Single breath CO measurements normalized to 5% CO2 in Coombs' test positive neonates

A portable, prototype instrument that measures peak CO, CO2 and H2 concentrations of breath samples was evaluated on 58 antibody positive, blood group incompatible infants. The reproducibility of 108 duplicate breath CO determinations improved when the result was normalized (CO(n)) for the simultaneously measured CO2 concentration (r = 0.97 versus r = 0.87). The average CO(n) for 18 antibody positive, ABO incompatible infants who received phototherapy was 1.2 ppm higher than the average for 32 who did not receive phototherapy (p < 0.001). There was a positive correlation between CO(n) and the duration of phototherapy (r = 0.75). Sodium acetate infusion and breath H2 did not affect the CO(n) results. In antibody positive infants, single breath CO to CO2 ratios provided more reproducible results than CO determinations that were not adjusted for the CO2 concentration. Therefore, a portable instrument that measures both gases on the same aliquot of exhaled air and that is not affected by H2 should have clinical utility as an indicator of heme catabolism and bilirubin production that is not distorted by hyper- or hypoventilation.     

Improved gas chromatographic quantitation of breath hydrogen by normalization to respiratory carbon dioxide.

A gas-solid chromatographic system using tandem silica gel and molecular sieve columns is described for the measurement of hydrogen, carbon dioxide, oxygen, and nitrogen in samples of respiratory gases. This system has a detection limit of 2 ppm of hydrogen in a 1 ml sample and can measure 120 ppm H2 and 5% CO2 with relative standard deviations of 1.3% and 1.7%, respectively. Improved sample storage and withdrawal techniques are described that give reproducible values for up to 6 weeks after collection. Finally we show that normalization of breath hydrogen values to an alveolar concentration, using the observed carbon dioxide concentrations, substantially reduces the range and variance of apparent H2 concentrations in human subjects. Normalization eliminates the need for rebreathing or end-expiratory collection techniques and substantially increases the reliability and clinical utility of hydrogen breath measurements in noninvasive tests of carbohydrate malabsorption.     

Retention and variability of hydrogen (H2) samples stored in plastic syringes

The utility of two brands of 20 ml plastic syringes for storage of hydrogen (H2) samples as obtained in H2 breath tests were studied. Plastipak syringes were found to be significantly better with regard to the stability of the H2 concentration and the variability between the H2 samples. Storage of the H2 samples in Plastipak syringes at 5 degrees C significantly improved the H2 retention, whereas refrigeration of H2 samples stored in Once syringes did not reduce H2 loss. Storage of H2 samples in refrigerated plastic syringes is efficient and reliable for several days if syringes with minimal sample variation are used.     

The inulin hydrogen breath test accurately reflects orocaecal transit time

BACKGROUND: The lactose[(13)C]ureide breath test ((13)C-LUBT) has been validated and established as a reliable, non-invasive test for the assessment of orocaecal transit time (OCTT). More recently, small studies have demonstrated that inulin could be an alternative substrate for H(2)-based breath testing of the small bowel transit (H(2)-INBT). We compared the performance of the H(2)-INBT with the (13)C-LUBT in an appropriate number of participants, determined by sample-size calculation. DESIGN: Twenty-nine people underwent a combined (13)C-LUBT/H(2)-INBT. Five Hundred mg of lactoseureide was ingested on the day before the test to induce an adequate enzyme activity in colonic bacteria. For the test, they received 500 mg of lactose[(13)C]ureide and 5 g inulin, dissolved in 400 mL of a standard enteral liquid nutrition orally. Breath samples were collected every 30 min for 8 h and analysed for H(2)[ p.p.m.] and (13)CO(2)-enrichment [delta-(13)C]. For the (13)C-LUBT, the OCTT was defined as the interval with an increase of delta > 2.5SD above the running average of all previous points. The latter was defined as a rise of > 10ppm above baseline regarding the H(2)-INBT. RESULTS: Breath tests produced evaluable data in 27/29 patients [93%]. Median OCTTs were 315 min (range 210-450 min) for the (13)C-LUBT and 300 min (180-420 min) for the H(2)-INBT (P = 0.15). The (13)C-LU-OCTT correlated well with the H(2)-IN-OCTT (r = 0.72). Bland-Altman blot showed that the mean H(2)-IN-OCTTs were approximately 30 min shorter than predicted with the (13)C-LUBT. CONCLUSIONS: Inulin is a reliable and inexpensive substrate for a hydrogen-based assessment of the OCTT. In contrast to the (13)C-LUBT, the H(2)-INBT does not require patients to refrain from physical activity and may additionally increase its acceptance for clinical purposes.     

Delayed gastric emptying in ventilated critically ill patients: measurement by 13 C-octanoic acid breath test

OBJECTIVE: To measure gastric emptying in ventilated critically ill patients with a new noninvasive breath test. DESIGN: Single-center, open study. SETTING: Combined medical and surgical intensive care unit of a university hospital. SUBJECTS: Thirty unselected mechanically ventilated critically ill patients receiving gastric feeding and 22 healthy volunteers. INTERVENTIONS: None. PATIENTS: After 4 hrs without feeding, intragastric infusion of 100 mL of a liquid meal (Ensure) labeled with 100 microL 13C-octanoic acid. End-expiratory breath samples were collected into evacuated tubes from the respirator circuit every 5 mins for the first hour, then every 15 mins for 3 hrs. End-expiratory breath samples were also collected from volunteers studied supine after an overnight fast following an identical infusion via a nasogastric tube. Breath 13CO2 was measured with an isotope ratio mass spectrometer. MEASUREMENTS AND MAIN RESULTS: Performance of the breath test posed no difficulty or interference with patient care. The CO2 level was >1% in 1297/1300 breath samples, indicating satisfactory end-expiratory timing. Data are median and interquartile range. Gastric emptying was slower in patients compared with volunteers: gastric emptying coefficient 2.93 (2.17-3.39) vs. 3.58 (3.18-3.79), p <.001 and gastric half emptying time, derived from the area under the 13CO2 curve, 155 min (130-220) vs. 133 min (120-145), p <.008. Fourteen of the 30 patients had a gastric emptying coefficient <95% of all volunteers and 11 had a gastric half emptying time longer than 95% of all volunteers. The Acute Physiology and Chronic Health Evaluation (APACHE II) score (median 22, range 13-43) either at admission or on the day of the study did not correlate with gastric emptying coefficient. CONCLUSION: Gastric emptying of a calorie-dense liquid meal is slow in 40% to 45% of unselected mechanically ventilated patients in a combined medical and surgical intensive care unit. The 13C-octanoic acid breath test is a novel and useful bedside technique to measure gastric emptying in these patients.     

Effect of ventilation on breath hydrogen measurements

Measurement of hydrogen (H2) in expired air by interval sampling after oral administration of carbohydrate detects sugar malabsorption. Standard breath H2 tests require comparison of H2 concentrations in expired air samples obtained immediately before and after delivery of a test substrate. Comparison of interval samples assumes that minute ventilation (VE) remains constant unless H2 is independent of VE. Because healthy individuals have variable VE, we determined how H2 is influenced by changes in VE. H2 concentration was studied at different ventilatory rates in eight healthy adults. It varied inversely with VE in all subjects. We also compared the effect of changes in VE on the relationship between H2 and carbon dioxide (CO2) concentrations in expired air samples. At constant VE, the relationship between H2 and CO2 was linear (r = 0.95, P less than 0.001). As VE changed, the relationship between H2 and CO2 became nonlinear. Changes in VE altered methane concentrations in expired air samples from two subjects in a manner comparable to the effect on H2. These results demonstrate that breath H2 concentrations vary with ventilatory rate. Under conditions where frequent changes in VE are likely, independent measures for ensuring constant VE over sampling times are necessary. Use of CO2 as an internal standard to normalize H2 values to an alveolar concentration is appropriate only under conditions of constant VE.     

The daytime breath hydrogen profile: technical aspects and normal pattern

A method is described for breath sampling which can be used for breath hydrogen estimations not only in clinical practice, but also at home. Sampling of end-expiratory air is performed using a 10-ml syringe with a side hole. The samples are transferred to 3-ml vacuum tubes, which can be stored and mailed without significant loss of hydrogen. The hydrogen concentration is estimated gas chromatographically using 0.4 ml of sampled air. This method was used to assess the breath hydrogen pattern under normal circumstances: the daytime breath hydrogen profile. Fourteen children sampled their breath at 30-min intervals during one full day, and recorded diet and activity. The normal daytime breath hydrogen profile showed a typical pattern. Morning values were low, but the evening values were markedly increased in half of the children. These patterns differed markedly from those registered in three children with carbohydrate malabsorption. The daytime breath hydrogen profile, which is easy to perform and applicable at home, might provide valuable additional information in the investigation of children with suspected carbohydrate malabsorption.     

A simple carbon monoxide breath test to estimate erythrocyte turnover.

Carbon monoxide is stoichiometrically released when heme is converted to bilirubin. This report describes and validates a novel technique that permits the estimation of heme turnover and red blood cell survival from the carbon monoxide concentration of end-expiratory breath samples. The end-alveolar Pco of a subject was corrected for environmental carbon monoxide exposure with a simple device that equilibrates with atmospheric carbon monoxide at the same rate as does the subject. The resultant value (endogenous Pco) was tested for its ability to predict heme turnover and red blood cell survival. Red cell survival times of 32 healthy subjects, as calculated from the endogenous Pco, averaged 101 +/- 19 days, a value close to the expected 110-day survival time; 13 patients with clinical evidence of shortened red blood cell survival times had measured erythrocyte life spans ranging from 10 to 59 days. The endogenous Pco of each of seven patients increased after red blood cell transfusion, demonstrating that this technique detected the known rapid turnover of a small fraction of transfused cells. A good correlation (r = 0.91) was observed between heme turnover calculated from endogenous Pco and total fecal biliary pigment output. Carbon monoxide measurements reflect red blood cell destruction in both the marrow and the circulation, therefore yielding shorter life spans than did chromium 51 survival studies. This breath test appears to yield a rapid, semiquantitative assessment of heme turnover and red blood cell survival that is not provided by any other presently available technique. This simple, noninvasive carbon monoxide breath test may find widespread use in the evaluation of anemia and jaundice.     

13CO2 breath test using naturally 13C-enriched lactose for detection of lactase deficiency in patients with gastrointestinal symptoms

A 13CO2 breath test using naturally enriched 13C-lactose as a substrate was performed in 47 patients with chronic abdominal pain or chronic diarrhea, taken from a population with a low prevalence of primary acquired lactase deficiency. The cumulative 13CO2 excretion 4 hours after 13C-lactose intake was compared with the H2 breath excretion and with jejunal lactase activity. A physiologically significant relation was found between the cumulative 13CO2 excretion (at 4 hours) and lactase activity, 14.5% 13CO2 excretion being the best cutoff point for discrimination between patients with low and normal lactase activity. The 13CO2 breath test was found to be more sensitive (0.84 versus 0.68) and more specific (0.96 versus 0.89) than the H2 breath test in detecting low jejunal lactase activity. Concordant results of both breath tests performed simultaneously give a reliable picture of the lactose absorption status of the patient. Discordance in results of 13CO2 and H2 lactose breath tests, if not explained by history, indicates in which patients a jejunal biopsy should be performed. If lactase activity and morphology of the biopsy are normal, other causes of discordance must be investigated.     

Retention and variability of hydrogen (H2) samples stored in plastic syringes

The utility of two brands of 20 ml plastic syringes for storage of hydrogen (H₂) samples as obtained in H₂ breath tests were studied. Plastipak® syringes were found to be significantly better with regard to the stability of the H₂ concentration and the variability between the H₂ samples. Storage of the H₂ samples in Plastipak® syringes at 5 °C significantly improved the H₂ retention, whereas refrigeration of H₂ samples stored in Once® syringes did not reduce H₂ loss. Storage of H₂ samples in refrigerated plastic syringes is efficient and reliable for several days if syringes with minimal sample variation are used.     

Highly sensitive,room temperature operated gold nanowire-based humidity sensor: adoptable for breath sensing

A novel, highly sensitive gold nanowire (AuNW) resistive sensor is reported here for humidity sensing in the relative humidity range of 11% to 92% RH as well as for breath sensing. Both humidity and breath sensors are widely needed. Despite a lot of research on humidity and breath sensors, there is a need for simple, inexpensive, reliable, sensitive and selective sensors, which will operate at room temperature. Here we have synthesized gold nanowires by a simple, wet chemical route. The nanowires synthesized by us are 4–7 nm in diameter and a few micrometers long. The nanowires are amine functionalized. The sensor was prepared by drop casting gold nanowires on an alumina substrate to form a AuNW layer with different thicknesses (10, 20, 30 μm). The AuNW sensor is highly selective towards humidity and shows minimum cross sensitivity towards other gases and organic vapors. At an optimum thickness of 20 μm, the humidity sensing performance of the AuNW sensor over 11% to 92% RH was found to be superior to that of 10 and 30 μm thick layers. The response time of the sensor is found to be 0.2 s and the recovery time is 0.3 s. The response of the AuNW sensor was 3.3 MΩ/% RH. Further, the AuNW sensor was tested for sensing human breathing patterns.

A novel, highly sensitive gold nanowire (AuNW) resistive sensor is reported here for humidity sensing in the relative humidity range of 11% to 92% RH as well as for breath sensing.     

During neonatal mechanical ventilatory support, the delivered nitric oxide concentration is affected by the ventilatory setting

OBJECTIVE: To assess whether the delivered nitric oxide (NO) concentration is affected by a change in the ventilatory setting during neonatal mechanical ventilatory support. DESIGN: Prospective, experimental study. SETTING: Laboratory at Nagoya City University Medical School. INTERVENTIONS: This study was performed by using a pressure-limited, time-cycled, ventilatory support with a neonatal circuit and a 50-mL silicone test lung. NO in N2 gas was administrated into the inspiratory limb at a distance of 4 cm, 80 cm, or 160 cm from the Y piece connected to the adapter of an endotracheal tube. The NO concentration was measured every 0.5 sec by a chemiluminescence analyzer at the Y piece. MEASUREMENT AND MAIN RESULTS: NO concentrations were compared with each of the ventilatory settings of peak inspiratory pressure (PIP) (10-30 cm H2O), positive end-expiratory pressure (0-10 cm H2O), ventilatory flow (10, 20, 30 L/min), and ventilatory rate (30, 40, 50, 60, 70 breaths/min), respectively. The NO concentration was significantly lower when NO was added at 4 cm than at 80 cm or 160 cm from Y piece at the same ventilatory setting of PIP, positive end-expiratory pressure and ventilatory flow, respectively, (p < .01). Although the NO concentration was increased as the settled PIP level was increased (p < .01 or p < .05), it was not changed when the settled positive end-expiratory pressure level was increased. A decrease was seen in the NO concentration as the settled ventilatory flow was increased (p < .01). Lastly, the NO concentration fluctuated greatly in association with the settled ventilatory rate. CONCLUSION: The NO concentration delivered to patients is influenced by the ventilatory setting during neonatal mechanical ventilatory support.     

Measurement of carbon monoxide in simulated expired breath

BACKGROUND: Environmental carbon dioxide (CO) detectors used as an early warning method have been adapted to measure CO concentration in expired breath. This technique has been validated in smokers with relatively low CO concentrations, but its applicability to poisoning has not been demonstrated. OBJECTIVE: To compare the reliability of toxicologically significant CO measurements performed using a portable CO detector with those obtained using infrared spectrometry, the standard method for blood CO concentration determination. DESIGN: Experimental study with a CO detector and infrared spectrometer. A balloon simulated respiratory movements and an expired breath. Balloon gas mixtures contained CO, in one of 21 different concentrations from 100 to 600 parts per million (ppm) in air. CO concentration was measured directly with the portable CO detector and two gas samples obtained at the beginning and end of the simulated expired breath were diluted, with validation, for spectrometric measures. MAIN OUTCOME MEASURES: Portable CO detector concentrations were compared with the mean value of the reference method. Simple linear regression was performed using ANOVA to evaluate the parallel between the model with the reference method. RESULTS: Portable CO detector concentration measurements were perfectly linear (R2=0.989, P<10(-3)) over a concentration range of 46-645 ppm. The difference from the reference plot was significant (P<0.01). CONCLUSION: Given the linearity of the measurements, the underestimation by the portable CO detector at higher concentrations can be corrected mathematically. A portable CO detector should measure CO in expired breath efficiently and reliably.     

Sensitivity and specificity of the hydrogen breath-analysis test for detecting malabsorption of physiological doses of lactose

We examined the changes in sensitivity and specificity that would occur with alterations in the sample-collection schedule and (or) cutoff criterion for the increase in hydrogen concentration in breath after administration of doses of lactose in the dietary range. In a breath-analysis test to classify individuals as lactose-absorbers or lactose-malabsorbers, 41 subjects drank 360 mL of intact cow's milk, containing 18 g of lactose, and breath samples were collected and analyzed at 30-min intervals for 5 h. An increase in H2 concentration of greater than or equal to 20 microL/L above basal values at any of the 10 intervals was diagnostic of malabsorption. Increases of greater than or equal to 18 or greater than or equal to 15 microL/L were only 85% as specific in classifying the same individuals. Reduction in the number of samples tested per subject uniformly reduced the sensitivity. However, a simplified procedure suitable for field studies (in which four samples--at 0, 2, 3, and 4 h--are collected and analyzed with greater than or equal to 20 microL/L as the cutoff value) gives 80% sensitivity and 100% specificity, as compared with the 11-sample procedure.     

Comparison of different protocols for 13C-urea breath test for the diagnosis of Helicobacter pylori infection in healthy volunteers

OBJECTIVE: The (13)C-urea breath test ((13)C-UBT) is the most accurate non-invasive method for diagnosis of Helicobacter pylori infection. However, several methodological issues have not been resolved yet. The aim of this study was to test different protocols of (13)C-UBT to find the optimal test drink and sampling interval. MATERIAL AND METHODS: (13)C-UBT was performed at 3-day intervals in 27 healthy volunteers using citric acid (test A), orange juice (B) and still water (C) as test drinks. Breath samples were collected from time 5 to 60 min. A total number of 2106 breath samples were analysed by isotope ratio mass spectrometry (cut-off value 3.5). RESULTS: Differences in delta values were greater than would be expected by chance (A versus B and A versus C at times 20, 25, 30, 35 and 40 min, p<0.05, Dunnett's method). There were no grey zone- or false-negative results among H. pylori-positive persons in test A at any time, but some were found in tests B and C. Optimal intervals for breath sampling are at times 20 or 25 min after (13)C-urea ingestion. CONCLUSIONS: Citric acid solution as a test drink and 20- or 25-min breath sampling intervals are optimal for the (13)C-UBT in healthy volunteers.     

Improved infrared spectrophotometer for point-of-care patient 13C-urea breath testing in the primary care setting

The 13C-urea breath test provides non-invasive testing for Helicobacter pylori infection with the possibility of analysis at the point of care. Point of care tests require accurate and efficient desktop instrumentation. OBJECTIVE: To compare results obtained from a new infrared spectrophotometer (10 kg, 2 min sample measurement) to the previously approved UBiT-IR300 (22.5 kg, 5-6 min sample measurement). DESIGN AND METHODS: Adults underwent urea breath testing; breath samples were analyzed using the new and the predicate instruments. RESULTS: There were 220 adults enrolled (age range 18-74 years; M/F = 35:65); with 86 UBT positive and 134 negative cases. The overall agreement between instruments was 99.6% (95% C.I. = 97.6 to 99.9); the positive agreement was 100%. CONCLUSION: Technical performance of the new instrument was excellent.     

Hepatic phenylalanine metabolism measured by the [13C]phenylalanine breath test

BACKGROUND: The amino acid clearance test including phenylalanine is known to reflect liver functional reserve, which correlates with surgical outcome; however, the procedure is not clinically useful because of its laborious and time-consuming nature. This study evaluates whether phenylalanine oxidation capacity measured by a breath test could reflect liver functional reserve. DESIGN: We determined phenylalanine oxidation capacity in 42 subjects using the L-[1-13C]phenylalanine breath test (PBT). The 13CO2 breath enrichment was measured at 10-min intervals for 120 min after oral administration of 100 mg of L-[1-13C]phenylalanine. Subjects were divided into the following three groups according to their plasma retention rate of indocyanine green at 15 min (ICG R15): Group I (ICG R15 < 10%), Group II (ICG R15 10--20%), and Group III (ICG R15 > 20%). First, we determined the parameters of the phenylalanine oxidation capacity that differentiated these groups and then, using these parameters, we compared the PBT with the ICG clearance test, Child-Pugh classification score and standard liver blood tests. RESULTS: The %13C dose h(-1) at 30 min and cumulative excretion at 80 min were significantly different among the three groups (P < 0.05). These two parameters significantly correlated with the ICG R15, Child-Pugh classification score (P < 0.0001) and results of standard liver blood tests (P < 0.05). CONCLUSIONS: Phenylalanine oxidation capacity measured by the PBT was reduced according to the severity of liver injury assessed by the ICG clearance test, Child-Pugh classification, and standard liver blood tests. These results indicate that the PBT can be used as a noninvasive method to determine liver functional reserve.     

A simple method of measuring breath hydrogen in carbohydrate malabsorption by end-expiratory sampling.

1. A simple method is described for measuring the hydrogen concentration in alveolar air by end-expiratory sampling, by using a modified Haldane-Priestley tube and gas chromatography. Hydrogen was generated in vivo by ingestion of the non-absorbable sugar lactulose. 2. Alveolar hydrogen concentration showed a highly significant correlation with hydrogen production measured either by a rebreathing technique or by a total collection procedure. 3. The coefficient of variation of the end-expiratory method, assessed by comparing sixty-one paired results, was 11-6%. The coefficient of variation in ten measurements in one subject at 1 min intervals was 17-6%.     

Determination of breath isoprene allows the identification of the expiratory fraction of the propofol breath signal during real-time propofol breath monitoring

Real-time measurement of propofol in the breath may be used for routine clinical monitoring. However, this requires unequivocal identification of the expiratory phase of the respiratory propofol signal as only expiratory propofol reflects propofol blood concentrations. Determination of CO₂ breath concentrations is the current gold standard for the identification of expiratory gas but usually requires additional equipment. Human breath also contains isoprene, a volatile organic compound with low inspiratory breath concentration and an expiratory concentration plateau. We investigated whether breath isoprene could be used similarly to CO₂ to identify the expiratory fraction of the propofol breath signal. We investigated real-time breath data obtained from 40 study subjects during routine anesthesia. Propofol, isoprene, and CO₂ breath concentrations were determined by a combined ion molecule reaction/electron impact mass spectrometry system. The expiratory propofol signal was identified according to breath CO₂ and isoprene concentrations and presented as median of intervals of 30 s duration. Bland–Altman analysis was applied to detect differences (bias) in the expiratory propofol signal extracted by the two identification methods. We investigated propofol signals in a total of 3,590 observation intervals of 30 s duration in the 40 study subjects. In 51.4 % of the intervals (1,844/3,590) both methods extracted the same results for expiratory propofol signal. Overall bias between the two data extraction methods was ?0.12 ppb. The lower and the upper limits of the 95 % CI were ?0.69 and 0.45 ppb. Determination of isoprene breath concentrations allows the identification of the expiratory propofol signal during real-time breath monitoring.     

The [14C]-triolein breath test is not valid as a test of fat absorption.

The [14C]-triolein breath test is used as a test of fat absorption. However, its validity has not been established. The aim of this study was to investigate, whether the absorption of [14C]-triolein could be estimated from the breath test, and whether the breath test could be useful as a clinical test. The [14C]-triolein absorption was estimated from faecal measurements, using 51CrCl3 as non-absorbable marker. The breath test was done according to the standard technique with hourly estimations of the 14CO2 expiration. Fifty-one patients participated. A nearly perpendicular, curvilinear relation between the 6-h cumulative 14CO2 expiration and the [14C]-triolein absorption was found, and no obvious cut-off level for normal 14CO2 expiration could be identified. Accordingly, the diagnostic sensitivity of the breath test was 80% at the expense of a specificity of 45%. In 19 patients duplicate measurements were done. A high intra- and inter-individual variation in the fraction of absorbed [14C]-triolein, expired within 6 h, was found. It is concluded that expiration of 14CO2 is influenced by factors other than the absorption of [14C]-triolein, and that the [14C]-triolein breath test is not useful as test of fat absorption.