In a recent study published in the journal Dr Nature’s medicineResearchers present a wireless broadband acousto-mechanical sensing (BAMS) system for continuous physiological monitoring.
In neonates and infants, cardiovascular and gastrointestinal problems are significant causes of death in the first five years of life. Use of continuous monitoring systems helps guide clinical decisions. Current hospital systems use sensors, wires and cables connected to monitors. Fortunately, however, advances in bioengineering have led to the development of wireless, skin-interfaced sensors for use in the simultaneous acquisition of different classes of signals.
Digital stethoscopes with wearable designs can provide (complementary) information on airway obstruction, bowel motility, heart activity, and lung sounds. However, due to some limitations they cannot be used for continuous monitoring, and as a result, clinical use of body noise usually occurs through periodic measurements.
A health care worker places a wearable device on a patient’s chest to capture sounds across the lungs associated with breathing. Image credit: Northwestern Universityity, study: Wireless Broadband Acousto-Mechanical Sensing System for Continuous Physiological Monitoring
Research and results
The present study introduced the wireless BAMS system for continuous physiological monitoring. The BAMS system can capture a wide range of signals from slow body movements (around 0.01 hertz). [Hz]) to high-frequency body sounds (up to 1 kHz). Gentle adherence of the device to the suprasternal notch may allow simultaneous measurement of respiratory and cardiac sounds.
Placement of time-synchronized devices in the stomach can enable spatiotemporal monitoring of gastrointestinal sounds. In an advanced implementation, 13 devices can be placed across target sites across the posterior and anterior chest to monitor pulmonary health, disease progression, and rehabilitation. This (advanced) can be applied to patients of any age, including neonates admitted to the Neonatal Intensive Care Unit (NICU).
The BAMS device includes body- and ambient-facing microphones, an inertial measurement unit, a flash memory, a wireless-charging antenna, and a standard Bluetooth low-energy system-on-a-chip mounted on a printed circuit board. The microphone captures sound from two directions and an adaptive filtering algorithm minimizes the contribution of body noise to ambient noise and vice versa.
The BAMS system can be used in everyday life situations, allowing monitoring of standard parameters (respiratory rate, heart rate) and autonomic measures such as cardiorespiratory coupling, swallowing and heart rate variability (HRV). The system can work across different activities such as sleep and exercise. In addition, the researchers compared BAMS data from a newborn admitted to the NICU with readings from a Food and Drug Administration (FDA)-approved clinical monitor.
Sound intensity and breath interval determined by the BAMS device correlates with breath and airflow rate intervals. In addition, the device demonstrated reliable long-term (three hours) monitoring of heart rate, respiratory sounds, and other parameters in a cohort of five neonates admitted to the NICU. Respiratory sounds aligned well with chest movement and respiratory inductance plethysmography and nasal temperature data.
Further analysis showed that bowel sounds captured by the BAMS device were correlated with electromyography signals from an adult’s abdomen. Additionally, the researchers used 13 devices mounted on 35 chronic lung disease patients and 20 healthy individuals. Data from a healthy subject show similar distributions of sound intensity, chest wall motion, and sound frequencies from the right and left sides of the body.
Similar measurements reflect their status in patients with surgical lung resection and chronic lung disease. One participant with resection surgery of the left upper lobe and right lower and upper lobes showed lower pulmonary function in the removed lobes, decreased sound intensity and airflow rate.
Comparative analysis of data from healthy subjects and patients with chronic lung disease highlights the importance of airflow volume, sound frequency, and airflow rate in the diagnosis of restrictive and obstructive lung disease. These results are based on data from BAMS devices placed in the posterior region of the chest (lower and upper) and suprasternal grooves with individual airflow rate and flow volume measurements using peak flow meters.
Sound power can be additionally calculated by integrating sound intensity over time. These parameters can help track disease progression and response to treatment. Air volume and airflow rate measurements can also facilitate monitoring of the Tiffenau-Pinelli index. Sound intensity in the suprasternal groove was higher in healthy participants than in patients with chronic lung disease, with a mean intensity of 54 decibels (dB).
However, the mean intensity was 38 dB in patients with chronic lung disease without lung resection, 36 dB in patients with right upper lung resection, and 30 dB in patients with left upper lung resection. Right upper expiratory dominant expiratory frequency was 219 Hz in healthy participants and 256 Hz in patients with chronic lung disease. Further analysis at different lung sites revealed stark differences between patients with chronic lung disease and healthy subjects.
The study presents technology for simultaneous measurement of body noise and movement as a source of physiological signals, with home and hospital applicability. Numerous characterization studies and benchmarking measurements have confirmed the accuracy of the BAMS system. Overall, the combination of a microphone pair, noise-separation algorithm, time-synchronized operation, and small skin-interfaced form creates unique possibilities for (continuous) patient monitoring.