Median Maximum Value Research Articles

Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument

Abstract. Precise and accurate hydroxyl radical (OH) measurements are essential to investigate mechanisms for oxidation and transformation of trace gases and processes leading to the formation of secondary pollutants like ozone (O3) in the troposphere. Laser-induced fluorescence (LIF) is a widely used technique for the measurement of ambient OH radicals and was used for the majority of field campaigns and chamber experiments. Recently, most LIF instruments in use for atmospheric measurements of OH radicals introduced chemical modulation to separate the ambient OH radical concentration from possible interferences by chemically removing ambient OH radicals before they enter the detection cell (Mao et al., 2012; Novelli et al., 2014a). In this study, we describe the application and characterization of a chemical modulation reactor (CMR) applied to the Forschungszentrum Jülich LIF (FZJ-LIF) instrument in use at the atmospheric simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber). Besides dedicated experiments in synthetic air, the new technique was extensively tested during the year-round Jülich Atmospheric Chemistry Project (JULIAC) campaign, in which ambient air was continuously flowed into the SAPHIR chamber. It allowed for performing OH measurement comparisons with differential optical absorption spectroscopy (DOAS) and investigation of interferences in a large variety of chemical and meteorological conditions. Good agreement was obtained in the LIF–DOAS intercomparison within instrumental accuracies (18 % for LIF and 6.5 % for DOAS) which confirms that the new chemical modulation system of the FZJ-LIF instrument is suitable for measurement of interference-free OH concentrations under the conditions of the JULIAC campaign (rural environment). Known interferences from O3+H2O and the nitrate radical (NO3) were quantified with the CMR in synthetic air in the chamber and found to be 3.0×105 and 0.6×105 cm−3, respectively, for typical ambient-air conditions (O3=50 ppbv, H2O = 1 % and NO3=10 pptv). The interferences measured in ambient air during the JULIAC campaign in the summer season showed a median diurnal variation with a median maximum value of 0.9×106 cm−3 during daytime and a median minimum value of 0.4×106 cm−3 at night. The highest interference of 2×106 cm−3 occurred in a heat wave from 22 to 29 August, when the air temperature and ozone increased to 40 ∘C and 100 ppbv, respectively. All observed interferences could be fully explained by the known O3+H2O interference, which is routinely corrected in FZJ-LIF measurements when no chemical modulation is applied. No evidence for an unexplained interference was found during the JULIAC campaign. A chemical model of the CMR was developed and applied to estimate the possible perturbation of the OH transmission and scavenging efficiency by reactive atmospheric trace gases. These can remove OH by gas phase reactions in the CMR or produce OH by non-photolytic reactions, most importantly by the reaction of ambient HO2 with NO. The interfering processes become relevant at high atmospheric OH reactivities. For the conditions of the JULIAC campaign with OH reactivities below 20 s−1, the influence on the determination of ambient OH concentrations was small (on average: 2 %). However, in environments with high OH reactivities, such as in a rain forest or megacity, the expected perturbation in the currently used chemical modulation reactor could be large (more than a factor of 2). Such perturbations need to be carefully investigated and corrected for the proper evaluation of OH concentrations when applying chemical scavenging. This implies that chemical modulation, which was developed to eliminate interferences in ambient OH measurements, itself can be subject to interferences that depend on ambient atmospheric conditions.

The Low-Dose ACTH Test: Usefulness of Combined Analysis of Serum and Salivary Maximum Cortisol Response in Pediatrics.

The low-dose (1 µg) ACTH test (LDT) is widely used to assess central adrenal insufficiency (CAI); however, the serum cortisol cutoff value is controversial. Salivary cortisol (SC) may be a more accurate measurement for CAI. To assess a new maximum cutoff value of serum cortisol after LDT in pediatric patients, taking into account serum and SC measurements. Prospective study in a pediatric tertiary referral center. The combined analysis of serum and SC response to LDT might improve LDT for CAI diagnosis. A total of 145 pediatric patients underwent LDT. Serum and SC levels were measured. A central adrenal sufficient (CAS) response was established according to the reference serum cortisol cutoff value of ≥497 nmol/L. The LDT study showed central adrenal sufficiency in 72 patients and CAI in 73 patients. Considering the lower quartile of maximum SC value (21 nmol/L) in the CAS group, an intermediate CAI (InCAI) group and a real CAI (RCAI) group were defined. Regarding the median maximum value of serum cortisol levels in the InCAI group, a new serum cortisol cutoff value of 450 nmol/L was established. Furthermore, 91% of the patients in the RCAI group were below this cutoff value. The combined evaluation of maximum serum and SC levels to LDT might be useful to define an InCAI group and to avoid unnecessary hormone replacement therapy. However, rigorous patient follow-up is required.

Accuracy of 9 intraoral scanners for complete-arch image acquisition: A qualitative and quantitative evaluation

Statement of problemDifferent intraoral scanners (IOSs) are available for digital dentistry. However, information on the accuracy of various IOSs for complete-arch digital scans is limited. PurposeThe purpose of this in vitro study was to evaluate the trueness and precision of complete-arch digital scans produced by 9 IOSs, using the superimposition method, and to compare them based on characteristics including the data capture principle and mode and the need for powder coating. Material and methodsNine IOSs were used to obtain standard tessellation language (STL) data for a bimaxillary complete-arch model with various cavity preparations (N=10). The scanning performance was evaluated quantitatively and qualitatively. For quantitative evaluation, the images were processed and analyzed using 3-dimensional (3D) analysis software. After we superimposed the datasets, trueness was obtained by comparing it with the reference scan, and precision was obtained from intragroup comparisons. The IOSs were compared based on the data capture principle and mode and the need for powder coating. Statistical analyses were conducted using a Kruskal-Wallis test, followed by multiple Mann-Whitney U tests for pairwise comparisons among groups (α=.05). For qualitative evaluation, surface smoothness and sharp edge reproducibility of the digital images were compared. ResultsThe median precision values were lowest in the TRIOS model (average, 34.70 μm; maximum, 263.55 μm) and highest in the E4D model (average, 357.05 μm; maximum 2309.45 μm). Median average trueness values were lowest in the TRIOS model (42.30 μm) and highest in the Zfx IntraScan model (153.80 μm). The CS 3500 model had the lowest median maximum trueness values (450.75 μm); the E4D model had the highest values (2680.55 μm). Individual image and video sequence data captures showed similar median average trueness values (P>.05); the median maximum values of individual images were higher than those of the video sequence (P<.05). Swept source optical coherence tomography (SS-OCT) exhibited higher trueness values than those of other scanning principles (P<.05). The FastScan and True Definition, which require powder coating, showed significantly better trueness than other IOSs that did not require powdering (P<.05). The E4D, PlanScan, and Zfx IntraScan models had an increased tendency to produce images with imperfect surface features and to round off sharp edges. ConclusionsThe E4D and Zfx IntraScan models did not perform as accurately as the other IOSs. The data capture principle of SS-OCT and the mode of individual image acquisition exhibited inferior trueness. The FastScan and True Definition, which require powder coating, exhibited better trueness. The qualitative aspects of the IOSs varied in terms of polygon shapes, sharp edge reproducibility, and surface smoothness.

Elevated intrathoracic CO2 pressure during thoracoscopic surgery decreases regional cerebral oxygen saturation in neonates and infants-A pilot study.

Intraoperative hypercapnia and acidosis are risk factors during thoracoscopy in neonates and infants. In a prospective pilot study, we evaluated the effects of thoracoscopy in neonates and infants on cerebral microcirculation, oxygen saturation, and oxygen consumption. Regional cerebral oxygen saturation and blood flow were measured noninvasively using a new device combining laser Doppler flowmetry and white light spectrometry. Additionally, cerebral fractional tissue oxygen extraction and approximated oxygen consumption were calculated. Fifteen neonates and infants undergoing thoracoscopy were studied using the above-mentioned method. The chest was insufflated with carbon dioxide with a pressure of 2-6 mm Hg. Single lung ventilation was not used. As control group served 15 neonates and infants undergoing abdominal surgery. Data are presented as median and range. The 95% confidence intervals for differences of means (95% CI) are given for the mean difference from baseline values. We observed a correlation between intrathoracic pressure exceeding 4 mm Hg and transient decrease in regional cerebral oxygen saturation of 12.7% (95% CI: 9.7-17.2, P<.001). Peripheral oxygen saturation was normal at the same time. Intraoperative increase in arterial paCO2 (median maximum value: 48.8 mm Hg, range: [36.5-65.4]; 95% CI: -16.0 to -3.0, P=.002) and decrease in arterial pH (median minimum value: 7.3, range: [7.2-7.4]; 95% CI: 0.04-0.12, P=.008) were observed during thoracoscopy with both parameters recovering at the end of the procedure. Periods of regional cerebral oxygen saturation below 20% from baseline were significantly more frequent during thoracoscopy as compared to the control group (median maximum value: 1.3%min/h, range: [0.0-66.2] vs median maximum value: 0.0%min/h, range: [0.0-4.0]; 95% CI: -16.6 to -1.1, P=.028). We suggest that thoracoscopic surgery in neonates and infants, although generally safe, may be associated with a decrease in regional cerebral oxygen saturation correlating with the applied intrathoracic pressure. According to our data an inflation pressure >4 mm Hg should be avoided during thoracoscopic surgery.

The origin of halitosis in cystinotic patients due to cysteamine treatment

Introduction Cystinosis is a rare autosomal recessive disorder characterized by the intralysosomal accumulation of cystine. Cysteamine removes cystine from the lysosome and slows down the progression of the disease. One of its side effects is the induction of halitosis, which can interfere with patients’ willingness to comply with cysteamine treatment. Objective To identify breath sulphur compounds causing halitosis induced by cysteamine therapy in patients with cystinosis. Study design After the ingestion of 15 mg/kg cysteamine whole blood ( n = 4), urine ( n = 4) and breath ( n = 8) volatile sulphur compounds levels were measured every 60 min over a 360 min period by gas chromatography and the cysteamine plasma concentrations ( n = 4) were measured by high-performance liquid chromatography. Results The expired air of cystinotic patients contained elevated concentrations of methanethiol (MT, median maximum value 0.5 (range 0–11) nmol/L) and, in particular, dimethylsulphide (DMS, median maximum value 15 (range 2–83) nmol/L). DMS concentrations higher than 0.65 nmol/L are known to cause halitosis. Maximal plasma values of cysteamine (median 46 (range 30–52) μmol/L) preceded those of MT and DMS, confirming that cysteamine is converted to MT and DMS. Less than 3% of the amount of cysteamine ingested was excreted as MT and DMS via expired air and 0.002% via urine. Conclusion Halitosis induced by cysteamine intake is caused by DMS and to a lesser extent by MT, excreted via the expired air. Further studies should focus on the possibilities of reducing the formation of these volatile sulphur compounds or masking their odour, which would improve the rates of compliance with cysteamine treatment.

Arterial pressure response to maximal isometric exercise inpregnant women

We studied the arterial pressure response to maximal leg exercise in 15 healthy volunteers at 29 and 35 weeks' pregnancy and at 8 weeks post partum. Resting mean arterial pressure at 35 weeks' gestation was similar to the postpartum control value of 88 mm Hg (range 73 to 111), but it was reduced by 10% at 29 weeks' gestation. Voluntary maximal effort averaged 2470 N (range 1450 to 3030) in the postpartum period, was similar at 29 weeks, and was reduced by 13% at 35 weeks' gestation. Mean arterial pressure showed a linear increase with force to a median maximum value of 131 (104 to 159) mm Hg, or 49% above the resting value in the postpartum period. The pressure response was unaffected by pregnancy, but was inversely related to maximal force, i.e., the individual's capacity to perform isometric exercise.