Pulse Wave Sensor Research Articles

Sleep-Mask-Type Pulse Wave and Respiration Rate Sensor Using a MEMS-Based Differential Pressure Sensing Element

Sleep-Mask-Type Pulse Wave and Respiration Rate Sensor Using a MEMS-Based Differential Pressure Sensing Element

Low-Cost Fiber-Optic Sensing System with Smartphone Interrogation for Pulse Wave Monitoring

Pulse wave measurement is a highly prominent technique used in biomedical diagnostics. The development of novel cost-effective pulse wave sensors will pave the way to more advanced healthcare technologies. This work reports on a pulse wave optical fiber sensor interrogated by a smartphone. The sensor performance was tested in terms of signal to noise ratio, repeatability of demodulated signal and suitability of demodulated signals for the extraction of information about direct and reflected waves. The analysis showed that the observed fluctuations of signal parameters are caused by variability of the state of the cardiovascular system and not by the system noise.

Biocompatible Piezoelectric Polymer Poly(Lactic Acid)-Based Stethoscope for Wearable Health Monitoring Devices

With the development of wearable devices and the Internet of Things (IoT), there is a growing demand for portable and comfortable human health monitoring devices. Because of the advantages of biocompatibility, relatively large piezoelectric coefficients, and nonpyroelectricity, poly(L-lactic acid) (PLLA) polymers have been greatly utilized in the applications of tissue engineering, sensors, and energy harvesting devices. In this investigation, the PLLA film was fabricated for the first time for real-time wearable stethoscope and pulse wave sensor applications. First, the stretched PLLA film was glued onto a Mylar film as the active layer of the PLLA film-based stethoscope (PFS) and pulse sensor device. After the PFS device was measured in a semianechoic chamber, the device showed a sensitivity of –53.4 dB at 1 kHz and it also exhibited a stable frequency response in the range of 100 Hz–4 kHz. In addition, the PFS device showed an output voltage of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim $ </tex-math></inline-formula> 90 mV when measuring the heart rate and pulse signal of an adult volunteer. Furthermore, the PFS device was integrated a portable stethoscope system, which can detect a clear pulse signal and send it to a data collection application designed in a cellphone. The biodegradability, stable frequency response, and temperature stability indicate the great potential of PFS device for wearable human health monitoring devices.

The Capacitive Sensing of the Pulsatile Liquid Flow—Investigation on a Physical Vascular Model

This article investigates a prospective capacitive sensing method for the measurement of physical characteristics of a pulsatile liquid flow. It was tested on a physical vascular model. The volume pulse wave sensor holds a high sensitivity and thus great potential in the field of industrial applications and also in biomedical applications where we also encounter a pulsating flow of blood. Two types of capacity sensors were developed and tested on our blood vessel model, currently used for the simulation of pulse wave propagation with the possibility of changes in vessel properties and many setups are reached for testing different pulse wave propagations. The newly developed capacitive sensor detects the capacity change of pulsating liquid flow in the vascular model. Data from the capacitive sensor are compared with two reference sensors, one for direct pressure sensing and the second for noncontact optical sensing of changes in diameter. The signal processing is used for all three types of sensors and analysis in the time and frequency domain to determine the accuracy. The use of capacitive sensors is promising since it can measure a negligible change in the diameter of the vessel in the range of tens of femtofarads (fF). We can confirm that the high precision measurement is dependent on the environment, which can cause the capacity change, but with proper shielding it can be eliminated.

Self-powered, high sensitivity printed e-tattoo sensor for unobtrusive arterial pulse wave monitoring

Self-powered, highly unobtrusive, low-cost and accurate arterial pulse wave monitoring devices need to be developed to enable cost-efficient monitoring of entire cardiovascular disease risk groups. We report the development of a scalable fabrication process for a highly unobtrusive piezoelectric ultra-thin (t ~ 4,2 µm) e-tattoo arterial pulse wave sensor which utilizes only transparent and biocompatible polymer-based materials. The ferroelectric performance of the ultra-thin P(VDF-TrFE) material layer is optimized through the use of crosslinked PEDOT:PSS electrodes; this results in ~70 % and ~34 % improvements in remanent polarization (Pr) and coercive field (Ec), respectively, when compared to the sensors with pristine PEDOT:PSS electrodes. The ultra-thin form factor enables access to the high bending mode sensitivity of the P(VDF-TrFE) material layer; the maximum sensitivity value achieved in uniaxial and multiaxial bending is ~1700 pC N-1, which is ~50 times higher than the measured normal mode sensitivity. The increased sensitivity is linked to a specific set of direct piezoelectric coefficients using combination of experimental results, statistical analysis and finite element modeling. Finally, the accuracy of the e-tattoo sensor is demonstrated in the non-invasive measurement of radial artery pulse wave by comparing the signal to that obtained with reference device from 7 study subjects.

Multiple factor analysis applied to calculation of blood pressure based on pulsometry data

Development of algorithms capable of determining arterial pressure (AP) according to the contour of a pulse wave (PW) remains a topical issue to be solved with long-time efforts by researchers who work for many years in the field of hemodynamics. There is no doubt that the PW contour contains the data on AP, however due to a great number of factors influencing AP to reveal the relationship between them is extremely complicated. Our paper offers an attempt to develop an algorithm to calculate AP with the use of a PW sensor with the desired medical accuracy which does not require preliminary calibration utilizing a reference sphygmomanometer.

Air‐Stable Ultra‐Flexible Organic Photonic System for Cardiovascular Monitoring

AbstractUltra‐flexible organic optical devices are increasingly attracting attention as devices for medical and healthcare applications because they can be directly attached to the skin and continuously monitor biological information in humans noninvasively. However, integrating different optical devices on the same ultra‐flexible substrate is difficult owing to the instability of the devices. In this study, the stability of ultra‐flexible organic light‐emitting diodes and photodiodes is successfully improved using an inverted structure that does not employ atmospherically unstable cathode materials. Furthermore, an ultra‐flexible organic pulse wave sensor is developed by integrating an organic light‐emitting diode and an organic photodiode on the same substrate.

Frequency Characteristics of Pulse Wave Sensor Using MEMS Piezoresistive Cantilever Element.

Wearable sensor devices with minimal discomfort to the wearer have been widely developed to realize continuous measurements of vital signs (body temperature, blood pressure, respiration rate, and pulse wave) in many applications across various fields, such as healthcare and sports. Among them, microelectromechanical systems (MEMS)-based differential pressure sensors have garnered attention as a tool for measuring pulse waves with weak skin tightening. Using a MEMS-based piezoresistive cantilever with an air chamber as the pressure change sensor enables highly sensitive pulse-wave measurements to be achieved. Furthermore, the initial static pressure when attaching the sensor to the skin is physically excluded because of air leakage around the cantilever, which serves as a high-pass filter. However, if the frequency characteristics of this mechanical high-pass filter are not appropriately designed, then the essential information of the pulse-wave measurement may not be reflected. In this study, the frequency characteristics of a sensor structure is derived theoretically based on the air leakage rate and chamber size. Subsequently, a pulse wave sensor with a MEMS piezoresistive cantilever element, two air chambers, and a skin-contacted membrane is designed and fabricated. The developed sensor is 30 mm in diameter and 8 mm in thickness and realizes high-pass filter characteristics of 0.7 Hz. Finally, pulse wave measurement at the neck of a participant is demonstrated using the developed sensor. It is confirmed that the measured pulse wave contains signals in the designed frequency band.

Preoperative apnea-hypopnea index predicts increased postoperative intrathoracic pressure during sleep in patients who underwent endoscopic nasal surgery

ObjectiveRespiratory condition could worsen during sleep in patients with nasal packing following endoscopic nasal and sinus surgery (ESS) under general anesthesia. Recently, a noninvasive intrathoracic pressure estimation sensor was developed that uses photoplethysmographic pulse wave technology. The purpose of this study was to noninvasively evaluate the effect of bilateral nasal packing on respiration during sleep, using a photoplethysmographic pulse wave sensor in perioperative patients who underwent ESS under general anesthesia. MethodsIn this observational cross-sectional case-control study, estimated intrathoracic pressure and SpO2 were noninvasively measured during sleep with a wristband-type photoplethysmographic pulse wave sensor and a pulse oximeter in 43 patients with chronic sinusitis, nasal allergy, or septal deviation who underwent bilateral ESS under general anesthesia. Measurements were taken preoperatively, at postoperative day 1 (POD1) with bilateral nasal packing in place, and at POD5 after the nasal packing was removed. Based on the preoperative obstructive apnea-hypopnea index (AHI) score determined by overnight polysomnography, patients were classified into those with moderate to severe obstructive sleep apnea (OSA) (AHI ≥ 15/h) and those with mild or non-OSA (AHI ≤ 15/h). ResultsSignificant changes were noted in estimated intrathoracic pressure, but not in SpO2 nadir, between time points. Estimated intrathoracic pressure decreased the most at POD1 with bilateral nasal packing in place in patients with OSA after ESS. Multivariate stepwise regression revealed the relative incidence of increased estimated intrathoracic pressure on POD1 was independently predicted by preoperative AHI, but not by age, body mass index, total nasal resistance, or preoperative SpO2 nadir. ConclusionUse of the photoplethysmographic pulse wave sensor to noninvasively measure intrathoracic pressure detected changes in perioperative respiratory effort that pulse oximetry did not. Attention should be paid to the use of postoperative bilateral nasal packing in patients with moderate to severe OSA who undergo ESS under general anesthesia. Our results support the concept of using less, short-term, or no nasal packing after ESS.

History of the arterial tonometer and the “Pranayama” gadget

An arterial tonometer that allows you to determine the pressurein the shoulder from the pulse wave of the radial artery withoutsqueezing the vessels with a cuff, today remains an unattainablegoal of many researchers due to the lack of suitable pulse wavesensors (PV). The article describes a mobile medicine device,which is a kind of “smart watch” with its original function of ahuman pulse wave analyzer. This function has become possibledue to an introduction of a matrix fiber-optic sensor (MFOS)developed by a team of Russian scientists at the A. A. BlagonravovIMASH at the Russian Academy of Sciences. Features ofthe device that distinguish it from existing analogues are givenbelow:1) Capability to determine blood pressure with medical accuracywithout squeezing blood vessels with a cuff,2) Capability to diagnose the cardiovascular system and assessits condition taking into account the age of a person,3) Capability to diagnose all human organ systems using spectralanalysis of heart rate variability,4) Capability to determine the code (modulation frequency)corresponding to the established disease after the diagnosisis established using this gadget, and to carry out targeted deliveryof an increased amount of blood to the affected organ,5) Capability to perform high-quality monitoring of blood pressure(over time).After diagnosis, the gadget determines the code (modulationfrequency) corresponding to the established disease and promotestargeted delivery of an increased amount of blood to theaffected organ. Treatment is carried out by organizing a certainrespiratory rate, which, in turn, generates certain modulationsof the heart rate. As a result, the affected organ receives anadditional amount of blood and recovers.

Comparison of Pulse Wave Signal Monitoring Techniques with Different Fiber-Optic Interferometric Sensing Elements

Pulse wave (PW) measurement is a highly prominent technique, used in biomedical diagnostics. Development of novel PW sensors with increased accuracy and reduced susceptibility to motion artifacts will pave the way to more advanced healthcare technologies. This paper reports on a comparison of performance of fiber optic pulse wave sensors, based on Fabry–Perot interferometer, fiber Bragg grating, optical coherence tomography (OCT) and singlemode-multimode-singlemode intermodal interferometer. Their performance was tested in terms of signal to noise ratio, repeatability of demodulated signals and suitability of demodulated signals for extraction of information about direct and reflected waves. It was revealed that the OCT approach of PW monitoring provided the best demodulated signal quality and was most robust against motion artifacts. Advantages and drawbacks of all compared PW measurement approaches in terms of practical questions, such as multiplexing capabilities and abilities to be interrogated by portable hardware are discussed.

Quartz Pulse Wave Sensor With a Capacitive Control for Healthcare Solutions

This article describes the design principles of a quartz pulse wave sensor with capacitive control for healthcare solutions. A constructive model of a quartz crystal sensor (QCS) with a frequency output is considered and an algorithm for linearizing the QCS calibration characteristics is presented. An electrical QCS model is constructed and a numerical analysis of control characteristics in the presence of parasitic electrical connections arising from the practical implementation of the principle of capacitive control is carried out. A simulation model of a pulse oscillation sensor based on a QCS with capacitive control is presented and a numerical simulation of the stress-strain state of a corrugated membrane in COMSOL/Multiphysics is carried out. Examples of practical application of pulse wave QCS in systems of sphygmography for determining the parameters of the human cardiovascular system are given.

A porous PDMS pulsewave sensor with haircell structures for water vapor transmission rate and signal-to-noise ratio enhancement.

We present a porous polydimethylsiloxane (PDMS) pulsewave sensor with haircell structures that improves both water vapor transmission rate (WVTR) and signal-to-noise ratio (SNR). The conventional planar PDMS pulsewave sensors have the problems of low WVTR and low SNR for real-time and long-term pulsewave monitoring. In order to improve WVTR, we fabricated a porous PDMS layer with the thickness of 40 μm and high porosity of 45% by crystallizing and dissolving citric acid powders in PDMS. On the porous PDMS layer, we form haircell structures to increase the skin contact area, thus enhancing SNR. The porous PDMS pulsewave sensor with haircell structures achieved an enhanced WVTR of 486.17 g−1 d−1 m−2 and an SNR of 22.89, respectively, 72% and 757% higher than those of the conventional PDMS pulsewave sensors without haircell structures. Furthermore, the enhanced WVTR is 13% higher than the human skin sweat rate of 432 g−1 d−1 m−2. The present pulsewave sensor shows strong potential for applications in real-time and long-term pulsewave monitoring with the lower skin irritation and the enhanced SNR.

Pulse Wave Velocity Measurement With Multiplexed Fiber Optic Fabry–Perot Interferometric Sensors

The paper presents an approach to noninvasively measure pulse wave delay and velocity by means of two multiplexed fiber-optic Fabry-Perot interferometric sensors interrogated by means of spectral interferometry. The pulse wave signals were measured with 1 kHz sampling rate. The obtained optical path difference resolutions are on the order of tens picometers, which allowed the pulse wave signal features as small as 100 pm to be clearly observed in the demodulated waveforms. The pulse wave velocity between different arteries was measured, demonstrating good agreement with the known data, where applicable. The paper also presents a mathematical model based on Cramer-Rao approach, describing the fundamental resolution limits of the pulse wave delay measurement. The derived mathematical model is not limited to fiber-optic pulse wave sensors and can be used for estimating the performance of other systems, such as photoplethysmographic and ultrasound. The reported work paves the way to development of novel all-optical non-invasive systems for medical diagnostics and vital signs monitoring, including portable devices.

Quantitative Comparison of the Performance of Piezoresistive, Piezoelectric, Acceleration, and Optical Pulse Wave Sensors.

The accurate measurement of the arterial pulse wave is beneficial to clinical health assessment and is important for the effective diagnosis of many types of cardiovascular disease. A variety of sensors have been developed for the non-invasive detection of these waves, but the type of sensor has an impact on the measurement results. Therefore, it is necessary to compare and analyze the signals obtained under a range of conditions using various pulse sensors to aid in making an informed choice of the appropriate type. From the available types we have selected four: a piezoresistive strain gauge sensor (PESG) and a piezoelectric Millar tonometer (the former with the ability to measure contact force), a circular film acceleration sensor, and an optical reflection sensor. Pulse wave signals were recorded from the left radial, carotid, femoral, and digital arteries of 60 subjects using these four sensors. Their performance was evaluated by analyzing their susceptibilities to external factors (contact force, measuring site, and ambient light intensity) and by comparing their stability and reproducibility. Under medium contact force, the peak-to-peak amplitude of the signals was higher than that at high and low force levels and the variability of signal waveform was small. The optical sensor was susceptible to ambient light. Analysis of the intra-class correlation coefficients (ICCs) of the pulse wave parameters showed that the tonometer and accelerometer had good stability (ICC > 0.80), and the PESG and optical sensor had moderate stability (0.46 < ICC < 0.86). Intra-observer analysis showed that the tonometer and accelerometer had good reproducibility (ICC > 0.75) and the PESG and optical sensor had moderate reproducibility (0.42 < ICC < 0.91). Inter-observer analysis demonstrated that the accelerometer had good reproducibility (ICC > 0.85) and the three other sensors had moderate reproducibility (0.52 < ICC < 0.96). We conclude that the type of sensor and measurement site affect pulse wave characteristics and the careful selection of appropriate sensor and measurement site are required according to the research and clinical need. Moreover, the influence of external factors such as contact pressure and ambient light should be fully taken into account.

Development of a Multi-Array Pressure Sensor Module for Radial Artery Pulse Wave Measurement.

This study proposes a new structure for a pressure sensor module that can reduce errors caused by measurement position and direction in noninvasive radial artery pulse wave measurement, which is used for physiological monitoring. We have proposed a structure for a multi-array pressure sensor with a hexagonal arrangement and polydimethylsiloxane that easily fits to the structure of the radial artery, and evaluated the characteristics and pulse wave measurement of the developed sensor by finite element method simulation, a push–pull gauge test, and an actual pulse wave measurement experiment. The developed sensor has a measuring area of 17.6 × 17.6 mm2 and a modular structure with the analog front end embedded on the printed circuit board. The finite element method simulation shows that the developed sensor responds linearly to external pressure. According to the push–pull gauge test results for each channel, there were differences between the channels caused by the unit sensor characteristics and fabrication process. However, the correction formula can minimize the differences and ensure the linearity, and root-mean-squared error is 0.267 kPa in calibrated output. Although additional experiments and considerations on inter-individual differences are required, the results suggested that the proposed multiarray sensor could be used as a radial arterial pulse wave sensor.

Evaluation of Printed P(VDF-TrFE) Pressure Sensor Signal Quality in Arterial Pulse Wave Measurement

In this contribution, we evaluate the performance of an additively fabricated piezoelectric poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) based dynamic pressure sensor in non-invasive arterial pulse wave (PW) measurement. Additively fabricated piezoelectric sensors have high potential for the realization of affordable and unobtrusive PW measurement systems which could enable the long-term monitoring of patients with cardiovascular diseases (CVDs). However, the accuracy and reliability of such sensors have not been extensively studied before. We propose an additive fabrication process for a P(VDF-TrFE) PW-sensor, measure PW from the radial artery at the wrist from 22 healthy volunteer subjects, calculate clinically relevant parameters based on the PW waveform and compare their values to the values obtained from concurrent measurement with an electromechanical film (EMFi) based reference sensor, used earlier in several clinical studies. We show that the signals recorded with the two sensors, as well as the radial augmentation index (rAIx) and the stiffness index (SI) calculated from them, are in good agreement with each other. These results demonstrate that the additively fabricated P(VDF-TrFE) PW sensors can reach a suitable level of accuracy and reliability for clinical use.

Pulse Wave Sensor Sensitivity to Changing the Point of Measurement

A method for measuring the pulse wave on the wrist based on a multipoint sensor with a fiber-optic transducer probe is proposed. The development and current state of techniques for recording the radial artery pulse wave signal are analyzed. It is noted that the problem of comfortable pulse wave detection without reinstalling the sensor has not yet been solved. The possibility of reducing the distortions in the pulse wave signal using the method of superposition of readings of reinstalled single-point sensor is considered. It was shown experimentally that at any position of the proposed sensor it is possible to reliably measure the pulse wave signal. Amplitude changes in the measuring channels corresponding to the displacement of the radial artery apex relative to the sensor could be traced in the recordings. Thus, it can be concluded that it is possible to design a mobile medical device for comfortable measurement of the pulse wave, which does not require special skills when installing the sensor. A name for such a device − matrix analyzer of pulse wave (MAPW) − is suggested.

Estimation of Blood Pressure in the Radial Artery Using Strain-Based Pulse Wave and Photoplethysmography Sensors.

Blood pressure (BP) is a crucial indicator of cardiac health and vascular status. This study explores the relationship between radial artery BP and wrist skin strain. A BP estimation method based on the physical model of wrist skin tissues and pulse wave velocity (PWV) is proposed. A photoplethysmography (PPG) sensor and strain gauge are used in this method. The developed strain-based pulse wave sensor consists of a pressing force sensor, which ensures consistent pressing force, and a strain gauge, which measures the cardiac pulsation on the wrist skin. These features enable long-term BP monitoring without incurring the limb compression caused by a cuff. Thus, this method is useful for individuals requiring continuous BP monitoring. In this study, the BP of each participant was measured in three modes (before, during, and after exercise), and the data were compared using a clinically validated sphygmomanometer. The percentage errors of diastolic and systolic BP readings were, respectively, 4.74% and 4.49% before exercise, 6.38% and 6.10% during exercise, and 5.98% and 4.81% after a rest. The errors were compared with a clinically validated sphygmomanometer.

Evaluation of nocturnal heart rate variability for strenuous exercise day using wearable photoelectric pulse wave sensor.

In this study, we examined whether or not the strenuous exercise in the evening change nocturnal heart rate variability (HRV) and recovers. Subjects were 8 healthy men belonging to the mature futsal team (age: 35±3 years) and Futsal was held from 5:00 p.m. to 6:30 p.m. on Sunday. Pulse waves during sleeping were measured at home on exercise day and on control day. The mean pulse interval (MPI), standard deviation pulse interval (SDPI), low frequency component (LF, 0.04–0.15 Hz), high frequency component (HF, 0.15–0.45 Hz) and the ratio of LF to HF (LF/HF) were calculated from pulse interval time series every 30 min. As a result, MPI, SDPI, LF, HF of exercise day were significantly lower than control day (P<0.0001). LF/HF of exercise day was significantly higher than control day (P<0.05). Regarding change of HRV for every 30 min, MPI (P<0.05), SDPI (P=0.0003), LF (P=0.0038), HF (P<0.05) were observed significant changes. MPI and HF before wake-up did not reach the level of control day. It is thought that strenuous exercise in the evening promotes sympathetic nervous activity during night sleep and suggesting that pulse rate and HRV have not recovered by the wake-up time.