Development of a wearable belt with built-in sensors to measure multiple physiological factors related to heart failure

Cardiovascular diseases (CVDs) are a group of diseases of the heart and blood vessels such as myocardial infarction, otherwise known as heart attack, heart failure, rheumatic heart disease, and pulmonary arterial disease.1,2. According to the World Health Organization (WHO), cardiovascular diseases are the number one cause of death with an estimated 17.9 million deaths worldwide.1. Heart failure (HF) is a critical cardiovascular disease with an estimated 64.34 million cases worldwide.3. HF is a progressive clinical syndrome characterized by a structural abnormality of the heart, in which the heart is unable to pump enough blood to meet the demands of the body. Due to this lack of blood supply, fluid builds up in the lungs, impeding oxygenation4,5,6. There are two types of HF: systolic HF with reduced ejection fraction (HFrEF) and diastolic HF with preserved ejection fraction (HFpEF). Common causes of HFrEF include cardiomyopathy, heart muscle disease, untreated hypertension, faulty heart valves, and coronary artery disease. A common cause of HFpEF is left ventricular hypertrophy (LVH), a condition in which the left ventricle of the heart thickens and the chamber is unable to fill with adequate cardiac output7,8,9. According to the Centers for Disease Control and Prevention (CDC), in 2018 there were 379,800 deaths, and 13.4% of all deaths in the United States were due to HF2. Moreover, according to the American Heart Association, there are currently 6.2 million adults diagnosed with hepatitis C in the United States, and this number is expected to increase to 8 million by 2030.10. Current HF treatment includes guided medications and surgically implanted devices which can be very expensive. According to the CDC, on average, $30.7 billion was spent on HF treatment across the United States in 2012.2. This financial burden is due to the downward course of HF which in later stages leads to repeat hospitalization. Because of this poor prognosis, 17-45% of deaths occur within one year of initial hospitalization and 45-60% of deaths occur within five years.11.

Continuous and true monitoring of HF symptoms can alert patients and reimbursement providers. The provider can then intervene with the medications to avoid hospitalization of the patient. Fluid buildup in the lungs is reflected by decreased chest resistance. Common symptoms of HF are associated with fluid overload and include fatigue, weight gain, and feeling short of breath7,8. These symptoms can be monitored for the development of HF. There are currently two implantable devices for monitoring symptoms of HF: the implantable cardioverter-defibrillator (ICD) and the CardioMEMS™ pulmonary artery monitor.8,12,13,14.

An implantable cardioverter-defibrillator (ICD) is recommended for patients with HFrEF because they are at higher risk for fatal arrhythmias. ICDs also measure chest resistance and can alert providers of low chest resistance, which indicates excess fluid in the lungs.15th. Surgically implanted under the skin, it detects fatal arrhythmias and restores a normal heart rhythm with an electric shock. ICDs have an additional function as a pacemaker, to speed up a very slow heart.16. An ICD requires an invasive surgical procedure for the initial implantation and when the battery needs to be replaced, usually within 3-7 years17. There are risks to any surgery and the procedure is also costly. According to the ICD Registry, the surgical replacement cost is approximately $37,00018. Furthermore, electromagnetic fields can disrupt the performance of an ICD, and the risk increases with increasing proximity.19,20,21,22,23. It is important to note that ICDs are only recommended for patients with HFrEF; There are no monitoring devices available for 50% of patients with HFpEF24.

CardioMEMS™, is a commercially available HF screening diagnostic tool that can alert caregivers of increased pressure in the lungs. It is a small device (15 mm x 3.5 mm x 2 mm) that is implanted in the pulmonary artery and monitors changes in pulmonary artery pressure. Pulmonary hypertension is an early indicator of worsening HF 25,26,27. It’s expensive, around $17,75011, and not without risks. CardioMEMS™ was approved by the Food and Drug Administration in 2014, for both HFrEF and HFpEF, and in the first three years, 5,500 devices have been implanted in unique patients. However, CardioMEMS™ failed to predict 22 deaths out of 5,500 transplants, 4 of which were due to HF28,29. Furthermore, sensor failure occurred in 46 cases, 13 required recalibration, 11 patients were hospitalized, and 14 sensors were neglected.28.

Both HF monitoring systems currently available are not only expensive but have significant safety concerns. Furthermore, the risks of invasive procedures cannot be ignored. Approximately half of patients with HF do not require an ICD and do not qualify for the thoracic monitoring it provides. Therefore, non-invasive solutions for continuous and true monitoring of HF progression are urgently needed. Healthcare wearable devices (HWDs) can fill this need because HWDs are not only cost effective but also safe and comfortable for the wearer. Moreover, it was found to be a suitable solution for continuous and real-time monitoring of various biomarkers30,31. In addition to the ICD and CardioMEMS, Sensible Medical’s Electrical Isolation Distance Sensing (ReDS), also measures lung fluid content but is also not portable and cannot be used for the point of care at all times32.

Moreover, VitalPatch from VitalConnect is a portable wearable device that can be used to monitor various vital signs related to cardiovascular diseases.33. These parameters include heart rate, heart rate variability, respiratory rate, body temperature, ECG, posture, and activity fall detection. However, it does not measure thoracic impedance, which is an important parameter for HF monitoring33.

In this paper, we present a HWD that has the potential to monitor important physiological parameters for patients with HF. These parameters include chest impedance, electrocardiogram (ECG), heart rate, and motion activity detection.

Thoracic impedance is an important biosignal for monitoring HF progression, ranging in magnitude from 60 to 1000 ohms depending on the subject under study and the number of electrodes used to measure chest impedance34. As discussed, at the onset of HF, fluid begins to accumulate in the chest region, and this fluid retention reduces the impedance in this region. Yu et al. In their study of 33 patients with hepatitis, they note that before the onset of HF, the thoracic impedance begins to decrease35. Therefore, this decrease in chest resistance is a vital consideration for the progression of HF36,37,38. Chest impedance is assessed by placing electrodes across the chest region, and measures the resistance to ion flow in this region. When the heart is not pumping efficiently, fluid fills the thoracic cavity and facilitates the flow of ions, as fluid is more conductive than air. 35,39,40. An increased flow of charges indicates a decrease in chest resistance. Similarly, with no liquid inside the chest region, the charges experience increased resistance to flow from one electrode to the other, indicating increased chest resistance.41.

Likewise, the ECG is a vital biosignal for the diagnosis and prognosis of cardiovascular disease. It is a representation of the flow of electrical signals through the heart42. As discussed, one of the symptoms of heart failure is an irregular heartbeat, commonly known as an arrhythmia.43. An arrhythmia is an abnormal heartbeat in which the EKG is irregular and distinguishable from normal sinus rhythm43. Arrhythmias can be identified using an electrocardiogram. Traditionally, in the outpatient setting, ECG measurements are done with a Holter monitor that is not suitable for point-of-care (POC) use. Furthermore, cardiomyopathy leads to a decreased ejection fraction, which results in a decreased percentage of blood pumped with each heartbeat.44. To compensate for the loss of blood supply, the heart may beat at a higher rate than normal (60-100 beats per minute). This may not be enough to provide the cardiac output needed by the body and lead to symptoms of HF.

Fatigue is another symptom of HF with swelling in the legs or edema7,8. O’Donnell et al. conducted a study on 13 patients infected with the virus and found that patients with severe HF were less able to perform physical activity and therefore had reduced activity45. Moreover, the discomfort caused by heart failure affects sleep patterns46,47. These symptoms can be monitored with position sensors that can be used to better manage heart failure.

This paper will highlight the materials and methods involved in developing HWD to acquire the aforementioned parameters along with their preliminary results. Furthermore, the challenges and future directions for using the discussed HWD to predict HF will also be discussed.

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