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Biomedical subjects

R M Langford

Publications and source records attributed to R M Langford.

At least 19 recordsLinked to original sources
PubMed2006

Current practices for postoperative pain management in Europe and the potential role of the fentanyl HCl iontophoretic transdermal system.

Survey results continue to reveal that postoperative pain is insufficiently managed throughout Europe and the rest of the world. However, the efficient use of existing resources, as well as the introduction of novel technologies, may aid in its improvement. Use of an acute pain service has the potential to improve pain management through specialized patient care and utilization of effective analgesic techniques. Multimodal analgesic techniques, which include adjuvant non-opioids and/or regional analgesic techniques, can provide effective analgesia and reduce the amount of systemic opioids (or obviate the need) for postoperative pain management. Patient-controlled analgesia modalities may also offer improvements to pain management, as in practice they provide pain relief superior to the intermittent administration of bolus doses of opioids. A novel patient-controlled analgesia modality that has been approved by the European Medicines Evaluation Agency (EMEA) for the treatment of acute, moderate-to-severe pain is the needle-free, pre-programmed fentanyl HCl iontophoretic transdermal system. This system was shown in a recent US clinical trial to be comparable in efficacy to a standard regimen of morphine intravenous patient-controlled analgesia. Adverse events associated with the use of the fentanyl iontophoretic transdermal system are generally similar to those experienced by patients using intravenous morphine patient-controlled analgesia. Considerations regarding the selection of patients for treatment with the fentanyl iontophoretic transdermal system are similar to those with other patient-controlled analgesia modalities; sufficient upper limb mobility and alertness are required to operate the system. Utilization of the fentanyl iontophoretic transdermal system, together with the guidance of an effective acute pain service, may lead to improvements in postoperative pain management.

Administration, Cutaneous↗
PubMed2006

Filtering techniques for the removal of ventilator artefact in oesophageal pulse oximetry.

The oesophagus has been shown to be a reliable site for monitoring blood oxygen saturation (SpO(2)). However, the photoplethysmographic (PPG) signals from the lower oesophagus are frequently contaminated by a ventilator artefact making the estimation of SpO(2) impossible. A 776th order finite impulse response (FIR) filter and a 695th order interpolated finite impulse response (IFIR) filter were implemented to suppress the artefact. Both filters attenuated the ventilator artefact satisfactorily without distorting the morphology of the PPG when processing recorded data from ten cardiopulmonary bypass patients. The IFIR filter was the better since it conformed more closely to the desired filter specifications and allowed real-time processing. The average improvements in signal-to-noise ratio (SNR) achieved by the FIR and IFIR filters for the fundamental component of the red PPG signals with respect to the fundamental component of the artefact were 57.96 and 60.60 dB, respectively. The corresponding average improvements achieved by the FIR and IFIR filters for the infrared PPG signals were 54.83 and 60.96 dB, respectively. Both filters were also compared with their equivalent tenth order Butterworth filters. The average SNR improvements for the FIR and IFIR filters were significantly higher than those for the Butterworth filters.

Artifacts↗
PubMed2006

Selective cyclooxygenase inhibition: its role in pain and anaesthesia.

Cyclooxygenase inhibitors reduce inflammation and hyperalgesia by decreasing prostaglandin E2 production. Traditional NSAIDs (inhibiting both COX-1 and 2) though ubiquitous in peri-operative pain practice, have well-known gastrointestinal (GI), cardiovascular and other risks. This article systematically addresses the main efficacy and safety issues pertaining to NSAID and selective COX-2 inhibitors (coxibs) use, focusing on the acute pain context, particularly post-operative pain management. NSAIDs and coxibs are of proven analgesic efficacy in post-operative pain control, and their opioid-sparing role in multimodal analgesia, leads to significantly reduced opioid related side effects. Although GI risk is regarded as less of an issue in short-term therapy, in patients with a past history of peptic ulceration who are denied NSAIDs, coxibs may be considered a suitable alternative. In the peri-operative setting, coxibs confer an additional advantage over NSAIDs by preserving the platelet thromboxane production and clotting. Cardiovascular safety has been assessed for the parenteral parecoxib and its active moiety valdecoxib, and was found to be satisfactory in major non-cardiac surgery, but increased thromboembolic complications occurred in coronary artery bypass surgery leading to contra-indication for this type of surgery. Coxibs and NSAIDs have similar renal effects and caution or avoidance is required with renal disease or reduced peri-operative renal perfusion. Coxibs may be safer in aspirin-sensitive asthmatics. Bone healing effects remain controversial, but only a few days therapy appears to be safe.

Blood Platelets↗
PubMed2006

Acute pain management for opioid dependent patients.

Patients requiring acute pain management may be opioid dependent as a result of either recreational or therapeutic opioid use, including those in opioid addiction programmes. Pain in these patients is often under-estimated and under-treated. In addiction, drug-seeking behaviour differentiates it from simple dependence. With few randomised controlled trials, current evidence predominantly consists of guidelines based on case reports, retrospective studies and expert opinion. Consensus recommendations include maintaining regular provision of the patient's pre-existing opioid requirement, with additional analgesia, ideally multimodal, in appropriate combinations of short-acting opioid (as required), local anaesthesia, and adjuvant anti-inflammatory analgesics and paracetamol. Patient controlled analgesia with higher bolus doses and shorter lock-out intervals is a recommended strategy. Transdermal opioid patches and implantable pumps will continue to deliver opioid, to which non-opioid and short-acting opioids may be added. Re-exposure to opioid is ideally avoided in previously addicted patients, but if not feasible, opioid therapy should be prescribed.

Acute Disease↗
PubMed2006

Focused ion beam nanofabrication: a comparison with conventional processing techniques.

Focused ion beam and dual platform systems are versatile tools for nanoengineering and nanoscience applications. These systems complement conventional processing methods and can be used to prototype and modify a diverse range of nano-devices and sensors. This article discusses FIB nanofabrication and compares it with other fabrication techniques such as electron beam lithography and reactive ion etching. Aspects such as the minimum feature size and side wall profiles are discussed and compared. In addition, the limitations and detrimental effects of FIB processes are discussed.

Ions↗
PubMed2006

Fabrication of nickel nanocontacts using nanostencils and electron beam assisted SiO2 deposition.

Nickel nanocontacts for studying ballistic magnetoresistance have been fabricated by sputtering through FIB prepared nanostencil masks and by using electron beam assisted deposition of SiO2 to reduce the size of FIB milled pores through silicon nitride membranes. These two methods are discussed in terms of the nanocontact sizes, fabrication, and yield. The smallest size of the nanocontacts prepared using the nanostencil method was 40 nm and by the filling method was 1-2 nm. The maximum magnetoresistance measured was 1% and no evidence of a large ballistic magnetoresistance was observed.

Crystallization↗
PubMed2005

Evaluation of oesophageal reflectance pulse oximetry in major burns patients.

Pulse oximetry is being used in everyday clinical practice in anaesthesia utilising a peripheral probe. However, it may be unreliable in certain clinical situations such as hypothermia, hypovolemia, vasoconstriction and decreased cardiac output. Similar situations occur in burns patients and, more importantly, burns to extremities which limit the sites available for measurement of peripheral oxygen saturation (SpO(2)). To overcome these limitations, the oesophagus has been investigated as an alternative measurement site, as perfusion may be preferentially preserved centrally. A miniaturised reflectance oesophageal saturation (SpO(2)) probe has been constructed utilising infrared and red photodiodes and a photodetector. Our study was aimed at evaluating the reliability of oesophageal pulse oximetry in major burns patients. Seven adult patients (five males, two females) were studied. They were sedated and ventilated as part of their routine care. Measurable photoplethysmographic (PPG) traces and SpO(2) values were obtained in the oesophagus of all patients at a mean depth of 15.6+/-1.8 cm (measured from the lips). It was found that the oesophageal pulse oximeter results were in good agreement with oxygen saturation measurements obtained by a CO-oximeter. The mean (+/-S.D.) of the differences between the oesophageal oxygen saturation results and those from CO-oximetry was 0.50+/-0.69%. A Bland and Altman analysis showed that the bias and the limits of agreement between the oesophageal and commercial toe pulse oximeters were 0.4% and -3.6% to 4.6%, respectively. 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.

Adult↗
PubMed2004

In situ lift-out using a FIB-SEM system.

An in situ 'lift-out' technique for preparing transmission electron microscopy specimens, which is performed using secondary electron imaging within the chamber of a focused ion beam-SEM system is presented. The main advantage of this in situ approach, relative to the ex situ lift-out technique, is that secondary electron imaging enables higher magnifications to be used than is possible with optical microscopy. This makes the lift-out procedure more controllable and thus increases the overall success rate especially for inexperienced users. The technique is also compared with another in situ lift-out approach, the 'wedge' technique.

Journal Article↗
PubMed2003

Evaluation of oesophageal pulse oximetry in patients undergoing cardiothoracic surgery.

Pulse oximetry probes placed peripherally may fail to give accurate values of blood oxygen saturation when the peripheral circulation is poor. Because central blood flow may be preferentially preserved, we investigated the oesophagus as an alternative monitoring site. A reflectance blood oxygen saturation probe was developed and evaluated in 49 patients undergoing cardiothoracic surgery. The oesophageal pulse oximeter results were in good agreement with oxygen saturation measurements obtained by a blood gas analyser, a CO-oximeter and a commercial finger pulse oximeter. The median (IQR [range]) difference between the oesophageal oxygen saturation results and those from blood gas analysis were 0.00 (-0.30 to 0.30 [-4.47 to 2.60]), and between the oesophageal oxygen saturation results and those from CO-oximetry were 0.75 (0.30 to 1.20 [-1.80 to 1.80]). Bland-Altman analysis showed that the bias and the limits of agreement between the oesophageal and finger pulse oximeters were -0.3% and -3.3 to 2.7%, respectively. In five (10.2%) patients, the finger pulse oximeter failed for at least 10 min, whereas the oesophageal readings remained reliable. The results suggest that the oesophagus may be used as an alternative monitoring site for pulse oximetry even in patients with compromised peripheral perfusion.

Adult↗
PubMed2002

Assessment of photoplethysmographic signals for the determination of splanchnic oxygen saturation in humans.

The need for a clinically applicable method of detecting splanchnic hypoxia has led to experimental animal studies which indicated the usefulness of intestinal pulse oximetry. Pulse oximetry relies on detection of photoplethysmographic signals. Before developing a pulse oximeter for the measurement of organ oxygen saturation peri-operatively, we designed a system based on a reflectance photoplethysmographic probe to investigate photoplethysmographic signals from human viscera (bowel, liver, and kidney). Recordings were obtained simultaneously from the abdominal viscera and the finger using identical probes. The probe was held sequentially for up to 2 min on the surface of viscera of 12 patients during routine laparotomy. Measurable splanchnic photoplethysmographic signals were recorded for the first time in humans. There were no statistically significant differences between photoplethysmographic amplitudes from viscera and those from the finger. Our results indicate the feasibility of pulse oximetry for the measurement of visceral oxygenation in humans.

Adult↗
PubMed2002

Preparation of transmission electron microscopy cross-section specimens of crack tips using focused ion beam milling.

The preparation of transmission electron microscope (TEM) thin foil specimens from metal alloys containing cracks is usually thwarted by the difficulty in preventing preferential erosion of material along the flanks and at the tips of cracks. Recent developments in focused ion beam (FIB) micromachining methods have the potential to overcome this inherent problem. In this article we describe the development of new procedures, one using FIB alone and the other using a combination of FIB with more conventional ion milling to generate TEM specimens that largely retain the microstructural information at stress corrosion cracks in austentic alloys. Examples of corrosion product phase identification and interfacial segregation are included to verify that detailed information is not destroyed by ion bombardment during specimen preparation.

Journal Article↗
PubMed2002

Investigation of oesophageal photoplethysmographic signals and blood oxygen saturation measurements in cardiothoracic surgery patients.

Pulse oximeter probes attached to the finger may fail to estimate blood oxygen saturation (SpO2) in patients with compromised peripheral perfusion (e.g. hypothermic cardiopulmonary bypass surgery). The measurement of SpO2 from a central organ such as the oesophagus is suggested as an alternative to overcome this problem. A reflectance oesophageal pulse oximeter probe and a processing system implemented in LabVIEW were developed. The system was evaluated in clinical measurements on 50 cardiothoracic surgery patients. Oesophageal photoplethysmographic (PPG) signals with large amplitudes and high signal-to-noise ratios were measured from various depths within the oesophagus from all the cardiothoracic patients. The oesophageal PPG amplitudes from these patients were in good agreement with previous oesophageal PPG amplitude measurements from healthy anaesthetized patients. The oesophageal pulse oximeter SpO2 results agreed well with the estimated arterial oxygen saturation (SaO2) values inferred from the oxygen tension obtained by blood gas analysis. The mean (+/- SD) of the differences between the oesophageal pulse oximeter SpO2 readings and those from blood gas analysis was 0.02 +/- 0.88%. Also, the oesophageal pulse oximeter was found to be reliable and accurate in five cases of poor peripheral perfusion when a commercial finger pulse oximeter probe failed to estimate oxygen saturation values for at least 10 min. These results suggest that the arterial blood circulation to the oesophagus is less subject to vasoconstriction and decreased PPG amplitudes than are the peripheral sites used for pulse oximetry such as the finger. It is concluded that oesophageal SPO2 monitoring may be of clinical value.

Adult↗
PubMed2001

Investigation of the human oesophagus as a new monitoring site for blood oxygen saturation.

Pulse oximeter probes placed peripherally may fail to give accurate values of arterial blood oxygen saturation (SpO2) when peripheral perfusion is poor. Since central blood flow may be preferentially preserved, the oesophagus was suggested as an alternative monitoring site. A reflectance oesophageal photoplethysmographic (PPG) probe and a multiplexed data acquisition system, operating simultaneously at two wavelengths and incorporating an external three-lead electrocardiogram (ECG) reference channel, has been developed. It has been used to investigate the suitability of the oesophagus as a possible monitoring site for SpO2 in cases of compromised peripheral perfusion. Oesophageal PPG signals and standard ECG traces were obtained from 16 anaesthetized patients and displayed on a laptop computer. Measurable PPG signals with high signal-to-noise ratios at both infrared and red wavelengths were obtained from all five oesophageal depths investigated. The maximum PPG amplitude occurred at 25 cm from the upper incisors in the mid-oesophagus. The measured pulse transit times (PTTs) to the oesophagus were consistent with previous measurements at peripheral sites and had a minimum value of 67 +/- 30 ms at a depth of 30 cm. There was broad agreement between the calculated values of oesophageal SpO2 and those from a commercial finger pulse oximeter.

Adult↗
PubMed2000

The IBIS project: data collection in London. Improved Monitoring for Brain Dysfunction during Intensive Care and Surgery.

The primary aim of the Improved Monitoring for Brain Dysfunction during Intensive Care and Surgery (IBIS) project was to create a unique and comprehensively annotated data library (DL) of multiple physiological, including neurophysiological, signals. Data collection was undertaken in Kuopio, Finland and London, UK, and comparable protocols were used at all the sites. In London, 43 patients were recruited at the Royal Brompton Hospital, followed by nine at St. Bartholomew's Hospital, all of whom underwent cardiac or combined cardiac and carotid artery surgery. Thirty-seven patients underwent a single operation, while 15 underwent two procedures. The protocols and equipment used, problems specific to the electrically hostile environment and preliminary results are described, including those of clinical interest. The DL is being used for the development of clinically applicable neurophysiological monitoring tools.

Adult↗
PubMed2000

Randomized placebo-controlled trial of the activity of the morphine glucuronides.

BACKGROUND: Morphine-6-glucuronide (M6G) is an active metabolite of morphine with potent analgesic activity. Morphine-3-glucuronide (M3G), the most prevalent metabolite, has minimal affinity for opioid receptors. It has been suggested from animal model data and by examination of metabolite ratios in humans that M3G may functionally antagonize the respiratory depressant and analgesic actions of morphine and M6G. METHODS: We performed a double-blind placebo-controlled trial with 10 healthy volunteers. The trial had 6 arms: (1) placebo, (2) 10 mg/70 kg of morphine, (3) 3.3 mg/70 kg of M6G, (4) 30.6 mg/70 kg of M3G, (5) 30.6 mg/70 kg of M3G with 10 mg/70 kg of morphine, and (6) 30.6 mg/70 kg of M3G with 3.3 mg/70 kg of M6G; all were give by slow intravenous bolus. Analgesia was assessed with the use of the submaximal ischemic pain model. The effects were quantified on numerical and visual analogue scales. Respiratory parameters and response to steady state 5% carbon dioxide challenge were assessed with spirometry, mass spectroscopy, and earlobe blood gas analysis. RESULTS: Morphine and M6G produced significant pain relief compared with placebo (morphine, P < .0001; M6G, P = .033). Pain relief after M6G was less than after morphine (P = .009) and M3G was no better than placebo (P = .26). Pain relief with morphine and M6G were not significantly altered by M3G (P = .59 and P = .28, respectively). Significant and similar dysphoria and sedation occurred with both morphine (P < .002) and M6G (P < .016) but were absent with both M3G and placebo. Respiratory parameters suggested that M6G produced less respiratory depression than morphine. Both morphine and M6G caused a significant reduction in respiratory drive compared with placebo (morphine, P = .002; M6G, P = .013); this effect was not reversed by M3G (P = .35 and P = .83, respectively). CONCLUSIONS: M3G appears to be devoid of significant activity; in these circumstances and at these doses, it does not antagonize either the analgesic or respiratory depressant effects of M6G or morphine.

Adult↗
PubMed2000

Repetitive synchronized cyclical oscillations of multisystem parameters subsequent to high-dose thiopental therapy for status epilepticus secondary to herpes encephalitis.

We report a case of status epilepticus secondary to herpes encephalitis, treated with thiopental infusion and mechanical ventilation. The computerized storage and analysis of physiological data led to the detection of repetitive synchronized cyclical oscillations of arterial pressure, heart rate, EEG parameters, peripheral temperature and core temperature. Arterial pressure oscillations have been described in patients who are severely systemically unwell; cardiovascular and brain electrical activity may also oscillate in the presence of raised intracranial pressure. In contrast, this patient had no features of severe systemic illness or of raised intracranial pressure. Our hypothesis is that high-dose thiopental may have been a cause of our findings by producing autonomic dysfunction.

Adolescent↗
PubMed1999

A system for investigating oesophageal photoplethysmographic signals in anaesthetised patients.

The monitoring of arterial blood oxygen saturation in patients with compromised peripheral perfusion is often difficult, because conventional non-invasive techniques such as pulse oximetry (SpO2) can fail. Poor peripheral circulation commonly occurs after major surgery including cardiopulmonary bypass. The difficulties in these clinical situations might be overcome if the sensor were to monitor a better perfused central part of the body such as the oesophagus. A new oesophageal photoplethysmographic (PPG) probe and an isolated processing system have been developed to investigate the pulsatile signals of anaesthetised adult patients undergoing routine surgery. Measurements were made in the middle third of the oesophagus, 25 cm to 30 cm from the upper incisors. The AC PPG signals are sampled by a data acquisition system connected to a laptop computer. The signals recorded correspond to infrared and red AC PPGs from the middle third oesophagus and the finger. Preliminary results from 20 patients show that good quality AC PPG signals can be measured in the human oesophagus. The ratio of the oesophageal to finger AC PPG amplitudes was calculated for the infrared and red wavelengths for each patient. The mean (+/- standard deviation) of this ratio was 2.9 +/- 2.1 (n = 19) for the infrared wavelength and 3.1 +/- 2.4 (n = 16) for the red wavelength. The red and infrared wavelengths used are appropriate for pulse oximetry and this investigation indicates that the mid-oesophagus may be a suitable site for the reliable monitoring of SpO2 in patients with poor peripheral perfusion.

Adult↗