The EdemaBand (North Carolina State University)

ABSTRACT

The EdemaBand is a class II medical device that empowers patients with congestive heart failure to manage their condition at home. Using an array of textile electrodes on a form-fitting band, the device measures bioimpedance to determine changes in one of the most prevalent symptoms of congestive heart failure: pulmonary edema. Decreases in bioimpedance indicate an increase in pulmonary edema. Based on experimental data obtained from animal trials, every milliliter of saline injected into the subject’s lungs results in a 3.37Ω decrease in bioimpedance. Once interthoracic impedance drops by 6%, the EdemaBand notifies the patient; if levels drop by 12% or more, the EdemaBand provides a visual and auditory alert to contact a physician. Commercial production of this device could be achieved at a cost of less than $50. Ultimately, the EdemaBand is a cost effective solution to congestive heart failure that preserves patient independence and limits hospital readmission rates.

BACKGROUND

Epidemiology of Congestive Heart Failure
Every year 550,000 individuals in the United States fall victim to congestive heart failure (1). Congestive heart failure (CHF) is characterized by a decrease in cardiac output which increases the pressure in the left heart chambers. This pressure is alleviated by transferring fluid to the pulmonary vein and lungs. The subsequent swelling is known as pulmonary edema, one of the most prevalent and most serious symptoms of CHF. The lung tissues that fill with fluid contain alveoli, which are responsible for the exchange of carbon dioxide and oxygen. Filling these regions with fluid severely hinders breathing, and in severe cases, results in death; 1 in 2 patients with CHF die within 5 years of diagnosis (1).

Economic Burden of Congestive Heart Failure
The hospitalization of patients with CHF accounts for $23 billion in United States healthcare expenditures per year (2). When patients with CHF check out of the hospital, their physicians mandate dietary restrictions and prescribe diuretics, which alleviate pulmonary edema through urination. Non-compliance with physician orders can result in destabilization and episodes of acute heart failure, which require urgent hospitalization. These episodes are prevalent: 1 in every 4 hospitalized patients with CHF are readmissions, and research shows that over half of these readmissions, which equate to $2.9 billion in costs, could have been prevented had the patient complied with their prescribed regimen (3).

Current Monitoring Techniques for Patients with Congestive Heart Failure
Patients with CHF currently monitor their condition at home by checking their blood pressure, their blood oxygen saturation level, and their weight once a day. Decreases in blood pressure and blood oxygen saturation, as well as sudden increases in weight, may indicate deterioration of the heart muscle. These metrics are not continuously monitored, nor are they relayed to a physician more than once a day. Moreover, this information describes the general physiological condition of the body, not specifically pulmonary edema.

Consumer Input
A survey was distributed to healthcare providers at Rex Healthcare in Raleigh, North Carolina to assess the product requirements of a congestive heart failure monitoring device. The data showed that stakeholders needed a device that could sound an alarm, followed by a device that could continuously monitor pulmonary edema levels. These capabilities corresponded with with a 2.78 and 2.67 rating on the three-point scale, making them essential product requirements.

PROBLEM STATEMENT

Patients with congestive heart failure need to quickly and accurately detect the onset of pulmonary edema to improve treatment options at home and prevent rehospitalization.

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DESIGN AND DEVELOPMENT

Product Implementation at Home

V3Solutions has developed the EdemaBand, a noninvasive wearable Class II medical device which will detect the early onset of pulmonary edema. When a hospitalized patient with CHF recovers sufficiently, the patient will return home with an EdemaBand. The patient will wear the device around their chest during waking hours, and the EdemaBand will intermittently check the lung fluid levels, which it will store and wirelessly transmit to the patient’s physician. The device will alert the patient in progressive stages as lung fluids begin to accumulate before the clinical signs of congestion, such as wheezing and rapid respiratory rate, arise (4). The EdemaBand’s early intervention will allow a patient to self-medicate with diuretics or to call their primary care physician for emergency action steps to avoid dangerous symptoms and subsequent rehospitalization.

EdemaBand being worn around chest

EdemaBand being worn around chest.

Edema Detection Technology
The EdemaBand uses bioimpedance analysis to detect pulmonary edema. Bioimpedance is a measure of resistance of human tissues to electrical current flow. Because liquids exhibit lower impedance than air, the bioimpedance measured across the patient’s lung right lung, also known as intrathoraic impedance (ITI), will decrease with increasing pulmonary edema. A clinical trial examining 328 patients established that a 12% ITI decrease from a pre-established healthy baseline ITI is a short-term predictor of dangerous pulmonary edema (4). So when a patient first puts on the EdemaBand after leaving the hospital in a healthy state, the EdemaBand will measure and store a baseline ITI value specific to that patient. Then, the EdemaBand will compare subsequent ITI measurements to the stored baseline by calculating the percentage change. If a patient’s ITI decreases by 6% or more, the patient receives a cautionary visual alert; if the ITI decreases by 12% or more, the patient receives a visual and auditory alert, which prompts the patient to call their primary care physician or to self-mediate with diuretics. Such proactivity will allow the patient to stay at home and live a more independent life.

Printed Circuit Board

Printed circuit board powering the EdemaBand.

Conceptual rendering of the EdemaBand interior. Shows device enclosure and first set of three textile electrodes.

Risk Assessment
A thorough fault modes and effects analysis was implemented throughout the development of the EdemaBand. Table 1 lists the potential failure modes, their associated effects, and the controls implemented to decrease the risk of the effects. Special

Failure Modes, Effects, Controls

Table 1: During the design process, failure modes of the EdemaBand were brainstormed along with their effects. Controls were subsequently implemented to minimize the effects of the failure modes.

EVALUATION AND RESULTS

Animal Testing
Through a partnership with the NCSU School of Veterinary Medicine, V3Solutions has tested the functionality of the EdemaBand on both dog and cat cadavers. Because of the size and anatomical differences between these animals and the human chest, the electrodes were detached from the band and physically attached to the animal’s chest.

Team member testing device on cat cadaver. A modified set of electrodes is being attached to the cat in preparation for impedance monitoring.

Measured internal thoracic impedance values taken from the cadavers were comparable to those published in literature. Moreover, a set of experiments were conducted in which the animal was intubated and saline was injected into the lungs in order to simulate pulmonary edema. As expected, the EdemaBand detected the drop in thoracic impedance. The figure below shows the results of this experiment. On average, internal thoracic impedance dropped by 3.37 ohms for every mL of saline injected.

The EdemaBand detected the rising lung fluids in an animal model as saline was injected through an intubation tube into the animal's lungs.

Measured results of injecting saline into lungs. The impedance dropped by 3.37 ohms for every mL of saline injected. After 10 mL of saline was injected, the lungs became saturated and the impedance remained constant. The black line shows the 12% threshold that would trigger a warning.

To evaluate the precision of the device, lung impedance measurements were repeated. The distribution of measured values is shown in the histogram below. With a standard devation of .6 ohms, V3Solutions is confident the EdemaBand will be able to detect drops in impedance due to edema.

Histogram of repeated impedance measurements

The EdemaBand has exhibited good repeatability in measuring the same intrathoracic impedance consecutive times. With a standard deviation of less than 1 ohm, the EdemaBand will provide reliable measurements that the user and their physician can trust.

Qualitative Evaluation

In addition to our quantitative animal testing, we consulted respiratory therapists from physicians and potential consumers with congestive heart failure. We showed them the EdemaBand and asked them to provide feedback on the comfort and usage of the device. Physicians at REX Healthcare have expressed their support and excitement over this device. Therapists from the Home Health division of REX appreciated the breathability of the fabric band and potential for the device to provide information to healthcare providers. We also found some unexpected support from veterinarians at the NC State College of Veterinary Medicine. According to one veterinarian, having a quantifiable, objective measure of pulmonary edema levels is invaluable because early detection of increased fluid allows more time to treat the animal. Differentiating between pulmonary complications is difficult, so using the EdemaBand to target pulmonary edema levels provides a great advantage to the vet. One physician mentioned that she currently has to

All stakeholders agreed that the form factor of the band is functional, comfortable, and feasible for the target demographic. Patients would not have trouble wearing the device for extended periods of time. One potential user compared the device to an existing heart rate monitor that he owns, which he wears on occasion. This patient was excited about the possibility of detecting troubling conditions sooner, so he can take his medication and stave away chest pain and a possible trip to the hospital.

COSTS AND IMPLICATIONS

Table 2 outlines the cost of materials for the prototyping and the future mass production of the EdemaBand. The manufacturing costs should not be prohibitive to market considering the competition within the market niche of pulmonary edema detection at home is little to none. The target market of the EdemaBand totals $2.9 billion, which is the cost of preventable readmissions of patients with congestive heart failure (1).

The materials used in the production of the EdemaBand

Table 2:The material costs of prototyping the EdemaBand, totaling to $117.29, decrease with economies of scale to $42.32 with mass production. The electrical components, which were soldered onto the prototype, can be attached en masse on a production line. The plastic casing, which was printed with a rapid prototyping machine, can be injection molded for a fraction of the cost.

In order to move towards product commercialization, V3Solutions will first need to generate at least $10,000 in seed money to produce 50 EdemaBands with 3 replacement fabric bands per device, in the event that one gets soiled or torn. These initial prototypes will be evaluated in the UNC Heart and Vascular Clinic, which treats a high volume of patients with congestive heart failure. The performance data from the evaluation will be utilized in a 510(k) application to the FDA for premarket notification. After securing this approval, V3Solutions will pitch the product to a large manufacturing corporation, such as Boston Scientific, in commercially produce and market the EdemaBand.

ACKNOWLEDGEMENTS

A special thanks to REX Healthcare who allowed V3Solutions to shadow their physicians. Also, a word of gratitude goes out to our collaborators at the North Carolina State University (NCSU) School of Veterinary Medicine for the use of their dog and cat cadavers for the device proof of concept, the NCSU Electrical Engineering Department for the use of its prototyping facilities, and the NCSU College of Textiles for the use of their sewing machines and fabrication equipment.

REFERENCES

[1] Go AS, et al. Heart disease and stroke statistics – 2013 update: a report from the American Heart Association. Circulation. 2013; 127.

[2] O’Connell JB. The Economic Burden of Heart Failure. Clin. Cardiol. 2000; 23.

[3] Vinson JM, et al. Readmission of elderly patients with CHF. J. Am Geriatr. Soc. 1990; 38.

[5] Charach G, et al. Transthoracic monitoring of the impedance of the right lung in patients with cardiogenic pulmonary edema. Crit. Care Med. 2001; 29.

CONTACT INFO

Daniel Salo

Eric Whitmire

Ahmed Farawi

Mike Shotzinger

Adam Vaden

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