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History of Suction-Pressure Boots
Physics and Lessons for Modern Boot Therapy
Benefits of Gravity
As seen in the figure below, the usage of pneumatic boots in medicine has a long history. The equipment reflects more the technology of the time than an understanding of vascular physiology. Various of these authors are listed in our library pneumatic boot section. The reference of Silverglade summarizes the success of these boots before they were abandoned in favor of surgical interventions allowed by the development of new antibiotics.
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Many ask why a suction phase is not incorporated into our Circulator Boot system. Suction does augment arterial flow into the leg, but it also impedes venous and lymphatic flow out of the leg and promotes edema. The thinner walled and more superficial veins are more affected than the deeper arteries. Further, the application of suction requires a seal at the junction of the vacuum chamber and the upper leg. An effective seal can be accomplished by adhesive materials or elastic bands. The latter, of course, impede arterial flow into the leg and venous and lymphatic flow out of the leg. The force of the elastic band bears a linear relationship to the amount of suction employed in the chamber. The more suction applied, the more the band must squeeze the leg to prevent air leaks. As shown in the vector analysis of pressure boots, the application of high pressure within the chamber pushes the tissue at the juncture of the upper leg and the chamber out of the chamber. With suction boots, the converse is true: the higher ambient pressure outside of the boot pushes tissue at the juncture into the boot and the ambient air pressure determines the tissue pressure at the junction of the chamber and the upper leg. Thus, all arterial, venous and lymphatic fluid channels get a boost of flow into the leg according to the difference between the pressure outside of the chamber and the pressure inside minus, of course, the pressure of the seal.
The suction-pressure boots were not cardiosynchronous like the Circulator Boot, but operated at much slower rates. Still, the tissue at the juncture of the chamber underwent considerable sheer force. It was forced into the chamber (suction phase) and extruded from the chamber (pressure phase) with the result that blistering and tissue breakdown were common problems. In contrast, the Circulator Long Boot in utilizing a single long double-walled bag required no seal or band. The end of the bag moves little while the tissue is modestly extruded during the pressurization of the boot. The sheer force of boot compression and the accompanying discomfort may be lessened in three ways: (1) usage of a full length boot bag that is stretched from the foot to the upper thigh so that inflation of the bag results in little movement up the thigh of the end of the bag; (2) placement of the end of the bag as close to the groin as possible (the tissue here is more fixed and cannot be pushed under the inginal ligament); and (3) use of the minimal effective inflation pressure. The suction-pressure boots obviously were/are not cardiosynchronous. Liu et al (Liu K et al: J Orthop Res 17: 415-20, 1999; J Orthop Res 17: 88-95, 1999; J Appl Physiol 92:559-66, 2002) have shown the importance of the speed with which a boot is inflated on its generation of nitrous oxide. Boots inflating in a half second or less generate sheer forces that boots inflating at slower rates like 5 seconds or more do not.
The fact that the flow of arteries is opposite that of veins and lymphatics has been troublesome. The application of suction like sequential boots acting in a proximal to distal direction especially decrease emptying of the thin-walled superficial veins. Venous back pressure can significantly decrease arterial inflow. To improve venous emptying, the suction pressure boots were commonly use in the supine position with the feet modestly elevated. The elevation, of course, had modest negative effect on arterial inflow.
Can treatment modalities be combined? Specifically, can a vacuum device be placed on a wound within the Circulator Boot? Yes, the clinician may use his/her judgement in this regard. One does well, however, to consider the effects of vacuum therapy in the past. "Cup therapy" is an old therapy still performed in many parts of the world. In this procedure, the inside of a cup may be heated with a match. The cup is rapidly placed over the lesion to be treated and as the gas within the cup cools, a vacuum is created within the cup. If the pressure inside the cup is reduced from one atmosphere (14.7 pounds/square inch) to perhaps to half an atmosphere (7.35 pounds/square inch), the 14.7 pounds is pushing the cup down on the lesion while 7.35 pounds is pushing the cup up. The 7.35 pound/square inch pressure difference on the cup surface is all applied to the rim of the cup which cuts into the tissue. Placing such a cup within a pressure boot adds to the pressure difference and increases the force the cup is pressed against the tissue. As one pound/square inch equals 55 mm Hg and the pressure in ischemic feet is commonly under 55 mm Hg, such force, hence, may block blood flow to the lesion. Obviously, such an arrangement has great potential for harm. It is one thing placing a cup over a large soft tissue mass such as a buttock, which has a rich deep blood supply, and another thing placing the cup over skin on the shin, for example, where the blood supply is more superficial and subject to interruption with the application of pressure.
Is it possible to devise an apparatus that operates in a fashion the provides an increasing gradient of arterial pressure from groin to feet and still empties the venous and lymphatic compartments thus increasing the arteriovenous gradient? Yes, the Circulator Boot does that! How? The device is designed to be used in the sitting position. Depending on the needs of the patient, the Circulator Boot Manual instructs the treating doctor to place the feet as low as necessary. A boot inflation pressure should be used to overcome the column of venous blood. Thus, with the legs extended horizontally and the patient sitting erect, the sternal angle is approximately 20 inches above the treatment table and a boot pressure over 20 inches of water pressure may be assumed to be adequate to return venous blood to the heart; we recommend usage of 30 inches of water pressure. For the Miniboot patient sitting in a chair with the sternal angle about 40 inches off the floor, we recommend an inflation pressure equal 45 inches of water. Gravity is providing our desired pressure gradient down the arterial tree. Properly utilized, the Circulator Boot is timed to let the heart and gravity prime the leg with each pulse wave and the boot inflation disseminates the blood volume around the leg while at the same time expelling the volume of the venous and lymphatic channels.
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Comparison of Angioplasty, Bypass and Circulator Boot therapies
Circulator Boot versus ECP
Circulator Boot and Topical Oxygen Therapy
Pneumatic Boot Abstracts,