Medically reviewed by Dr. Michael Darder OBGYN — Written by Kari Johnson
Published July 29th, 2020
Millimeter of Mercury (mmHg) describes the pressure generated by a column of mercury. The unit of measurement is defined as: "Equal to the pressure exerted by a column of mercury 1 millimeter high at 0°C and under the acceleration of gravity." (-Merriam Webster)
This approximate measure has been used since the 1640's. Prior to the advent of the metric system, a comparable unit was called a torr.
For a pressure measuring 15-25 mmHg:
Think of a force that is 15-20 times greater than the one exerted by a column of mercury under the circumstances described above.
If you're talking about blood pressure, 15-25 mmHg would be a low measurement. 15-25 mmHG would be an extremely low measurement for atmospheric pressure (which is normally around 760 mmHg), and one that would put us all in considerable danger.
For compression socks, on the other hand, 15-20 mmHg works perfectly. That compression range offers a number of significant health benefits, while remaining comfortable to wear. At Comrad, our Companion line features a new range of graduated compression of 15-25mmHg. We call it the “compression sweet spot.
What Are the Benefits of Compression Socks?
The health benefits of compression socks vary, depending on the amount of pressure that they exert on the lower legs. Graduated compression socks provide more pressure on the ankle and less pressure towards the calf. By pushing deoxygenated blood and waste fluid up the ankle towards the calf, graduated compression garments reduce swelling and assist the circulatory system.
Graduated compression socks and stockings come labeled with a pressure range, in which the lower number represents the amount of pressure at the calf and the higher number represents the amount of pressure at the ankle.
To understand the benefits of graduated compression, let's look at some of the pressure ranges available and the medical benefits that each range provides.
Light Compression: 8-15 mmHg
Light compression socks reduce minor leg swelling and discomfort caused by prolonged periods of sitting or standing. Pregnant women who hope to avoid spider veins and varicose veins during pregnancy often choose light compression because it's the most comfortable form of compression therapy.
Mild Compression: 15-20 mmHg
This compression range helps to prevent swelling, achy legs, and deep vein thrombosis, and is a popular choice for frequent flyers. Mild compression can also be used to alleviate pain from existing vascular problems, such as varicose veins.
Medium Compression: 20-30 mmHg (Medical Grade Class I)
Class I compression socks offer a number of health benefits. They relieve the symptoms of severe edema and lymphedema. In addition to relieving the milder symptoms of chronic venous insufficiency, medium compression also offers enough pressure for the management of severe symptoms like active ulcers. Plus, the symptoms of post-thrombotic syndrome (PTS), orthostatic hypotension, and superficial thrombophlebitis can be considerably reduced by applying medium compression. This is also an optimal compression level for athletic recovery and endurance.
Firm Compression: 30-40 mmHg (Medical Grade Class II)
Class II compression socks treat more severe cases of edema, post-thrombotic syndrome, orthostatic hypotension, and superficial thrombophlebitis. For patients at extreme risk of developing DVT, such as post-surgical patients, doctors often recommend firm compression.
Extra Firm Compression: 50-60 mmHg (Medical Grade Class III)
Class III compression socks can be used to treat acute lower body swelling, severe varicose veins, and existing cases of deep vein thrombosis. Extra firm compression garments can only be purchased through a medical supply store or a pharmacy and require a prescription.
How Do 15-25 mmHg Compression Socks Promote Good Circulation?
As mentioned above, mild compression socks can be used to reduce mild to moderate leg swelling and discomfort, prevent varicose and spider veins, reduce the risk of developing deep vein thrombosis, and alleviate the pain caused by varicose veins and other vascular problems. It may be helpful to take a look at how mild compression socks are used to treat and prevent these medical conditions.
Leg Swelling and Discomfort
Sitting or standing in the same position for a long period of time has been shown to cause discomfort, swelling, and increased risk of developing DVT. In occupations that require many hours of standing, employees find themselves at two-fold risk of incident heart disease compared to those who sit, according to one Canadian study. (Smith 31) When a person stands, his or her veins must work against the force of gravity to return deoxygenated blood and waste fluids to the heart. This puts additional strain on the circulatory system. According to the researchers, "The potential mechanisms linking prolonged standing to cardiovascular outcomes include blood pooling in the lower limbs, increased hydrostatic venous pressure, and enhanced oxidative stress." (27) For people who work long hours standing upright, knee high compression socks can help improve blood flow. In particular, the gradient compression that graduated compression socks provide can help to reduce the pooling of blood in the lower limbs and venous pressure and, by extension, reduce cardiovascular strain.
For those who sit for long periods of time, leg swelling and discomfort are also common complaints. As Deepak L. Bhatt, editor in chief of Harvard Heart Letter, explains, when you're seated, "...your leg muscles don't contract, which normally helps push blood back toward the heart." He says that swelling commonly occurs during any prolonged period of sitting, including rides in planes, buses, trains, and cars. Over-the-counter graduated compression socks can assist the veins by pushing fluid up from the ankle to the calf, allowing for a reduction in swelling and fatigue.
Medical conditions such as lymphedema, pregnancy, and venous disease may also cause swelling in the lower legs. Compression socks, hosiery, and other compression garments work to reduce swelling and discomfort, whether it's caused by sitting, standing, lymphedema, pregnancy, or vascular problems.
Chronic Venous Insufficiency
Arteries carry blood away from the heart and to the extremities, then blood travels through veins on the return journey to the heart. To prevent blood from flowing down with the force of gravity, veins contain small valves that only permit blood flow in one direction. When a person develops chronic venous insufficiency (CVI), those small valves within the vein fail. This allows the blood to flow in the wrong direction and become stagnant, leading to the formation of varicose or spider veins. Bulging veins, dilated blood vessels, discomfort, swelling, and ulcers may result.
Some people have risk factors that increase their chances of developing CVI, including pregnant women and those over 50. Studies have shown that compression socks may lessen your chances of developing venous failure. Vascular surgeon Dr. Claire Griffin explains, "Compression socks help prevent the backup of blood, which is what leads to incompetent veins, and incompetent veins is what leads to varicose veins." ("Compression") For those who have already developed CVI, compression socks work to treat the symptoms, which can include fatigue, swelling, unsightly veins, and ulcers. Griffen says, "They make a difference, and often people notice an immediate symptomatic improvement..." To completely eliminate varicose veins, medical interventions, such as sclerotherapy treatment or vein ligation, are required.
Deep Vein Thrombosis
Deep vein thrombosis occurs when blood clots form in the deep veins. Sometimes, people call DVT "economy class syndrome" because the formation of deep vein blood clots is especially common in people who sit for long periods of time, as with those who take long-haul flights. DVT is particularly dangerous because the blood clots have the potential to break off and form blockages. For example, pulmonary embolism, a potentially fatal condition, happens when a blood clot moves to lungs, causing a blockage. Not only do compression socks help prevent DVT, but they are also recommended for patients who have existing blood clots in the deep veins.
Studies indicate that graduated compression therapy reduces the risk of blood clots during long-haul flights (Clarke) and after operations (Sachdeva). Moreover, a 2017 review of scientific literature asserts that people with DVT can reduce their chances of developing post thrombotic syndrome, a condition that develops in one third of people with DVT, by wearing compression garments. Symptoms of post thrombotic syndrome include chronic pain, swelling, and skin changes in the legs. The authors write, "We found that people with DVT who wear elastic compression stockings are less likely to develop PTS..." (Appelen) To prevent DVT, 15-20 mmHg compression socks should be sufficient; however, to treat the symptoms of DVT and post thrombotic syndrome, most doctors recommend medium compression.
Where Can You Buy 15-25 mmHg Compression Socks?
If you're shopping for mild compression socks with a 15-20 millimeters of mercury range, you can find them online, in pharmacies, and in medical supply stores. At Comrad, we offer Guides, which come in a soft, cozy, moisture-wicking Merino wool. For something with a bit more support, we also offer 15-25 mmHg Companions, which occupy the "sweet spot" between medium and mild compression levels. Companions are mild enough to be comfortable, but strong enough to relieve the symptoms of DVT and moderate varicose veins.
Unlike most other compression socks and stockings, which look like medical garments, our socks offer both form and function. They're designed to be worn multiple times, and they feature antimicrobial fabrics that keep your feet looking (and smelling) fresh. For anyone who sits, stands, walks, or flies, compression therapy gives you a great way to boost your circulation and promote good health.
Sources:
Appelen D, van Loo E, Prins MH, Neumann MHAM, and Kolbach DN. "Compression therapy for prevention of post-thrombotic syndrome." Cochrane Database of Systematic Reviews, Issue 9, 2017, https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004174.pub3/epdf/abstract.
Bhatt, Deepak L. MD, MPH. “Ask the doctor: Compression stockings for long-distance travel?” Harvard Health Publishing, Harvard Medical School, Aug 2014, https://www.health.harvard.edu/heart-health/ask-the-doctor-compression-stockings-for-long-distance-travel-.
Clarke MJ, Broderick C, Hopewell S, Juszczak E, Eisinga A. "Compression stockings for preventing deep vein thrombosis in airline passengers." Cochrane Database of Systematic Reviews, Iss. 9, 2016, https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004002.pub3/abstract.
“Compression socks can help prevent varicose veins.” The Scope, University of Utah, Jan 10, 2018, https://healthcare.utah.edu/the-scope/shows.php?shows=0_u6yd3xaw.
Health Quality Ontario. “Compression Stockings for the Prevention of Venous Leg Ulcer Recurrence: A Health Technology Assessment.” Ontario health technology assessment series vol. 19, 2 1-86. 19 Feb. 2019, https://pubmed.ncbi.nlm.nih.gov/30828407/.
"mm Hg." Merriam-Webster.com. Merriam-Webster, 2020, https://www.merriam-webster.com/medical/mm%20Hg.
Sachdeva, Ashwin. “Graduated compression stockings for prevention of deep vein thrombosis during a hospital stay,” Cochrane Vascular Group, Nov 3, 2018, https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD001484.pub4/abstract.
Smith, P., Ma, H., Glazier R. H., Gilbert-Ouimet, M., Mustard, C. "The Relationship Between Occupational Standing and Sitting and Incident Heart Disease Over a 12-Year Period in Ontario, Canada." American Journal of Epidemiology, vol. 187, Iss. 1, Jan. 2018, pp. 27–33, https://academic.oup.com/aje/article/187/1/27/4081581.
Van Uffelen, J.G.Z., Wong, J., Chau, J. Y., van der Ploeg, H. P., Riphagen, I. Gilson, N. D., Burton, N. W, Healy, G. N., Thorp, A. A., Clark, B. K., Gardiner, P. A., Dunstan, D. W., Bauman, A., Owen, N., and Brown, W. J. "Occupational Sitting and Health Risks: A Systematic Review." American Journal of Preventive Medicine, vol. 39, Iss. 4, 2010, pp. 379-388, https://www.sciencedirect.com/science/article/abs/pii/S0749379710004125.