Rationale for developing tunable laser spectroscopy (TLS) technology for high resolution real-time carbon dioxide monitoring (capnography) in human breath

Real-time monitoring of exhaled carbon dioxide (CO₂), also known as capnography, is a valuable hospital tool for assessing patient health during anesthesia and in both the emergency department and critical care units. The fundamental measurement is referred to as end-tidal carbon dioxide concentration that reflects pulmonary gas exchange of CO₂representing systemic metabolism. The shape of the exhaled CO₂concentration for individual inhalation/exhalation breath cycles can offer additional information regarding lung function, airway obstruction, alveolar ventilation, and worsening disease. The most frequent use is to indicate appropriate placement of an endotracheal tube but and it is also employed in the assessment of disease severity and response to treatment (e.g. asthma). Other applications include outpatient monitoring with oxygen supplementation (nasal cannula) and continuous positive airway pressure control for sleep apnea. As technology has evolved, CO₂measurements have become more mobile; capnography systems are now used by emergency medical services personnel for verifying proper placement of airway devices in 'pre-hospital' environments. The use of CO₂diagnostics has evolved to identify breathing system disruptions in 'on-demand' regulator/masks equipment, both in medical and occupational settings. Most recently, miniaturized tunable laser spectroscopy sensors have been implemented for assessing pilot breathing in high-performance military aircraft. This editorial describes the use of CO₂breath sensors and proposes some new applications based on miniaturized sensors that can be directly inserted into breathing masks.

Herriott cell spot imaging increases the performance of tunable laser spectrometers

With the availability of high-power (milliwatts) single-mode tunable laser sources that operate at room temperature across the infrared (IR) region, tunable laser spectrometers have seen an explosion of growth in applications that include commercial, Earth and planetary science, and medical and industrial sensing. While the laser sources themselves have shown steady improvement, the detection architecture of using a single-element detector at one end of a multipass cell has remained unchanged over the last few decades. We present here an innovative new approach using a detector array coupled to an IR-transmissive mirror to image all or part of the multipass spot pattern of the far mirror and record spectra for each pixel. This novel approach offers improved sensitivity, increased dynamic range, laser power normalization, contaminant subtraction, resilience to misalignment, and reduces the instrument power requirement by avoiding the need for "fringe-wash" heaters. With many tens of pixels representing each spot during the laser spectral scan, intensity and optical fringe amplitude and phase information are recorded. This allows selection and manipulation (e.g., co-addition, subtraction) of the pixel output spectra to minimize optical interference fringes thereby increasing sensitivity. We demonstrate a factor of ∼20 sensitivity improvement over traditional single-element detection. Dynamic range increase of a factor of ∼100 is also demonstrated through spot selection representing different pathlengths. Additionally, subtracting the spectrum of the first spot from that of the higher pass normalizes the laser power and removes the contribution of contaminant gas and fringes in the fore-optics region. These initial results show that this imaging method is particularly advantageous for multi-channel laser spectrometers, and, once the image field is analyzed, pixel selection can be used to minimize data rate and volume collection requirements. This technique could be beneficial to enhanced-cavity detection schemes.

Simulating Serpentinization as It Could Apply to the Emergence of Life Using the JPL Hydrothermal Reactor

The molecules feeding life's emergence are thought to have been provided through the hydrothermal interactions of convecting carbonic ocean waters with minerals comprising the early Hadean oceanic crust. Few laboratory experiments have simulated ancient hydrothermal conditions to test this conjecture. We used the JPL hydrothermal flow reactor to investigate CO₂ reduction in simulated ancient alkaline convective systems over 3 days (T = 120°C, P = 100 bar, pH = 11). H₂-rich hydrothermal simulant and CO₂-rich ocean simulant solutions were periodically driven in 4-h cycles through synthetic mafic and ultramafic substrates and Fe>Ni sulfides. The resulting reductants included micromoles of HS^- and formate accompanied possibly by micromoles of acetate and intermittent minor bursts of methane as ascertained by isotopic labeling. The formate concentrations directly correlated with the CO₂ input as well as with millimoles of Mg²⁺ ions, whereas the acetate did not. Also, tens of micromoles of methane were drawn continuously from the reactor materials during what appeared to be the onset of serpentinization. These results support the hypothesis that formate may have been delivered directly to a branch of an emerging acetyl coenzyme-A pathway, thus obviating the need for the very first hydrogenation of CO₂ to be made in a hydrothermal mound. Another feed to early metabolism could have been methane, likely mostly leached from primary CH₄ present in the original Hadean crust or emanating from the mantle. That a small volume of methane was produced sporadically from the ¹³CO₂-feed, perhaps from transient occlusions, echoes the mixed results and interpretations from other laboratories. As serpentinization and hydrothermal leaching can occur wherever an ocean convects within anhydrous olivine- and sulfide-rich crust, these results may be generalized to other wet rocky planets and moons in our solar system and beyond.

Background levels of methane in Mars’ atmosphere show strong seasonal variations

Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.

Mars atmosphere. Mars methane detection and variability at Gale crater

Reports of plumes or patches of methane in the martian atmosphere that vary over monthly time scales have defied explanation to date. From in situ measurements made over a 20-month period by the tunable laser spectrometer of the Sample Analysis at Mars instrument suite on Curiosity at Gale crater, we report detection of background levels of atmospheric methane of mean value 0.69 ± 0.25 parts per billion by volume (ppbv) at the 95% confidence interval (CI). This abundance is lower than model estimates of ultraviolet degradation of accreted interplanetary dust particles or carbonaceous chondrite material. Additionally, in four sequential measurements spanning a 60-sol period (where 1 sol is a martian day), we observed elevated levels of methane of 7.2 ± 2.1 ppbv (95% CI), implying that Mars is episodically producing methane from an additional unknown source.

Atmospheric CO2 measurements with a 2 μm airborne laser absorption spectrometer employing coherent detection

We report airborne measurements of CO(2) column abundance conducted during two 2009 campaigns using a 2.05 μm laser absorption spectrometer. The two flight campaigns took place in the California Mojave desert and in Oklahoma. The integrated path differential absorption (IPDA) method is used for the CO(2) column mixing ratio retrievals. This instrument and the data analysis methodology provide insight into the capabilities of the IPDA method for both airborne measurements and future global-scale CO(2) measurements from low Earth orbit pertinent to the NASA Active Sensing of CO(2) Emissions over Nights, Days, and Seasons mission. The use of a favorable absorption line in the CO(2) 2 μm band allows the on-line frequency to be displaced two (surface pressure) half-widths from line center, providing high sensitivity to the lower tropospheric CO(2). The measurement repeatability and measurement precision are in good agreement with predicted estimates. We also report comparisons with airborne in situ measurements conducted during the Oklahoma campaign.

Aircraft and balloon in situ measurements of methane and hydrochloric acid using interband cascade lasers

Aircraft and balloon in situ measurements of CH4 and HCl using cw distributed feedback (DFB) interband cascade (IC) lasers are reported. In the stratosphere and upper troposphere, sensitivity toward CH4 and HCl is better than 10 ppbv (1 s) and 90 pptv (50 s), respectively. These are the first flight measurements of trace gas-phase species using cw DFB IC lasers.

Experimental and ab Initio Study of the HO2·CH3OH Complex: Thermodynamics and Kinetics of Formation

Near-infrared spectroscopy was used to monitor HO2 formed by pulsed laser photolysis of Cl2-O2-CH3OH-N2 mixtures. On the microsecond time scale, [HO2] exhibited a time dependence consistent with a mechanism in which [HO2] approached equilibrium via HO2 + HO2.CH3OH (3, -3). The equilibrium constant for reaction 3, K(p), was measured between 231 and 261 K at 50 and 100 Torr, leading to standard reaction enthalpy and entropy values (1 sigma) of delta(r) = -37.4 +/- 4.8 kJ mol(-1) and delta(r) = -100 +/- 19 J mol(-1) K(-1). The effective bimolecular rate constant, k3, for formation of the HO2.CH3OH complex is .10(-15).exp[(1800 +/- 500)/T] cm3 molecule(-1) s(-1) at 100 Torr (1 sigma). Ab initio calculations of the optimized structure and energetics of the HO2.CH3OH complex were performed at the CCSD(T)/6-311++G(3df,3pd)//MP2(full)/6-311++G(2df,2pd) level. The complex was found to have a strong hydrogen bond (D(e) = 43.9 kJ mol(-1)) with the hydrogen in HO2 binding to the oxygen in CH3OH. The calculated enthalpy for association is delta(r) = -36.8 kJ mol(-1). The potentials for the torsion about the O2-H bond and for the hydrogen-bond stretch were computed and 1D vibrational levels determined. After explicitly accounting for these degrees of freedom, the calculated Third Law entropy of association is delta(r) = -106 J mol(-1) K(-1). Both the calculated enthalpy and entropy of association are in reasonably good agreement with experiment. When combined with results from our previous study (Christensen et al. Geophys. Res. Lett. 2002, 29; doi:10.1029/2001GL014525), the rate coefficient for the reaction of HO2 with the complex, HO2 + HO2.CH3OH, is determined to be (2.1 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1). The results of the present work argue for a reinterpretation of the recent measurement of the HO2 self-reaction rate constant by Stone and Rowley (Phys. Chem. Chem. Phys. 2005, 7, 2156). Significant complex concentrations are present at the high methanol concentrations used in that work and lead to a nonlinear methanol dependence of the apparent rate constant. This nonlinearity introduces substantial uncertainty in the extrapolation to zero methanol.

Lack of menstrual cycle effects on hypothalamic-pituitary-adrenal axis response to insulin-induced hypoglycaemia

OBJECTIVE

Limited data are available on the effects of the menstrual cycle on the hypothalamic-pituitary-adrenal axis (HPA) function. This study evaluates HPA axis reactivity to insulin-induced hypoglycaemia over the menstrual cycle.

PATIENTS

Twelve normal women were randomized to placebo and evaluated during three successive menstrual cycles. Menstrual phase was documented by menstrual diary and by oestradiol and progesterone levels at the time of each insulin tolerance test (ITT). Six normal men were included as a comparison in the statistical analysis.

MEASUREMENTS

Afternoon ITTs were performed initially on the second or third day of menses in women, then seven more ITTs followed at one or two week intervals during the next 10 weeks. Serum measurements of glucose, adrenocorticotrophin (ACTH) and cortisol were obtained.

RESULTS

The glucose and ACTH responses to the ITTs were similar between men and women. Cortisol levels at baseline and during the test were higher in men than in women, although the amount of change was similar. Glucose, ACTH and cortisol response to insulin-induced hypoglycaemia did not vary over the menstrual cycle or during repeat testing in men or women.

CONCLUSIONS

These data show that it is unnecessary to control for menstrual cycle during insulin tolerance tests performed at 1600 hours. It is, however, necessary to control for the effect of sex on cortisol levels. Repeat testing more than one week apart does not appear to influence the glucose, ACTH or cortisol response to insulin stress.

Results of late surgery for presumed congenital cataracts

We reviewed the results of cataract extraction and visual rehabilitation in 76 eyes of 47 infants and children with presumed congenital cataracts who were first seen after they were 10 months old. Eighteen patients underwent surgery for unilateral cataracts, including five patients with persistent hyperplastic vitreous, five with posterior lenticonus, one with a nuclear cataract, six with posterior subcapsular cataracts, and one with a lamellar cataract. Of these 18 patients, seven (39%) attained a visual acuity of 20/60 or better, one (6%) had a visual acuity of 20/100, and ten (60%) had a visual acuity of 20/200 or worse. Twenty-nine patients (62 eyes) underwent bilateral cataract extraction. The visual acuity could be measured in 22 patients (44 eyes). Visual acuity improved to 20/60 or better in 32 eyes (73%), was between 20/70 and 20/150 in 11 eyes (25%), and became worse than 20/200 in one eye (2%). Results were good in patients with persistent hyperplastic primary vitreous, posterior lenticonus, and bilateral cataracts.

Adjustable suture strabismus surgery

We examined 333 patients between the ages of 11 and 70 years who underwent strabismus surgery with adjustable sutures over a ten-year period. The type of strabismus, the number and amount of adjustments, the postoperative drift, and complications were evaluated. A large percentage of patients required adjustment to obtain the desired postoperative position. The postoperative drift patterns were characteristic for each type of preoperative deviation and were similar to that reported for nonadjustable procedures. Adjustable suture techniques were especially helpful in selected horizontal deviations, vertical deviations, and the more complex strabismus problems. The complications from adjustable suture operations in this series were minimal.

The effects of ear removal on senescence and metabolism of maize

Ears were removed from field grown maize (Zea mays L.) to determine the effects on senescence and metabolism and to clarify conflicting literature reports pertaining to these effects. Ears were removed at three days after anthesis and comparisons were made of changes in metabolism between eared and earless plants until grain of the eared plants matured as judged by black layer formation.The initial visual symptom following ear removal was the development of reddish colored leaves. As judged by leaf yellowing, the removal of ears not only initiated an earlier onset but enhanced the rate of senescence. With this exception, the visual patterns of senescence were similar for earless and eared plants. Other characteristics associated with ear removal were: (a) marked decrease in dry weight and reduced N accumulation by the whole plant; (b) progressive, parallel decreases in leaf reduced N, nitrate reductase activity, and chlorophyll; (c) increases in carbohydrate content of both the leaf and stalk and of reduced N in the stalk. These changes indicate that ear removal reduced photosynthesis and nitrate reduction by approximately equal proportions and that the stalk serves as an alternate sink for both carbohydrate and nitrogen.The remobilization of nitrogen from the leaf was not dependent on the presence of an ear. A logical reason for the more rapid loss of nitrogen from the leaf of the earless plants appears to be the cessation of nitrate uptake and/or flux of nitrate to the leaves.From these results and from related experiments we tentatively conclude that the loss of nitrogen from the leaf is a major cause of death of the intact maize plant.

Availability of reduced N and carbohydrates for ear development of maize

Changes in dry weights, reduced N, nitrate, and nitrate reductase activity of various plant parts of the above ground vegetation (stover) and ears of field grown maize were measured at intervals between anthesis and grain maturity. Nonstructural carbohydrate contents were also measured in some instances. Changes in dry weight and reduced N content were used to approximate net in situ photosynthetic and nitrate assimilation activities and to determine whether the availability of photosynthate or reduced N was limiting grain production.Of the five hybrids studied, all showed extensive remobilization (loss) of reduced N from the stover during grain development. This loss of stover N was initiated by 18 to 21 days after anthesis. Most of this loss of N (about 70%) was from the leaves. In contrast, three of the five hybrids had more vegetative dry weight at grain maturity than at anthesis, while the loss of stover dry weight by the other two hybrids was negligible. By 42 days after anthesis when the bulk of the ear weight had been acquired, the average gain in stover dry weight for the five hybrids was 12% while the loss of stover reduced N was 28%. Where measured, the increase in stover dry weight was largely due to deposition of carbohydrates in the stalk. These results show that the photosynthetic capacity was adequate while nitrate reduction capacity was inadequate for ear demands. The changes in the rate of accumulation of dry weight and reduced N by the ear indicated that the rate of supply of reduced N to the ear could have limited ear development for one of the five hybrids. The dry weight and carbohydrate (where measured) accumulation in the vegetation during the first 42 days after anthesis infers that the rate of supply of photosynthate to the ear was probably not a limiting factor for any of the five hybrids.The maximum remobilization of stover N during grain development was 1.8 g N plant(-1) for the genotypes examined, while the amount of reduced N accumulated by the grain varied from 1 to 5 g plant(-1). The amount of newly reduced N (nitrate reduced after anthesis) provided from 48 to 72% of the total N accumulated by the ear. The relative amounts of newly reduced N and remobilized N vary with genotype and environment. With respect to insuring high productivity, it was concluded that there is more flexibility in the system (genotype and environment) for increasing the supply of newly reduced N than in enhancing the remobilization of vegetative N.