A wrist worn SpO 2 monitor with custom finger probe for motion artifact removal
01 Aug 2016-Vol. 2016, pp 5777-5780
TL;DR: A wrist worn device with a custom finger probe with an integrated accelerometer to remove motion artifacts is presented and an algorithm which can run on low power systems with processing constraints is implemented on the device.
Abstract: Continuous monitoring of blood oxygen saturation (SpO2) level and heart rate is critical in surgery, ICUs and patients suffering from Chronic Obstructive Pulmonary Diseases. Pulse oximeters which compute SpO2 using transmittance photoplethysmography (PPG), is widely accepted for continuous monitoring. Presence of motion artifacts in PPG signals is a major obstacle in the extraction of reliable cardiovascular parameters, in real time and continuous monitoring applications. In this paper, a wrist worn device with a custom finger probe with an integrated accelerometer to remove motion artifacts is presented. An algorithm which can run on low power systems with processing constraints is implemented on the device. The device does continuous acquisition of PPG and accelerometer waveforms and computes SpO2 using the proposed light weight algorithm. The measurement results are continuously synced with an Android tablet, which acts as a gateway and is pushed on to the cloud for further analysis. The accuracy in SpO2 measured by the device was validated using Fluke ProSim 8 SpO2 simulator and the efficiency in accurately computing SpO2 in the presence of motion was validated over 40 healthy volunteers in a controlled setting.
Citations
More filters
TL;DR: A taxonomy of sensors, functionalities, and methods used in non-invasive wrist-wearable devices was assembled and the main features of commercial wrist- wearable devices are presented.
Abstract: Wearable devices have recently received considerable interest due to their great promise for a plethora of applications. Increased research efforts are oriented towards a non-invasive monitoring of human health as well as activity parameters. A wide range of wearable sensors are being developed for real-time non-invasive monitoring. This paper provides a comprehensive review of sensors used in wrist-wearable devices, methods used for the visualization of parameters measured as well as methods used for intelligent analysis of data obtained from wrist-wearable devices. In line with this, the main features of commercial wrist-wearable devices are presented. As a result of this review, a taxonomy of sensors, functionalities, and methods used in non-invasive wrist-wearable devices was assembled.
180 citations
12 Mar 2018
TL;DR: The benefits of compact low-cost Wi-Fi module can be harnessed to develop a wireless continuous heart rate monitoring system enhancing possibility of atrial fibrillation detection.
Abstract: Detection of atrial fibrillation is done by checking the variations in the period of the heart rate, if a patient has atrial fibrillation then the period between each heart beat will vary. A light-based sensor can be used to detect these variations in heart rate; this is done by using Photoplethysmography (PPG) sensor which is non-invasive. The sensor consists of a LED with a photodetector and is able to detect the variations in blood volume or blood flow in the body and directly correlates to heart rate. The detected signal needs to be amplified and filtered as the signal contains a lot of high frequency noise as well as low frequency motion artifacts. The benefits of compact low-cost Wi-Fi module can be harnessed to develop a wireless continuous heart rate monitoring system enhancing possibility of atrial fibrillation detection.
24 citations
Posted Content•
TL;DR: This work uses a custom wrist-worn pulse oximeter to find that existing algorithms used in traditional fingertip SpO2 sensors are a poor match for taking measurements from the wrist and can lead to over 90% of readings being inaccurate.
Abstract: Peripheral blood oxygen saturation Sp02 is a vital measure in healthcare. Modern off-the-shelf wrist-worn devices, such as the Apple Watch, FitBit, and Samsung Gear, have an onboard sensor called a pulse oximeter. While pulse oximeters are capable of measuring both Sp02 and heart rate, current wrist-worn devices use them only to determine heart rate, as Sp02 measurements collected from the wrist are believed to be inaccurate. Enabling oxygen saturation monitoring on wearable devices would make these devices tremendously more useful for health monitoring and open up new avenues of research. To the best of our knowledge, we present the first study of the reliability of Sp02 sensing from the wrist. Using a custom-built wrist-worn pulse oximeter, we find that existing algorithms designed for fingertip sensing are a poor match for this setting, and can lead to over 90% of readings being inaccurate and unusable. We further show that sensor placement and skin tone have a substantial effect on the measurement error, and must be considered when designing wrist-worn Sp02 sensors and measurement algorithms. Based on our findings, we propose \codename, an alternative approach for reliable Sp02 sensing. By selectively pruning data, \codename achieves an order of magnitude reduction in error compared to existing algorithms, while still providing sufficiently frequent readings for continuous health monitoring.
12 citations
Cites background from "A wrist worn SpO 2 monitor with cus..."
...While the pulse oximeters sensors on these devices are fundamentally the same as the ones used in hospital and commercial fingertip SpO2 monitors, calculating oxygen saturation from a wrist-worn sensor leads to unreliable measurements due to poorly-fitting devices, wrist and arm motion, low blood perfusion, interference from ambient light, motion, and the effects of skin tone [6]–[9]....
[...]
11 Jun 2018
TL;DR: The preliminary analysis of beat to beat reflectance PPG signal from finger, forehead, wrist and chest concur well with the reference measurement and gives enough scope to measure SpO2 from various measurement sites like finger, forearm, wrist, chest and chest.
Abstract: Blood oxygen saturation level (SpO 2 ) is a clinically accepted vital sign for patient care and diagnostics. Oximeters are widely used by people suffering from asthma, congestive heart failures and pulmonary disorders as part of their routine care. Transmittance and reflectance pulse oximeters play a pivotal role in patient care and clinical decision making. In this paper, we study the feasibility of using reflectance photo plethysmography (PPG) for SpO 2 monitoring from various measurement sites on body. A preliminary study was conducted in a clinical setting on 10 subjects with pulmonary disorders. Arterial blood gas (ABG) analysis was used as a reference measure in the study. An SpO 2 data acquisition platform was developed, which uses custom-made dual wavelength reflectance SpO 2 sensor probes, Nellcor™ transmittance probe for beat to beat SpO 2 measurement. The preliminary analysis of beat to beat reflectance PPG signal from finger, forehead, wrist and chest concur well with the reference measurement and gives enough scope to measure SpO 2 from various measurement sites like finger, forehead, wrist and chest.
8 citations
Cites methods from "A wrist worn SpO 2 monitor with cus..."
...The transmittance SpO2 computation uses the conventional techniques based on R-value and calibration coefficients, as discussed in several publications [10], [11], [12]....
[...]
22 Mar 2021
TL;DR: Wang et al. as mentioned in this paper proposed WristO 2, an alternative approach for reliable peripheral blood oxygen saturation (SpO 2 ) measurements from the wrist, by selectively pruning unreliable data, which achieves an order of magnitude reduction in error compared to existing algorithms, while still providing sufficiently frequent readings for continuous health monitoring.
Abstract: Peripheral blood oxygen saturation (SpO 2 ) is a vital health signal with many clinical applications. Modern wrist-worn devices, such as the Apple Watch, FitBit, and Samsung Gear, have pulse oximeter sensors, making them theoretically capable of measuring SpO 2 . However, current techniques for SpO 2 measurements using pulse oximeter sensors are based on readings taken from the fingertip. Readings collected from the wrist are unreliable and often inaccurate, due to motion and insufficient skin contact. Enabling accurate oxygen saturation monitoring on wearable devices would allow continuous health monitoring and open up new avenues of research. In this work, we explore the reliability of SpO 2 measurements from the wrist. Using a custom wrist-worn pulse oximeter, we find that existing algorithms used in traditional fingertip SpO 2 sensors are a poor match for taking measurements from the wrist and can lead to over 90% of readings being inaccurate. We further show that skin tone, IMU sensors, and user-level calibration affect measurement error, and must be considered when designing wrist-worn SpO 2 sensors and measurement algorithms. Next, based on our findings, we propose WristO 2 , an alternative approach for reliable SpO 2 sensing. By selectively pruning unreliable data, WristO 2 achieves an order of magnitude reduction in error compared to existing algorithms, while still providing sufficiently frequent readings for continuous health monitoring.
8 citations
References
More filters
23 Oct 1997
TL;DR: In this paper, the authors present a user interface for a pulse oximeter, based on an interface provided by Lozano-Nieto and Schowalter, with a discussion of the application of pulse oximetry.
Abstract: Normal oxygen transport (S A Clark). Motivation of pulse oximetry (D J Sebald). Blood oxygen measurement (J Farmer). Light absorbance in pulse oximetry (O Wieben). Light-emitting diodes and their control (B W J Bourgeois). Photodetectors and amplifiers (J S Schowalter). Probes (M V S Reddy). Electronic instrument control (K S Paranjape). Signal processing algorithms (S Palreddy). Calibration (J S Schowalter). Accuracy and errors (S Tungjitkusolmun). User interface for a pulse oximeter (A Lozano-Nieto). Applications of pulse oximetry (J B Ruchala). Glossary. Index.
478 citations
"A wrist worn SpO 2 monitor with cus..." refers background or methods in this paper
...If concentration in arterial blood of hemoglobin without oxygen (reduced hemoglobin, Hb) is NHb and that of the oxygenated hemoglobin (oxyhemoglobin, HbO) is NHbO, then blood oxygen saturation level is computed as shown in (1) [2]....
[...]
...Accurate and reliable measurements of arterial blood oxygen saturation using photoplethysmography still remains an open area of research and researchers among the world face issues due to motion artifacts caused by seizures, tremors, incorrect sensor placement, presence of airgap between sensors and fingertip, incorrect probe size, dark skin pigmentation, cold hands, presence of nail polish, artificial nails and varying perfusion levels [2], [3]....
[...]
...Cells will be damaged if they are deprived of oxygen for a prolonged period [2]....
[...]
...Deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass through [5],[2]....
[...]
12 Nov 2012
TL;DR: An algorithm for motion artifact detection, which is based on the analysis of the variations in the time and period domain characteristics of the PPG signal, shows that both time and especially period domain features play an important role in the discrimination of motion artifacts from clean PPG pulses.
Abstract: The presence of motion artifacts in the photoplethysmographic (PPG) signals is one of the major obstacles in the extraction of reliable cardiovascular parameters in real time and continuous monitoring applications. In the current paper we present an algorithm for motion artifact detection, which is based on the analysis of the variations in the time and period domain characteristics of the PPG signal. The extracted features are ranked using a feature selection algorithm (NMIFS) and the best features are used in a Support Vector Machine classification model to distinguish between clean and corrupted sections of the PPG signal. The results achieved by the current algorithm (SE: 0.827 and SP: 0.927) show that both time and especially period domain features play an important role in the discrimination of motion artifacts from clean PPG pulses.
42 citations
TL;DR: This work presents calibration-free pulse oximetry for measurement of SpO2, based on PPG pulses of two nearby wavelengths in the infrared, which can be derived from the PPG parameters with no need for calibration.
Abstract: The assessment of oxygen saturation in arterial blood by pulse oximetry (SpO2) is based on the different light absorption spectra for oxygenated and deoxygenated hemoglobin and the analysis of photoplethysmographic (PPG) signals acquired at two wavelengths. Commercial pulse oximeters use two wavelengths in the red and infrared regions which have different pathlengths and the relationship between the PPG-derived parameters and oxygen saturation in arterial blood is determined by means of an empirical calibration. This calibration results in an inherent error, and pulse oximetry thus has an error of about 4%, which is too high for some clinical problems. We present calibration-free pulse oximetry for measurement of SpO2, based on PPG pulses of two nearby wavelengths in the infrared. By neglecting the difference between the path-lengths of the two nearby wavelengths, SpO2 can be derived from the PPG parameters with no need for calibration. In the current study we used three laser diodes of wavelengths 780, 785 and 808 nm, with narrow spectral line-width. SaO2 was calculated by using each pair of PPG signals selected from the three wavelengths. In measurements on healthy subjects, SpO2 values, obtained by the 780–808 nm wavelength pair were found to be in the normal range. The measurement of SpO2 by two nearby wavelengths in the infrared with narrow line-width enables the assessment of SpO2 without calibration.
40 citations
"A wrist worn SpO 2 monitor with cus..." refers background in this paper
...Deoxygenated hemoglobin absorbs more red light and allows more infrared light to pass through [5],[2]....
[...]
TL;DR: In vitro photoplethysmograms used to determine a patient’s blood oxygenation and pulse rate have been measured accurately via self-mixing interferometry by a compact laser diode with a ball lens integrated into the package, which can be easily integrated into a commercial sensor.
Abstract: Currently, photoplethysmograms (PPGs) are mostly used to determine a patient's blood oxygenation and pulse rate. However, PPG morphology conveys more information about the patient's cardiovascular status. Extracting this information requires measuring clean PPG waveforms that are free of artifacts. PPGs are highly susceptible to motion, which can distort the PPG-derived data. Part of the motion artifacts are considered to result from sensor-tissue motion and sensor deformation. It is hypothesized that these motion artifacts correlate with movement of the sensor with respect to the skin. This hypothesis has been proven true in a laboratory setup. In vitro PPGs have been measured in a skin perfusion phantom that is illuminated by a laser diode. Optical motion artifacts are generated in the PPG by translating the laser diode with respect to the PPG photodiode. The optical motion artifacts have been reduced significantly in vitro, by using a normalized least-mean-square algorithm with only a single coefficient that uses the laser's displacement as a reference for the motion artifacts. Laser displacement has been measured accurately via self-mixing interferometry by a compact laser diode with a ball lens integrated into the package, which can be easily integrated into a commercial sensor.
39 citations
01 Dec 2012
TL;DR: In this paper, the frequency characteristics of photoplethysmogram (PPG) signal were analyzed to improve the accuracy of SpO 2 by reducing the motion artifacts, and the results showed that most of PPG signals analyzed in this study consisted of the fundamental, 2nd and 3rd harmonic components caused by arterial blood flow and component caused by motion artifact.
Abstract: In this study, we analyzed frequency characteristics of photoplethysmogram (PPG) signal to improve the accuracy of SpO 2 by reducing the motion artifacts. 23 kinds of different signals generated by SpO 2 test equipment were used for this analysis. The results of analysis showed that most of PPG signals analyzed in this study consisted of the fundamental, 2nd and 3rd harmonic components caused by arterial blood flow and component caused by motion artifact. The result also showed the relative magnitudes of its three frequency components. The signals could be divided into four groups based on the relative locations of these frequency components. But four different algorithms would be required to discriminate the signal and motion artifact frequency components.
12 citations