The importance of a source term in modeling multibreath inert gas washout.

The single path model (SPM) of airway gas transport with a distributed blood source term was used to simulate multiple breath inert lung gas washout of N2, He, and SF6 after total body equilibration with these gases. Normalized phase III inert gas washout slopes were computed for each breath and compared with published experimental data obtained under similar conditions on human subjects. The model predicts a normalized slope asymptote which agrees with experimental results within two standard deviations or less of the mean, depending on the lengths and diameters assumed in the acinar airways of the SPM. In the model and in the human subject data, the asymptote represents the development of a quasi-steady state in which the volume of inert gas exhaled at the mouth is equal to the volume transported into the acinar airways by the pulmonary blood during each breath. The present study indicates that at least in the steady state, airway inhomogeneity is not essential to model lung washout data, and that a distributed blood source term in the SPM yields good agreement with experiment.

dCAPS, a simple technique for the genetic analysis of single nucleotide polymorphisms: experimental applications in Arabidopsis thaliana genetics.

PCR-based detection of single nucleotide polymorphisms is a powerful tool for the plant geneticist. Cleaved amplified polymorphic sequence analysis is the most widely used approach for the detection of single nucleotide polymorphisms. However, this technique is limited to mutations which create or disrupt a restriction enzyme recognition site. This paper presents a modification of this technique where mismatches in a PCR primer are used to create a polymorphism based on the target mutation. This technique is useful for following known mutations in segregating populations and genetic mapping of isolated DNAs used for positional based cloning of new genes. In addition, a computer program has been developed that facilitates the design of these PCR primers.

Volumetric capnography in children. Influence of growth on the alveolar plateau slope.

BACKGROUND: Lung growth in children is associated with dramatic increases in the number and surface area of alveolated airways. Modelling studies have shown the slope of the alveolar plateau (phase III) is sensitive to the total cross-sectional area of these airways. Therefore, the influence of age and body size on the phase III slope of the volumetric capnogram was investigated. METHODS: Phase III slope (alveolar dcCO2/dv) and airway deadspace (VDaw) were derived from repeated single-breath carbon dioxide expirograms collected on 44 healthy mechanically ventilated children (aged 5 months-18 yr) undergoing minor surgery. Ventilatory support was standardized (VT = 8.5 and 12.5 ml/kg, f = 8-15 breaths/min, inspiratory time = 1 s, end-tidal partial pressure of carbon dioxide = 30-45 mmHg), and measurements were recorded by computerized integration of output from a heated pneumotachometer and mainstream infrared carbon dioxide analyzer inserted between the endotracheal tube and anesthesia circuit. Experimental data were compared to simulated breath data generated from a numeric pediatric lung model. RESULTS: An increased VDaw, a smaller VDaw/VT, and flatter phase III slope were found at the larger tidal volume (P < 0.01). Strong relationships were seen at VT = 12.5 ml/kg between airway deadspace and age (R2 = 0.77), weight (R2 = 0.93), height (R2 = 0.78), and body surface area (R2 = 0.89). The normalized phase III slopes of infants were markedly steeper than that of adolescents and were reduced at both tidal volumes with increasing age, weight, height, and body surface area. Phase III slopes and VDaw generated from modelled carbon dioxide washout simulations closely matched the experimental data collected in children. CONCLUSIONS: Morphometric increases in the alveolated airway cross-section with lung growth is associated with a decrease of the phase III slope. During adolescence, normalized phase III slopes approximate those of healthy adults. The change in slope with lung growth may reflect a decrease in diffusional resistance for carbon dioxide transport within the alveolated airway resulting in diminished acinar carbon dioxide gradients.