Are the Circulator Boot Systems Unique?

What do people ask us?

Why a rigid boot? Newton's 3rd Law states that to every action there is an equal and opposite reaction. When a compression bag inflates around the leg, it pushes against the leg on one side of the bag and, in the case of a rigid boot, against the stable walls and ends of the boot; the leg can be compressed while the wall of the boot cannot. The energy is, hence, directed against the leg. In the real world, there is a big difference between a cannon and a bazooka; the charge between the end of the cannon and the shell pushes the shell on its way while the bazooka requires a rocket on its projectile to continually accelerate it.

Why a boot at all? Why not use cuffs? Cuffs collapse between compressions. Air must first be introduced to fully inflate the cuff before additional air will raise the cuff pressure. From Boyle's Gas Law, one can calculate that a collapsed cuff requires 106.8% of its distended volume to achieve a compression pressure of 1 PSI. Further, as the cuff inflates it pushes the volume of blood beneath it both proximally out of the leg and distally against the venous valves potentially distending or rupturing them.(http://www.circulatorboot.com/introduction/VascPhys.html). Finally, the elaboration of various endothelial factors is proportional to the volume of tissue being compressed. Obviously, the production of nitric oxide, prostacyclin and fibrinolysins produced by massaging a finger is far far less than that produced by pumping on a whole leg.

Why not use multiple cuffs as opposed to your single boot compression bag? Each cuff pushes the fluid contents below it both proximally and distally. Any exposed tissue between the cuffs can be seen to swell as the cuffs are inflated; the swelling represents a loss of energy. If the distal cuff has a higher pressure than the proximal cuff, it obstructs flow to the distal portions of the leg; if the proximal cuff has the higher pressure, it obstructs venous return. A single compression bag guarantees equal pressure on all parts of the leg.

Why cardiosynchronous? Why not just pump every few seconds? Water is non-compressible. While the actual stroke volume of each heart beat remains in the ascending aorta, the pressure wave its ejection produced travels rapidly to the legs during late systole and early diastole. Indeed, the reflected waveform in ultrasound tracings of the femoral artery is normally seen to rapidly follow the peak of the flow into the leg. End-diastolic compressions allow the waveform and its accompanying blood volumes to enter the leg. Compressions during systole significantly increase cardiac afterload decreasing cardiac output in ASHD patients and block the entrance of the pulse wave into the leg, while end-diastolic compressions increase pre-load, decrease afterload, increase cardiac output and stroke volume and allow the inflow of blood into the leg where the compressions can help disseminate it throughout the tissue.. Indeed, some patients will experience numbness of the foot when the Circulator Boot is used in the automatic mode independent of the heartbeat and find the numbness disappears when it is switched to the end-diastolic mode.

Why a monitor with a computer? Why not just release the leg with the detection of a QRS complex? Our early monitors did just that. However, if the patient skipped a beat the boot kept inflating until a QRS was detected and excessive pressure was applied to the leg. We needed a means to either control pressure with each compression or a means to ensure a stable compression time. Answer: (1) Build a monitor that tracks the pulse rate and the RR interval; (2) Have a dial-in that sets an appropriate compression time; and (3) Have the monitor subtract the compression time from the calculated next RR interval and use the difference as a delay time between the QRS and the pre-set compression time thus placing the compression in end-diastole. These features, not only appropriately time the compression time but free up the boot technician who previously had to observe the monitor lights to be sure the compressions were appropriate for the patient's heart rate.

Why try to release the leg 0.04 seconds before anticipated next QRS complex? The column of blood in the aorta may be likened to a vertical yardstick. If you pull the dependent end rapidly down, the top end, of course, drops an equal amount. Likewise, when the boot explosively deflates, the column of blood is left unsupported and falls. For a significant reduction in cardiac afterload to occur, the yardstick need only fall the distance needed to accommodate a portion of the the stroke volume of the heart. Considering also the inertia of our apparatus, we have determined that we best accomplish these things by ending the compression time 0.04 seconds before the next anticipated QRS complex.

Why build a monitor that tries to anticipate the next beat in atrial fibrillation? Many of our patients have had atrial fibrillation which has made it difficult to set the compressions in end-diastole. Having built a monitor to handle this arrhythmia, we have essentially handled all rhythm disturbances. Further, the boot has been successful in/or associated with the conversion of some patients with recent onset atrial fibrillation to normal sinus rhythm. The rationale being in such cases that reduction in afterload increases stroke volume and atrial emptying, which in turn may decrease the atrial dilatation commonly associated with the atrial fibrillation.

Pumping at 30 inches of water pressure in the Long Boots and 45 inches in the Miniboot? Historically we thought of the columns of water from the knee and ankle to the base of the heart. These pressures correspond to 56.2 and 84.9 mm Hg or 1.09 and 1.63 PSI respectively, values close to normal diastolic pressures at the respective levels of the leg. Pumping at diastolic pressures is preferable to avoid pumping arterial blood backward and to always allow systolic flow to enter the legs. When possible the boot bags enclose six inches of normally vascularized tissue. The boot compressions are designed to disseminate blood to the low pressure areas. Finally, when the boot releases the leg, it is releasing a pressure the aorta is currently experiencing thus accomplishing the desired decrease in afterload. Pressures in the Long Boots much above 30 inches of water produce discomfort in the upper thighs for many patients. Pressures above 45 inches of water is the Miniboot increase the possibility of "march" fractures in patients with osteoporosis.

Must we buy three different Long Boots? If you want to treat most all people, yes. People do come in different sizes and the Long Boot must conform to the leg sufficiently to minimize dead space around the leg if effective rapid compressions are to be produced.

Are we stuck with Circulator Boot Corporation being our only supplier? If you buy a Ford car, you will likely find appropriate spare parts at a Ford dealer. If you want your Circulator Boots to work appropriately, you do well to use the components designed by Circulator Boot Corporation for their boots. Boot compression bags are a case in point. They have a bursting threshold as a safety factor. As they do not collapse to any degree between compressions, they require only the 6.8% volume of the dead space around the leg to achieve therapeutic pressure. Circulator Boot Corporation cannot guarantee that other bags will achieve appropriate pressures. Finally, each patient has their own disposable bag which (a) decreases the chances for cross-contamination among patients and (b) for a given patient is easily repaired for longer life with Scotch Tape.

When is therapy with the Circulator Boot indicated as opposed to therapy with other devices? While the Circulator Boot is a vascular support device and could be used in all cases of ischemia, osteomyelitis and cellulitis, obviously many cases can heal without it. Extremely advanced cases, like cases #1 and #2 in our case history section, likely could not have been healed by any other means... and would have been healed sooner if referred for therapy sooner. In general, if patients seem to be responding briskly to the therapies applied to them, the Circulator Boot is not necessary. If, however, infection is rapidly progressing and/or the vascular laboratory data suggests healing is unlikely (transcutaneous PO2 zero to 20 mmHg), immediate referral for Circulator Boot therapy is desirable.

The future? We hope to see our boots in every hospital, clinic and nursing home. As you may have noted, we have had no marketing program in the past in the belief that the world will come to us when it is appreciated that we can do what others cannot. We will look for help in developing such a marketing program. We will continue to make the effort to see that our designs are as appropriate and modern as possible. Good booting to all who have read this far. Please do come visit our booth at the World Union of Wound Healing Societies Meeting in Toronto, June 4th-8th, 2008.