PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 9311514

Water vapour and carbon dioxide decrease nitric oxide readings.

T W van der Mark·E Kort·R J Meijer·D S Postma·G H Koëter
View original source ↗Export metadata ↓

Abstract

Measurement of nitric oxide levels in exhaled air is commonly performed using a chemiluminescence detector. However, water vapour and carbon dioxide affect the chemiluminescence process. The influence of these gases at the concentrations present in exhaled air, has not yet been studied. For this in vitro study, mixtures of 50, 100 and 200 parts per billion (ppb) NO in air were prepared and fed into the NO analyser either directly or bubbled through water. Mixtures with CO2 were prepared by adding 0-10% CO2 to the diluent air. We found a significant decrease in NO readings in the water-saturated samples compared to the dry gas (p < 0.001), strongly dependent on the partial pressure of water. NO levels in exhaled air (mean 10 +/- 2 ppb) showed a decrease of 17 +/- 3% when water vapour was not absorbed. From the experiments with CO2 we found a decrease in NO reading of 1.04 +/- 0.07% per volume CO2 (%). Presence of water vapour, thus, leads to a systematic underestimation of NO levels. Insertion of a water absorber might, therefore, be advantageous. The influence of CO2 concentrations in the normal respiratory range is negligible. With high expiratory CO2 levels as applied in permissive hypercapnia, the effects may be substantial.

Explore related subjects

Carbon DioxideGasesLuminescent MeasurementsNitric OxideRespirationWaterJournal Article

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

T W van der Mark, E Kort, R J Meijer, D S Postma, G H Koëter. 1997. Water vapour and carbon dioxide decrease nitric oxide readings.. https://doi.org/10.1183/09031936.97.10092120

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1999

Peroxynitrite induces long-lived tyrosyl radical(s) in oxyhemoglobin of red blood cells through a reaction involving CO2 and a ferryl species.

Peroxynitrite-mediated oxidative chemistry is currently the subject of intense investigation owing to the toxic side effects associated with nitric oxide overproduction. Using direct electron spin resonance spectroscopy (ESR) at 37 degrees C, we observed that in human erythrocytes peroxynitrite induced a long-lived singlet signal at g = 2.004 arising from hemoglobin. This signal was detectable in oxygenated red blood cells and in purified oxyhemoglobin but significantly decreased after deoxygenation. The formation of the g = 2.004 radical required the presence of CO2 and pH values higher than the pKa of peroxynitrous acid (pKa = 6.8), indicating the involvement of a secondary oxidant formed in the interaction of ONOO- with CO2. The g = 2.004 radical yield leveled off at a 1:1 ratio between peroxynitrite and oxyhemoglobin, while CO-hemoglobin formed less radical and methemoglobin did not form the radical at all. These results suggest that the actual oxidant is or is derived from the ONOOCO2- adduct interacting with oxygenated FeII-heme. Spin trapping with 2-methyl-2-nitrosopropane (MNP) of the g = 2.004 radical and subsequent proteolytic digestion of the MNP/hemoglobin adduct revealed the trapping of a tyrosyl-centered radical(s). A similar long-lived unresolved g = 2.004 singlet signal is a common feature of methemoglobin/H2O2 and metmyoglobin/H2O2 systems. We show by spin trapping that these g = 2.004 signals generated by H2O2 also indicated trapping of radicals centered on tyrosine residues. Analysis of visible spectra of hemoglobin treated with peroxynitrite revealed that, in the presence of CO2, oxyhemoglobin was oxidized to a ferryl species, which rapidly decayed to lower iron oxidation states. The g = 2.004 radical may be an intermediate formed during ferrylhemoglobin decay. Our results describe a new pathway of peroxynitrite-dependent hemoglobin oxidation of dominating importance in CO2-containing biological systems and identify the g = 2.004 radical(s) formed in the process as tyrosyl radical(s).

Carbon Dioxide↗
PubMed1999

Peroxide-modified titanium dioxide: a chemical analog of putative Martian soil oxidants.

Hydrogen peroxide chemisorbed on titanium dioxide (peroxide-modified titanium dioxide) is investigated as a chemical analog to the putative soil oxidants responsible for the chemical reactivity seen in the Viking biology experiments. When peroxide-modified titanium dioxide (anatase) was exposed to a solution similar to the Viking labeled release (LR) experiment organic medium, CO2 gas was released into the sample cell headspace. Storage of these samples at 10 degrees C for 48 hr prior to exposure to organics resulted in a positive response while storage for 7 days did not. In the Viking LR experiment, storage of the Martian surface samples for 2 sols (approximately 49 hr) resulted in a positive response while storage for 141 sols essentially eliminated the initial rapid release of CO2. Heating the peroxide-modified titanium dioxide to 50 degrees C prior to exposure to organics resulted in a negative response. This is similar to, but not identical to, the Viking samples where heating to approximately 46 degrees C diminished the response by 54-80% and heating to 51.5 apparently eliminated the response. When exposed to water vapor, the peroxide-modified titanium dioxide samples release O2 in a manner similar to the release seen in the Viking gas exchange experiment (GEx). Reactivity is retained upon heating at 50 degrees C for three hours, distinguishing this active agent from the one responsible for the release of CO2 from aqueous organics. The release of CO2 by the peroxide-modified titanium dioxide is attributed to the decomposition of organics by outer-sphere peroxide complexes associated with surface hydroxyl groups, while the release of O2 upon humidification is attributed to more stable inner-sphere peroxide complexes associated with Ti4+ cations. Heating the peroxide-modified titanium dioxide to 145 degrees C inhibited the release of O2, while in the Viking experiments heating to this temperature diminished but did not eliminated the response. Although the thermal stability of the titanium-peroxide complexes in this work is lower than the stability seen in the Viking experiments, it is expected that similar types of complexes will form in titanium containing minerals other than anatase and the stability of these complexes will vary with surface hydroxylation and mineralogy.

Carbon Dioxide↗