Toward optimisation of water use efficiency in dryland pastures using carbon isotope discrimination as a tool to select plant species mixtures.

Pastoral agriculture is important for supplying global demand for animal products but pasture productivity is often water limited. Increased plant diversity has been shown to increase water use efficiency (ω) and productivity under water limitation but the optimal mix of species varies spatially, dependent on climate, soil type, and plant water requirements. Consequently, a cost-effective method to screen for high ω plant species and mixes in situ at farm scale is needed. Using carbon isotope discrimination (∆13C) to examine ω is attractive because the method integrates over useful time scales, does not modify the measurement environment, and is cost-effective. Field scale ω was measured using eddy covariance (EC) at two sites with contrasting plant diversity (2 species, 7 species) and compared to the seasonal progression of ω calculated from foliage ∆13C (ω∆). Soil water evaporation (ES) was removed from EC measured total ecosystem evaporation using a modelling approach and canopy ω (ωC) was calculated as gross primary production (GPP) divided by canopy evaporation. Mixed species foliage samples were harvested pre-grazing, dried, sub-sampled, ground, and the ratio of 13C to 12C was measured. A strong positive correlation was found between ω∆ and ωC at both study sites (r2 > 0.83, p < 0.01). In addition to bulk biomass samples, individual species were also harvested seasonally. Relative increases in both ω∆ and production for some species showed that manipulation of pasture species mixtures may lead to increased ω. Combined with production monitoring, ∆13C could be developed as a tool to optimise species selection for site specific climate and soil conditions to maximise ω and farm production and profit.

Human milk vacuolating cytotoxin A immunoglobulin A antibodies modify Helicobacter pylori infection in Gambian children.

We collected data, including the weights, urea breath test results, and presence of maternal milk cytotoxin-associated gene-specific and vacuolating cytotoxin A-specific immunoglobulin A monthly from 48 mothers and infants (to 44 weeks of age) in The Gambia. In all, 11 children (23%) had negative urea breath test results, and 37 (77%) had positive results. Weight loss associated with Helicobacter pylori colonization was restricted to children whose mothers did not produce anti-vacuolating cytotoxin A antibodies in their milk (P=.028, by t test).

Growth faltering in rural Gambian infants is associated with impaired small intestinal barrier function, leading to endotoxemia and systemic inflammation.

Growth faltering of rural Gambian infants is associated with a chronic inflammatory enteropathy of the mucosa of the small intestine that may impair both digestive/absorptive and barrier functions. The aim of this study was to determine whether the enteropathy was associated with a compromised barrier function that allowed translocation of antigenic macromolecules from the gut lumen into the body, with subsequent systemic immunostimulation, resulting in growth retardation. Rural Gambian infants were studied longitudinally at regular intervals between 8 and 64 wk of age. On each study day, each child was medically examined, anthropometric measurements were made, a blood sample was taken and an intestinal permeability test performed. Evidence of chronic immunostimulation was provided by abnormally elevated white blood cell, lymphocyte and platelet counts, and frequently raised plasma concentration of C-reactive protein. Intestinal permeability was abnormal and associated with impaired growth (r = -0.41, P < 0.001). Plasma concentrations of endotoxin and immunoglobulin (Ig)G-endotoxin core antibody were also elevated and related to both growth (r = -0.30, P < 0.02; r = -0.64, P < 0.0001, respectively) and measures of mucosal enteropathy. Plasma IgG, IgA and IgM levels increased rapidly with age toward adult concentrations. Raised values were related to poor growth but also to measures of mucosal enteropathy and the endotoxin antibody titer. The interrelationships among these variables and growth suggested that they were all part of the same growth-retarding mechanism. These data are consistent with the hypothesis of translocation of immunogenic lumenal macromolecules across a compromised gut mucosa, leading to stimulation of systemic immune/inflammatory processes and subsequent growth impairment.

The African enigma: low prevalence of gastric atrophy, high prevalence of chronic inflammation in West African adults and children.

BACKGROUND: Helicobacter pylori infection is very common in Africa, yet peptic ulcer disease and gastric malignancy are rare. AIM: The aim of this study was to quantify mucosal responses to H. pylori in Gambian adults and children and to estimate the prevalence of antibodies to bacterial virulence factors (cagA and vacA) in a symptomatic population. PATIENTS AND METHODS: Adults (mean 36 SD 12 years) with dyspepsia and children (mean 1.4 years SD 0.4 years) with malnutrition underwent gastroscopy with biopsy. Blood was simultaneously drawn for cagA and vacA antibody status. Histopathological scoring used the modified Sydney classification. RESULTS: Both adults (n = 45) and children (n = 37) mainly demonstrated chronic mild antral inflammation. Only 2/83 cases of focal atrophy (GA) and 4/83 cases of intestinal metaplasia (IM) were observed. Adults tended to demonstrate more frequent acute (AI) and chronic inflammation (CI) (38% compared with 18% and 85% compared with 72%, respectively). Sixty-seven percent of children were cagA IgG+ and 21% vacA IgG+ and 93% of adults were IgG cagA+ and 86% vacA+. There were no differences in mucosal responses between those who were cagA or vacA positive compared with those who were negative. CONCLUSION: Gambian adults and children mount a CI response to H. pylori but GA, IM and AI are uncommon. cagA and vacA are commonly expressed in Gambian strains of H. pylori. Further studies are needed in order to confirm that GA and IM are not late findings in old age.

Interpreting the 13C-urea breath test among a large population of young children from a developing country.

The 13C-urea breath test is a noninvasive tool for the diagnosis of gastric Helicobacter pylori infection. However, it has not been validated in young children from the developing world, where infection is very common. 13C urea breath tests were performed on 1532 occasions on 247 Gambian infants and children aged from 3 to 48 mo. The means and variances of the separate sub-populations of 13C enrichment results contained within the overall dataset were estimated by a Genstat procedure using the EM algorithm, thereby identifying a cut-off value to discriminate positive from negative results. To illustrate the appropriateness of this calculated cut-off value, 13C urea breath tests were performed upon a small group of 14 patients aged 6 to 28 mo undergoing diagnostic upper endoscopy. Fixed gastric antral biopsies were examined to identify H. pylori. Two subpopulations were identified within the large dataset. A cut-off value of 5.47 delta per thousand relative to Pee Dee Belemnite limestone above baseline at 30 min identified 95% of the normally distributed negative sub-population and 99.4% of the log normal distributed positive sub-population. Comparison with endoscopic data confirmed that this cut-off value was appropriate for this population, as 7/7 children without H. pylori on their gastric biopsies had negative urea breath tests, and 6/7 children with gastric H. pylori colonization had positive urea breath tests. These findings confirm the value of the urea breath test as a diagnostic tool in young children from developing countries. They also offer a way to calculate the most appropriate cut-off value for use in different populations and the likelihood that it will correctly assign any value into the appropriate sub-population, without the need for endoscopy.

Airway pressure changes observable with constant-flow inflation and an end-inspiratory pause.

Constant-flow inflation and a prolonged end-inspiratory pause were studied, observing the airway pressures in model lungs. The technique demonstrated the changes associated with compliance, resistance and gas redistribution under varying conditions. The studies suggest that when intratracheal pressures indicate a large element of gas redistribution, constant flow inflation and end-inspiratory pause produce pendelluft, and other pressure patterns are preferable for I.P.P.V.

Respiratory mechanics with constant flow inspiration. A comparison of two measurement techniques.

Resperatory compliance and resistance were measured during positive pressure ventilation in anaesthtized, paralysed dogs. Airway pressures measured during constant-flow inspiration allowed the calculation of pulmonary and chest-wall resistances, and static and non-static compliances. Contiguous studies of dynamic compliance and resistance allowed comparison of the two techniques, and the level of agreement was reasonalble. Cconstant-flow inflation of the lungs allows a simple means of measuring respiratory mechanics, and should be valid for the observation of short-term changes in the apnoeic patient.

Accurate volume ventilation of neonates with maintenance of humidification.

A method is presented for producing adequate humidification and accurate volume ventilation of neonates. This was effected by pressurizing the humidifier and fresh gas flow up to the T-piece. By using a ventilator which acted as a timed occluder of the T-piece, the system functioned as an accurate flow generator. Its precision of ventilation was confirmed with a neonatal test lung.