This study was designed to explore the effect of GCS on lower extremity venous blood flow velocity and venous deformation during ankle pump exercise. In our study, we found that GCS could significantly decrease the cross-sectional area of SV, PTV and GSV in supine position at rest and maximum ankle plantar flexion. But the compression effect of GCS to SV and GSV was not observed during maximum ankle dorsiflexion. We also found that GCS application significantly reduced the peak flow velocity of the femoral vein during ankle plantar flexion and ankle dorsiflexion, but this effect was not significant in supine position at rest..
These results of the calf-vein deformation agreed with our previous study, which have indicated that knee-length GCS can significantly compress most measured veins including the SV, gastrocnemius vein (GV), PTV, fibular vein, anterior tibial vein and GSV while at rest in the supine position in elderly patients awaiting total knee arthroplasty [20]. Similarly, Partsch et al. [27] determined that low pressure compression stocking can reduce the cross section of superficial and deep veins while in the supine position. Another study conducted by Jeanneret et al. [28] also found that measured parameters including the lateromedial diameter and anteroposterior diameter of the calf veins (GV, PTV and short saphenous vein) were significantly smaller in the prone position when wearing GCS. Of course, there are also some different results. In the standing position, Jeanneret et al. [28] and Rastel et al. [29] found that the results may not be the same, the vein diameter of the SV, PTV and fibular vein would not be compressed by compression stockings. The cross-sectional area changes of the SV and GSV before and after wearing GCS during maximum ankle dorsiflexion were not in accordance with our expected results. With maximum ankle dorsiflexion, soleus veins were closed in 15 of these 16 patients and were closed in in all of the 16 patients in the context of GCS-mediated compression. So, we were unable to determine whether there was a statistical difference before and after wearing GCS. The cross-sectional area changes of the GSV after wearing GCS during maximum ankle dorsiflexion, eight patients reported an increase, and four patients reported no change, four patients reported a decrease. The cross-sectional area of GSV is very small, so there may be errors in the measurement. And a significant GCS-related reduction in the lateromedial diameter of the GSV was observed in these patients with maximum ankle dorsiflexion. Consequently, we considered that GCS can significantly compress GSV during maximum ankle dorsiflexion.
Previous research has mainly focused on observing the changes in lower limb venous flow velocities during ankle pump exercise whereas research about the calf-vein deformation is sparse [23, 24, 30]. In this study, we focused on the calf-vein deformation in three positions of the leg (flat, maximum ankle plantar flexion and maximum ankle dorsiflexion). And we show for the first time that soleus veins were completely closed in 15 of these 16 patients with maximum ankle dorsiflexion. The possible reason for this phenomenon is that the gastrocnemius muscle and soleus muscle of the patients was lengthened during maximum ankle dorsiflexion. And the veins are therefore subjected to a more uniform pressure similar to intermuscular pressure. Some studies found that the intermuscular vein is the location where DVT often occurs, and soleus vein dilatation is an independent risk factor for deep venous thrombosis after orthopedic surgery [31, 32]. Thus, the results obtained in this study could be considered as one of the possible mechanisms to explain that ankle pump exercise can prevent intramuscular venous thrombosis, which also needs to be further studied.
To our surprise, our results were entirely counter to our hypothesis. This study showed that GCS application significantly reduced the peak flow velocity of the femoral vein during ankle exercise. This outcome is also contrary to that of Stein et al. [33] who found that a significant thigh length GCS-related increase in the time-averaged peak velocity of the popliteal vein was observed in those volunteers from 25cm/s (95% CI = 20–29 cm/s) to 29 cm/s (95% CI = 22–35 cm/s) during supine ankle exercise. And there was no significant difference between the GCS wearing and non-GCS wearing while during exercise while sitting. Espeit et al. [34] concluded that the peak velocity of the popliteal vein was reported to be 38.4 ± 52.4% (p < 0.001) greater for GCS + local vibration than local vibration while resting in a prone position. And Sakai et al. [26] showed that intermittent pneumatic compression with active ankle exercise (76.2 cm/s [95% CI = 69.0–83.4 cm/s]) lead to a significant increase in femoral vein peak venous velocity compared to active ankle exercise alone (47.1 cm/s [95%CI = 38.7–55.6 cm/s], p < 0.001). There are also some prior studies that were consistent with our results. Warwick et al. [35] found that GCS application significantly reduced the popliteal venous peak velocity in each position of the leg (foot-up, flat and foot-down) when the AV Impulse Foot Pump was activated. This result may be explained by the fact that a reduced preload of the foot venous plexus would limit the volume available for expulsion.
As we know, ankle pump exercise can promote lower extremity venous reflux by contracting and relaxing gastrocnemius and soleus muscles. In this study, it was observed that GCS application reduced the cross-sectional area of the calf veins, which might restrict the preload of the veins. And this restriction in its preload induced a reduction in the volume available for expulsion, which eventually caused a decrease in the peak flow velocity of the femoral vein when GCS was used simultaneously with ankle pump exercise. Another possible reason is that muscle contraction and relaxation are time limited. So, if the contraction and relaxation of muscle is too fast, the pumping and reflux of blood will be affected.
Peak flow velocity of the lower extremity is considered as an alternative measure for preventing thrombosis [36]. And a comparative prospective trial involving 800 patients also showed that the incidence of thromboembolism after total hip or knee replacement did not differ between patients treated with foot pumps alone and with the combination of foot pumps and GCS. Nevertheless, foot pumps without GCS could also increase patient compliance [37]. Thus, what we need to do is optimizing the use of GCS in combination with ankle pump exercise in the patients after joint replacement surgery, from these standpoints. To best improve venous hemodynamic of patients after joint replacement, it is critical to find more suitable frequency, intensity, duration and so on during ankle pump exercise. The specific practices need to be further studied.
This study has some limitations. Firstly, in the present study, the movements of the ankle joint focused solely on the dorsiflexion and plantarflexion. Other movements consisted of eversion, inversion, internal rotation and external rotation might lead to different outcomes. Furthermore, we hypothesized that the results in the patients before joint replacement could be applied to patients after joint replacement. Although studies involving postoperative patients would be more relevant to confirm our outcomes, the accuracy of the results may be affected due to the patient’s post-operative pain, discomfort and swelling. Thirdly, we focused exclusively in knee-length GCS and did not assess the possible effects of thigh-length GCS. Some studies found that thigh-length GCS enables better improvement of venous hemodynamic [33, 38]. Finally, there are no randomized clinical trials to confirm the question if the stockings should be used with ankle pump exercise.