Administering labelled water to exclusively breast-fed infants in studies involving stable isotope dilution techniques

Stable isotope techniques using deuterium or (18)O are reference methods for assessing total body water (TBW) for body composition. In combination, they provide total energy expenditure and human milk intake in exclusively breast-fed (EBF) infants. These techniques require an oral administration of an accurately quantified dose of labelled water to infants, who often have no prior experience of consuming water. In the present study, (18)O labelled water was administered to 47 EBF infants at two time points. Route of administration, duration of dosing and spills were quantified and recorded. Eighty-seven out of 94 (92.6%) dose administrations were successful. In two-thirds of dose administrations, >90% of the prepared dose was consumed. Spills ranged from 0.2% to 57%. Approaches to correct for spills can introduce bias in the calculation of TBW. Minimising and recording all dose spills is an important issue for the accuracy and precision of stable isotope techniques, when applied to EBF infants.     

A comparison of threshold estimation methods in children 6-11 years of age

Estimating detection threshold for auditory stimuli in children can be problematic because of lapses in attention and the time limits usually imposed by scheduling restrictions or fatigue. Data reported here were collected to compare the stability of threshold estimation procedures in testing children ages 6 to 11 in a three-alternative, forced-choice paradigm. Stimuli consisted of a 1-kHz tonal signal and a Gaussian noise masker, bandpass filtered between 500-2,000 Hz and presented at 25-dB spectrum level. The signal was either presented for 400 ms in the presence of a continuous masker (simultaneous masking) or for 10 ms just prior to a 400-ms masker (backward masking). For each masking paradigm the 79% correct threshold was assessed via each of three procedures: 3-down, 1-up adaptive staircase (Levitt), maximum likelihood estimation (MLE), and method of constant stimuli. Percent correct was measured at the end of the study for a signal 10 dB above the previously determined threshold in order to estimate the most appropriate psychometric function asymptote for fitting data collected via the method of constant stimuli. Both the MLE and Levitt procedures produced equally stable threshold estimates for both conditions and age groups. This was the case despite considerable variability in backward-masking thresholds.     

Assessment of body composition and total energy expenditure in humans using stable isotope techniques; IAEA Human Health Series No. 3

During the last decade compound-specific deuterium (²H) analysis of plant leaf wax-derived n-alkanes has become a promising and popular tool in paleoclimate research. This is based on the widely accepted assumption that n-alkanes in soils and sediments generally reflect δ²H of precipitation (δ²H_prec). Recently, several authors suggested that δ²H of n-alkanes (δ²H_n-alkanes) can also be used as a proxy in paleoaltimetry studies. Here, we present results from a δ²H transect study (～1500 to 4000 m above sea level [a.s.l.]) carried out on precipitation and soil samples taken from the humid southern slopes of Mt. Kilimanjaro. Contrary to earlier suggestions, a distinct altitude effect in δ²H_prec is present above ～2000 m a.s.l., that is, δ²H_prec values become more negative with increasing altitude. The compound-specific δ²H values of nC₂₇ and nC₂₉ do not confirm this altitudinal trend, but rather become more positive both in the O-layers (organic layers) and the A_h-horizons (mineral topsoils). Although our δ²H_n-alkane results are in agreement with previously published results from the southern slopes of Mt. Kilimanjaro [Peterse F, van der Meer M, Schouten S, Jia G, Ossebaar J, Blokker J, Sinninghe Damsté J. Assessment of soil n-alkane δD and branched tetraether membrane lipid distributions as tools for paleoelevation reconstruction. Biogeosciences. 2009;6:2799–2807], a re-interpretation is required given that the δ²H_n-alkane results do not reflect the δ²H_prec results. The theoretical framework for this re-interpretation is based on the evaporative isotopic enrichment of leaf water associated with the transpiration process. Modelling results show that relative humidity, decreasing considerably along the southern slopes of Mt. Kilimanjaro (from 78?% in ～2000 m a.s.l. to 51?% in 4000 m a.s.l.), strongly controls δ²H_{leaf water}. The modelled ²H leaf water enrichment along the altitudinal transect matches well the measured ²H leaf water enrichment as assessed by using the δ²H_prec and δ²H_n-alkane results and biosynthetic fractionation during n-alkane biosynthesis in leaves. Given that our results clearly demonstrate that n-alkanes in soils do not simply reflect δ²H_prec but rather δ²H_{leaf water}, we conclude that care has to be taken not to over-interpret δ²H_n-alkane records from soils and sediments when reconstructing δ²H of paleoprecipitation. Both in paleoaltimetry and in paleoclimate studies changes in relative humidity and consequently in δ²H_n-alkane values can completely mask altitudinally or climatically controlled changes in δ²H_prec.     

A simple polymer electrolyte membrane system for enrichment of low-level tritium (3H) in environmental water samples

Tritium (³H) is an essential tracer of the Earth's water cycle; yet widespread adoption of tritium in hydrologic studies remains a challenge because of analytical barriers to quantification and detection of ³H by electrolytic pre-concentration. Here, we propose a simple tritium electrolytic enrichment system based on the use of solid polymer electrolyte membranes (PEMs) that can be used to enrich ³H in 250–3000?mL environmental water samples to a 10-mL final volume. The IAEA PEM-³H system reported here can produce high enrichment factors (>70-fold) and, importantly, removes some of the deterrents to conventional ³H enrichments methods, including the use of toxic electrolysis and neutralization chemicals, spike standards, a complex electrolysis apparatus that requires extensive cooling and temperature controls, and improves precision by eliminating the need for tracking recovery gravimetrics. Preliminary results with varying operating conditions show ³H enrichments to 70-fold and higher are feasible, spanning a wide range of tritium activities from 5 to 150 TU with a precision of ～4.5?%. Further work is needed to quantify inter-sample memory and to establish lower ³H detection limits. The IAEA PEM-³H system is open source, with 3-D CAD and design files made freely available for adoption and improvement by others.     

Assessment of the amount of body water in the Red Knot (Calidris canutus): an evaluation of the principle of isotope dilution with 2H, (17)O, and (18)O as measured with laser spectrometry and isotope ratio mass spectrometry

We have used the isotope dilution technique to study changes in the body composition of a migratory shorebird species (Red Knot, Calidris canutus) through an assessment of the amount of body water in it. Birds were quantitatively injected with a dose of water with elevated concentrations of 2H, (17)O, and (18)O. Thereafter, blood samples were taken and distilled. The resulting water samples were analysed using an isotope ratio mass spectrometry (for 2H and (18)O only) and a stable isotope ratio infrared laser spectrometry (2H, (17)O, and (18)O) to yield estimates of the amount of body water in the birds, which in turn could be correlated to the amount of body fat. Here, we validate laser spectrometry against mass spectrometry and show that all three isotopes may be used for body water determinations. This opens the way to the extension of the doubly labelled water method, used for the determination of energy expenditure, to a triply labelled water method, incorporating an evaporative water loss correction on a subject-by-subject basis or, alternatively, the reduction of the analytical errors by statistically combining the (17)O and (18)O measurements.     

Superfluid equation of state of dilute composite bosons or how to include 3- and 4-body problems in the many body problem

We show how the 3 and 4-body problems emerge in the BEC limit of the BEC-BCS crossover, where we treat explicitly dimers as made of two fermions. We give the argument leading, at zero temperature, to the calculation of the equation of state. We find that, when expanding the chemical potential in powers of the density n up to the Lee-Huang-Yang order, proportional to n ^3/2, the result is identical to the one of elementary bosons in terms of the dimer-dimer scattering length a _M , the composite nature of the dimers appearing only in the next order term proportional to n ².     

A numerical prediction of spin-lattice relaxation enhancement of water protons by paramagnetic metal ions and free radicals. A contribution to the basic principles of relaxometry in MRI

The Solomon-Bloembergen and several simplified equations from literature are critically evaluated with the purpose of selecting an equation for rapid numerical predictions of spin-lattice relaxation data of water protons induced by paramagnetic transition metal and lanthanide ions and organic free radicals. The following equation is proposed for practical applications: $$\frac{1}{{T_1 }} \approx F\frac{{\pi ^2 \gamma _{\rm I} ^2 \gamma _S ^2 \hbar ^2 N}}{k} \frac{{m\eta }}{T} S(S + 1) \approx F 1.06^7 \frac{{m\eta }}{T} S(S + 1),$$ , whereT ₁ is the spin-lattice relaxation time, 1/T ₁ is the spin-lattice relaxation rate, γ₁ is the gyromagnetic ratio of the proton of water, γ_S is the gyromagnetic ratio of the electron,k is the Boltzman constant,h is the Plank constant, ? =h/2π,N is the number of paramagnetic species per cubic centimeter, i.e. the Avogadro number/1000,m is the concentration of the paramagnetic species in mM, η is the viscosity in centipoise at appropriate temperature,T is the appropriate absolute temperature,S is the spin quantum number, andF is a methodical factor which can range between 1–2.7, depending on the magnetic properties of the instrumentation, i.e. ～1.07 MHz (0.025 T)–90 MHz (2.1 T), and the relaxation enhancing agent. It is proposed to useF=1 for rapid numerical predictions. This equation is based on models involving translational motions and is suitable for rapid estimatesin vitro of spin-lattice relaxation times and rates of protons in water, and water protons in plasma and other biological fluids in the presence of paramagnetic metal ions, their low molecular weight complexes, and free radicals, as exemplified by nitroxyl (aminoxyl) radicals. Although this equation will be used for measurementsin vitro, the results could also be applied to project the effectiveness of new contrast agentsin vivo. It is believed that this equation will be useful in research involving the development of new contrast agents for MRI.