Chemical functionalization of emulsion-templated porous polymers by thiol–ene “click” chemistry

Highly porous polymers (polyHIPEs) have been prepared by the photopolymerization of high internal phase emulsions (HIPEs) with varying ratios of thiol and acrylate monomers. The resulting polymers have a nominal porosity of 80%, and are seen to have a well-defined, interconnected pore morphology, with average pore diameters ranging from 30 to 60 μm. The polyHIPE polymers have been shown using a colourimetric (Ellman's) assay to contain residual thiols which are reactive towards a range of (meth)acrylates (hexafluoroisopropyl acrylate, fluorescein O-acrylate and poly(ethylene glycol) methyl ether methacrylate). Functionalization was explored using thermally- and UV-initiated radical-mediated “click” reactions and an amine-catalysed Michael addition reaction. The extent of functionalization was investigated qualitatively and quantitatively using a range of techniques (solid state NMR spectroscopy; FTIR spectroscopy; X-ray photoelectron spectroscopy (XPS); observation of fluorescence); high levels of conversion (up to 90–95%) were observed for the thermally-initiated radical reaction and the Michael reaction

Design and evaluation of a new electro-optical system for monitoring oesophageal photoplethysmographs

When peripheral perfusion is poor and barely pulsatile, arterial blood oxygen saturation (SpO2) readings from commercial pulse oximeter probes placed peripherally can become unreliable or cease. The human oesophagus has been investigated as a potential measurement site on the hypothesis that perfusion may be better preserved at this central site. A new reflectance photoplethysmographic (PPG) optical sensor and a signal processing and data acquisition system have been developed. Oesophageal PPG signals were obtained from 16 anaesthetised patients and displayed on a laptop computer. PPGs with high signal-to-noise ratio at two wavelengths (red and infrared) and five oesophageal depths were recorded. Signals from the middle oesophagus were larger than those from the upper and deep oesophagus

Investigation of the characteristics of photoplethysmographic signals in the human oesophagus in anaesthetised patients undergoing routine surgery

The continuous monitoring of arterial blood oxygen saturation in patients with compromised peripheral perfusion is often difficult or impossible, since conventional non-invasive techniques such as pulse oximetry (SpO2) fail. Measurements of oxygen saturation are unreliable when patients are peripherally cool with low cardiac output or poor peripheral circulation. These clinical situations commonly occur after major surgery including cardiopulmonary bypass. It is suggested that the above difficulties might be overcome if the sensor were to monitor a better perfused central part of the body such as the oesophagus. A reflection probe has been constructed utilising miniaturised opto-electronic devices designed to fit into a transparent oesophageal stomach tube. A system to detect and preprocess the photoplethysmograph (PPG) signals has been developed. The PPG output is sampled and recorded by a data acquisition system and a laptop personal computer. The characteristics of the pulsatile signal in the oesophagus of anaesthetised adult patients undergoing routine elective surgery has been investigated. Preliminary results show that good quality photoplethysmograpic (PPG) signals can be measured in the human oesophagus. The oesophageal signal amplitudes were found to be approximately a factor of two greater than the amplitudes of conventional finger PPGs. The characteristics of the PPG signals obtained at various depths in the oesophagus have been studied and the results will be presented. This investigation indicates the suitability of the oesophagus as an alternative site for the reliable monitoring of oxygen saturation (SpO2) in patients with poor peripheral perfusion

Electro-optical techniques for the investigation of oesophageal photoplethysmographic signals and blood oxygen saturation in burns

Pulse oximetry is widely used in anaesthesia and intensive care monitoring. It is a valuable, non-invasive optical monitoring technique used for continuous measurement of arterial blood oxygen saturation (SpO2). Sites for pulse oximeter sensors are frequently difficult to find in patients with major thermal injury. Therefore blood oxygen saturation readings are often unobtainable at just the time when they would be most valuable. An oesophageal SpO2 probe has been designed to record reliable photoplethysmographic (PPG) signals and SpO2 values from the oesophagus of burned patients. Seven adult patients were studied. Good quality oesophageal PPG signals with large amplitudes were measured from various depths within the oesophagus. The optimal monitoring oesophageal depth ranged from 13 cm to 20 cm, measured from the upper lip. It was found that the oesophageal pulse oximeter saturation results were in good agreement with those from the CO-oximeter. This study suggests that the oesophagus can be used as an alternative site for monitoring arterial blood oxygen saturation by pulse oximetry in burned patients

Investigation of photoplethysmographic signals in the human oesophagus

The continuous monitoring of blood oxygen saturation in patients with compromised peripheral perfusion is often difficult or impossible, since conventional non-invasive techniques such as pulse oximetry fail. Measurements of oxygen saturation are unreliable when patients are peripherally cool with low cardiac output and poor peripheral circulation. These clinical situations commonly occur after major surgery including cardiopulmonary bypass. We suggest that the above difficulties might be overcome if the sensor were to monitor a more central part of the body. It is proposed to use the oesophagus as measurement site and reflection techniques on the hypothesis that this site should be better perfused. A new probe was constructed utilising miniaturised opto-electronic devices designed to fit into a transparent oesophageal stomach tube. One infrared wavelength was used in this study at 880 nm and a circuit to analyse the photoplethysmograph (PPG) signal was developed. The output PPG signals were sampled and recorded by a data acquisition system and a laptop personal computer. Initial measurements were carried out to investigate the amplitude of the pulsatile signal in the oesophagus and preliminary results are presented

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 (SpO2) 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 LabVIEW were developed. The system was evaluated in clinical measurements on 49 cardiothoracic surgery patients. The SpO2 values from the esophagus were in good agreement with arterial blood oxygen saturation (SaO2) values obtained from blood gas analysis and CO-oximetry. The means (+/-SD) of the differences between the esophageal SpO2 and SaO2 results from blood gas analysis and CO-oximetry were 0.02 +/- 0.88% and -0.73 +/- 0.72%, respectively. In five (10.2%) of the patients, the finger pulse oximeter failed for at least 10 min while the esophageal SpO2 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