Ethane In Breath Research Articles

Enhancement Acetone Sensing Performances of SnO2 Nanorod Arrays By Decorating Noble Metal Catalysts

Introduction Breath analysis using gas chromatography (GC) to identify more than 200 compounds in the human breath came into practice in the 1970s [1]. Endogenous compounds such as inorganic gases (NO, CO) and VOCs (acetone, ethanol, ammonia, ethane and pentane) in the human breath serve as a biomarker for several diseases [2]. Breath acetone is related to diabetes [3], fasting [4], fat metabolism [5], and other numerous diseases [6].The breath acetone concentration is measured by gas chromatography-mass spectrometry (GC-MS), selected ion flow tube mass spectrometry (SIFT-MS), ion mobility spectrometry (IMS), and proton transfer reaction mass spectrometry (PTR-MS), which are commonly used in the laboratory. As the conventional tools for breath analysis are disadvantageous in terms of cost, portability, and the complexity, so we developed a cheap, and portable breath analyzer.Method The breath acetone analyzer comprised a sampling loop, a packed column, three solenoid valves, a mini-sized pump, and a sensor based on SnO2 nanorod (NR) arrays. SnO2 is one of the metal oxide materials that shows high sensitivity to small amount of gases and has strong durability. The mixed gas was passed through the column for the separation of acetone by the difference of interaction with stationary phase. Acetone is separated from the exhaled breath by the packed column within 100 seconds. The operation temperature of the column is maintained at 30 oC. The separated acetone gas was detected by the SnO2-based sensors.The SnO2 NR arrays were synthesized by using glancing angle deposition method on SiO2 wafers. And various kinds of catalyst such as Au, Pd, Pt were deposit on the surface of SnO2 NR arrays. The tests performed at various temperatures (154 - 434 oC) optimized the operation temperature of the breath acetone analyzer system within the boundary. The breath acetone analyzer was used to detect air balanced acetone gas (50 ppm). At optimized operation temperature, the air balanced acetone gas was used to confirm the detection limits of SnO2 NR arrays-based sensors. The resistance of the SnO2 NR arrays –based sensor was converted to a sensor signal (log(R)) by the breath acetone analyzer. The response of the SnO2 NR arrays sensor was defined as:Sensor Signal: ∆(log(R)) = log(R)max – log(R)min , where log(R)max is the maximum resistance before exposure of the acetone and log(R)min is the minimum resistance at acetone exposure. Results and Conclusions The response of the sensor increased with the operating temperature and decreased after an optimal point. Optimal temperature for bare SnO2 NR, Pd-coated SnO2, Pt-coated SnO2 NR, and Au-coated SnO2 NR were 315 oC, 275 oC, 315 oC and 434 oC, respectively. The Figure 1 shows response of bare and catalysts decorated SnO2 NR arrays for various concentrations of acetone. It exhibits the effect of various metal catalysts on sensing properties. The Au-coated SnO2 NR arrays had superior acetone sensing properties than other sensors. The response of the SnO2 NR array based sensors increased with increasing acetone concentration. Au-coated SnO2 NR array sensors could detect acetone as low as 0.1 ppm at 434 oC, which is sufficient to analyze breath acetone (~ 0.5 ppm for normal cases). Depending on the type of gases, there should be a difference in time due to the difference of interaction between the stationary phase and gas. Therefore, we will conduct experiments with mixed gas samples and confirm selectivity of the device. In conclusion, we demonstrated that Au metal catalyst exhibited the largest enhancement among metal decorated SnO2 NR sensors for the detection of acetone.

Breath ethane concentrations in healthy volunteers correlate with a systemic marker of lipid peroxidation but not with omega-3 Fatty Acid availability.

Ethane in human breath derives from lipid peroxidation, specifically the reaction between omega-3 fatty acids and reactive oxygen species. It has been proposed to be a non-invasive marker of oxidative stress, a deleterious process which may play an important role in the pathophysiology of several common diseases. It is unclear, however, whether ethane concentration actually correlates with systemic oxidative stress or whether it is primarily a marker of airway biochemistry. To investigate this possibility the breath ethane concentrations in 24 healthy volunteers were compared to that of a systemic measure of oxidative stress, plasma hydroperoxides, as well as to blood concentrations of the lipophilic anti-oxidant vitamin E, and the abundance of omega-3 fatty acids. Breath ethane concentrations were significantly (p < 0.05) positively correlated with blood hydroperoxide concentrations (rp = 0.60) and negatively with that of vitamin E (rp = −0.65), but were not correlated with either the total omega-3 fatty acid concentration (rp = −0.22) or that of any individual species of this fatty acid class. This data supports the hypothesis that breath ethane is a marker of systemic lipid peroxidation, as opposed to that of omega-3 fatty acid abundance.

The Relationship between Impaired Methylnicotinate Response and Oxidative Stress in Schizophrenia

MNA response applied methylnicotinate (MNA) results in an arachidonic acid and cyclooxygenase-dependent vasodilatatory response which is diminished in patients with schizophrenia. This observation has been suggested to form the basis of a diagnostic test for the illness although the potential utility of such a procedure is diminished since the underlying mechanism is unclear. In this study we sought to discover if reduced MNA response in schizophrenia is related to increased oxidative stress i.e. whether or not the two measures are negatively correlated with each other. MNA response was assessed visually in 17 patients with schizophrenia and 16 healthy controls and compared to the extent of oxidative stress in each participant assessed by quantifying the lipid peroxidation product ethane in breath. Serum vitamin E, a lipid soluble antioxidant, concentrations was also assessed. While MNA response was correlated with breath ethane concentrations, the expected relationship between the two measures was not observed. Instead a positive relationship between them suggests that some patients with schizophrenia have impaired fatty acid utilization leading to both diminished lipid peroxidation and cyclo-oygenation. This was not related to vitamin E concentrations, however, suggesting that lipid soluble anti-oxidant availability did not underlie our findings. Our data shed further light on the mechanism of impaired MNA response in schizophrenia and support the notion that this occurs consequent to a change in lipid metabolism.

Breath analysis by optical fiber sensor for the determination of exhaled organic compounds with a view to diagnostics

Breath analysis constitutes a promising tool in clinical and analytical fields due to its high potential for non-invasive diagnostics of metabolic disorders and monitoring of disease status. An optical fiber (OF) sensor has been developed for determination of volatile organic compounds (ethane, pentane, heptane, octane, decane, benzene, toluene and styrene) in human breath for clinical diagnosis.The analytical system developed showed a high performance for breath analysis, inferred for the analytical signal intensity and stability, linear range, and detection limits ranging from 0.8pmolL−1, for heptane, and to 9.5pmolL−1, for decane. The OF sensor also showed advantageous features of near real-time response and low instrumentation costs, besides showing an analytical performance equivalent to the breath analysis by gas chromatography–mass spectrometry (GC–MS), used as the reference method.

Ethane and n-pentane in exhaled breath are biomarkers of exposure not effect

The relationship of exhaled ethane and n-pentane to exhaled NO, carbonylated proteins, and indoor/outdoor atmospheric pollutants were examined in order to evaluate ethane and n-pentane as potential markers of airway inflammation and/or oxidative stress. Exhaled NO and carbonylated proteins were found to have no significant associations with either ethane (p = 0.96 and p = 0.81, respectively) or n-pentane (p = 0.44 and 0.28, respectively) when outliers were included. In the case where outliers were removed n-pentane was found to be inversely associated with carbonylated proteins. Exhaled hydrocarbons adjusted for indoor hydrocarbon concentrations were instead found to be positively associated with air pollutants (NO, NO2 and CO), suggesting pollutant exposure is driving exhaled hydrocarbon concentrations. Given these findings, ethane and n-pentane do not appear to be markers of airway inflammation or oxidative stress.

A comparison of oxidative stress in smokers and non-smokers: an in vivo human quantitative study of n-3 lipid peroxidation

BackgroundCigarette smoking is believed to cause oxidative stress by several mechanisms, including direct damage by radical species and the inflammatory response induced by smoking, and would therefore be expected to cause increased lipid peroxidation. The aim was to carry out the first study of the relationship of smoking in humans to the level of n-3 lipid peroxidation indexed by the level of ethane in exhaled breath.MethodsSamples of alveolar air were obtained from 11 smokers and 18 non-smokers. The air samples were analyzed for ethane using mass spectrometry.ResultsThe two groups of subjects were matched with respect to age and gender. The mean cumulative smoking status of the smokers was 11.8 (standard error 2.5) pack-years. The mean level of ethane in the alveolar breath of the group of smokers (2.53 (0.55) ppb) was not significantly different from that of the group of non-smokers (2.59 (0.29) ppb; p = 0.92). With all 29 subjects included, the Spearman rank correlation coefficient between ethane levels and cumulative smoking status was -0.11 (p = 0.58), while an analysis including only the smokers yielded a corresponding correlation coefficient of 0.11 (p = 0.75).ConclusionOur results show no evidence that cigarette smoking is related to increased n-3 lipid peroxidation as measured by expired ethane.

Portable optical spectroscopy for accurate analysis of ethane in exhaled breath

We report on a maintenance-free, ward-portable, tunable diode laser spectroscopy system for the ultra-sensitive detection of ethane gas. Ethane is produced when cellular lipids are oxidized by free radicals. As a breath biomarker, ethane offers a unique measure of such oxidative stress. The ability to measure real-time breath ethane fluctuations will open up new areas in non-invasive healthcare. Instrumentation for such a purpose must be highly sensitive and specific to the target gas. Our technology has a sensitivity of 70 parts per trillion and a 1 s sampling rate. Based on a cryogenically cooled lead-salt laser, the instrument has a thermally managed closed-loop refrigeration system, eliminating the need for liquid coolants. Custom LabVIEW software allows automatic control by a laptop PC. We have field tested the instrument to ensure that target performance is sustained in a range of environments. We outline the novel applications underway with the instrument based on an in vivo clinical assessment of oxidative stress.

Automatically tunable continuous-wave optical parametric oscillator for high-resolution spectroscopy and sensitive trace-gas detection

We present a high-power (2.75 W), broadly tunable (2.75–3.83 μm) continuous-wave optical parametric oscillator based on MgO-doped periodically poled lithium niobate. Automated tuning of the pump laser, etalon and crystal temperature results in a continuous wavelength coverage up to 450 cm-1 per poling period at <5×10-4 cm-1 resolution. The versatility of the optical parametric oscillator as a coherent light source in trace-gas detection is demonstrated with photoacoustic and cavity ring-down spectroscopy. A 17-cm-1-wide CO2 spectrum at 2.8 μm and multi-component gas mixtures of methane, ethane and water in human breath were measured using photoacoustics. Methane (at 3.2 μm) and ethane (at 3.3 μm) were detected using cavity ring-down spectroscopy with detection limits of 0.16 and 0.07 parts per billion by volume, respectively. A recording of 12CH4 and 13CH4 isotopes of methane shows the ability to detect both species simultaneously at similar sensitivities.

Clinical Implications of the Ethane in Exhaled Breath in Patients With Acute Paraquat Intoxication

Pulmonary fibrosis due to lipid peroxidation is a major symptom of paraquat intoxication. Ethane in the expired breath (exEth) reflects lipid peroxidation and may be a measure of the damage effected by oxygen radicals in acute lung injury. The purpose of this study was to evaluate the clinical efficacy of exEth as a measure of exposure to paraquat and as an indicator of lung damage. Exposure levels were evaluated by the amount ingested, semiquantitative measurement of urine paraquat levels, and plasma paraquat concentration. End-tidal breath was collected for measurement of ethane 24 h after paraquat ingestion. Renal function and blood gas analyses were conducted on the same day as the breath collection, and the final clinical outcome was defined as either recovery or death. Associations between exEth and paraquat exposure profiles and clinical outcomes were assessed using linear regression models. Twenty-one patients poisoned by paraquat were selected for the study during 2001 and 2002. exEth could not be used as a predictor of laboratory parameters such as Pa(O2), Pa(CO2), serum creatinine, and lung injury (as graded by high-resolution CT). A logistical analysis revealed that only the amount of paraquat ingested was a significant predictor of fatality (p = 0.021). The strength of the association between exEth and fatality was unaffected by the addition of potential confounders such as age, sex, and time interval and paraquat concentration. exEth cannot be used as either an independent predictor of survival or a specific marker of lung injury in patients with acute paraquat poisoning.

The potential offered by real-time, high-sensitivity monitoring of ethane in breath and some pilot studies using optical spectroscopy

Breath analysis applied to biomedical applications has gained much momentum is recent years due to the growing research demonstrating that breath gas can provide clinically useful data. Particularly exciting is the area of real-time breath analysis which, when coupled with appropriately chosen target species, can offer a novel method for non-invasive patient monitoring. Here we describe the role of ethane, a breath gas of universal appeal in assessing in vivo oxidative stress (cell damage). We first present a review of emerging applications where real-time ethane monitoring could yield original new results for healthcare. We then report on results from a portable ethane spectroscopy system (accuracy better then 100 parts per trillion (1?part in 1010) over a 1?s time response) that we have developed to exploit some of these applications. By presenting some initial results from pilot studies in the life sciences, we comment on the requirements that the next stage of optical spectroscopy technology has to meet in order to benefit clinical end-users.

Parts per trillion sensitivity for ethane in air with an optical parametric oscillator cavity leak-out spectrometer.

Spectroscopic detection of ethane in the 3-microm wavelength region was performed by means of a cw optical parametric oscillator and cavity leak-out. We achieved a minimum detectable absorption coefficient of 1.6 x 10(-10) cm 1/square root of Hz, corresponding to an ethane detection limit of 6 parts per trillion/square root of Hz. For 3-min integration time the detection limit was 0.5 parts per trillion. The levels are to our knowledge the best demonstrated so far. These frequency-tuning capabilities facilitated multigas analysis with simultaneous monitoring of ethane, methane, and water vapor in human breath.

A Validated Method for Rapid Analysis of Ethane in Breath and its Application in Kinetic Studies in Human Volunteers

Oxidative stress may initiate lipid peroxidation that generates ethane. Ethane, at low concentrations, is eliminated by pulmonary exhalation. Previous methods have not allowed frequent sampling, thus ethane kinetics has not been studied in man. A validated method over the range 3.8-100,000 ppb with a limit of quantitation of 3.8 ppb (CV 9.3%) based on cryofocusing technique of a 60 ml breath sample allowed frequent sampling. Due to a rapid analytical procedure batches of more than 100 samples may be analyzed. In human volunteers (24-55 years) uptake was studied for up to 23 min <formula>(<italic>n</italic>=9)</formula>, elimination was studied for 210 min <formula>(<italic>n</italic>=9).</formula> Ethane was inhaled (concentrations varied from 16 to 29 ppm (parts per million)) through a non-rebreathing system; sampling was performed with short intervals from the expiratory limb. Samples were also drawn from the inhalatory limb. Ninety-five percent of steady state (inspired) concentration was reached within 1.75 min. Five percent of the initially inhaled concentrations was found in exhaled air 1.5 min after termination of inhalation. A terminal mean half life of 31 min for ethane was also observed. The data indicate that frequent sampling will be necessary to capture relevant changes in breath ethane.

Real-time monitoring of ethane in human breath using mid-infrared cavity leak-out spectroscopy

We report on spectroscopic real-time analysis of ethane traces in exhaled human breath. Ethane is considered the most important volatile marker of free-radical induced lipid peroxidation and cell damage in the human body. Our measurements were carried out by means of mid-infrared cavity leak-out spectroscopy in the 3 μm region, a cw variant of cavity ring-down spectroscopy. The spectrometer is based on a CO overtone laser with tunable microwave sidebands. The resulting system proved to be an unique tool with high sensitivity and selectivity for rapid and precise breath testing. With a 5 s integration time, we achieved a detection limit on the order of 100 parts per trillion ethane in human breath. Thus, sample preconcentration is unnecessary. Time-resolved monitoring of the decaying ethane fraction in breath after smoking a cigarette is demonstrated.

Effect of age on the profile of alkanes in normal human breath

Ethane and pentane in breath are markers of oxidative stress, produced by ROS-mediated lipid peroxidation of n-3 and n-6 polyunsaturated fatty acids (PUFAs), but little is known about other n-alkanes in normal human breath. We investigated the spectrum of alkanes in normal human alveolar breath, and their variation with age. Fifty normal humans were studied (age range 23–75, median 35). Volatile organic compounds (VOCs) in alveolar breath were captured on sorbent traps and assayed by gas chromatography and mass spectroscopy. Alveolar gradients (concentration in breath minus concentration in ambient room air) of alkanes were determined. C4–C20 alkanes were observed in breath and room air. Their mean alveolar gradients were negative from C4 to C12 and positive from C13 to C20. The mean alveolar gradients of four alkanes (C5–C8) were significantly less negative in the older subjects (p < 0.05). There were no significant differences between males and females. Normal human breath contained a spectrum of alkanes which may include new markers of oxidative stress. The mean rate of clearance (via cytochrome p450) exceeded the mean rate of synthesis (by ROS-mediated oxidative stress) for C4–C12 alkanes, while synthesis was greater than clearance for C13–C20 alkanes. The elevated alkane profile in older subjects was consistent with an age-related increase in oxidative stress, though an age-related decline in alkane clearance rate may have contributed.

Direct Method for Quantification of Free Malondialdehyde with High-Performance Capillary Electrophoresis in Biological Samples

Lipid peroxidation, a general mechanism of tissue damage by free radicals, damages cells and may induce pathological events (1). Analytical tests to assess lipid peroxidation include the following techniques: fluorometry of lipofuscin-like substances in serum (2); spectrophotometry of conjugated dienes in lipid extracts of plasma and microsomes (3)(4); gas chromatography of ethane or pentane in exhaled breath (5); hydroperoxide determination (6); malondialdehyde (MDA) evaluation with or without thiobarbituric acid (TBA) reaction and spectrophotometry (7), fluorometry (8), and high-performance liquid (9)(10) or gas–liquid (11)(12) chromatographies; measurements of other saturated and unsaturated aldehydes (13); and oxygen uptake during lipid peroxidation (14). The most widely used method is the TBA reaction with MDA. This method is of particular interest because of its procedural simplicity and nanomolar sensitivity. However, its specificity has been questioned (10)(11)(12)(13)(14)(15)(16), and it overestimates MDA (17)(18)(19)(20)(21). We describe a method to measure free MDA with use of high-performance capillary electrophoresis (HPCE). We used a Waters Quanta-4000 Capillary System with UV detection at 280 nm, AUFD 0.002, mercury lamp, phosphor window and cElect-P175 (Supelco) neutral hydrophilic phase capillary (75 μm x 60 cm). Buffer with 10 mmol/L sodium tetraborate, 10 mmol/L sodium monophosphate (Sigma Chemical Co.), pH 8.0, with 100 mL/L acetonitrile (analytical grade, Fisher Scientific) was filtered with a 0.45-μm filter; running voltage was +18 kV. Samples were injected hydrostatically in 10 s. Data were recorded on a Waters-746 integrator. In …

Concentrating Breath Samples Using Liquid Nitrogen: A Reliable Method for the Simultaneous Determination of Ethane and Pentane

The measurement of ethane and pentane in breath offers a sensitive and noninvasive means to assessin vivolipid peroxidation in animals and humans. However, numerous technical obstacles inherent in collecting and concentrating air-breath samples have limited the wider application of these measurements for the assessment ofin vivolipid peroxidation. We have developed a relatively simple, inexpensive, rapid, and reliable method to collect, concentrate, and measure breath ethane and total-body pentane from rats. This method, which concentrates alkanes from 4 liters of collected air-breath on adsorbant cooled to −174°C, was found to be superior to similar cryofocusing techniques at −130°C, which fail to effectively trap highly volatile ethane from large volumes of air. We found ethane evolves predominantly through breath, whereas a significant amount of pentane evolves from sources other than breath. Mean evolution rate for ethane was 1.08 pmol/100 g body wt/min. Pentane evolution rates displayed more inter-rat and day-to-day variability with a mean of 0.52 pmol/100 g body wt/min. We also found that excreted rat feces exude large amounts of ethane and pentane.

Acute and chronic hepatic steatosis lead to in vivo lipid peroxidation in mice

Background/Aims: Several liver diseases that are characterized by chronic steatosis lead to steatohepatitis lesions in some susceptible subjects. We tested the hypothesis that acute or chronic steatosis may lead to lipid peroxidation. Methods: Diverse steatogenic treatments were administered to mice, and lipid peroxidation was assessed by measuring thiobarbituric acid reactants in the liver and the exhalation of ethane in breath. Results: Administration of ethanol (5 g/kg), tetracycline, chlortetracycline, demeclocycline (0.25 mmol/kg each), amineptine (1 mmol/kg), amiodarone (1 mmol/kg), pirprofen (2 mmol/kg), or valproate (2 mmol/kg) led to microvesicular steatosis of the liver and lipid peroxidation. After tetracycline administration, hepatic triglycerides reached a maximum at 24 h and then declined; ethane exhalation followed a similar time course. Microvesicular steatosis and lipid peroxidation were also observed after 4 days of treatment with either ethionine (0.02 mmol/kg daily) or dexamethasone (0.25 mmol/kg daily) or after 7 days of tetracycline (0.25 mmol/kg daily) administration. Administration of ethanol in the drinking water for 5.5 months led to macrovacuolar and microvesicular steatosis, lipid peroxidation, and a few necrotic hepatocytes. Conclusions: We conclude that acute or chronic fat deposition due to a variety of compounds was associated with lipid peroxidation in mice. We suggest that the presence of oxidizable fat in the liver leads to peroxidation, and that chronic lipid peroxidation might represent the common (but not exclusive) mechanism for the possible development of steatohepatitis lesions in conditions characterized by chronic steatosis.

Cigarette smoking and ethane exhalation in humans.

The time course of exhaled ethane gas was determined in the alveolar expirate of healthy, fasting smokers and nonsmokers after smoking a cigarette. Baseline ethane was measured by gas chromatography and corrected for background ethane after a 2-min washout using purified air. Ethane was measured immediately after smoking and hourly thereafter. Ethane was highest immediately after smoking, reflecting ethane in cigarette smoke. An exponential decline of ethane in smokers returned ethane to baseline within 3 h. Ethane in nonsmokers also peaked immediately after smoking but returned to baseline by 1 h. Ethane from smokers, measured 3 h after the last cigarette, was compared with ethane from healthy ex-smokers and nonsmokers. Mean (+/- SEM) baseline ethane in smokers was 2.90 +/- 0.52 pmol/min/kg, 1.55 +/- 0.36 pmol/min/kg in ex-smokers and 1.11 +/- 0.26 pmol/min/kg in nonsmokers (p < 0.05). Ethane in two smokers measured before and after a week of oral beta carotene supplementation (60 mg/d) fell by 80 and 35%. We conclude that cigarette smokers have increased baseline ethane in exhaled breath compared with non-smokers. Trials with antioxidant agents are warranted to assess their ability to reduce expired ethane levels.

Thermal desorption-gas chromatographic determination of ethane and pentane in breath as potential markers of lipid peroxidation.

Formation of free radicals and lipoperoxidation occur at the onset of cellular damage. These effects are produced during normal metabolism and in pathological states. The peroxidation of polyunsaturated fatty acids, i.e. linoleic acid and linolenic acid, which are both cellular membrane compounds, induces ethane and pentane formation in pulmonary air exhalation. These two volatile hydrocarbons can be considered as potential lipoperoxidation markers. Methodological difficulties limit the use of these gases for assessment of free oxygen radical activity but we have developed and validated a non-invasive technique. A study was performed with ten healthy volunteers.

Studies on the biochemical effects of nitrogen dioxide: IV. Relation between the change of lipid peroxidation and the antioxidative protective system in rat lungs upon life span exposure to low levels of NO 2

This study examined the relation between lipid peroxidation and the antioxidative protective system in lungs of rats exposed to low levels of nitrogen dioxide (NO 2). JCL:male Wistar rats were exposed to 0, 0.04, 0.4, and 4 ppm NO 2 for 9, 18, and 27 months. Lipid peroxidation measured by TBA method, increased significantly in the 4 ppm NO 2 group of the 9-month exposure and in the 0.4 and 4 ppm NO 2 groups of the 18-month exposure. The activity of glutathione peroxidase measured with hydrogen peroxide as substrate decreased significantly in the 4 ppm NO 2 group of the 9-month exposure and in the 0.4 and 4 ppm NO 2 groups of the 18-month exposure. Furthermore, the activities of two glutathione S-transferases, aryl and aralkyl S-transferase, also decreased in the 0.4 and 4 ppm NO 2 groups of the 18-month exposure, but not in any groups of the 9-month exposure. The activity of glutathione peroxidase measured with cumene hydroperoxide as substrate did not show any significant changes in any NO 2 group. The activities of glucose-6-phosphate dehydrogenase and glutathione reductase were significantly higher than those in the control group for the 9-month exposure. In the 18-month exposure, however, they showed a tendency to return to control level. The activities of superoxide dismutase and disulfide reductase upon NO 2 exposure for 9 and 18 months were not different from control values. To confirm that lipid peroxidation was increased with greater NO 2 concentrations and exposure times, ethane and pentane exhalation in breath as an index of lipid peroxidation was examined. Ethane exhalation increased significantly following 0.04, 0.4, and 4 ppm NO 2 exposure for 9 and 18 months. Furthermore, ethane formation of rats exposed to 0.04 and 0.4 ppm NO 2 for 27 months also increased to twice the control level. On the other hand, after exposure to 4 ppm NO 2 for 27 months, ethane levels returned to control level. Pentane formation increased significantly only in the 0.04 and 0.4 ppm groups in the 18-month exposure. Ethane exhalation in rats exposed to 0.04, 0.12, and 0.4 ppm NO 2 for 9 and 18 months was similar. These results suggested that the antioxidative protective ability was decreased with prolonged exposure, while formation of cytotoxic lipid peroxides was increased. Furthermore, it was shown that in vivo lipid peroxidation, measured by ethane exhalation, was a good index of the biochemical effects induced by exposure to low levels of NO 2.