A novel approach on pneumatic compression therapy for Deep Vein

International Conference on Embedded Systems - (ICES 2014)

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A novel approach on pneumatic compression therapy for Deep Vein Thrombosis Apoorva.S

Jithin Krishnan

Deepa Madathil

SBST VIT UNIVERSITY Vellore,Tamil Nadu, India [email protected]

BMT Wing SCTIMST Trivandrum, Kerala, India [email protected]

SBST VIT UNIVERSITY Vellore,Tamil Nadu, India [email protected]

Abstract – Sequential compression technique using external cuff is one of the well established treatment methods to prevent deep vein thrombosis in surgical especially the bed ridden patients. The proposed project describes equipment named EPCE (EXTERNAL PNEUMATIC COMPRESSION EQUIPMENT) for DVT (Deep Vein Thrombosis) treatment. This device has an array of bladders which is placed inside a cuff. The bladders are provided with closed loop monitoring of pressure levels in each bladder and are controlled by employing pneumatic valves which is driven by a microcontroller. The device is equipped with a more efficient air pump. This model ensures an increased life span of the air pump by controlling the timing chains of bladder inflation and deflation by PWM switching from the microcontroller. A power supply back up is also included in the device to serve in case of power failure for longer runs. Keywords: Deep vein thrombosis, modulation, closed loop monitoring.

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I. INTRODUCTION Deep vein thrombosis (DVT) can be referred to as the formation of blood clot, otherwise called thrombus, in the deep veins of human leg. It has the ability to cause serious and permanent damage to the leg such as post-thrombotic syndrome, or a lifethreatening pulmonary embolism. [38] In United States, every year around 600,000 new cases are diagnosed. One among every 100 people who were detected with DVT dies. It is being referred to as Economy class syndrome as it can occur after sitting for long hours in flights Human leg has mainly two types of veins in them namely, the superficial veins and deep veins. The veins that lie just beneath the skin and those which are seen easily on the surface are called superficial veins. As the name implies, the deep veins are the ones located deep within the leg muscles. Blood from the superficial veins pass through small perforator veins and reaches the deep veins. These perforator veins act as a sieve thereby preventing the blood clots from entering the deep veins. Thus the clots formed in the superficial veins do not lead to pulmonary embolism. . The deep

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veins located near the centre of the leg have powerful muscles surrounding them. On contraction of these muscles the deoxygenated blood is forced to return to the lungs and the heart. When this muscle activity is hindered due to several medical conditions like, illness or injury, the blood has a tendency to slow down which in turn leads to the pooling or accumulation of blood. This causes blood clot formation. When this clot blocks the blood flow, it leads to pooling of blood at that site. This can cause frequent inflammation accompanied with severe pain also. It commonly occurs in the lower leg region, mainly the thigh and calf portion. Deep vein thrombosis can develop as an after effect of any major surgery. Usually people who underwent surgery on legs and hip are at risk. Out of all the patients suspected of having DVT or pulmonary embolism, only 15-20% would actually have this disease. [34] Individuals suspected with DVT may be tested using a clinical prediction rule such as the Wells score. A D-dimer test may also be used to assist with excluding the diagnosis (because of its high sensitivity) or to signal a need for further testing. This is done by measuring the level of D-dimer, formed due to the breakdown of cross-linked fibrin, which gets elevated during the conditions of DVT. [32] A combination of low Wells score and a low D-dimer value proves the absence of DVT. Diagnosis is most commonly done with ultrasound of the suspected veins. A. Reasons for DVT It is necessary that the blood clots whenever required else it can lead to huge blood loss even when subjected to a very small injury. At the same time it blood clots unnecessarily that can lead to serious health problems. German pathologist Rudolph Virchow, in 1884, proposed that the three etiologic factors that contribute to Deep Vein Thrombosis (DVT) are venous stasis, hypercoagulability of blood and damage to the blood vessel walls now known as Virchow's triad. [2] 1) Venous stasis The walls of veins are smooth and they help the blood to flow freely. While flowing, it merges with


naturally occurring agents (anticoagulants) in the blood that helps in preventing formation of blood clots. When the free flow of blood is hindered or when it does not merge with the anticoagulant, it can lead to blood clot formation. This is more common in bed ridden people. 2) Hypercoagulability The increased tendency of blood to form blood clots is another reason for deep vein thrombosis DVT. During surgery collagen tissue, fats, or debris can be released into the blood. Blood tend to thicken (coagulate) around them leading to formation of blood clots. 3) Damage to the vein walls When the wall of a blood vessel gets damaged, it tends to become narrowed or blocked, which can lead to the formation of a blood clot. This damage in blood vessels can occur as a result of injuries like broken bones or damages in muscles. Some of the medical conditions like vasculitis (inflammation of the vein wall), varicose veins and some medications like chemotherapy, also can cause damage to the blood vessels. 4) Other factors There are other factors that contribute to the formation of blood clots in the veins. Patients’ age, previous history of deep vein thrombosis, vein disease like varicose veins, smoking, pregnancy, obesity, and also some genetic factors. B. Risk factors of DVT The complications caused due to deep vein thrombosis can be very serious. Some of the key problems are discussed below: 1) Pulmonary embolism One of the most severe and most life threatening complication due to deep vein thrombosis is pulmonary embolism. The blood clots formed in the deep veins has a tendency to break off and travel along with the blood. This clot can partly or completely the blood vessels of the lungs. This medical condition is termed as pulmonary embolism. This blood clot on reaching the lungs cut the oxygen supply leading to heart failure. This can occur right after the formation of the clot or may also happen after many days. This condition can be serious and even fatal. If deep vein thrombosis is treated at an early stage, it might reduce the risk of developing a fatal pulmonary embolism. A person suspected to have pulmonary embolism may need immediate hospitalisation for emergency treatment. It is estimated that one among 100 patients diagnosed with DVT die as a result of pulmonary embolism. 2) Post-thrombotic syndrome Post thrombotic syndrome, otherwise called as postphlebitic syndrome, is the result of the damage occurred in the veins. This is a common after-effect

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of DVT when treated using blood thinners, as the clots still remain in the blood. Quite contrary to the popular belief, blood thinners do not have the ability to actively dissolve the already formed clots. They just prevent further clot formation. Eventually the clot gets dissolved and by the time it happens the veins might have undergone some serious damage. This can lead to high pressure in the veins of the legs and eventually cause pain and swelling for longer periods of time. During severe conditions it can also lead to ulcer formation on the patient’s leg. 3) Limb ischaemia One of the rare complications that occur in cases of severe DVT is limb ischaemia. The presence of blood clot can cause an increase in pressure in the patient veins, thereby blocking the blood flow through the arteries. So the amount of oxygen carried to the affected leg gets reduced considerably. This can result in developing skin ulcers, infections and gangrene. C. Early treatment methods The initial standard treatment method for deep vein thrombosis was the usage of blood thinners. These drugs tend to reduce the ability of blood to clot. They don't have the ability to break up existing blood clots but they prevent clots from becoming larger. Thereby, they reduce the risk of developing additional clots. Warfarin and heparin are two blood thinners used to treat DVT. [3] The main disadvantage of these medications is the serious side effects like an increased risk of bleeding, if you take too much. Also if the dose is too low, there is an increased risk of additional blood clot formation. Clot busters are used in cases of a more severe type of deep vein thrombosis or pulmonary embolism. It is also used when other medications fails to work. Drugs like tissue plasminogen activator (TPA) [1] are given directly via an intravenous (IV) line in order to break down the blood clots. As these drugs can lead to serious bleeding, they are employed only in life-threatening situations. Another treatment method employed for DVT treatment was the use of vena cava filters. The filter is surgically inserted into the large vein (the vena cava) of abdomen. This filter prevents clots from reaching the lungs. Compression stockings were also used which help in preventing the formation of swelling due to deep vein thrombosis. These stockings are worn on the leg from the foot portion towards the knee portion. Conventional treatment methods showed very disappointing results for long term use. Evidences from random clinical trials proved that usage of heparin and other anticoagulants are least effective and highly unsafe [4]. Studies proved that, even though the occurrence of pulmonary emboli was less in people using filters but the recurrence of DVT was very much larger in people having filters. Therefore the use of filters could not be recommended for patients having venous thrombosis.


The proposed model aims at developing an equipment which provides long term support to bed ridden patients. Bedridden patients fail to give the adequate pressure at the foot that aids in the blood flow in backward direction. So this device provides this pressure externally for around 6 – 7 hours. This helps in providing proper blood flow. An air pump is used here to inflate the cuff which is controlled by a pulse width modulated signal. The pulse width modulated signal, generated using microcontroller, aids in increasing the life time of the air pumps. One of the major disadvantages of previous models was alleviated this way. The pressure at each cuff is being monitored continuously using a pressure sensor and through a closed loop feedback system the microcontroller is made aware of the pressure in each cuff. The microcontroller accordingly controls the pneumatic valves and air pumps. This closed loop monitoring increase the efficiency of the system. . Since it is being used for bedridden people, availability of continuous power supply to this device is a must. A continuous power back up is being provided in this proposed device which is an added advantage. II.

WORKING:

This model has the following sections. a) b) c) d) e)

A controller section An air pump Pressure monitoring section A set of pneumatic valves An array of cuffs

The controller section has a microcontroller which controls the entire functioning of the device. This controller generates a PWM signal that is used to drive the air pump. Since the voltage output from the microcontroller is not sufficient enough to drive the air pump we have used a driver circuit, using bipolar junction transistor, to boost the voltage value. The microcontroller also controls the opening and closing of the pneumatic valves through a closed loop feedback mechanism. The air pump driven by the microcontroller blows air into the cuff bladder thereby inflating them. Air pump receives 24Vdc which is provided with the help of a driver circuit accompanied with a 24V delay. The pressure monitoring section includes a pressure sensor that detects the pressure value built in the air pump. Once the pressure sensor detects the optimum pressure developed at the air pump it sends signals to the microcontroller. The microcontroller turns on/off the pneumatic valves as per the requirement. This forms the closed loop feedback network.

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Pressure sensor is followed by a set of pneumatic valves which is controlled by the microcontroller. The valves then decide which cuff bladder has to be inflated or deflated. We have used a set of four pneumatic valves here. First valve in its normal condition inflates the bladder upon receiving signals from the microcontroller for the same. Once the valve gets turned on, this sends the air to the next valve’s input which in turn inflates the second and third bladder of the cuff. The third and fourth valve controls the deflation of all three cuffs. A cuff forms the last part of this device and comes in contact with the patient body. This cuff, made of polyurethane, is segmented into 3 bladders. One bladder encloses the thigh region and the next two bladders enclose the calf region. A cuff in the knee region is avoided as the application of pressure at the knee might damage them. The proposed device has an array of bladders placed inside a cuff which is inflated and deflated in a sequential manner. An air pump driven by a pulse width modulated (PWM) signal is employed in this device to inflate the array of bladders. The PWM signal is generated using a microcontroller and this PWM signal helps in increasing the efficiency and life cycle of the air pump. This is a major advantage of this device. The air pump is connected to the cuffs via solenoid valves which control the amount of air reaching the cuffs. Once the cuff attains the desired pressure, a pressure sensor connected to the cuff detects the value and sends it to the microcontroller. The microcontroller then controls the air pump accordingly. This closed loop feedback mechanism provided in this device is another major advantage of this device. The proposed model aims in providing an all time support to bed ridden DVT patients and therefore is provided with an external power supply option. The first bladder is inflated unless the pressure inside it reaches 80mm Hg during which all the pneumatic valves other than the valve to this cuff remain closed. Once it gets filled the second pneumatic valve is opened thereby filling the second cuff and this process repeats for all the bladders.


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volume greater than the second cuff as its elasticity was much higher compared to the other. The PWM signal generated using a PIC microcontroller was used to drive the air pump with the help of a BJT driver circuit. The cuffs were inflated simultaneously and the pressure was measured for three different set ups using an analog manometer.

Figure 1 .Block diagram

III.

RESULTS AND DISCUSSIONS

The components were assembled and tested for their medical standards. A. Tests-Linearity: The linearity of the pressure sensor was measured. Linearity is defined as the deviation of the sensor output curve from an ideal straight line. An analog voltage was given externally and using a comparator circuit it was compared with the voltage due to the pump. The measurements were taken using an analog manometer. The graph obtained was an almost linear one as shown in figure 2.

Figure 3. Graph showing Pressure Gradient at 5V

The first set up used a pump operating voltage of about 5V and it draws a current of 220 mA. The graph above shows that it is not a linear one but is switching type. So this set up is most desirable as it allows gradual building up of pressure. The second setup uses an operating voltage of 9V and draws a current of 340mA.


Figure 2. Graph showing linearity of Pressure Sensor

B. Pressure gradient: Pressure gradient was measured for three different set ups using two cuffs. First cuff had a

The graph in figure 4 shows a switching curve here also. Finally an operating voltage of 12 V was given. Here the pump draws a current of 500mA. This setup gives an almost linear graph as shown in figure 5


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The pressure values were displayed on a JHD162A LCD display. This display can be driven directly using ARDUINO, PIC, ATMEGA and many other microcontrollers.

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