Biochemical pathways of breath ammonia (NH3) generation in patients with end-stage renal disease undergoing hemodialysis.

Breath ammonia (NH3) has been proposed as a potential biomarker in monitoring hemodialysis (HD) adequacy, since a strong correlation between blood urea and mouth-exhaled breath NH3 has been observed in patients with end-stage renal disease (ESRD) undergoing HD. However, the biochemical pathways for breath NH3 generation from blood urea have not been demonstrated. In this study, we show a strong correlation (r s = 0.77, p < 0.001) between blood and salivary urea, indicating that salivary urea levels reflect blood urea levels. Salivary urea is in turn strongly correlated to salivary ammonia ([Formula: see text] + NH3) in most of the patients. This confirms that the hydrolysis of urea by urease generates ammonia in the oral cavity. A further strong correlation between salivary ammonia and breath NH3 indicates that salivary ammonia evaporates into gas phase and turns to breath NH3. Therefore, blood urea is a major biochemical source of breath NH3. Since breath NH3 is generated predominantly in the oral cavity, the levels of breath NH3 are influenced significantly by the patient's oral condition including urease activity and salivary pH. Our results agree with previous studies that have shown a connection between salivary urea and breath NH3.

The origin of mouth-exhaled ammonia.

It is known that the oral cavity is a production site for mouth-exhaled NH3. However, the mechanism of NH3 production in the oral cavity has been unclear. Since bacterial urease in the oral cavity has been found to produce ammonia from oral fluid urea, we hypothesize that oral fluid urea is the origin of mouth-exhaled NH3. Our results show that under certain conditions a strong correlation exists between oral fluid urea and oral fluid ammonia (NH4(+)+NH3) (rs = 0.77, p < 0.001). We also observe a strong correlation between oral fluid NH3 and mouth-exhaled NH3 (rs = 0.81, p < 0.001). We conclude that three main factors affect the mouth-exhaled NH3 concentration: urea concentration, urease activity and oral fluid pH. Bacterial urease catalyses the hydrolysis of oral fluid urea to ammonia (NH4(+)+NH3). Oral fluid ammonia (NH4(+)+NH3) and pH determine the concentration of oral fluid NH3, which evaporates from oral fluid into gas phase and turns to mouth-exhaled NH3.

Hydrogen cyanide in the headspace of oral fluid and in mouth-exhaled breath.

Mouth-exhaled hydrogen cyanide (HCN) concentrations have previously been reported to originate from the oral cavity. However, a direct correlation between the HCN concentration in oral fluid and in mouth-exhaled breath has not been explicitly shown. In this study, we set up a new methodology to simultaneously measure HCN in the headspace of oral fluid and in mouth-exhaled breath. Our results show that there is a statistically significant correlation between stimulated oral fluid HCN and mouth-exhaled HCN (rs = 0.76, p < 0.001). This confirms that oral fluid is the main contributor to mouth-exhaled HCN. Furthermore, we observe that after the application of an oral disinfectant, both the stimulated oral fluid and mouth-exhaled HCN concentrations decrease. This implies that HCN production in the oral cavity is related to the bacterial and/or enzymatic activity.

Ammonia in breath and emitted from skin.

Ammonia concentrations in exhaled breath (eNH3) and skin gas of 20 healthy subjects were measured on-line with a commercial cavity ring-down spectrometer and compared to saliva pH and plasma ammonium ion (NH(+)4), urea and creatinine concentrations. Special attention was given to mouth, nose and skin sampling procedures and the accurate quantification of ammonia in humid gas samples. The obtained median concentrations were 688 parts per billion by volume (ppbv) for mouth-eNH3, 34 ppbv for nose-eNH3, and 21 ppbv for both mouth- and nose-eNH3 after an acidic mouth wash (MW). The median ammonia emission rate from the lower forearm was 0.3 ng cm(-2) min(-1). Statistically significant (p < 0.05) correlations between the breath, skin and plasma ammonia/ammonium concentrations were not found. However, mouth-eNH3 strongly (p < 0.001) correlated with saliva pH. This dependence was also observed in detailed measurements of the diurnal variation and the response of eNH3 to the acidic MW. It is concluded that eNH3 as such does not reflect plasma but saliva and airway mucus NH(+)4 concentrations and is affected by saliva and airway mucus pH. After normalization with saliva pH using the Henderson-Hasselbalch equation, mouth-eNH3 correlated with plasma NH(+)4, which points to saliva and plasma NH(+)4 being linked via hydrolysis of salivary urea.

Background levels and diurnal variations of hydrogen cyanide in breath and emitted from skin.

The hydrogen cyanide (HCN) concentration in exhaled human breath and skin gas samples collected with different sampling techniques was measured using near-infrared cavity ring-down spectroscopy. The median baseline HCN concentrations in samples provided by 19 healthy volunteers 2-4 h after the last meal depended on the employed sampling technique: 6.5 parts per billion by volume (ppbv) in mixed (dead space and end-tidal) mouth-exhaled breath collected to a gas sampling bag, 3.9 ppbv in end-tidal mouth-exhaled breath, 1.3 ppbv in end-tidal nose-exhaled breath, 1.0 ppbv in unwashed skin and 0.6 ppbv in washed skin samples. Diurnal measurements showed that elevated HCN levels are to be expected in mouth-exhaled breath samples after food and drink intake, which suggests HCN generation in the oral cavity. The HCN concentrations in end-tidal nose-exhaled breath and skin gas samples were correlated, and it is concluded that these concentrations best reflect systemic HCN levels.

Acetylene in breath: background levels and real-time elimination kinetics after smoking.

We have measured the acetylene concentration in the exhaled breath of 40 volunteers (31 non-smokers, nine smokers) using near-infrared cavity ring-down spectroscopy. The acetylene levels were found to be the same as in ambient air for non-smokers, whereas elevated levels were observed for smokers. Real-time measurements with sub-second time resolution have been applied to measure the elimination kinetics of acetylene in breath after exposure to tobacco smoke. Three exponential time constants can be distinguished from the data and these can be used to define the residence times for different compartments, according to the multi-compartment model of the human body.

High-Resolution Infrared Spectrum of nu5, nu4, nu3, nu4 + nu5, and 2nu4 Band Systems of Deuterobromoacetylene.

High-resolution vibration-rotation spectra of gas-phase deuterobromoacetylene have been recorded in the 240-990 cm-1 infrared region. The analyzed band systems are rich in hot bands and have a high density of lines. Five band systems and a total of 124 vibration-rotation bands of the isotopic species DCC79Br and DCC81Br have been rotationally analyzed. Accurate rotational parameters and vibrational wavenumbers for 33 vibrational states of each species have been obtained from the rotational analysis. l doubling and rotational l resonance have been observed on some states and the respective resonance parameters have been obtained through nonlinear least-squares optimization. A Fermi resonance block model with perturbation terms has been used for the analysis of the vibrational states. With optimized parameters, the model produces root-mean-square deviations of observed - calculated wavenumbers of about 0.3 cm-1 for both isotopic species. Copyright 1999 Academic Press.

The H2S Spectrum around 0.7 µm.

The overtone spectrum of H2S has been recorded by intracavity laser spectroscopy in the 14100-14400 cm-1 spectral region. The rovibrational analysis was performed allowing one to assign not only lines involving the pair of interacting states {(402), (303)} ({(60(+), 0), (60(-), 0)} in local mode notation), but also lines involving the interacting states {(322), (223)} ({50(+), 2), (50(-), 2)} in local mode notation). Indeed, apart from the strong H22 interactions that link the rotational levels of the states (60(+/-), 0) on the one hand, and the rotational levels of the states (50(+), 2) on the other hand, we observe that the rotational levels of the two pairs of states interact strongly through anharmonic and Coriolis-type resonances. These resonances transfer intensity to lines involving the (50(+), 2) pair of states. Altogether 80 rotational upper-state levels have been observed and reproduced satisfactorily using an Hamiltonian matrix that takes explicitly into account the various interactions and assumes the same vibrational energy and rotational constants for the two components of the local mode pairs. The following band centers have been obtained: nu0 (60(+), 0) = 14291.122 cm-1 and nu0 (50(+/-), 2) = 14284.705 cm-1. Finally a local mode-type behavior is evidenced by the values of the Hamiltonian constants, and refined vibrational local mode parameters are obtained. Copyright 1998 Academic Press.

High-Resolution Photoacoustic Overtone Spectrum of Monobromoacetylene, HCCBr, above 11 600 cm-1

Photoacoustic overtone spectra of monobromoacetylene, HCCBr, have been recorded in the wavenumber region 11600-13400 cm-1 using a titanium:sapphire ring laser spectrometer. All together, eight overtone bands of HCC79Br and eight bands of HCC81Br have been observed in the rotational analysis. A Fermi resonance model based on conventional normal coordinate theory has been used to vibrationally assign the rotationally analyzed bands. The resonance model employed reproduces well the observed vibrational band origins and rotational constants. Copyright 1998 Academic Press. Copyright 1998Academic Press

High-Resolution FTIR and Photoacoustic Overtone Spectrum of HCCI

The first and second C-H overtone vibration-rotation absorption spectra of monoiodoacetylene (HCCI) have been recorded using an FTIR spectrometer with an instrument resolution of about 0.005 cm-1 (0.9/MOPD). The third overtone spectrum has been obtained using a titanium:sapphire ring laser spectrometer with a spectral resolution of about 0.02 cm-1. Due to anharmonic resonances like Fermi and Darling-Dennison resonances, accompanying bands can be observed close to the main overtone band. All the observed bands have been rotationally analyzed. Published vibrational data together with present results are used in a model which includes anharmonic resonances. Vibrational assignments of the observed bands are based on this calculation. The agreement between calculated and observed energy levels is good considering the amount of data available. Copyright 1997 Academic Press. Copyright 1997Academic Press