Application of laser spectroscopy for measurement of exhaled ethane in patients with lung cancer.

There is increasing interest in ethane (C(2)H(6)) in exhaled breath as a non-invasive marker of oxidative stress (OS) and thereby a potential indicator of disease. However, the lack of real-time measurement techniques has limited progress in the field. Here we report on a novel Tunable Diode Laser Spectrometer (TDLS) applied to the analysis of exhaled ethane in patients with lung cancer. The patient group (n=52) comprised randomly selected patients presenting at a respiratory clinic. Of these, a sub-group (n=12) was subsequently diagnosed with lung cancer. An age-matched group (n=12) corresponding to the lung cancer group was taken from a larger control group of healthy adults (n=58). The concentration of ethane in a single exhaled breath sample collected from all subjects was later measured using the TDLS. This technique is capable of real-time analysis of samples with accuracy 0.1 parts per billion (ppb), over 10 times less than typical ambient levels in the northern hemisphere. After correcting for ambient background, ethane in the control group (26% smokers) ranged from 0 to 10.54 ppb (median of 1.9 ppb) while ethane in the lung cancer patients (42% smokers) ranged from 0 to 7.6 ppb (median of 0.7 ppb). Ethane among the non-lung cancer patients presenting for investigation of respiratory disease ranged from 0 to 25 ppb (median 1.45 ppb). We conclude that, while the TDLS proved effective for accurate and rapid sample analysis, there was no significant difference in exhaled ethane among any of the subject groups. Comments are made on the suitability of the technique for monitoring applications.

Effects of changes to the stable environment on the exhalation of ethane, carbon monoxide and hydrogen peroxide by horses with respiratory inflammation.

The aim of this study was to assess the effects of changes to the stable environment on exhaled markers of respiratory inflammation in six horses with clinical histories of recurrent airway obstruction. The horses were maintained for two weeks under conventional stable management (straw bedding and hay) and for two weeks on a reduced-dust regimen (paper bedding and ensiled grass), in a crossover study design. Exhaled ethane and carbon monoxide (CO) and exhaled breath condensate hydrogen peroxide (H(2)O(2)) were measured every three days under each regimen. The presence of clinical signs of airway inflammation (nasal discharge and cough) was monitored daily. The reduced-dust regimen was associated with fewer clinical signs of airway inflammation than the conventional regimen. Exhaled ethane and CO were significantly lower on the reduced-dust regimen and these markers were correlated with clinical signs of respiratory inflammation, but exhaled H(2)O(2) was not affected by the management regimen.

Breath ethane peaks during a single haemodialysis session and is associated with time on dialysis.

There is growing evidence that oxidative stress is increased in haemodialysis patients and that dialysis per se is a contributory factor. The elevated oxidant stress, a result of increased production of reactive oxidant species (ROS), may be due to increased pro-inflammatory activity and reduced antioxidant mechanisms. ROS are transitory molecules and therefore surrogate markers of oxidant damage are required. Identification of potential causes of oxidative damage such as dialyser membranes or dialysate has been proposed and therefore assessment of oxidative damage during a single dialysis session would be of interest. We have used breath ethane, a widely accepted marker of oxidative stress, to investigate the cause and extent of the resulting oxidative damage during single dialysis sessions. Our study involved assessment of breath ethane levels during haemodialysis in an end-stage renal failure haemodialysis population (n = 24). Breath samples were collected using discrete sampling techniques and were subsequently analysed using laser spectroscopy. Each patient adopted the role of longitudinal control in this study and his or her breath ethane level was monitored regularly during the dialysis session. Significant breath ethane elevation was observed at the beginning (within the first 10 min) of each dialysis session. This paper provides an in-depth statistical analysis and clinical discussion of the recent findings. A regression analysis of the collected breath ethane data showed a trend towards increased ethane levels for patients on dialysis for a shorter duration of time (r = 0.656, R-Sq = 43.3%, p = 0.001). Multiple linear regression was undertaken to further assess these associations and revealed that peak ethane levels were significantly and independently associated with time period on dialysis (p < 0.000), vascular access (p = 0.013) and male sex (p = 0.005). However, whilst diabetes status had demonstrated a correlation with peak ethane levels (0.525, p = 0.008) this was not independent of vascular access status. This multivariate linear model was significantly associated with Ln peak ethane levels (S = 0.744, R-Sq = 80.8%). The observed rapid rise in oxidative stress during the first few minutes after commencement of dialysis gives new insight into the dynamics of the oxidative damage resulting from dialysis treatment.

Response of a Fabry-Perot optical cavity to phase modulation sidebands for use in electro-optic control systems.

The worldwide endeavor to build long baseline laser interferometers to detect and study gravitational radiation is well under way. In the German-British GEO600 project, it is proposed to pass the sidebands induced on the light by an electro-optic phase modulator through a Fabry-Perot optical cavity used in transmission, called a mode cleaner. This can be achieved when the phase modulation frequency is matched to the first longitudinal-mode frequency of the mode cleaner cavity so that both carrier and sidebands are transmitted. The primary function of the mode cleaner is to reduce the geometry fluctuations associated with the light, and thus any such noise induced by the modulation process is also suppressed. We present the results of an experiment that investigates the feasibility of passing modulation sidebands through an optical cavity and the factors limiting its success. In particular, we show that it is possible to avoid introducing excess noise associated with the transmitted sidebands, provided that certain experimental criteria are satisfied. The research was carried out on a prototype mode cleaner cavity built and tested at Glasgow University but which is similar to the equivalent apparatus planned for GEO600.