A multi-point heart rate monitoring using a soft wearable system based on fiber optic technology

Abstract

Early diagnosis can be crucial to limit both the mortality and economic burden of cardiovascular diseases. Recent developments have focused on the continuous monitoring of cardiac activity for a prompt diagnosis. Nowadays, wearable devices are gaining broad interest for a continuous monitoring of the heart rate (HR). One of the most promising methods to estimate HR is the seismocardiography (SCG) which allows to record the thoracic vibrations with high non-invasiveness in out-of-laboratory settings. Despite significant progress on SCG, the current state-of-the-art lacks both information on standardized sensor positioning and optimization of wearables design. Here, we introduce a soft wearable system (SWS), whose novel design, based on a soft polymer matrix embedding an array of fiber Bragg gratings, provides a good adhesion to the body and enables the simultaneous recording of SCG signals from multiple measuring sites. The feasibility assessment on healthy volunteers revealed that the SWS is a suitable wearable solution for HR monitoring and its performance in HR estimation is strongly influenced by sensor positioning and improved by a multi-sensor configuration. These promising characteristics open the possibility of using the SWS in monitoring patients with cardiac pathologies in clinical (e.g., during cardiac magnetic resonance procedures) and everyday life settings.

Precordial Vibrations: A Review of Wearable Systems, Signal Processing Techniques, and Main Applications

“…The FBGs are the widespread fiber optic technology employed for monitoring precordial vibrations. They are preferred to traditional electrical and mechanical sensors due to their advantageous metrological properties [ 86 ] and immunity to electromagnetic interferences, which allows their use in harsh environments such as MRI procedures in the clinical application [ 87 ]. For what concerns cardiac monitoring, the high ε sensitivity (up to 1 pm/με) and linearity in a wide range of ε values, short response time (<10 ms), and proper frequency response of FBGs make them good candidate for detecting the small and rapid heart-induced deformations of the chest surface.…”

“…Hence, a filtering stage is required prior to the actual signal processing and HR analysis to remove the respiratory contribution and reveal the heartbeat signal. The filters used in the literature are bandpass filters with lower cutoff frequencies [ 86 ] of 0.8 Hz, 3 Hz, and 5 Hz and higher cutoff frequencies of 2 Hz, 20 Hz, and 30 Hz [ 88 , 93 , 94 , 95 ]. Often, upper and lower envelopes are additionally performed on the filtered signals to better emphasize the AO-related peak on the SCG signal [ 86 ].…”

“…The filters used in the literature are bandpass filters with lower cutoff frequencies [ 86 ] of 0.8 Hz, 3 Hz, and 5 Hz and higher cutoff frequencies of 2 Hz, 20 Hz, and 30 Hz [ 88 , 93 , 94 , 95 ]. Often, upper and lower envelopes are additionally performed on the filtered signals to better emphasize the AO-related peak on the SCG signal [ 86 ]. The filtered signals are processed by following two main approaches: time- and frequency-domain analysis.…”

“…FBG-based sensors are tightly fixed to the subject’s chest in correspondence with the chosen measurement point using adhesive tape or a contact strip such as a Velcro fasten belt, allowing the mechanical stress to be transferred to the sensing element. In the literature, different measurement points on the frontal plane have been investigated (see Figure 3 c): xiphoid process [ 94 , 95 ], the area of the sternum below the nipple [ 94 ], the area above the umbilicus [ 86 , 94 ], lower thorax [ 93 , 96 ], and pulmonic area near to the heart [ 88 ]. As for SCG recording with accelerometers, FBG-based SCG monitoring is still lacking for standard measurement locations and filtering stages.…”

Biocompatible and Biodegradable Polymer Optical Fiber for Biomedical Application: A Review

“…The small size, low cost, nontoxicity, and electromagnetic insensitivity of biocompatible POFs make them ideal for devices applied in or near the body that shed some light on novel therapies in immunology, cardiology, neurology, oncology, and gastroenterology, among other fields [ 33 , 34 , 35 ]. For example, it is reported that wearable optical fiber based on fiber Bragg gratings can be used to monitor heart rate [ 36 ] and detect basic activities, such as walking, sitting, and squatting [ 15 ], which is promising for chronic disease prevention. Due to the increasing prevalence of diseases such as cancer, lithiasis, and angiocardiopathy, as well as the growth of minimally invasive surgery, there is an urgent need for more biocompatible, more photoconductive, and less invasive optical fibers, as well as nontoxic, tissue-like materials and low-cost, high-productivity, and versatile fabrication methods.…”