Markus Metsälä

Background levels of hydrogen cyanide in human breath measured by infrared cavity ring down spectroscopy

Hydrogen cyanide (HCN) in breath has been suggested as a diagnostic tool for cyanide poisoning and for cyanide-producing bacterial infections. To distinguish elevated levels of breath HCN, baseline data are needed. Background levels of HCN were measured in mixed exhaled air from 40 healthy subjects (26 men, 14 women, age 21–61 years; detection limit: 1.5 ppb; median: 4.4 ppb; range <1.5–14 ppb) by near-infrared cavity ring down spectroscopy (CRDS). No correlation was observed with smoking habits, recent meals or age. However, female subjects had slightly higher breath levels of HCN than male subjects. CRDS has not previously been used for this purpose.

Laser-locked, high-repetition-rate cavity ringdown spectrometer

We describe the design, construction, and initial performance evaluation of a high-repetition-rate cavity ringdown spectrometer. The spectrometer is based on the use of the Pound-Drever-Hall technique to lock the laser frequency to the maximum of a transmission fringe of the interferometer used as a sample cell. This results in continuous injection of light into the interferometer. The injection is repetitively interrupted with an acousto-optical modulator to generate ringdowns (exponential decays) at a typical rate of 10 kHz. Averaging of these large numbers of fitted ringdown times allows us to attain a minimum detectable absorption of 1.43×10−11 cm−1 Hz−1/2 short term and 9.0×10−11 cm−1 Hz−1/2 long term. In addition, the spectrometer has a continuous tuning capability of ∼1 cm−1, which allows the use of standard linearization and frequency calibration techniques for the spectrum. To illustrate the operation and sensitivity of the spectrometer, part of the Q-branch of a weak acetylene overtone has been recorded.

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 sensitivity trace gas detection by cantilever-enhanced photoacoustic spectroscopy using a mid-infrared continuous-wave optical parametric oscillator

Highly sensitive cantilever-enhanced photoacoustic detection of hydrogen cyanide and methane in the mid-infrared region is demonstrated. A mid-infrared continuous-wave frequency tunable optical parametric oscillator was used as a light source in the experimental setup. Noise equivalent detection limits of 190 ppt (1 s) and 65 ppt (30 s) were achieved for HCN and CH(4), respectively. The normalized noise equivalent absorption coefficient is 1.8 × 10(-9) W cm(-1) Hz(-1/2).

Laser-induced dispersed vibration-rotation fluorescence of acetylene: Spectra of ortho and para forms and partial trapping of vibrational energy

The laser-induced dispersed vibration–rotation fluorescence method has been developed further when compared with a previous publication [Saarinen et al., J. Chem. Phys. 110, 1424 (1999)]. More than one order of magnitude better signal-to-noise ratio has been achieved in the wave-number region 2900–3500 cm−1 by taking advantage of directionality of the fluorescence signal. The improvement has been applied to overtone spectroscopy of normal acetylene where for high CH stretching excitations separate spectra of ortho and para forms are obtained containing basically just single CH stretching vibrational quantum transitions from the pumped antisymmetric vibrational (ν1+3ν3(Σu+) and ν2+3ν3(Σu+)) and close-lying symmetric vibrational local mode (4ν3(Σg+) and ν1+ν2+2ν3(Σg+)) states. No nuclear spin conversion is observed in these spectra. Two new symmetric vibrational states (ν1+2ν2+4ν40(Σg+)(29%) and (50%)) have been observed and the precision of the spectroscopic parameters of previously published symmetric sta...

High-resolution cavity ring-down study of acetylene between 12 260 and 12380cm−1

Abstract The cavity ring-down laser method using a continuously tunable titanium:sapphire ring laser with an external high-finesse cavity has been used to record a high-resolution overtone spectrum of a gaseous 12 C 2 H 2 sample in the wavenumber region 12 260–12 380 cm −1 . A direct non-linear least-squares fitting of the ring-down signal is found to lead to increased sensitivity when compared with the linear-least squares methods. Two new bands have been observed and rotationally analysed. A comparison of the new results with previous theoretical work shows a good agreement.

Exhaled Breath Biomonitoring Using Laser Spectroscopy

Biological monitoring usually relies on the collection of blood and urine samples. Although being non-invasive and providing an inextinguishable sampling pool, the analysis of exhaled breath is not ...

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 patients 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.

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.