In-Home Cardiovascular Monitoring System for Heart Failure: Comparative Study

Nicholas J Conn, Karl Q Schwarz, David A Borkholder, Nicholas J Conn, Karl Q Schwarz, David A Borkholder

Abstract

Background: There is a pressing need to reduce the hospitalization rate of heart failure patients to limit rising health care costs and improve outcomes. Tracking physiologic changes to detect early deterioration in the home has the potential to reduce hospitalization rates through early intervention. However, classical approaches to in-home monitoring have had limited success, with patient adherence cited as a major barrier. This work presents a toilet seat-based cardiovascular monitoring system that has the potential to address low patient adherence as it does not require any change in habit or behavior.

Objective: The objective of this work was to demonstrate that a toilet seat-based cardiovascular monitoring system with an integrated electrocardiogram, ballistocardiogram, and photoplethysmogram is capable of clinical-grade measurements of systolic and diastolic blood pressure, stroke volume, and peripheral blood oxygenation.

Methods: The toilet seat-based estimates of blood pressure and peripheral blood oxygenation were compared to a hospital-grade vital signs monitor for 18 subjects over an 8-week period. The estimated stroke volume was validated on 38 normative subjects and 111 subjects undergoing a standard echocardiogram at a hospital clinic for any underlying condition, including heart failure.

Results: Clinical grade accuracy was achieved for all of the seat measurements when compared to their respective gold standards. The accuracy of diastolic blood pressure and systolic blood pressure is 1.2 (SD 6.0) mm Hg (N=112) and -2.7 (SD 6.6) mm Hg (N=89), respectively. Stroke volume has an accuracy of -2.5 (SD 15.5) mL (N=149) compared to an echocardiogram gold standard. Peripheral blood oxygenation had an RMS error of 2.3% (N=91).

Conclusions: A toilet seat-based cardiovascular monitoring system has been successfully demonstrated with blood pressure, stroke volume, and blood oxygenation accuracy consistent with gold standard measures. This system will be uniquely positioned to capture trend data in the home that has been previously unattainable. Demonstration of the clinical benefit of the technology requires additional algorithm development and future clinical trials, including those targeting a reduction in heart failure hospitalizations.

Keywords: BCG; ECG; Internet of Things; IoT; PPG; SpO2; ballistocardiogram; blood pressure; electrocardiogram; heart failure; photoplethysmogram; remote monitoring; stroke volume.

Conflict of interest statement

Conflicts of Interest: None declared.

©Nicholas J Conn, Karl Q Schwarz, David A Borkholder. Originally published in JMIR Mhealth and Uhealth (http://mhealth.jmir.org), 18.01.2019.

Figures

Figure 1
Figure 1
A toilet seat–based cardiovascular monitoring system (left) is integrated into an individual’s daily routine without requiring any change in habit, thereby addressing patient adherence. The system captures a comprehensive set of clinically relevant measurements automatically (right).
Figure 2
Figure 2
The toilet seat–based cardiovascular monitoring system is completely self-contained, battery-powered, wireless, and cleanable with all sensors and electronics instrumentation integrated inside of the seat. It can measure the electrocardiogram (ECG), photoplethysmogram (PPG), and the ballistocardiogram (BCG).
Figure 3
Figure 3
A floating hinge ensures that the weight on the seat is completely captured by the load cells under each standoff rather than having a portion of it carried by the hinge. This is a requirement for accurate ballistocardiogram monitoring on a toilet seat.
Figure 4
Figure 4
The ballistocardiogram (BCG) amplitude and timing vary greatly based on the cardiovascular state. Heart failure (HF) BCG waveforms have a much smaller amplitude when compared with the normal BCG waveform at rest and poststress.
Figure 5
Figure 5
When characterizing the R-value for SpO2 (peripheral oxygen saturation) estimation on the seat with controlled desaturation testing, the R-curve slope matches literature and is the same across subjects. A different offset necessitates the use of a per-subject calibration for absolute SpO2 estimation. The shaded regions represent the acceptable level of error around the best fit line according to the ISO standard for pulse oximetry.
Figure 6
Figure 6
The toilet seated–based cardiovascular monitoring system has been shown to accurately measure blood pressure over an 8-week period. Both the diastolic (left) and systolic (right) blood pressure (BP) estimates from the seat exceed the accuracy required by the Association for the Advancement of Medical Instrumentation (AAMI) standard converted to a limits of agreement (shaded regions).
Figure 7
Figure 7
The seat estimate of stroke volume (SV) strongly correlates to the echocardiography measure of SV measured from the left ventricular outflow tract (LVOT). In comparison, the literature shows that the echocardiogram SV measure has a limits of agreement of 35.2 mL (shaded region) compared to an arterial gold standard.
Figure 8
Figure 8
The limits of agreement for SpO2 (peripheral oxygen saturation) is 4.5% with an ARMS (root mean square error) of 2.3%. This exceeds the accuracy required by the ISO standard for SpO2 where ARMS, MAX is 3.5%, which equates to a limits of agreement of 6.9% (shaded region).

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