Long-term acquisition of respiratory and heart signals is useful in a variety of applications, including sleep analysis, monitoring of respiratory and heart disorders, and so on. Ballistocardiography (BCG), a non-invasive technique that measures micro-body vibrations caused by cardiac contractions as well as motion caused by breathing, snoring, and body movements, would be ideal for long-term vital parameter acquisition. Turtle Shell Technologies Pvt. Ltd.'s Dozee device, which is based on BCG, is a contactless continuous vital parameters monitoring system. It is designed to measure Heart Rate (HR) and Respiratory Rate (RR) continuously and without contact in a hospital setting or at home. A validation study for HR and RR was conducted using Dozee by comparing it to the vitals obtained from the FDA-approved Patient Monitor. This was done in a sleep laboratory setting over 110 nights in 51 subjects to evaluate HR and over 20 nights in 17 subjects to evaluate RR at the National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, India. Approximately 789 hours data for HR and approximately 112 hours data for RR was collected. Dozee was able to achieve a mean absolute error of 1.72 bpm for HR compared to the gold standard ECG. A mean absolute error of ~1.24 breaths/min was obtained in determining RR compared to currently used methods. Dozee is ideal for long-term contactless monitoring of vital parameters due to its low mean absolute errors in measuring both HR and RR.
Clinical Relevance
Continuous and long-term vitals monitoring is known to enable early screening of clinical deterioration, improve patient outcomes and reduce mortality. Current methods of continuous monitoring are overly complex, costly, and rely heavily on patient compliance. The proposed remote vitals monitoring solution based on BCG was found to be at par with gold standard methods of recording HR and RR. As a result, clinicians can use it to effectively monitor patients in both the hospital and at home.
Introduction
Continuous monitoring of vital signs, especially Heart Rate (HR) and Respiration Rate (RR), is a common practice in intensive care, medium care, operating rooms, and recovery wards. Continuous vital signs monitoring can help in faster detection of health deterioration and thereby help doctors in taking timely interventions. This becomes even more crucial considering that changes in vital signs can be detected 8-24 hours before a serious event such as cardiac arrest, ICU admission or death (1). The gold standard for any type of cardiac measurement, including HR, is electrocardiography (ECG), which works on the principle of monitoring electrical activity in the circulatory system (2). External electrodes must, however, be physically linked to a person at appropriate locations over the skin for this to work, rendering them unsuitable for long-term continuous data collection. In a clinical environment, RR is measured using a nasal thermistor or Respiratory Inductance Plethysmography (RIP) belts for the belly and/or chest to monitor air flow or respiratory effort (3). The equipment needs to be installed by skilled professionals, are expensive, and cause patient discomfort making them unsuitable for long-term use. This necessitates the development of new, innovative, and non-invasive solutions that can enable long-term continuous monitoring of HR and RR in both the hospital and home environments.
One such promising technique is ballistocardiography (BCG). While it was originally intended for recording cardiac and cardiovascular-related mechanical motions, the phenomenon can also detect any other physiological functions that produce a motion – including breathing, snoring and limb movements (4). In addition, it works in a contactless manner provided there is a medium to carry the vibrations, for e.g., if a person is lying on a mattress and the BCG data is recorded from underneath it. Despite its benefits, BCG's practical adoption has been hampered by two major challenges: (a) it captures other forces produced by the human body, such as movements, respiration, and snoring, which affect the accuracy and detection rate of cardiac and respiratory measurements, and (b) the measurements can vary depending on the setup and placement of the sensors, as well as body postures. Turtle Shell Technologies Pvt. Ltd. has developed a BCG based Dozee device for monitoring of vitals. The Dozee device has addressed the two major challenges mentioned above, with a novel unsupervised clustering algorithm [5,6] that is effectively able to isolate cardiac contractions and respiratory events from the unconstrained BCG signal. Dozee is designed to be a remote patient monitoring system for vitals and sleep monitoring. The data collected can be accessed by the patient/clinician/caretaker/user via the mobile application or a web-based platform (Figure 1).
To validate this device for HR and RR, a study was done at the National Institute of Mental Health and Neurosciences (NIMHANS), Bangalore, India on patient populations undergoing polysomnography level 1 study in the sleep lab. The vitals determined by the Dozee device were validated with the vitals acquired via patient monitor to determine the mean absolute error (MAE) in measuring HR and RR. The validation parameters were set as MAE equal to or less than ±5 for HR and ±1.5 for RR, and a detection rate greater than 90% for both HR and RR. This was based on the predicate device EarlySense (ES), a BCG-based device approved by the FDA and CE and the current standard of care for vitals monitoring in hospital wards.
