissues of the calf were simplified as a homogenous material with hyperelastic properties. The effective bulk modulus of the material was evaluated at a chosen transverse section for each subject, which was also applied to three other locations at 2mm, 6mm and 10mm below the original section. Comparison between the simulation and measurement showed good agreement in area reduction of deep veins (discrepancy=8.7±6.4%), especially for sections close to the chosen location where the effective bulk modulus was evaluated. Beyond a certain distance, the discrepancies increased and became quite variable. The reason for this is that the architecture and stiffness of the calf tissues vary along the leg. The results also showed considerable variation in effective bulk modulus among the four subjects examined.

Analysis of flow and wall shear stress in the peroneal veins under external compression based on real-time MR images

As a widely accepted prophylaxis for deep vein thrombosis, the underlying mechanism of compression stocking still remains unclear. In this study, computational fluid dynamics was applied to in vivo data to provide quantitative insight into the hemodynamic response of the deep venous system to static external compression. The geometry and flow information of deep veins before and after compression was acquired from ten healthy volunteers using magnetic resonance imaging. Our results indicated that application of the compression stocking led to a small reduction in blood flow rate but a significant reduction in cross-sectional area of the peroneal veins in the calf, resulting in an increase in wall shear stress (WSS), but the individual effects were highly variable. The mean volume reduction of the deep veins was 58%, while the time-averaged WSS showed an average increase of 398% after compression (median 98%). The analysis also showed a strong linear correlation between the time-averaged WSS and mean blood velocity, suggesting that flow in the deep veins under the level of compression examined here can be approximated by Poiseuille's law despite local geometric variations. It is hoped that quantitative analysis of WSS in the deep venous system will aid in the future design and optimisation of the compression stocking.

MR phase-contrast velocity mapping methods for measuring venous blood velocity in the deep veins of the calf

PURPOSE

To evaluate the feasibility of using un-gated, real-time MRI for venous blood velocity mapping in the calf, comparing an interleaved spiral k-space sequence (ISP) against a standard segmented gradient echo sequence (GRE).

MATERIALS AND METHODS

A flow phantom with a variable flow-rate was scanned using both GRE and ISP sequences for an in vitro comparison. Seven subjects were scanned prone, performing metronome guided breathing, using the (externally triggered) segmented GRE and real-time ISP sequences. The segmented GRE acquisition duration was 2.5 mins (22 guided respiratory cycles) and the ISP sequence ran continuously for 35 s, 4 full guided respiratory cycles. Mean velocity from each of the deep veins was measured and peak mean velocity, peak flow rate and cumulative volume flow over a respiratory cycle compared between sequences.

RESULTS

The two sequences compared well both in vitro and in vivo. The real-time ISP sequence showed short-term variations in mean velocity superimposed on the respiratory induced flow, which were averaged out using the segmented GRE sequence.

CONCLUSION

Real-time ISP provides comparable time-averaged flow results to the standard sequence with additional information on real-time flow variations and so could be used for further investigation into venous blood flow in the lower leg.

Effects of elastic compression stockings on wall shear stress in deep and superficial veins of the calf

The purpose of this study was to estimate wall shear stress (WSS) in individual vessels of the venous circulation of the calf and quantify the effects of elastic compression based on change of vessel geometry and velocity waveform. The great saphenous vein and either a peroneal or posterior tibial vein have been imaged in four healthy subjects using magnetic resonance imaging, with and without the presence of a grade 1 medical stocking. Flow through image-based reconstructed geometries was numerically simulated for both a range of steady flow rates and ultrasound-derived transient velocity waveforms, scaled to give a standardized time averaged flow rate. For steady flow, the stocking produced an average percentage increase in mean WSS of approximately 100% in the great saphenous vein across a range of 0.125-1.25 ml/s. The percentage increase in the peroneal/posterior tibial veins varied from 490 to 650% across a range of 0.5-5 ml/s. In addition, application of the stocking eliminated periods of very low or zero flow from the transient waveforms. The average minimum value of WSS in all vessels without the stocking was <0.1 Pa. With the stocking, this was increased to 0.7 Pa in the great saphenous and 0.9 Pa in the peroneal/posterior tibial veins. The pathophysiological effects of these changes are discussed. In conclusion, the flight stocking was effective in raising venous WSS levels in prone subjects, and this effect was much more pronounced in the deep vessels. The stocking also tended to prevent cessation of flow during periods of increased downstream pressure produced by respiration.