Peter Rolfe

The Selected Ion Flow Tube Method for Workplace Analyses of Trace Gases in Air and Breath: Its Scope, Validation, and Applications

Abstract We report the results of experiments that have validated our novel selected ion flow tube (SIFT) method as a rapid, real-time determination of the concentrations of trace organic vapors in air. This flow tube method relies on the soft ionization of the trace gases (to the exclusion of the major atmospheric gases) with an appropriate precursor ion species; in all these validation experiments H3O+ ions were used. Standard atmospheres were created in air of several organic vapors, including ethanol, acetone, benzene, and toluene, over the concentration range from 10 ppb to 30 ppm using both the syringe dilution and the permeation tube methods, and the concentrations were measured directly using our flow tube method. Good agreement is observed between the generated concentrations as derived by these standard methods and those measured by our flow tube method, with the regression coefficients ranging from 0.91 to 1.13, the measured values being on average about 10 percent higher than the syringe-gener...

In vivo chemical sensors for intensive-care monitoring

There is a need for rapid assessment of a patients biochemical status during intensive care so that therapies may be optimised. Chemical sensors for key species have the potential to allow continuous in vivo monitoring, and some progress is being made with certain sensors. Gases, ions and certain catabolites such as glucose and urea may be measured with devices based on mass spectrometric, electrochemical or optical principles. The physical form, and size of sensors must be matched to the measurement site, which can include the airway, the intravascular space, tissue and the skin surface. Electrochemical sensors for measurement of O2, pH and glucose have been the most widely used to date, although fibre-optic devices are currently attracting considerable interest. Invasive sensors still suffer from the problem of poor biocompatibility, particularly devices used in arteries and veins. Noninvasive methods may be successful in certain circumstances and in some patient groups, but peripheral measurements are often significantly influenced by circulatory phenomena such as shock. Further research is required if these limitations of both invasive and noninvasive sensors are to be overcome and continuous chemical monitoring is to be established as a routine clinical technique.

Computer modelling of the adsorption of proteins on solid surfaces under the influence of double layer and van der Waals energy

The study of protein interactions with surfaces is important in many branches of biomedical engineering. A computer model has been set up in order to aid the understanding and prediction of the likelihood of protein adsorption at a surface and of coagulation between two proteins. In this model, a protein is represented as a hard sphere, neglecting conformation changes which may occur during the adsorption process. The sphere is assumed to be in a medium whose properties are described by the ionic strength, the pH and the dielectric permittivity. It is considered to interact both with an infinite plane, representing the surface, and with another sphere, representing another protein. The model focuses on the total interaction energy between a protein and a surface and between two proteins. The energy is expressed according to the DLVO theory of colloidal stability, which assumes that the adsorption behaviour of proteins at a surface depends, first, on the van der Waals interactions energy and, second, on the electrostatic double layer interaction energy. The conditions under which adhesion is prevented correspond to the presence of local extremes of the enegy function, whereas the conditions under which adhesion is likely to take place correspond to absence of local extremes.

Near infrared spectroscopy: Blood and tissue oxygenation in renal ischemia-reperfusion injury in rats

Near infrared spectroscopy was used to monitor blood (HbO2, Hb, and Hbtot) and tissue oxygenation (oxidized cyt aa3) of both left and right kidneys of ratsin vivo simultaneously, during either 45 or 80 minutes of left renal ischemia followed by 4.5 hours of reperfusion. Ischemia significantly reduced HbO2 (p< 0.0001) and increased Hb (p<0.05) concentration change in the left kidney compared with the right kidney (control). Reperfusion with oxygenated blood reached control levels after 1 hour. The rate of change in HbO2 (p<0.05) and Hbtot (p<0.05) concentration during reperfusion was dependent upon the duration of ischemia, being slower after the longer ischemic period of 80 minutes. The concentration change of oxidized cyt aa3 of the 80-minute ischemic group slowly increased compared with the stable redox state of the 45-minute ischemic group, during the latter stages of reperfusion (p<0.05). Near infrared spectroscopy is a promising new development that will enable the effects of interventional treatment upon ischemia and reperfusion injury to be studied.

Correlation of near infrared spectroscopy cerebral blood flow estimations and microsphere quantitations in newborn piglets

We compared cerebral blood flow (CBF) estimated using transmission mode near infrared spectroscopy (NIRS) and a modification of the Fick principle with CBF quantitations by radioactive microspheres (MSs) in newborn piglets. Thirteen piglets were studied during steady state, ischemia, and during two reflow periods. NIRS and MS flows were not significantly different during any measurement period. NIRS flows were compared to total brain blood flows and to regional brain blood flows quantitated with MSs and correlated best with temporal cortical flows. Linear regression analysis of the NIRS flows plotted against MS-quantitated temporal cortical flows showed r = 0.71. Thus, CBFs obtained with NIRS were not significantly different from, showed the same directional changes, and correlated acceptably with flows quantitated by MSs.

Negative extrathoracic pressure ventilation — evaluation of the neck seal

The effect of the neck seal used in the application of negative extra-thoracic pressure ventilation was studied using near infrared spectroscopy. Changes in cerebral blood volume (CBV) were monitored during discontinuation of negative pressure and during removal of the neck seal. CBV increased by 0.17 ml 100 ml brain-1 (95% CI +0.0875 to +0.481) when negative pressure was discontinued. Removal of the neck seal had no significant effect on CBV. It is concluded that the neck seal does not cause significant jugular venous occlusion.

High frequency variability of transcephalic electrical impedance — A new parameter for monitoring of neonatal cerebral circulation?

Transcephalic electrical impedance, ECG, respirogram and arterial blood pressure were continuously monitored for 30 minutes at 8-hour intervals during the first day of life in 50 neonates at the neonatal intensive care unit. In 10 infants who developed severe intracerebral haemorrhage high-frequency fluctuatios of impedance signal were significantly lower when compared to controls or infants with mild intraventricular haemorrhage. The fluctuations seemed to be also small in infants with cerebral echodensities and periventricular leucomalacia. This could imply disturbed control of cerebral circulation in these critically ill newborns. We conclude that the variability of the transcephalic electrical impedance is an interesting new parameter for monitoring cerebral circulation which may be helpful already during the first day of life.

Critical appraisal and further development of the methodology for open circuit calorimetry in neonates

A non-invasive technique for open circuit calorimetry based on a Vickers 79 incubator as the gas collection chamber was developed and evaluated. The technique, which involved drawing air from the incubator hood at 11 1/min for gas analysis, did not have a significant cooling effect on the infant and the noise levels within the incubator did not exceed current safety standards. A new technique for checking the calibration of the whole system was developed as the traditional alcohol burn method proved unsatisfactory. Either pure oxygen or carbon dioxide were fed into the incubator hood at controlled physiological rates using a calibrated throttling valve. Over a number of calibration checks the mean error of the system proved to be +/- 4.3% for oxygen and +/- 4.45% for carbon dioxide. Less than a fifth of this error was attributable to the pump and flow meter. When oxygen is introduced to the system at a constant physiological rate it takes 30 min for a plateau to be reached. Therefore it is recommended that this system is used when readings are to be taken in a steady state situation or data is to be cumulated over a long period of time such as in an energy balance study. A run in period of 30 min before collecting data is essential. It is recommended that a calibration check is performed before each study.

Analysis techniques for pulsatile components of cardiac near infra-red absorbance measurements

Introduction The ultimate aim of this project is to apply the proven technique of near infra-red spectroscopy (nirs) [1,2] to monitor myocardial oxygenation and metabolism. The aim of the initial work presented here was to identify a significant pulsatile component in near infra-red absorbance measurements. Analysis of pulsatile components is considered to offer a practicable method of isolating the myocardial readings from those due to surrounding tissue: the chest wall, ribs, blood in the heart chambers and vessels, etc.

Otakar Koldovsky, MD, PhD, Professor of Pediatrics

My friend died suddenly on April 5 in his home. In an e-mail message, Otakar wrote to me that he fell off a podium in New Zealand and then got up and presented his work, pointing out that he had fallen into another hole 40 years ago in Warsaw, and that within no time Stalin had died; he asked who was going to die this time. Well, it was Dr. Otakar Koldovsky himself. We shall always miss him, not only for his science but also for his humanity and his sense of humor. I met him in the fifties, when he started as a student im my laboratory in Prague. He very soon found his research feet and started to examine the development of the intestine in rats and human fetuses. For this work he was awarded a CIBA prize in London. Once, when visiting England, he was asked by the customs officer for the purpose of his trip. He replied: ‘To study the everted sac of Professor Smith.’ Our group was interested in long-term development, and it was Otakar, together with Dr. Kubat, who first showed that plasma cholesterol in the adult rat is conditioned by early nutrition. In 1968, many of us left Czechoslovakia for good. Otakar ended up in the Pediatric Department in Philadelphia, where he not only discovered new aspects of digestion, but at the same time studied to obtain an American qualification as a physician. This was hard