Compression therapy has been used to treat a number of conditions ranging from tired, aching legs to varicose veins, chronic venous disease, and deep venous thrombosis (DVT). It has recently gained media attention due to the increased incidence of economy-class syndrome (blood clots resulting from long distance air travel become dislodged and travel to the heart and lungs, causing sudden death).1 Furthermore, as the population ages, chronic venous disease is becoming more prevalent.2 Compression therapy is also finding uses in sports medicine to help athletes recover.3
With respect to wound and ulcer care, the first step in the treatment process involves management of the underlying pathology. Compression therapy plays a key role in this, with healing rates of 40-70% (after 3 months), and 50-80% (after 6 months), being reported.4,5 Bandages, stockings, and intermittent pneumatic compression (IPC) devices can be used to deliver compression therapy. Of these, bandages and stockings are more widely used.
There are many different types of compression bandages available on the market. They are mainly divided along the lines of extensibility or stiffness. Short-stretch, or inelastic and semi-rigid bandages, have a high stiffness factor. They supply large amounts of pressure when the wearer is active by rigidly opposing the increase in calf muscle volume. However, they deliver relatively little pressure when the wearer is at rest. These bandages are often left in place for a number of days, but have a tendency to lose significant amounts of pressure within the first few hours of wear.Sup>6,7
Long-stretch bandages are more elastic in nature, utilizing this recoil force to provide compression during both activity and rest. Although they are not able to achieve the same levels of pressure as short-stretch bandages, they are able to maintain a more constant pressure profile for a longer amount of time.6,7
Short- and long-stretch bandages can be used together in a multi-layer system. Bandage systems have an advantage in terms of compression therapy because they can fit an unlimited range of patients. In general, short-stretch bandages are used to provide focal compression, while long-stretch bandages are used to hold this wrapping in place. This is particularly useful for preventing veins from refilling after radiofrequency (RF) and Laser ablation or sclerotherapy procedures.8
Both short- and long-stretch bandages have been shown to achieve similar healing rates, and there is no strong evidence to suggest that one is better than the other.6 However, the effectiveness of bandages is heavily dependent upon how they are wrapped.5-7 Unfortunately, without some means of feedback, most people cannot accurately gauge the amount of pressure being applied.4,6 If bandages are wrapped too loosely, it may take longer to see a reduction in swelling, and the wound will not close as quickly.5 However, if bandages are too tight, blood flow may be reduced to dangerously low levels and the tissue will become necrotic.5 Many people find long-stretch bandages easier to use6, but safe levels of pressure can be achieved with either provided that sufficient training and feedback is available.7
Compression hosiery can most simply be described as socks or stockings that are knitted to provide the greatest amount of pressure at the ankle, and gradually less at the more proximal aspects of the limb. They are mainly classified based on the amount of pressure provided (specified at the ankle, or B-level), although stiffness and length can also vary. They are similar to long-stretch bandages insofar as they are elastic in nature, meaning that they deliver compression both during activity and rest. However, unlike bandages that require a trained professional for wrapping, compression stockings have defined compression levels, are simpler to apply and remove, and can be changed daily. One study reported that compression stockings significantly reduced healing time and pain compared to short-stretch bandages.5 This study also reported that patients found stockings more comfortable and easier to put on/take off compared to bandages.5 Compression hosiery does, however, have a limited fitting range.
The notion of graduated versus uniform compression is based on a study conducted by Siegel et al. in the 1970’s.9 This group investigated the effects of changing the level of pressure in five bladders (ankle, calf, knee, lower thigh, and mid-thigh). They found that gradient pressure increased venous blood flow velocity to a greater extent than comparable levels of uniform pressure. They also concluded that an 18 to 8 mmHg gradient was ideal for a recumbent patient.
In a series of two studies, Partsch and Partsch set out to determine the amount of pressure needed to collapse the superficial veins in ambulatory patients.10,11 Narrowing or collapsing of the superficial veins is needed to increase venous blood flow velocity and relieve edema and swelling (this process is discussed in more detail in the Mechanism of Action section). The first study looked at the small sapehnous vein and the posterior tibial vein at the knee level.10 They found that initial narrowing occurred at a median pressure of 30-40mmHg when the person was sitting or standing. Full occlusion was achieved at a median pressure of 20-25mmHg in the supine position, 50-60mmHg in the sitting position, and 70mmHg in the standing position. The authors also noted that higher occlusion pressures were needed for larger veins, but the difference was not statistically significant. The second study looked at the saphenous vein at the mid-thigh level. They reported occlusion pressure of 20, 45, and 71mmHg in the supine, sitting, and standing positions.11 Results, however, were highly variable.
Aside from pressure, the stiffness of the stocking must also be considered. Stiffer stockings apply higher levels of pressure when the wearer is active. Van Geest et al. investigated the effects of stocking stiffness by looking at three types of products (ie, Type 1: low stiffness, 30 mmHg; Type 2: high stiffness, 30 mmHg; and Type 3: low stiffness, 34.5mmHg).12 This study showed that stiffer and/or higher pressure stockings achieved similar effects, resulting in statistically faster healing times compared to less stiff, lower pressure stockings. Unfortunately, stiffer and/or higher pressure stockings are generally harder to put on. This is particularly problematic for elderly or arthritic patients, so lower pressure stockings can be layered in order to attain the desired level of compression. For example, a first layer compression stocking can be applied with additional compression socks or stockings placed over it. If designed properly, the two layers will produce the higher compression levels required for wound and ulcer care. Additionally, if the under-stocking has sufficient compression, the wearer can leave this layer on at night (ie, when they are recumbent), but enjoy the benefits of higher compression when they are ambulatory.
INTERMITTENT PNEUMATIC COMPRESSION (IPC) SYSTEMS
IPC’s consist of a pump and a bladder(s) that is periodically inflated/deflated according to a pre-defined regimen. Single bladders can be used to deliver uniform pressure, or a system of bladders can be combined to achieve a graduated profile.
IPC’s have shown mixed results for improving wound and ulcer healing. Two studies found no significant difference between the use of IPC’s versus compression bandages or stockings.13,14 Other studies have investigated the effects of using IPC’s to supplement conventional treatment with bandages or stockings. Two studies found a significant improvement in healing time, while another study reported no difference.13,15 However, the two studies that reported a significant difference used a sequential compression regimen, whereas the other study used a single bladder to deliver uniform levels of pressure. This finding seems to further advocate the use of a graduated versus uniform compression regimen.9
VASCULAR MECHANICS 101
While many people seem to have heard of compression therapy, in particular compression hosiery and bandages, the details of its mechanism of action remain unclear. In order to understand why compression is needed, I will briefly review the anatomy and physiology of the peripheral vascular system.
The peripheral vascular system can be thought of as containing two sub-systems: the superficial and the deep. Blood normally flows from the superficial veins, to the deep veins, and back to the heart. One-way valves connecting the two help to prevent backflow. However, when these valves start to deteriorate, they become incompetent and blood begins to pool in the superficial system. This increased fluid accumulation causes the veins to become enlarged (varicosed), and pressure increases locally. Fluid can also be forced into the surrounding tissue, resulting in swelling and edema. If this is left untreated and the leg continues to swell, the skin will eventually break down, resulting in the formation of a venous leg ulcer. Oxygen delivery is also disrupted, causing the tissue to become necrotic.
MECHANISM OF ACTION
The mechanism(s) of action of compression therapy is not fully understood. However, it has been shown that compression increases venous blood flow velocity by causing a narrowing of the superficial veins.16 This increased velocity moves more blood back through the deep system and to the heart, and helps prevent dangerous blood clots from forming. Additionally, if compression is applied in a graduated manner (ie, with the most pressure being applied distally), a pressure gradient favoring blood flow back to the heart is created. By preventing pooling, the pressure on the surrounding tissue is relieved, and the filtration-diffusion equilibrium is restored.6,7 Also, simply by applying compression, further swelling is restricted. If ulcers have formed, this reduction in volume allows the wound to close and begin to heal.
In general, lower levels of pressure are applied for less critical conditions (ie, treatment for tired, aching legs and athletics), or when the wearer is expected to remain immobile for long periods of time (ie, on a long flight or during prolonged bed rest to prevent DVT).6 Higher levels or pressure are used to treat more acute conditions (ie, edema or wound and ulcer care).5,6
Because the mechanism(s) of action of compression therapy is not well understood, there are disagreements concerning the ideal level of pressure needed to achieve significant improvements. Different classifications and standards (ie, test procedures) for products among countries are partially to blame for this confusion (see Table 1 in the Print Version). This makes it difficult to sort through literature reporting on the effects of compression therapy.
In Europe, an effort is currently underway to develop a unified classification system (CEN) for compression garments. However, the U.S. currently does not use a defined standard testing system. This has forced many manufacturers to adopt one of the European specifications. (ie, the British/BSI or the German/RAL). With respect to HCPCS descriptions, compression hosiery is defined as providing compression of 18-30mmHg, 30-40mmHg, and 40-50mmHg with no testing specification referenced. Unfortunately, these do not align accurately with the European standards, adding to the confusion. Additionally, the 18-30mmHg HCPCS range is very broad, and covers stockings that could be used for treating everything from minor varicose veins to chronic venous insufficiency.
The manner in which compression products are measured also differs between countries. Additionally, recent studies have revealed discrepancies concerning the quoted pressure levels and those measured in practice17,18 This means that the “same” stocking developed by different manufacturers can deliver different amounts of pressure depending upon what device was used to write the specification.
Traditionally, the pressure profiles of medical compression products are extrapolated from tension measurements using LaPlace’s Law: P = T/r (where P is the interface pressure, T is the amount of tension in the fabric, and r is the radius of the limb). The HATRA (Segar Design)19 and the HOSY (Forschungsinstitut Hohenstein)20 are the two most common devices for characterizing compression stockings. However, these devices fail to capture changes to the pressure profile resulting from complex limb geometries, differences in the shape of the limb, and changes to the mechanical properties of the stocking over time.21
The pressure profiles can be directly measured directly using the SIGG-test (SIGaT-Sigvaris Interface-pressure Gauge advanced Tester), HAID-test (modified by Mϋhe et al.), and the Borgnis Medical Stocking Tester (MST). The SIGG- and modified HAID-tests use an air-filled bladder worn under the garment, and determine the pressure profile based upon the back-pressure.21,22 The MST device features a thin tube that is placed between the limb and compression garment.21 Air is slowly pumped in to the system until the electrical contacts in the tube separate. While simple, these tests tend to give high readings because the bladders/tubes balloon from the leg, causing pressure spikes.22 In addition to these pneumatic solutions, the Van Der Molen sensor and various piezoelectric sensors have been applied for directly measuring interface pressure.17,22 However, there exists no standard system for measuring pressure beneath a compression stocking while it is being worn.
Again, the European Union is trying to agree on a common standard for testing compression garments. Although a movement was made to adopt the HATRA testing device, discussions are still underway in light of relatively recent studies indicating that indirect techniques do not correlate well with direct measurements on the limb. Other issues which must be resolved before a standard is written include: (1) where the measurement points should be located, (2) how stiffness should be quantified, and (3) what procedures for wash-testing and durability should be adopted.
Since the U.S. has not adopted a standard testing protocol, most of the stockings sold here are tested using either the BSI or RAL standards.
Compression therapy, which can be delivered in the form of bandages, stockings, or IPC’s, can be used to treat a wide variety of conditions. Each product has its associated advantages and disadvantages. For example, compression bandages and stockings can be worn when a person is up and moving around, but the user must be seated in order to use an IPC device. However, the compression profile delivered by an IPC device can be adjusted on-the-fly, but bandages require a re-wrap and stockings require a new prescription.
In terms of wound and ulcer management, compression therapy has been shown to significantly reduce healing times. Factors such as the amount of pressure applied and the stiffness of the material can have an influence on clinical outcomes. Compression therapy could be improved through standardization. This includes developing common definitions for products between countries, as well as devising a method for measuring the pressure being applied by the garment or device while it is being worn.
Meghan Hegarty (MS) is a graduate student in biomedical engineering at North Carolina State University. She is a research assistant with the Center for Robotics and Intelligent Machines, and is working to assess the health benefits of compression stockings.