Breath analysis as promising indicator of hemodialysis efficiency.

BACKGROUND: The measurement of trimethylamine and isoprene in exhaled breath collected from dialysed patients indicates the changes in concentration of both compounds during dialysis. The aim of the presented study was to confirm diagnostic usefulness of TMA and isoprene detected in breath, as potential biomarkers of hemodialysis efficiency. METHODS: The samples of exhaled breath were collected from 22 dialyzed patients (9 women, 13 men) before and after hemodialysis (HD). All analyses were carried out using a gas chromatograph equipped with a mass spectrometer. Thermal desorption was used as breath sample enrichment method. RESULTS: Chromatographic analysis of breath samples indicated statistically significant differences in trimethylamine (TMA) and 2-methyl-1,3-butadiene (isoprene) concentrations in patients' breath collected before and after HD. TMA concentrations measured in breath samples, before dialysis, ranged from 0.024 to 0.461 nmol/L. After dialysis, the values of detected TMA were lower versus output values and ranged from 0.008 to 0.050 nmol/L. Isoprene concentrations before dialysis were present in the range from 0.236 to 9.718 nmol/L, after dialysis in the range from 0.478 to 26.182 nmol/L. Additionally, the dependences of TMA and isoprene concentrations, detected in breath with renal efficiency parameters detected in blood, were studied. The relationships between TMA and urea (r = 0.67; p < 0.00001) and creatinine (r = 0.61; p = 0.00002) were checked. In case of isoprene considerably higher concentrations were observed after dialysis, but no statistically significant correlation of isoprene with blood parameters was noticed. CONCLUSION: The observed decrease of TMA concentrations during dialysis could be useful as a measure of dialysis efficiency. The explanation of isoprene increase in breath during dialysis requires further investigation.

The application of chromatographic breath analysis in the search of volatile biomarkers of chronic kidney disease and coexisting type 2 diabetes mellitus.

Chromatographic studies on breath composition are aimed at finding volatile markers useful for medical diagnostics or in screening investigations. Studies leading to the development of screening breath tests are especially important for the diagnostics of chronic kidney disease (CKD) and type 2 diabetes mellitus (T2DM). The aim of the presented study was to confirm diagnostic usefulness of chosen volatile compounds detected in breath, which are suggested as potential biomarkers of renal dysfunction and diabetes. Breath analysis were carried out in three groups: 10 healthy volunteers, 10 patients with CKD and 10 patients with CKD and T2DM. All exhaled air samples were analyzed using gas chromatograph (Agilent 6890GC) coupled with mass spectrometer (5975MSD). Thermal desorption was applied as the enrichment method. TMA was detected only in CKD patients. Higher breath concentrations of methanethiol (MeSH) were observed in CKD patients with coexisting diabetes than in patients with renal dysfunction only or in the healthy group. There was a tendency of increasing MeSH concentration in breath with increasing total glutathione in plasma (r=0.53, p=0.0026). Also, a trend of increasing dimethylsulfide (DMS) levels detected in breath was noticed with an increase of hydrogen sulfide concentration in plasma (r=0.74; p=0.00001) as well as with aspartate aminotransferase (AST), (r=0.61; p=0.001). The presented results suggest the possibility of applying TMA, MeSH, and DMS detection in breath as diagnostic methods.

The use of a custom mode electron capture detector to determine mixing ratios of environmental tracers: Sulfur hexafluoride, chlorotrifluoromethane and bromotrifluoromethane.

Atmospheric concentrations of anthropogenic trace gases, such as sulfur hexafluoride, SF6, chlorotrifluoromethane, CF3Cl, and bromotrifluoromethane, CF3Br, are increasing. Their long lifetimes and limited chemical reactivity make them attractive environmental tracers for hydrology and oceanography. While ambient SF6 concentrations can be readily measured using GC-ECD, the simultaneous analysis of CF3Cl and CF3Br is hampered due to their low ECD sensitivity. The response of a commercial ECD for those gases was enhanced using the resonance detection mode which is based on shifting the mean energy of electrons in the ECD detector towards the region where the electron-capture reaction reveals a distinct maximum. A custom electronic system enabled operation of a commercial ECD in the resonance detection mode. An approximately 50-fold amplification of the ECD signal was obtained for CF3Cl by application of high-frequency electric field (amplitude of 50V and frequency of 40MHz). For CF3Br, a 3.5-fold increase of the ECD signal was obtained, with a lower HF field (20-30V). In the case of SF6 the application of the HF field reduces the magnitude of ECD signal by a factor of 40. The electron-capture coefficients for SF6, CF3Cl and CF3Br were determined from 453 to 633K in the standard and the resonance modes. The electron-capture coefficients for CF3Cl and CF3Br increase with increasing temperature for both modes, while that for SF6 decreases slightly with increasing temperature. The application of the resonance detection mode to a commercial ECD provides an attractive and cost-effective alternative to GCMS for high-quality quantitative analyses of CF3Cl and CF3Br as environmental tracers.

A simplified model of the ECD.

A simplified model of the ECD is presented, which is based on the assumption that only a change in the concentration of electron is generating a signal. The model allows to determine four different time constants related to: the collection of electrons (tau(1)), the loss of electrons in the capture process by the impurity molecules (tau(2)), the loss of sample molecules by electron capture (tau(n)) and the removing rate of molecules from the detector volume by the carrier gas (tau(v)). The values of these time constants have been estimated to be in the range of micros for tau(1), ms for tau(2), a part of a second for tau(n) and a few seconds for tau(v). The electron capture efficiency coefficient (p) and the detection coefficient (S(d)) have been defined. These coefficients serve in the model for the coulometric calculation of the mass of analyzed compounds, if the detector works using the conditions described.