Perspectives in Circulation Today

The Art of Pneumatic Boot Therapy

Patients with advanced vascular disease: None of the above observations have benefited patients with advanced heart disease or limb-threatening PVD. With nothing apparently to be lost for the patient, invasive procedures have flourished since the development of antibiotics to counter wound infections and an adequate blood bank to restore blood volumes. Few if any of these procedures have been justified by controlled studies but have greatly increased hospital income. (See our previous Newsletter at http://www.circulatorboot.com/Newsletter/vol2numb10.html. And many patients are not candidates for either the cardiac or peripheral vascular procedures. What to do with these advanced cases? Enter mechanical vascular support devices.

Early Mechanical Vascular Support Devices: Perhaps the earliest vascular support device was reported by Murray in 1812. A variety of others were described over the next 100 years (Dillon, Angiology 37:47-55, 1986). Clinical success in healing ischemic ulcers was described with the use of the suction pressure boots of Reid and Herrman(1922) and Landis and Gibbon (1933), actually impressive results considering the fact that they were in the pre-antibiotic era. None of these devices were cardiosynchronous or considered cardiac support devices. Indeed, when they were pressurized, they decreased arterial inflow into the leg and increased cardiac afterload

Early Widespread Usage of Vascular Pneumatic Devices was achieved with the use of lymphedema pumps and intermittently pressurized leggings for the prophylaxis of thromboembolism. The former have to be used with care in patients at risk of congestive heart failure both because in impeding arterial runoff into the legs they increase cardiac afterload and because they increase the return of fluid to the lungs which may already be overloaded with fluid. The mechanism of action of the latter became the subject of numerous clinical research papers. The benefits of both were initially attributed to their mechanical action in moving fluid and blood (preventing stasis).

The Endothelium, The Biggest Endocrine Organ in the Body: The endothelium is not only a target for many of the classical hormones but itself elaborates hormones, fibrinolysins, and various growth factors (www.circulatorboot.com/Newsletter/vol2numb7.html) explaining in part the action of our vascular support devices. Knight (1976), for example, showed that pumping on arms significantly deceased euglobulin lysis times and the incidence of thrombi in the legs. Tarnay et al (1980) showed that the fibrinolytic effect increased as the volume of tissue being pumped increased. Toyota et al (1999) showed that the increase in coronary blood flow associated with the use of the aortic balloon is blocked by inhibiting the production of nitric oxide. Subsequently, studies involving the ECP (External Counter-Pulsation) devices have shown their use is associated with increases in nitric oxide, prostcyclin, atrial natriuretic peptide (but not brain natriuretic peptide), vascular endothelial growth factors and fibrinolysins and a decrease in endothelin-1. Further, Braith et al (2010) showed EECP decreased the proinflammatory cytokines tumor necrosis factor-α (-16% versus +12%), monocyte chemoattractant protein-1 (-13% versus +0.2%), soluble vascular cell adhesion molecule-1 (-6% versus +1%), high-sensitivity C-reactive protein (-32% versus +5%), and the lipid peroxidation marker 8-isoprostane (-21% versus +1.3%) in treatment versus sham groups, respectively (all P<0.05). No such systemic biochemical benefits accompany invasive vascular procedures.

Sheer Forces and the Importance of Timing.In vitro studies have shown that a rapid change in flow rates/pressure may stimulate the endothelial cell to elaborate nitric acid, for example (LI 2005). In vivo studies like those of Liu et al (1999 and 2002) showed that a vasodilatory response was marked if their device inflated in 0.5 seconds, diminished if it inflated over 5 seconds, and absent if it inflated over 10 seconds. The rapid inflation of the ECP cuffs (commonly 340 msec in duration, thus comprising both the time of inflation and time to deflation) supports the effectiveness of rapid inflation. The duration of the Circulator Boot pressure waves is again 0.34 to 0.42 seconds. Both the ECP and the Circulator Boot are cardiosynchronous and may provide a compression after each heartbeat. In contrast, the ArtAssist device operates independent of the heartbeat and provides a pulse every 20 seconds lasting three seconds in duration and is claimed to inflate over 0.3 seconds. During its 9 seconds of pressure it impedes blood flow into the leg and because of both its slow rate and the limited amount of tissue compressed, it may be expected to elicit less of a humoral response than either the ECP or the Circulator Boot. We are aware of no reports of the ArtAssist either eliciting a measured increase in any of the factors listed for the ECP or producing any systemic effect. It’s manufacturer, however, lists the generation of nitric acid as one of its likely benefits.

ECP/EECP timing vs that of the Circulator Boot: Both devices are queued off the QRS complex of the EKG. Historically, the ECP technician was taught to initiate compressions before the “J” of the pulse wave and to use elevation of the “J” as evidence of flow augmentation. The “J” represents closure of the aortic valve and commonly coincides with the end of the T-wave of the EKG. In elevating the “J” wave, hence, it is necessary to initiate ECP compressions in late systole or before the QT interval has elapsed. The normal QT interval is rate dependent and about 0.42 seconds for a pulse of 60 decreasing about 0.02 seconds for each increase of ten heartbeats per minute. Thus, given a pulse rate of 60, an R-R interval (time between QRS complexes) of 1 second, a QT of 0.42 sec, initiation of the compression at 0.38 sec after the QRS (seeking to demonstrate augmentation of the “J”) and a compression time of 0.340 seconds, decompression would begin 0.72 seconds after the QRS or in mid-diastole. Or given a pulse rate of 80, an R-R interval of 0.75 sec, a QT of 0.38 sec, initiation of the compression 0.34 sec after the QRS and again a compression time of 0.340 sec, decompression would begin 0.68 sec after the QRS or 0.07 sec before the next QRS. In contrast, studies with the Circulator Boot have shown that maximal unloading of the heart is achieved if the boot vents 0.04 sec before the next QRS complex. To accomplish this, the Circulator Boot monitor keeps a running average of the R-R intervals, applies a nomogram if necessary to predict the arrival of the next QRS complex and signals decompression 0.04 seconds before the anticipated arrival of the next QRS complex. The moment boot compressions are initiated is calculated on a beat by beat basis to continually allow a fixed compression time to end in end-diastole. Obviously, at some faster pulse rates both devices may have similar timing. But, in general, the goal differs between the two devices. The EECP attempts to heighten the diastolic coronary pressure in hopes of improving the pressure gradient across the myocardium and in doing so it pushes/expels blood from the legs and blocks inflow into the legs. Indeed, Werner et al (2007) found average flow volumes in the posterior tibial artery decreased 69% during EECP in patients thought to have no peripheral vascular disease. The Circulator Boot attempts to maximize afterload reduction to increase cardiac output and to delay leg compressions as much as possible to allow inflow into the legs. The higher compression pressures and earlier onset of pressure as classically used by the ECP may push some patients into heart failure. Recent recommended D/S pressure ratios have reduced this problem (Vijavaraghavan K et al 2005), Still, the ECP has been shown to adversely affect peripheral blood flow is contraindicated in the presence of significant PVD. The Circulator Boot is designed to help patients with PVD.

The physical apparatuses: The ECP consists of three cuffs that are inflated sequentially distal to proximal: one on the calves, one on the thighs and one on the buttocks. As they collapse between compressions, the early part of compression is spend in tensing the cuffs before pressure can rise. As the calf cuff inflates, fluid and blood are forced both distally and proximally. A pulse volume cuff on the distal leg and on the knee both may record a modest swelling as blood is forced both ways, distally stressing the venous valves. Again, as the thigh cuff inflates, fluid is forced both distally contributing to swelling of a knee cuff and again stressing the venous valves and proximally pushing blood into the pelvis. In contrast, the Long Circulator Boot employs a single leg bag within a rigid boot, both bag and boot extending from the high groin to the toes. It applies an even pressure to the legs avoiding stressing the veins. And the rigid boot does not collapse between compressions. Its design acts somewhat like a torpedo tube and expels the elastic soft tissue of the upper thigh. With decompression, the tissue rocks back into the boot giving the patient the sensation that it is exerting a negative pressure and, indeed, at this moment a pulse volume cuff around the upper thigh may record a pressure below baseline. Palpation of the femoral artery at this time may reveal the simultaneous arrival of the femoral pulse, which is unopposed in the Circulator Boot but blocked in the ECP. For that matter, any device which decreases the arterial flow into the legs, whether an inflated lymphedema boot or a tourniquet around the femoral arteries during bypass surgery (Henein MY et al, 1966) increases afterload and decreases cardiac output.
The ArtAssist consists of two cuffs: one around the calf and one around the midfoot. Inflation of the distal cuff occurs first and is followed a second later by inflation of the calf cuff. The pressures are factory set to 120 mm mercury and last three seconds. Three compressions are delivered a minute. During the nine seconds of inflation arterial inflow is blocked in patients with advanced arterial insufficiency and calf blood pressures below 120mm mercury and in such patients inflation of the cuffs may expel both arterial and venous blood from the lower legs. This system is best compared to the Circulator Miniboot which inflates a bag around the entire lower leg below the knee in end-diastole to a pressure of 85 mm mercury or 45 inches water pressure. As the latter commonly matches the hydrostatic pressure in the leg in the sitting position, it does not push the arterial column of blood out of the leg but disseminates it throughout the pressurized area of the leg.

Compressors. Both the ArtAssist and the ECP devices come equipped with appropriate compressors. The Circulator Boot does not, lessening the cost of each system but adding to the difficulty in launching a Circulator Boot program. On the other hand, every room in a hospital equipped with a compressed air line is a potential site for a Circulator Boot clinic. And if the clinician can appropriately estimate the size of his/her clinic, the purchase of a single compressor can provide air for multiple boot stations. Thus, one compressor in the basement provided compressed air for 16 stations in Bryn Mawr,

Clinical Application of the systems compared: The ECP devices. Reimbursement policies commonly dictate the usage of all systems. In the case of the ECP devices, Medicare has set a policy adopted by many insurance companies. Patients with disabling angina who are not considered reasonable candidates for invasive interventions such as PTCA or coronary bypass because their condition is inoperable, their coronary anatomy is not readily amenable to such procedures or they have co-morbid conditions which create excessive risk. Such a policy obviously encourages invasive procedures if they can be done. Again patients with Heart Failure who have ischemic or idiopathic cardiomyopathy, an Ejection Fraction <40% or co-morbid conditions that increase the risk of complications or revascularization procedures are covered. Listed precautions/contraindications have included the presence of an abdominal aortic aneurysms >3.0cm, severe aortic regurgitation or aortic valve disorder, phlebitis or deep vein thrombosis, blood pressure over 180/110 or under 80/50, uncontrolled atrial fibrillation, peripheral vascular disease, and severe pulmonary disease. The treatment is commonly approved for 35 sessions of one hour each over a seven week period which would deliver 35 x 60 x 75 or 157,500 compressions for a patient with a pulse of 75 if the hour appointments represented time actually receiving treatment and setup and breakdown times were not included in the hour.

ArtAssist: The Art Assist is advertised as potentially benefiting patients with diabetic/arterial foot ulcers, intermittent claudication and rest pain. Listed contraindications include infected limbs, limbs with suspected deep vein thrombi or arterial clots, during episodes of inflammatory phlebitis or pulmonary emboli, or when increased venous or lymphatic return is undesirable (congestive heart failure). Recommended for use three times daily for one hour each and for three to six months and delivering three compressions a minute, it would deliver 180 compressions an hour, 540 a day, 48,600 in three months and 97,200 over six months. The apparatus has the advantage of home use for those capable of and indeed willing to follow the recommended programs.

Circulator Boot: The Circulator Boot systems are the most flexible of the three devices. The area of treatment is chosen according to the individual needs of the patient. Treatment can be directed to the entire leg(s) from groin to toes, from groin to ankle, from knee to toes, or from the ankle to the toes. It can deliver end-diastolic compressions after each beat, every second or every third beat. In addition, it can be set to run on a clock mode compressing the leg from ten to 120 times a minute. It is commonly combined with local antibiotics either or both delivered by injection or included in soak solutions that may bathe the foot during therapy. Contraindications to Long Boot therapy include deep vein thrombi, severe aortic valvular regurgitation and symptomatic aortic aneurysms. Designed initially to help patients with heart failure/coronary heart disease and with peripheral arterial insufficiency, it has been used in patients with the many debilities that are commonly found in patients with peripheral arterial insufficiency. Thus in our Case History section on our website over 200 case histories illustrate its usage in patients with advanced ischemic leg disease, neuropathic ulcers, venous ulcers, necrotizing cellulitis, osteomyelitis, congestive heart failure, ongoing myocardial infarction, renal failure, trash feet and thromboembolic disease, Buerger’s disease, lymphedema, and small vessel disease in the leg (diabetic dermopathy) or areas remote from the legs (diabetic retinopathy). Linked to the heartbeat like the ECP, it delivers many more compressions in a given time period than the ArtAssist. We know of no other compression device capable of safely benefiting such a variety of vascular problems. The treatment has been commonly administered for 40 miinutes. This time period was arrived at empirically: patients commonly could not tolerate being "cooped up" for longer periods of time. Further, electrical impedance data commonly showed a steady increase in stroke volume and cardiac output during the first 20 minutes of Long Boot therapy and a leveling off thereafter. Again, as the Long Boot functions as a cardiac-assist device, it promotes urine production leading many patients to seek relief after 40 minutes of treatment.