Electrochemical sensor system for breath analysis of aldehydes, CO and NO.

Bulky and hyphenated laboratory-based analytical instrumentation such as gas chromatography/mass spectrometry is still required to trace breath biomarkers in the low ppbV level. Innovative sensor-based technologies could provide on-site and point-of-care (POC) detection of volatile biomarkers such as breath aldehydes related to oxidative stress and cancer. An electrochemical sensor system was developed for direct detection of the total abundance of aldehydes in exhaled breath in the ppbV level and for simultaneous determination of the airway inflammation markers carbon monoxide (CO) and nitric oxide (NO). The sensor system was tested in vitro with gaseous standard mixtures and in vivo in spontaneously breathing patients and under mechanical ventilation in an animal model. The sensor system provided in vitro and in vivo detection of trace levels of aldehydes, CO and NO. Inertness of the tubing system was important for reliable results. Sensitivity of the aldehyde sensor increased with humidity. Response time for analysis of breath samples was about 22 s and relative standard deviations of sensor amplitudes were <5%. Detection limits in the low ppbV range and a linear range of more than two orders of magnitude could be achieved for volatile aldehydes. Cross sensitivities were moderate for alcohols such as ethanol or isopropanol and negligible for other typical breath volatile organic compounds such as acetone, isoprene or propofol. In proof of concept analyses in patients suffering from lung cancer and diabetes, aldehyde and CO sensor signals differed between the groups. Elevated CO levels indicated previous smoking. In a mechanically ventilated pig, continuous monitoring of breath aldehyde concentrations in the low ppbV was realized. Cumulative aldehyde measurements may add interesting and complementary information to the conventional parameters used in clinical breath research. POC applicability, easy handling and low cost of sensors facilitate measurements in large patient cohorts.

Breath acetone-aspects of normal physiology related to age and gender as determined in a PTR-MS study.

The present study was performed to determine the variations of breath acetone concentrations with age, gender and body-mass index (BMI). Previous investigations were based on a relatively small cohort of subjects (see Turner et al 2006 Physiol. Meas. 27 321-37). Since exhaled breath analysis is affected by considerable variation, larger studies are needed to get reliable information about the correlation of concentrations of volatiles in breath when compared with age, gender and BMI. Mixed expiratory exhaled breath was sampled using Tedlar bags. The concentrations of a mass-to-charge ratio (m/z) of 59, attributed to acetone, were then determined using proton transfer reaction-mass spectrometry. Our cohort, consisting of 243 adult volunteers not suffering from diabetes, was divided into two groups: one that fasted overnight prior to sampling (215 volunteers) and the other without a dietary control (28 volunteers). In addition, we considered a group of 44 healthy children (5-11 years old).The fasted subjects' concentrations of acetone ranged from 177 ppb to 2441 ppb, with an overall geometric mean (GM) of 628 ppb; in the group without a dietary control, the subjects' concentrations ranged from 281 ppb to 1246 ppb with an overall GM of 544 ppb. We found no statistically significant shift between the distributions of acetone levels in the breath of males and females in the fasted group (the Wilcoxon-Mann-Whitney test yielded p = 0.0923, the medians being 652 ppb and 587 ppb). Similarly, there did not seem to be a difference between the acetone levels of males and females in the group without a dietary control. Aging was associated with a slight increase of acetone in the fasted females; in males the increase was not statistically significant. Compared with the adults (a merged group), our group of children (5-11 years old) showed lower concentrations of acetone (p < 0.001), with a median of 263 ppb. No correlation was found between the acetone levels and BMI in adults. Our results extend those of Turner et al's (2006 Physiol. Meas. 27 321-37), who analyzed the breath of 30 volunteers (without a dietary control) by selected ion flow tube-mass spectrometry. They reported a positive correlation with age (but without statistical significance in their cohort, with p = 0.82 for males and p = 0.45 for females), and, unlike us, arrived at a p-value of 0.02 for the separation of males and females with respect to acetone concentrations. Our median acetone concentration for children (5-11 years) coincides with the median acetone concentration of young adults (17-19 years) reported by Spanel et al (2007 J. Breath Res. 1 026001).

Isoprene and acetone concentration profiles during exercise on an ergometer.

A real-time recording setup combining exhaled breath volatile organic compound (VOC) measurements by proton transfer reaction-mass spectrometry (PTR-MS) with hemodynamic and respiratory data is presented. Continuous automatic sampling of exhaled breath is implemented on the basis of measured respiratory flow: a flow-controlled shutter mechanism guarantees that only end-tidal exhalation segments are drawn into the mass spectrometer for analysis. Exhaled breath concentration profiles of two prototypic compounds, isoprene and acetone, during several exercise regimes were acquired, reaffirming and complementing earlier experimental findings regarding the dynamic response of these compounds reported by Senthilmohan et al (2000 Redox Rep. 5 151-3) and Karl et al (2001 J. Appl. Physiol. 91 762-70). While isoprene tends to react very sensitively to changes in pulmonary ventilation and perfusion due to its lipophilic behavior and low Henry constant, hydrophilic acetone shows a rather stable behavior. Characteristic (median) values for breath isoprene concentration and molar flow, i.e., the amount of isoprene exhaled per minute are 100 ppb and 29 nmol min(-1), respectively, with some intra-individual day-to-day variation. At the onset of exercise breath isoprene concentration increases drastically, usually by a factor of ∼3-4 within about 1 min. Due to a simultaneous increase in ventilation, the associated rise in molar flow is even more pronounced, leading to a ratio between peak molar flow and molar flow at rest of ∼11. Our setup holds great potential in capturing continuous dynamics of non-polar, low-soluble VOCs over a wide measurement range with simultaneous appraisal of decisive physiological factors affecting exhalation kinetics. In particular, data appear to favor the hypothesis that short-term effects visible in breath isoprene levels are mainly caused by changes in pulmonary gas exchange patterns rather than fluctuations in endogenous synthesis.

Impact of inspired substance concentrations on the results of breath analysis in mechanically ventilated patients.

A well-defined relationship has to exist between substance concentrations in blood and in breath if blood-borne volatile organic compounds (VOCs) are to be used as breath markers of disease or health. In this study, the impact of inspired substances on this relationship was investigated systematically. VOCs were determined in inspired and expired air and in arterial and mixed venous blood of 46 mechanically ventilated patients by means of SPME, GC/MS. Mean inspired concentrations were 25% of expired concentrations for pentane, 7.5% for acetone, 0.7% for isoprene and 0.4% for isoflurane. Only if inspired concentrations were <5% did substance disappearance rates from blood and exhalation rates correlate well. Exhaled substance concentrations depended on venous and inspired concentrations. Patients with sepsis had higher n-pentane and lower acetone concentrations in mixed venous blood than patients without sepsis (2.27 (0.37-8.70) versus 0.65 (0.33-1.48) nmol L-1 and 69 (22-99) versus 18 (6.7-56) micromol L-1). n-Pentane and acetone concentrations in breath showed no differences between the patient groups, regardless whether or not expired concentrations were corrected for inspired concentrations. In mechanically ventilated patients, concentration profiles of volatile substances in breath may considerably deviate from profiles in blood depending on the relative amount of inspired concentrations. A simple correction for inspired substance concentrations was not possible. Hence, substances having inspired concentrations>5% of expired concentrations should not be used as breath markers in these patients without knowledge of concentrations in blood and breath.

Analysis of volatile disease markers in blood.

BACKGROUND: The diagnostic potential of breath analysis has been limited by a lack of knowledge on origin, distribution, and metabolism of the exhaled substances. To overcome this problem, we developed a method to assess trace amounts of hydrocarbons (pentane and isoprene), ketones (acetone), halogenated compounds (isoflurane), and thioethers (dimethyl sulfide) in the blood of humans and animals. METHODS: Arterial and venous blood samples were taken from mechanically ventilated patients. Additional blood samples were taken from selected vascular compartments of 19 mechanically ventilated pigs. Volatile substances were concentrated by means of solid-phase microextraction (SPME), separated by gas chromatography, and identified by mass spectrometry. RESULTS: Detection limits were 0.02-0.10 nmol/L. Venous concentrations in pigs were 0.2-1.3 nmol/L for isoprene, 0-0.3 nmol/L for pentane, and 1.2-15.1 nmol/L for dimethyl sulfide. In pigs, substances were not equally distributed among vascular compartments. In humans, median arteriovenous concentration differences were 3.58 nmol/L for isoprene and 1.56 nmol/L for pentane. These values were comparable to pulmonary excretion rates reported in the literature. Acute respiratory distress syndrome (ARDS) patients had lower isoprene concentration differences than patients without ARDS. CONCLUSIONS: The SPME method can detect volatile substances in very low concentrations in the blood of humans and animals. Analysis of volatile substances in vascular compartments will enlarge the diagnostic potential of breath analysis.

Volume-dependent compliance and ventilation-perfusion mismatch in surfactant-depleted isolated rabbit lungs.

OBJECTIVE: Volume-dependent alterations of lung compliance are usually studied over a very large volume range. However, the course of compliance within the comparably small tidal volume (intratidal compliance-volume curve) may also provide relevant information about the impact of mechanical ventilation on pulmonary gas exchange. Consequently, we determined the association of the distribution of ventilation and perfusion with the intratidal compliance-volume curve after modification of positive end-expiratory pressure (PEEP). DESIGN: Repeated measurements in randomized order. SETTING: An animal laboratory. SUBJECTS: Isolated perfused rabbit lungs (n = 14). INTERVENTIONS: Surfactant was removed by bronchoalveolar lavage. The lungs were ventilated thereafter with a constant tidal volume (10 mL/kg body weight). Five levels of PEEP (0-4 cm H2O) were applied in random order for 20 mins each. MEASUREMENTS AND MAIN RESULTS: The intratidal compliance-volume curve was determined with the slice method for each PEEP level. Concurrently, pulmonary gas exchange was assessed by the multiple inert gas elimination technique. At a PEEP of 0-1 cm H2O, the intratidal compliance-volume curve was formed a bow with downward concavity. At a PEEP of 2 cm H2O, concavity was minimal or compliance was almost constant, whereas higher PEEP levels (3-4 cm H2O) resulted in a decrease of compliance within tidal inflation. Pulmonary gas exchange did not differ between PEEP levels of of 0, 1, and 2 cm H2O. Pulmonary shunt was lowest and perfusion of alveoli with a normal ventilation-perfusion was highest at a PEEP of 3-4 cm H2O. Deadspace ventilation did not change significantly but tended to increase with PEEP. CONCLUSIONS: An increase of compliance at the very beginning of tidal inflation was associated with impaired pulmonary gas exchange, indicating insufficient alveolar recruitment by the PEEP level. Consequently, the lowest PEEP level preventing alveolar atelectasis could be detected by analyzing the course of compliance within tidal volume without the need for total lung inflation.