| More than 5,000,000 Americans suffer from heart failure, a progressive disorder where the heart cannot meet the metabolic demands of the tissues and organs. Approximately 1.5 million hospitalizations each year are related to heart failure in the US. After release from the hospital, the American Heart Association recommends monitoring heart failure patients at home by measuring body weight daily---upward trends of more than a few pounds could indicate edema, and the need for rehospitalization. Recently, in addition to simply monitoring weight, many researchers have investigated new devices for monitoring hemodynamics in the home to reduce unnecessary rehospitalizations.;This work proposes measuring both body weight and hemodynamics on the same device: a modified bathroom scale. Body weight measurement on a scale is straightforward; for hemodynamic monitoring, a combination of ballistocardiography and electrocardiography sensing technologies were developed.;When a patient stands on the scale, small fluctuations in body weight caused by the heartbeat---the ballistocardiogram (BCG)---are measured and related to the strength of cardiac contractions. Furthermore, while standing on the scale, a patient grips detachable handlebar electrodes, allowing simultaneous measurement of an electrocardiogram (ECG) signal. These two signals were fused using a novel estimation algorithm, and the BCG signal was reconstructed from the recorded waveform composed of both signal and measurement noise, such as motion artifacts.;To further improve robustness to motion, electromyogram (EMG) signals acquired from the subject's feet were recorded, and the correlation between the EMG power and the BCG noise was investigated. Floor vibrations represent another source of interference, and were mitigated by using a seismic sensor on the floor next to the scale and an adaptive algorithm. Using this approach, BCG recordings were obtained on a parked bus with the engine running---even under such extreme conditions the vibration interference was effectively eliminated.;With this system, normal standards at rest were established for 92 healthy subjects. The timing and amplitude features of the signal were found to be comparable to those measured using cumbersome bed- or table-based BCG measurement systems. Frequency domain features were also explored: the power spectral density of the BCG signal was estimated and characterized. A correlation analysis yielded that features of the BCG signal combined with height and weight were correlated to left ventricular mass (R2 = 0.60, p < 0.001) and stroke volume (R2 = 0.60, p < 0.01), two important cardiovascular parameters estimated using echocardiography. The correlation to left ventricular mass is an especially encouraging result, as the system could potentially be used in large scale screening of athletes for hypertrophy.;After establishing standards at rest, the hemodynamics were modulated to determine the capability of the system to detect changes in cardiac output. For 10 trials involving nine healthy subjects, each subject exercised for 15 minutes then recovered while standing on the scale for 10 minutes. During the recovery, the gold standard for noninvasive cardiac output estimation---Doppler echocardiography---was used to measure this parameter repeatedly. The changes in cardiac output measured by Doppler were strongly correlated to the changes in root mean square (RMS) power of the BCG (R2 = 0.85, n = 275 data points, p < 0.001). The prediction error, calculated based on Bland-Altman methods, was found to be lower than any other noninvasive method disclosed to date.;With this technology, heart failure patients could monitor both weight gain and cardiac output at home on the same device: an inexpensive, compact, modified commercial weighing scale. The subject compliance would be excellent, since the device is already a commonly-used household item and does not require anything to be attached to the body. By using the BCG/ECG-equipped weighing scale every day for less than 15 seconds at a time, unnecessary rehospitalizations could decrease, improving the quality of care for the large population of heart failure patients. |
