Photoplethysmography Sensor Research Articles

Pulse transit time as a quick predictor of a successful axillary brachial plexus block

It can take up to 30 min to determine whether or not axillary block has been successful. Pulse transit time (PTT) is the time between the R-wave on electrocardiography (ECG) and the arrival of the resulting pressure pulse wave in the fingertip measured with photoplethysmography. It provides information about arterial resistance. Axillary block affects vasomotor tone causing loss of sympathetic vasoconstriction resulting in an increased PTT. Early objective assessment of a block can improve efficacy of operating room time and minimize patient's fear of possible conversion to general anesthesia. This study explores whether PTT can objectively, reliably and quickly predict a successful axillary block. Forty patients undergoing hand surgery under axillary block were included. A three-lead ECG and photoplethysmographic sensors were placed on both index fingers. Measurements were made from 2 min before until 30 min after induction of the block or less if the patient was transferred for operation. Afterwards, PTT was calculated as the time between the R-wave on ECG and a reference point on the photoplethysmogram. To assess the change in PTT caused by the block, the PTT difference between the control and blocked arm was calculated. Sensitivity and specificity of PTT difference were calculated using receiver operating characteristic analysis. In a successful block, the mean PTT difference significantly increased after 3 min by 12 (standard error of the mean 3.9) ms, sensitivity 87% and specificity 71% (area under the curve 0.87, P = 0.004). PTT is a reliable, quick and objective method to assess whether axillary block is going to be successful or not.

Chronic Performance of a Subcutaneous Hemodynamic Sensor

A subcutaneous photoplethysmography (PPG) sensor uses light to detect changes in vascular volume from a location outside the bloodstream. Incorporation into a chronically implanted device, such as a pacemaker or an implantable cardioverter defibrillator, may facilitate therapy optimization and disease monitoring by providing continuous assessment of hemodynamic function and arterial oxygen saturation. However, performance of a chronically placed subcutaneous sensor has not been established. Six dogs were implanted with 2-4 PPG sensors subcutaneously in the neck or posterior thorax. Half of the sensors were directed toward deep tissue and half toward overlying cutaneous tissue. Each sensor contained a red and an infrared light emitting diode, a photodetector, and supporting electronics, which were encapsulated in epoxy and attached to a transcutaneous connector. Data were collected at implant and every 3 ± 1 days for 4-9 months starting 3 weeks postimplant. At explant, the fibrous encapsulation was histologically analyzed. A minimally to moderately neovascularized encapsulation formed over all sensors, consisting of fibrous and granulation tissue. Higher cardiac pulse amplitudes and direct current (DC) components were recorded in sensors oriented toward deep tissue, but no significant difference between orientations was found in respiratory wave amplitude. Cardiac pulse amplitude, respiratory wave amplitude, and DC component amplitude, as recorded by the sensor, did not significantly change over time. Despite fibrous encapsulation of PPG sensors, cardiac pulses and respiratory waves could easily be measured throughout the study and remained constant over time. These results suggest suitability of subcutaneous PPG technology for chronic applications.

Spectral analysis of Heart Rate Variability in psychiatric patients: autonomic nervous system evaluation in psychotic, anxiety and depressive disorders

The aim of this study was to test the primary hypothesis of altered Heart Rate Variability (HRV) and heart rate in a sample of patients with mental disorders and the secondary hypothesis of normalization of HRV values as a result of clinical improvement. The study was conducted on a sample of 90 patients with psychotic, anxiety and mood disorders. Each patient was subjected to detection of HRV and heart rate via a photoplethysmographic sensor and evaluated with rating scales based on the specific disorder. The parameters detected in the sample were compared with a control group of healthy subjects. There were no significant differences of cardiac autonomic modulation between the group of patients in whom is possible exclude the drug influence and the control group; significantly lower values of HRV parameters in the group of patients with drug influence, and especially in subgroup of psychotic patients, compared to controls, are, instead, detected. The study also shows a significant increase in heart rate as a common feature in mental disorders, regardless of treatment. Clinical improvement appears to promote the normalization of the variability in patients with high DS of tachogram. The study suggests a potential increased risk of cardiovascular mortality in patients, as evidenced by the increased values of heart rate, regardless of drug treatment. This risk is even more pronounced in psychotic patients in drug treatment because of the simultaneous significant reduction of HRV parameters.

Optical Sensor for Indian Siddha Diagnosis System

Traditional Indian medicine has been using the pulse as a form of disease diagnosis. The roots of this pulse diagnosis lie in the three radial pulses which are known as vata, pitta, and kapha. In this project, a photoplethysmographic sensor is presented for pulse diagnosis. PPG sensor is used to monitor the blood flow rate. The sensor is placed at identified radial points corresponding vatta, pitta, kapha. The output of the sensor is analyzed using Lab VIEW software.PPG values are taken at wrist for subjects in different age groups. The acquired PPG signal is compared with the values taken by the Siddha Practitioner and classified the subjects as of vata, pitta, and kapha type.

A Portable Multi-sensor System for Non-invasive Measurement of Biometrical Data

Abstract In the last years, the availability of performing personal computing devices, like smartphones, opens new scenarios to the so called Body Area Network, i.e., sensor networks used to monitor physical conditions of the user. Generally speaking, the sensors adopted to monitor physical parameters, like heartbeat or exertion level, are not suitable for run–time measurements. However, the physical performance of athletes may be improved by a continuous monitoring of the body conditions. In this work, a simple, portable and low-cost system for non-invasive measurement of physical parameters is proposed and experimentally characterized. It is based on two different sensors combined in a unique structure to be applied in a clip-like fashion to the earlobe or analogue body part of a person. A photoplethysmographic sensor is used to optically measure the change in volume of blood in the arteries, thus to acquire information about heart beating, blood pressure, and arrhythmias. The second sensor is composed of two electrodes, thus an impedance measurement of the tissue is conducted. The impedance estimation can be used to monitor application-specific parameters, such as blood pH. The structure is compact in size and low-power, making it suitable for portable and battery-operated systems. The experimental characterization of the prototype demonstrates the feasibility of the proposed approach.

Non-invasive estimate of blood glucose and blood pressure from a photoplethysmograph by means of machine learning techniques

This work presents a system for a simultaneous non-invasive estimate of the blood glucose level (BGL) and the systolic (SBP) and diastolic (DBP) blood pressure, using a photoplethysmograph (PPG) and machine learning techniques. The method is independent of the person whose values are being measured and does not need calibration over time or subjects. The architecture of the system consists of a photoplethysmograph sensor, an activity detection module, a signal processing module that extracts features from the PPG waveform, and a machine learning algorithm that estimates the SBP, DBP and BGL values. The idea that underlies the system is that there is functional relationship between the shape of the PPG waveform and the blood pressure and glucose levels. As described in this paper we tested this method on 410 individuals without performing any personalized calibration. The results were computed after cross validation. The machine learning techniques tested were: ridge linear regression, a multilayer perceptron neural network, support vector machines and random forests. The best results were obtained with the random forest technique. In the case of blood pressure, the resulting coefficients of determination for reference vs. prediction were R(SBP)(2)=0.91, R(DBP)(2)=0.89, and R(BGL)(2)=0.90. For the glucose estimation, distribution of the points on a Clarke error grid placed 87.7% of points in zone A, 10.3% in zone B, and 1.9% in zone D. Blood pressure values complied with the grade B protocol of the British Hypertension society. An effective system for estimate of blood glucose and blood pressure from a photoplethysmograph is presented. The main advantage of the system is that for clinical use it complies with the grade B protocol of the British Hypertension society for the blood pressure and only in 1.9% of the cases did not detect hypoglycemia or hyperglycemia.

An Investigation of Pulse Transit Time as a Non-Invasive Blood Pressure Measurement Method

The objective of this paper is to examine the Pulse Transit Method (PTT) as a non-invasive means to track Blood Pressure over a short period of time. PTT was measured as the time it takes for an ECG R-wave to propagate to the finger, where it is detected by a photoplethysmograph sensor. The PTT method is ideal for continuous 24-hour Blood Pressure Measurement (BPM) since it is both cuff-less and non-invasive and therefore comfortable and unobtrusive for the patient. Other techniques, such as the oscillometric method, have shown to be accurate and reliable but require a cuff for operation, making them unsuitable for long term monitoring. Although a relatively new technique, the PTT method has shown to be able to accurately track blood pressure changes over short periods of time, after which re-calibration is necessary. The purpose of this study is to determine the accuracy of the method.

Photoplethysmographic sensors for perfusion measurements in spinal cord tissue

Sensors for recording photoplethysmographic signals from the nervous tissue of the spinal cord are described. The purpose of these sensors is to establish whether perfusion is compromised in various states of injury which occur in certain animal models of spinal cord injury, for example compression injury. Various measures of perfusion are applicable such as the amplitude of the photoplethysmograph signal and the oxygen saturation, measured using a dual wavelength configuration. Signals are usually compared to baseline measurements made in uninjured subjects. This paper describes two types of probe, one based on optical fibres, and one in which optotes are placed in direct contact with the tissue surface. Results from a study based on a compression model utilising a fibreoptic sensor are presented.

Investigation of photoplethysmographic signals and blood oxygen saturation values obtained from human splanchnic organs using a fiber optic sensor

A reliable, continuous method of monitoring splanchnic organ oxygen saturation could allow for the early detection of malperfusion, and may prevent the onset of multiple organ failure. Current monitoring techniques have not been widely accepted in critical care monitoring. As a preliminary to developing a continuous indwelling device, this study evaluates a new handheld fiber optic photoplethysmographic (PPG) sensor for estimating the blood oxygen saturation (SpO(2)) of splanchnic organs during surgery. A fiber optic splanchnic PPG sensor, instrumentation system and virtual instrument were developed to facilitate PPG and SpO(2) measurement from splanchnic organs. Following Local Research Ethics Committee approval, the sensor was evaluated on seventeen ASA 1 and 2 patients undergoing open laparotomy. PPG signals were obtained from the large bowel, small bowel, liver and stomach. Simultaneous PPG signals from the finger were also obtained using an identical fiber optic sensor. Good quality PPG signals with high signal-to-noise (SNR) ratios were obtained from all splanchnic sites under investigation. Analysis of the ac and dc amplitudes of the red and infrared PPG signals showed there to be a statistically significant difference between PPG signals obtained from splanchnic organs with those obtained from the finger (using fiber optic sensors). Estimated SpO(2) values from the splanchnic organs show good agreement with those obtained from the finger using both a fiber optic sensor and a commercial device. Furthermore, the results of a Bland and Altman analysis indicate that fiber optic splanchnic pulse oximetry, particularly of the bowel, may provide a suitable method for monitoring splanchnic organ perfusion. The evaluation of a new fiber optic sensor on anaesthetized patients undergoing laparotomy demonstrated that good quality PPG signals and SpO(2) estimates can be obtained from splanchnic organs. Such a sensor may provide a useful tool for the intraoperative assessment of splanchnic perfusion.

Ratiometric Artifact Reduction in Low Power Reflective Photoplethysmography

This paper presents effective signal-processing techniques for the compensation of motion artifacts and ambient light offsets in a reflective photoplethysmography sensor suitable for wearable applications. A ratiometric comparison of infrared (IR) and red absorption characteristics cancels out noise that is multiplicative in nature and amplitude modulation of pulsatile absorption signals enables rejection of additive noise. A low-power, discrete-time pulse-oximeter platform is used to capture IR and red photoplethysmograms so that the data used for analysis have noise levels representative of what a true body sensor network device would experience. The proposed artifact rejection algorithm is designed for real-time implementation with a low-power microcontroller while being robust enough to compensate for varying levels in ambient light as well as reducing the effects of motion-induced artifacts. The performance of the system is illustrated by its ability to extract a typical plethysmogram heart-rate waveform since the sensor is subjected to a range of physical disturbances.

Can we improve delivery room monitoring for newborns? A novel photoplethysmographic heart rate monitor evaluated among stable nicu infants

BackgroundHeart rate (HR) is considered the most reliable indicator of successful newborn resuscitation. Current recommended assessment is by auscultation but this is subject to human error1 and can interrupt resuscitation....

Oximeter-Based Autonomic State Indicator Algorithm for Cardiovascular Risk Assessment

Cardiovascular (CV) risk assessment is important in clinical practice. An autonomic state indicator (ASI) algorithm based on pulse oximetry was developed and validated for CV risk assessment. One hundred forty-eight sleep clinic patients (98 men, mean age 50 ± 13 years) underwent an overnight study using a novel photoplethysmographic sensor. CV risk was classified according to the European Society of Hypertension/European Society of Cardiology (ESH/ESC) risk factor matrix. Five signal components reflecting cardiac and vascular activity (pulse wave attenuation, pulse rate acceleration, pulse propagation time, respiration-related pulse oscillation, and oxygen desaturation) extracted from 99 randomly selected subjects were used to train the classification algorithm. The capacity of the algorithm for CV risk prediction was validated in 49 additional patients. Each signal component contributed independently to CV risk prediction. The sensitivity and specificity of the algorithm to distinguish high/low CV risk in the validation group were 80% and 77%, respectively. The area under the receiver operating characteristic curve for high CV risk classification was 0.84. β-Blocker treatment was identified as an important factor for classification that was not in line with the ESH/ESC reference matrix. Signals derived from overnight oximetry recording provide a novel potential tool for CV risk classification. Prospective studies are warranted to establish the value of the ASI algorithm for prediction of outcome in CV disease.

Position Dependency in Photoplethysmographic sensor -Comparison of adjoining PPG signals in Light Sources and Measurement Sites-

This study examined position dependency in photoplethysmography (PPG). For transmitted-light PPG, a sensor is usually attached on a fingertip and transmitted light is monitored. Although simple to use, a fingertip sensor and transmitted-light PPG cannot monitor vital signs during exercise and daily activities because the sensor attachment becomes disturbed. Reflected-light PPG can be applied to any part of the body. However, differences in cutaneous blood supply to different regions have been reported, and the accuracy of measurements can vary among neighboring sites. This position dependency can cause the pulse count to fail and necessitate sensor reattachment. The light source can also affect the characteristics of reflected-light PPG. To investigate position dependency in PPG, we compared the reflected light signals obtained from green and infrared PPG sensors at different sites. Eight young healthy subjects were recruited to participate in the study. Green and infrared PPG signals were collected simultaneously from three sites on the left arm of each participant. The correlations among adjoining green PPG signals were higher than those among adjoining infrared signals. Furthermore, the difference in the pulse interval was smaller among adjoining green PPG signals than among infrared signals. These results suggest that green-light PPG has less position dependency and thus may be more suitable for monitoring the pulse rate during daily activities.This study examined position dependency in photoplethysmography (PPG). For transmitted-light PPG, a sensor is usually attached on a fingertip and transmitted light is monitored. Although simple to use, a fingertip sensor and transmitted-light PPG cannot monitor vital signs during exercise and daily activities because the sensor attachment becomes disturbed. Reflected-light PPG can be applied to any part of the body. However, differences in cutaneous blood supply to different regions have been reported, and the accuracy of measurements can vary among neighboring sites. This position dependency can cause the pulse count to fail and necessitate sensor reattachment. The light source can also affect the characteristics of reflected-light PPG. To investigate position dependency in PPG, we compared the reflected light signals obtained from green and infrared PPG sensors at different sites. Eight young healthy subjects were recruited to participate in the study. Green and infrared PPG signals were collected simultaneously from three sites on the left arm of each participant. The correlations among adjoining green PPG signals were higher than those among adjoining infrared signals. Furthermore, the difference in the pulse interval was smaller among adjoining green PPG signals than among infrared signals. These results suggest that green-light PPG has less position dependency and thus may be more suitable for monitoring the pulse rate during daily activities.

A novel mathematical approach for blood flow signal analyses

We performed continuous synchronized recordings of the blood flow in the brachial artery, electrocardiogram (ECG) and respiration, in different body positions, using a newly developed photoplethysmograph (PPG) sensor. Study of the arterial blood flow was done using a novel mathematical method developed for this purpose. The analyses of 5-minute recording sessions, at constant breathing frequency, showed a high correlation between the arterial blood flow and the heart rate. In addition, the analyses of blood flow recordings from the carotid artery revealed a significant correlation with the heart rate, despite the signal disturbance induced by neck muscle movement during the respiratory circle. Along with arterial blood flow, we performed recordings of peripheral blood flow using an identical PPG sensor. The analyses demonstrate that the arterial blood flow is in better correlation with the heart rate than the peripheral blood flow.

Relationship Between Measurement Site and Motion Artifacts in Wearable Reflected Photoplethysmography

Pulse rates obtained from wearable photoplethysmography (PPG) sensors are important for monitoring cardiovascular condition, especially during exercise. However, it is difficult to precisely count pulse rates during exercise because PPG is sensitive to body movement. The artifacts from body movement are caused by a change in the blood volume at the measurement site, in addition to pulsatile changes. Here, we investigated the influence of motion artifact with respect to light source and anatomical sites. In this study, we compared the signal from green-light PPG to that from infrared PPG at different anatomical sites. In these experiments, 11 subjects were asked to either assume a resting position or generate spontaneous motion artifact by jumping and swinging their arm. As a result, pulse rates obtained from green-light PPG showed a higher correlation with the ECG R-R interval as compared to those obtained with infrared. Additionally, the signal from the upper arm showed less artifact than did the peripheral one. Therefore, the green-light PPG may be useful for pulse rate monitoring.

Measurement of splanchnic photoplethysmographic signals using a new reflectance fiber optic sensor

Splanchnic organs are particularly vulnerable to hypoperfusion. Currently, there is no technique that allows for the continuous estimation of splanchnic blood oxygen saturation (SpO(2)). As a preliminary to developing a suitable splanchnic SpO(2) sensor, a new reflectance fiber optic photoplethysmographic (PPG) sensor and processing system are developed. An experimental procedure to examine the effect of fiber source detector separation distance on acquired PPG signals is carried out before finalizing the sensor design. PPG signals are acquired from four volunteers for separation distances of 1 to 8 mm. The separation range of 3 to 6 mm provides the best quality PPG signals with large amplitudes and the highest signal-to-noise ratios (SNRs). Preliminary calculation of SpO(2) shows that distances of 3 and 4 mm provide the most realistic values. Therefore, it is suggested that the separation distance in the design of a fiber optic reflectance pulse oximeter be in the range of 3 to 4 mm. Preliminary PPG signals from various splanchnic organs and the periphery are obtained from six anaesthetized patients. The normalized amplitudes of the splanchnic PPGs are, on average, approximately the same as those obtained simultaneously from the periphery. These observations suggest that fiber optic pulse oximetry may be a valid monitoring technique for splanchnic organs.

Development of an Implantable Pulse Oximeter

A long-term implantable photoplethysmographic sensor system is proposed. The system employs an elastic cuff which is directly wrapped around an arterial blood vessel. The optically transparent cuff is equipped with light emitting diodes and a photo transistor including the technology of pulse oximetry. The sensor will permit real-time, continuous monitoring of important vital parameters such as arterial blood oxygen saturation and pulse rate over a long-term period in vivo. We emphasize on the specific requirements for design and instrumentation of the implantable sensor and discuss first in vitro data acquired with that new photonics-based sensor.

Theoretical Study on the Effect of Sensor Contact Force on Pulse Transit Time

Pulse transit time (PTT) has been widely used for noninvasive examination of the arterial viscoelastic properties, such as elasticity, compliance, and stiffness of the vessel walls. PTT is usually determined as the time interval between the peak of the electrocardiogram R wave and the foot of the photoplethysmogram (PPG). However, it was observed that the PPG is affected by the applied contact force between the photoplethysmographic sensor and the measurement site, e.g., finger. In this study, the nonlinear biomechanical properties of the finger arterial wall were considered when investigating the changes in PTT with varying contact force. Emphasis was placed on the changes in the shape of the arterial wall pressure-volume curve. The simulation results indicated that at positive transmural pressure, PTT increased with the applied contact force, reaching the maximum at zero transmural pressure and remaining at a constant level at negative transmural pressure. The theoretical analysis was further verified by the experiments carried out on thirty young subjects and six elderly subjects using twelve discrete levels of contact force.

A LED–LED-based photoplethysmography sensor

A high sensitivity, low power and low cost sensor has been developed for photoplethysmography (PPG) measurement. It uses standard light emitting diodes (LEDs) as both light emitter and detector, pulse-based signal conversion techniques instead of the classical analogue-to-digital convertors (ADCs) and a general purpose microcontroller for the implementation of measurement protocol. The main advantages of the proposed approach are that it leads to better spectral sensitivity, increased and adjustable resolution, reduction in cost, dimensions and power consumption, and it avoids the need for expensive and precise operation amplifiers, ADCs and other external components. The basic sensing configuration presented uses only two I/O pins and two LEDs and is capable of detecting the PPG signal from a finger or toe. It is then very simple to extract the vital signs such as heart rate and heart rate variability from such a signal. The basic configuration can easily be expanded to include a pulse oximeter for the determination of oxygen saturation (SpO2) by the addition of only two more LEDs. The proposed technique is also suitable for a wide range of other photometric applications.

The effect of applied sensor contact force on pulse transit time

Pulse transit time (PTT) is usually determined as the time interval between the peak of the electrocardiogram (ECG) R wave and a characteristic point of the peripheral pulse measured by photoplethysmography. However, it was found that the photoplethysmogram (PPG) is affected by the contact force between the photoplethysmographic sensor and the measurement site, i.e. finger. Therefore, we hypothesized that the PTT may be altered by the applied sensor contact force. An ECG and PPG were recorded simultaneously from 30 healthy subjects using 12 magnitudes of contact force (0.1 N–1.8 N). Three characteristic points of the PPG were selected to determine the PTT, including the points near the foot (PTT1), on the systole phase (PTT2) and near the peak (PTT3). Both PTT1 and PTT2 increased significantly (p = 0.014 for PTT1 and p = 0.038 for PTT2) with the sensor contact force until the transmural force reached −0.1 N. With further increase in the contact force, they kept at an almost constant level. Such a changing trend was not found in PTT3. The results of this study suggest that the applied sensor contact force should be carefully controlled in PTT measurement to avoid diminishing its value as a diagnostic tool.