D. P. Jones

Esophageal pulse oximetry utilizing reflectance photoplethysmography

Peripheral perfusion is often poor and barely pulsatile in patients undergoing prolonged major surgery. Hence, the arterial blood oxygen saturation (SpO/sub 2/) readings from commercial finger pulse oximeters can become unreliable or cease when they are most needed. To overcome this limitation, the esophagus has been investigated as an alternative measurement site, as perfusion may be preferentially preserved centrally. A reflectance esophageal pulse oximeter probe, and a processing system implemented in Lab VIEW were developed. The system was evaluated in clinical measurements on 49 cardiothoracic surgery patients. The SpO/sub 2/ values from the esophagus were in good agreement with arterial blood oxygen saturation (SaO/sub 2/) values obtained from blood gas analysis and CO-oximetry. The means (/spl plusmn/SD) of the differences between the esophageal SpO/sub 2/ and SaO/sub 2/ results from blood gas analysis and CO-oximetry were 0.02/spl plusmn/0.88% and -0.73/spl plusmn/0.72%, respectively. In five (10.2%) of the patients, the finger pulse oximeter failed for at least 10 min while the esophageal SpO/sub 2/ readings remained reliable. The results confirm that the esophagus may be used as an alternative monitoring site for pulse oximetry even in patients with compromised peripheral perfusion.

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. Analysis of the photoplethysmographic waveforms produced by these sensors is beginning to shed light on some of the potentially useful information hidden in these signals. Summary The use of novel reflectance pulse oximetry sensors has been successfully demonstrated. Such sensors, combined with the application of more advanced signal processing, will hopefully open new avenues of research leading to the development of new types of pulse oximetry-based monitoring techniques.

Preliminary evaluation of a new fibre-optic cerebral oximetry system

A new system for measuring the oxygen saturation of blood within tissue has been developed, for a variety of patient monitoring applications. A particular unmet need is in the central nervous system, and this project aims to devise a means for measuring blood oxygen saturation in the brain tissue of patients recovering from neurosurgery or head injury. Coupling light sources and a photodetector to optical fibres results in a probe small enough to pass through a cranial bolt of the type already in use for intra-cranial pressure monitoring. The development and evaluation of a two-wavelength fibre-optic reflectance photoplethysmography (PPG) system are described. It was found that good quality red and near-infrared PPG signals could be obtained from the finger using a fibre-optic probe. Experiments were conducted to find the inter-fibre spacings that yield signals most suitable for calculating oxygen saturation. Reliable signals could be obtained for inter-fibre spacings between 2 mm and 5 mm, the latter being the size of the maximum aperture in the cranial bolt. A preliminary measurement from human brain tissue is also presented.

A pilot study of neonatal and pediatric esophageal pulse oximetry

BACKGROUND:In this pilot study we explored the suitability of the esophagus as a new measuring site for blood oxygen saturation (Spo2) in neonates. METHODS:A new miniaturized esophageal pulse oximeter has been developed. Five patients (one child and four neonates) were studied. RESULTS:Spo2 values were obtained in the esophagus of all patients. A Bland and Altman plot of the difference between Spo2 values from the esophageal pulse oximeter and a commercial toe pulse oximeter against their mean showed that the bias and the limits of agreement between the two pulse oximeters were +0.3% and +1.7% to −1.0%, respectively. CONCLUSIONS:This study suggests that the esophagus can be used as an alternative site for monitoring blood oxygen saturation in children and neonates.

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. The mean value of the oxygen saturation recorded from the esophagus for all subjects is 94.0 ± 4.0%. These results demonstrate that SpO(2) may be estimated in the esophagus using a fiber-optic probe.

Cerebral Arterial Oxygen Saturation Measurements Using a Fiber-Optic Pulse Oximeter

BackgroundA pilot investigation was undertaken to assess the performance of a novel fiber-optic cerebral pulse oximetry system. A fiber-optic probe designed to pass through the lumen of a cranial bolt of the type used to make intracranial pressure measurements was used to obtain optical reflectance signals directly from brain tissue.MethodsShort-duration measurements were made in six patients undergoing neurosurgery. These were followed by a longer duration measurement in a patient recovering from an intracerebral hematoma. Estimations of cerebral arterial oxygen saturation derived from a frequency domain-based algorithm are compared with simultaneous pulse oximetry (SpO2) and hemoximeter (SaO2) blood samples.ResultsThe short-duration measurements showed that reliable photoplethysmographic signals could be obtained from the brain tissue. In the long-duration study, the mean (±SD) difference between cerebral oxygen saturation (ScaO2) and finger SpO2 (in saturation units) was −7.47(±3.4)%. The mean (±SD) difference between ScaO2 and blood SaO2 was −7.37(±2.8)%.ConclusionsThis pilot study demonstrated that arterial oxygen saturation may be estimated from brain tissue via a fiber-optic pulse oximeter used in conjunction with a cranial bolt. Further studies are needed to confirm the clinical utility of the technique.

Investigation of photoplethysmographic signals in neonatal and paediatric patients

METHODS. Fifteen healthy small pigs with continuous mechanical ventilation were randomly divided into group A (VT=16 ml/kg£¬PEEP=0), group B ( VT=6 ml/kg, PEEP=16cmH2O) and group C (VT=6 ml/kg, PEEP=8cmH2O). Immuno-histochemistry and western blot were respectively used to evaluate the expression of ICAM-1 protein and the phosphorylation of p38 MAPK levels in lung tissues 3 hours following ventilation£¬ the pulmonary histopathological change was observed as well.

An oesophageal pulse oximetry system utilising a fibre-optic probe

A dual-wavelength fibre-optic pulse oximetry system is described for the purposes of estimating oxygen saturation (SpO2) from the oesophagus. A probe containing miniature right-angled glass prisms was used to record photoplethysmographic (PPG) signals from the oesophageal wall. Signals were recorded successfully in 19 of 20 patients, demonstrating that PPG signals could be reliably obtained from an internal vascularised tissue site such as the oesophageal epithelium. The value of the mean oxygen saturation recorded from the oesophagus was 94.0 ± 4.0%. These results demonstrate that SpO2 may be estimated in the oesophagus using a fibre-optic probe.

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. To address this, a method for calculating the change in photon direction following a scattering event is described, thus illuminating one of the fundamental ‘building blocks’ for researchers developing their own Monte Carlo models. The equations derived in this paper may be readily incorporated into applicable Monte Carlo program code.

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. The value of the mean oxygen saturation recorded from the esophagus was 94.0 ± 4.0%. These results demonstrate that SpO2 may be estimated in the esophagus using a fiber-optic probe and this may be the first report of such measurements.