Electrical stimulation of the foot can increase blood flow out of the leg. This increased
blood flow can prevent blood clots from forming in the leg veins.
Blood clots in the leg veins can break off and form life-threatening blood clots in the
Intermittent external pneumatic (air) compression of the foot is already used to increase
blood flow in at risk patients.
Hypothesis: Electrical stimulation of the foot increases blood flow out of the legs to the
same degree as intermittent external pneumatic (air) compression of the foot.
ABSTRACT Background: Venous stasis caused by immobility is an important risk factor for
venous thromboembolic disease. This is especially true for orthopedic patients with multiple
trauma and those undergoing other orthopedic procedures. A safe and convenient method for
reducing venous stasis would be useful for preventing venous thrombosis in patients while in
hospital and particularly after discharge during rehabilitation. In a prior study, we
demonstrated that electrical stimulation of the foot was a safe and convenient method for
counteracting venous stasis. In this study, we compare the effects on venous blood flow of
intermittent pneumatic compression, an established method, to electrical stimulation of the
Methods: 40 healthy volunteers aged 50 - 80 were seated for 4 hours during which they
received mild electrical stimulation of the sole of the foot (plantar plexus of muscles) or
intermittent pneumatic compression. Popliteal and femoral venous blood flow velocities were
measured via Doppler ultrasound. Blood flow in the non-stimulated or non-compressed lower
extremity served as a simultaneous control. Subjects completed a questionnaire regarding
their acceptance and tolerance of both treatments.
INTRODUCTION Venous thrombosis and pulmonary embolism or venous thromboembolism (VTE) are
important complications of medical and surgical conditions that are associated with
prolonged immobilization. This is especially true for orthopedic patients with multiple
trauma and those undergoing other orthopedic procedures. Immobilization is also a major
contributor to the increased risk of VTE associated with prolonged air travel.
Despite good evidence that prophylaxis is effective, there is widespread under utilization
of prophylaxis for VTE following major surgical procedures as well as medical conditions
that produce weakness or prolonged bed rest. There is also good evidence that the risk of
VTE continues for weeks after major orthopedic as well as other types of surgery. It is now
recognized that VTE occurring in the hospital and outside the hospital setting is a single
entity and that extended prophylaxis with anticoagulants reduces the risk.
Anticoagulant prophylaxis after hospital discharge although indicated in certain high risk
groups is inconvenient since the recommended methods, LMWH and fondaparinux must be
administered by subcutaneous injection and warfarin requires laboratory monitoring.
Physical methods that increase blood flow in the leg veins are effective for reducing venous
thrombosis in high-risk hospitalized medical and surgical patients. These methods include:
high intensity electrical calf stimulation during surgery, graduated compression stockings
and intermittent pneumatic compression of the leg or foot. Of these, only graduated
compression stockings, which are not very effective, can be used after hospital discharge.
Graduated compression stockings, however, cannot be adapted to fit all leg shapes, may be
improperly applied, have a tendency to slip down the leg and are found to be uncomfortable
by many patients. High intensity electrical calf muscle stimulation is painful and can only
be used during general anesthesia. AC powered external pneumatic compression can only be
used while the patient is fully immobilized. Thus, alternative convenient methods are
needed which can be used both in the immobilized and partly mobile patient, particularly
after hospital discharge.
We have attempted to overcome the limitations of currently available physical devices by
using mild electrical stimulation of the plantar muscles of the feet. Each electrical
discharge elicits a foot twitch that causes the intrinsic foot muscles to contract. This
contraction compresses the plantar plexus of veins, thereby increasing venous velocity in
the popliteal and femoral veins that is transmitted proximally up the leg veins.
Our plantar foot stimulation device is powered by a 9-volt battery and small enough to be
inserted into a sock. It has the potential to be worn while a patient is immobile, standing
or walking, and therefore is suitable for use both during the initial period of
immobilization and throughout convalescence.
In an earlier study we reported that mild electrical stimulation of the plantar foot muscles
caused an increase in blood flow comparable to that produced by direct calf stimulation.
The aim of this new study is to determine if, over a 4 hour period, mild electrical
stimulation of the plantar foot muscles increases venous blood flow velocity to the same
degree as intermittent pneumatic compression (IPC) of the leg in both obese and non-obese
MATERIALS AND METHODS IRB approval and informed consent was obtained from all subjects.
Forty healthy subjects (N = 40) between the ages of 50 to 80 participated in the study. Half
of the subjects (N = 20) were non-obese with a Body Mass Index (BMI) < 30. The other half of
the subjects (N = 20) were obese with a BMI > 30. Exclusion criterion included a prior
history of deep vein thrombosis or pulmonary embolism, or any trauma or surgery involving
any part of the lower extremities.
Subjects were studied over 2 sessions. At each session, subjects received either electrical
foot stimulation or intermittent pneumatic compression of one foot. The other lower
extremity served as a control. Subjects received either therapy at one session and the other
therapy at a second session at least 48 hours later. The right or left leg of each subject
was randomly assigned as the same control leg for both studies. The type of therapy given at
the first session was also randomly assigned.
The study otherwise followed the protocol used in our initial study of electrical foot
stimulation. Subjects were seated for 4 hours in chairs placed at a fixed distance apart.
They were constantly monitored throughout the study to ensure that they remained seated.
Subjects were allowed to use a bathroom located several feet away only twice during the 4
hour period. During the 4 hour study period subjects were offered a maximum of 16 ounces of
fluid and a normal lunch.
Electrical foot stimulation was produced by surface electrodes placed on the sole of the
foot over the plantar muscle group. Electrical stimulation was delivered by the Focus™
Neuromuscular Stimulation System, Empi, Inc. (St. Paul, MN.) The crucial stimulus
parameters were: biphasic symmetrical square wave at 50 pulses per second, phase duration of
300 microseconds, a starting ramp up time of 2 seconds and a finishing ramp down time of 2
seconds per stimulation cycle, and a stimulation cycle of 12 seconds "on" and 48 seconds
"off" per minute. Stimulation was increased to an intensity just sufficient to create a
slight visible muscle twitch. This level of intensity caused no evident discomfort in any of
the subjects in our first study. Subjects were continually monitored throughout this study
for any indication of discomfort.
Intermittent pneumatic compression of the leg consisted of external intermittent pneumatic
compression with a knee high device. A Tyco Healthcare Kendall Novamedix A-V impulse system®
Model 6060 (Mansfield, MA 02048) was used. Operating parameters were: 130mmHg impulse
pressure with a 3 second impulse duration; "Program Preset 1" for deep vein thrombosis
prophylaxis. The compression followed the approved standard patient protocol used at our
institution detailed in "Utilization of Intermittent Pneumatic Compression (IPC) Stockings
for DVT Prophylaxis".
Popliteal and femoral venous peak blood flow velocities were measured bilaterally using a
Doppler ultrasound device at 0, 15, 120, and 240 minutes. The same ultrasound technician
obtained all Doppler studies on all subjects throughout the study. All Doppler tracings were
be read by the same independent reader in a blinded fashion. Immediately following
completion of each 4 hour session of electrical foot stimulation or intermittent pneumatic
compression, subjects were asked to complete a brief questionnaire regarding their
acceptance and tolerance of electrical stimulation or intermittent pneumatic compression.
STATISTICAL METHODS This study utilized a repeated measures design with two within group
factors: time to measurement, and stimulation (stimulation, control). Stimulation groups
[electrical foot stimulation and intermittent pneumatic compression (IPC)] were not
independent. Blood flow measurements (at time = 120, 240) were analyzed with t tests and a
mixed model. Within the mixed model, the group effect is a fixed effect, and the subject
parameter is a random effect. The primary research question was the non-inferiority of the
experimental treatment (electrical foot stimulation) relative to standard treatment
(intermittent pneumatic compression). The non-inferiority index was 5.0 cm/sec; this index
was formulated prior to analysis. The questionnaire results were analyzed using Fisher's
Exact test. P-values that were less than 0.05 were considered to be statistically
significant. All analyses were done with SAS 9.1, Cary, NC.
- Healthy volunteers
- Venous or arterial disease of the lower limbs
- Cardiac pacemaker
- Known allergy to materials of surface electrodes
- Neurologic disorder
- Lower extremity fracture history
- History of joint replacement surgery
- Anticoagulation therapy other than aspirin