A Novel Photoplethysmography Sensor for Vital Signs Monitoring from the Human Trachea.

Current pulse oximeter sensors can be challenged in working accurately and continuously in situations of reduced periphery perfusion, especially among anaesthetised patients. A novel tracheal photoplethysmography (PPG) sensor has been developed in an effort to address the limitations of current pulse oximeters. The sensor has been designed to estimate oxygen saturation (SpO) and pulse rate, and has been manufactured on a flexible printed circuit board (PCB) that can adhere to a standard endotracheal (ET) tube.

Investigating optical path and differential pathlength factor in reflectance photoplethysmography for the assessment of perfusion.

Photoplethysmography (PPG) is an optical noninvasive technique with the potential for assessing tissue perfusion. The relative time-change in the concentration of oxyhemoglobin and deoxyhemoglobin in the blood can be derived from DC part of the PPG signal. However, the absolute concentration cannot be determined due to the inadequate data on PPG optical paths.

Dual pO/pCO fibre optic sensing film.

A fibre optic multi-sensor has been developed for biomedical sensing applications using a tip coating solution sensitive to both oxygen and carbon dioxide. An oxygen sensitive phosphorescence quenching complex based on platinum octaethylporphyrin (PtOEP) was combined with a carbon dioxide sensitive phosphorescence compound based on 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS). When excited by blue light (470 nm), the resultant coating had two fluorescent peaks at 515 nm (green) and 645 nm (red) which responded to partial pressure of CO and O respectively.

Fiber-optic fluorescence-quenching oxygen partial pressure sensor using platinum octaethylporphyrin.

The development and bench testing of a fiber-optic oxygen sensor is described. The sensor is designed for measurement of tissue oxygen levels in the mucosa of the digestive tract. The materials and construction are optimized for insertion through the mouth for measurement in the lower esophagus.

A fiberoptic sensor for tissue carbon dioxide monitoring.

We present a new fiberoptic carbon dioxide sensor for transcutaneous and mucosa (indwelling) blood gas monitoring. The sensor is based on optical fluorescence of molecules sensitive to pH changes associated with dissolved CO2. A three layer chemical coating was dip-coated onto the distal tip of an optical fiber (600μm core radius).

Intraoperative monitoring of intestinal viability: Evaluation of a new combined sensor.

A dual wavelength photoplethysmography (PPG) and laser Doppler flowmetry (LDF) sensor was developed to investigate the suitability of these techniques for monitoring bowel viability intraoperatively. Clinical measurements were obtained from thirty patients undergoing bowel surgery. Three measurements were performed at different stages of the operation.

Differential pathlength factor estimation for brain-like tissue from a single-layer Monte Carlo model.

A Monte Carlo simulation-based computational model has been developed for tracing the pathway of light within a single layer of tissue like bloodless human brain. A reflectance mode source-detector geometry is assumed to illuminate the tissue slab with an irradiation of a near infrared wavelength and to detect the re-emitted light intensity. Light is considered to be attenuated within tissue by scattering and absorption.

Investigation of peripheral photoplethysmographic morphology changes induced during a hand-elevation study.

A hand-elevation study was carried out in the laboratory in order to alter peripheral blood flow with the aim of increasing understanding of factors affecting the morphology of peripheral photoplethysmographic signals. Photoplethysmographic (PPG) signals were recorded from twenty healthy volunteer subjects during a hand-elevation study in which the right hand was raised and lowered relative to heart level, while the left hand remained static. Red and infrared (IR) PPG signals were obtained from the right and left index fingers using a custom-made PPG processing system.

Comparison of foot finding methods for deriving instantaneous pulse rates from photoplethysmographic signals.

The suitability of different methods of finding the foot point of a pulse as measured using earlobe photoplethysmography during stationary conditions was investigated. Instantaneous pulse period (PP) values from PPG signals recorded from the ear in healthy volunteer subjects were compared with simultaneous ECG-derived cardiac periods (RR interval). Six methods of deriving pulse period were used, each based on a different method of finding specific landmark points on the PPG waveform.

Vascular changes associated with spinal root avulsion injury.

This paper has investigated the hypothesis that spinal root avulsion (SRA) injury produces alterations in blood flow that contribute to avulsion injury induced pain-like behaviour in rodents. Photoplethysmography (PPG) is an established way of assessing blood flow in the central nervous system (CNS) and laser Doppler flowmetry (LDF) is the most widely used technique for measuring tissue perfusion. Using an established model of SRA injury that produces mechanical hypersensitivity, the PPG and LDF signals were recorded in animals 2 weeks post-injury and compared to naive recordings.

Comparison of methods for determining pulse arrival time from Doppler and photoplethysmography signals.

The aim of this study was to compare three foot-finding methods applied to ultrasound Doppler and photoplethysmographic (PPG) signals: maximum 1st derivative, maximum 2nd derivative and an 'intersecting tangents' method. The pulse arrival times of each method were compared. Also the precision of each method was evaluated by comparing instantaneous cardiac periods derived using each method from simultaneous Doppler and PPG with a reference measurement: the R-R interval calculated from a simultaneously recorded ECG.

Effect of respiratory-induced intensity variations on finger SpO2 measurements in volunteers.

Photoplethysmographic (PPG) signals were recorded from the fingers of 16 healthy volunteers with periods of timed and forced respiration. The aim of this pilot study was to compare estimations of arterial oxygen saturation (SpO2) recorded using a dedicated pulse oximetry system while subjects were breathing regularly with and without a mouthpiece containing a flow resistor. The experiments were designed to mimic the effects of mechanical ventilation in anesthetized patients.

Evaluation of a combined reflectance photoplethysmography and laser Doppler flowmetry surface probe.

This study presents evaluation of a system combining laser Doppler flowmetry and photoplethysmography (PPG) in a single probe for the simultaneous measurement of perfusion and blood flow in the finger. A cuff sphygmomanometer was used to partially occlude the arteries supplying the hand to investigate the effect of low pressure on photoplethysmographic and laser Doppler signals and also on calculated arterial blood oxygen saturation values (SpO2). Red and infrared PPG and Doppler signals were recorded from six healthy volunteers at various pressures.

Perfusion assessment in rat spinal cord tissue using photoplethysmography and laser Doppler flux measurements.

Animal models are widely used to investigate the pathological mechanisms of spinal cord injury (SCI), most commonly in rats. It is well known that compromised blood flow caused by mechanical disruption of the vasculature can produce irreversible damage and cell death in hypoperfused tissue regions and spinal cord tissue is particularly susceptible to such damage. A fiberoptic photoplethysmography (PPG) probe and instrumentation system were used to investigate the practical considerations of making measurements from rat spinal cord and to assess its suitability for use in SCI models.

Modulation of finger photoplethysmographic traces during forced respiration: venous blood in motion?

Photoplethysmographic (PPG) signals were recorded from the fingers of 10 healthy volunteers during forced respiratory inspiration. The aim of this pilot study was to assess the effect of negative airway pressure on the blood volumes within the tissue bed of the finger, and the resultant modulation of PPG signals. The acquired signals were analysed and oxygen saturations estimated from the frequency spectra in the cardiac and respiratory frequency ranges.

Evaluation of electrical and optical plethysmography sensors for noninvasive monitoring of hemoglobin concentration.

Completely noninvasive monitoring of hemoglobin concentration has not yet been fully realized in the clinical setting. This study investigates the viability of measuring hemoglobin concentration noninvasively by evaluating the performance of two types of sensor using a tissue phantom perfused with a blood substitute. An electrical sensor designed to measure blood volume changes during the cardiac cycle was used together with an infrared optical sensor for detection of erythrocyte-bound hemoglobin.

Electro-optical plethysmography for non-invasive estimation of hemoglobin concentration.

Novel sensors and instrumentation are currently being investigated with the intended application of determining the concentration of hemoglobin and other optically absorbing compounds in blood using non-invasive methods. In order to measure concentration, the mass or amount of a compound must be known in addition to the volume of liquid. In principle, it may be possible to estimate hemoglobin concentration from a change in optical absorbance occurring over the cardiac cycle divided by a corresponding change in measured blood volume during the cycle measured from peripheral tissue, e.

Photoplethysmographic measurements from the esophagus using a new fiber-optic reflectance sensor.

A prototype fiber-optic reflectance-mode pulse oximetry sensor and measurement system is developed for the purposes of estimating arterial oxygen saturation in the esophagus. A dedicated probe containing miniature right-angled glass prisms coupled to light sources and a photodetector by means of optical fibers is designed and used to record photoplethysmographic (PPG) signals from the esophageal epithelium in anesthetized patients. The probe is inserted simply by an anesthesiologist in all cases, and signals are recorded successfully in all but one of 20 subjects, demonstrating that esophageal PPG signals can be reliably obtained.

Evaluation of a multimode photoplethysmographic sensor during cuff-induced hypoperfusion.

Photoplethysmography (PPG) is a technique widely used to monitor volumetric blood changes induced by cardiac pulsations. Pulse oximetry uses the technique of PPG to estimate arterial oxygen saturation values(S(p)O(2)). In poorly perfused tissues, S(p)O(2) readings may be compromised due to the poor quality of the PPG signals.

Calculation of photon path changes due to scatter in Monte Carlo simulations.

Computation using Monte Carlo simulations is widely used for modelling the light-tissue interaction. Despite this, many of the methods used for building such simulations are poorly described in the literature. In particular, a scheme for translating the scatter angles produced from a phase function into updated photon direction vectors is not explicitly reported.

Evaluation of a fiber-optic esophageal pulse oximeter.

A dual-wavelength fiber-optic pulse oximetry system was developed for the purposes of estimating oxygen saturation from the esophagus. A probe containing miniature right-angled glass prisms was used to record photoplethysmographic (PPG) signals from the esophageal wall. Signals were recorded successfully in 19 of 20 patients, demonstrating that PPG signals could be reliably obtained from an internal vascularized tissue site such as the esophageal epithelium.

Investigation of photoplethysmographic changes using a static compression model of spinal cord injury.

Little is known about cell death in spinal cord tissue following compression injury, despite compression being a key component of spinal injuries. Currently models are used to mimic compression injury in animals and the effects of the compression evaluated by observing the extent and duration of recovery of normal motor function in the days and weeks following the injury. A fiber-optic photoplethysmography system was used to investigate whether pulsation of the small arteries in the spinal cord occurred before, during and after compressive loads were applied to the tissue.

A novel non-invasive trans-reflectance photoplethysmographic probe for use in cases of low peripheral blood perfusion.

The acquisition of reliable and meaningful photo-plethysmographic (PPG) signals using conventional pulse oxime-try technology may be compromised by conditions of low tissue perfusion. We have developed a novel 'trans-reflectance' PPG measurement system which combines reflectance and transmit-tance together into a single mode. For comparison purposes the system also enables the independent display of reflectance and transmittance PPG signals simultaneously.

Monitoring brain oxygenation in head-injury patients.

Over the last few decades, many methods have been developed to try to monitor the oxygenation status of the brain tissue. These methods have been the subject of a large body of research attempting to understand and interpret the measurements, thus producing clinically useful indicators to guide clinical interventions with the ultimate aim of improving patient outcome. Many techniques have remained in the research domain or have simply been abandoned, but some have generated substantial interest and have been developed into commercially available products in widespread use around the world.

Pulse oximetry and photoplethysmographic waveform analysis of the esophagus and bowel.

Purpose Of Review: This article reviews the development of novel reflectance pulse oximetry sensors for the esophagus and bowel, and presents some of the techniques used to analyze the waveforms acquired with such devices.

Recent Findings: There has been much research in recent years to expand the utility of pulse oximetry beyond the simple measurement of arterial oxygen saturation from the finger or earlobe. Experimental sensors based on reflectance pulse oximetry have been developed for use in internal sites such as the esophagus and bowel.