We performed multiple-breath N2 washouts (MBNW) with tidal volumes of 1 liter at 8-16 breaths/min and constant flow rates in six normal subjects. For each breath we computed the slope of the alveolar plateau, normalized by the mean expired N2 concentration (Sn), the Bohr dead space (VDB), an index analogous to the Fowler dead space (V50), and the normalized slope of phase II (S2). In four subjects helium (He) and sulfur hexafluoride (SF6) were washed out after equilibration with a 5% gas mixture of each tracer. The Sn for He and SF6 increased in consecutive breaths, but the difference (delta Sn) increased only over the first five breaths, remaining constant thereafter. In all six subjects Sn, VDB, and V50 increased progressively in consecutive breaths of the MBNW, the increase in Sn being the greatest, approximately 290% from the first to the 23-25th breath. In contrast, S2 was unchanged initially and decreased after the sixth breath. The results indicate that after the fifth breath the increase in Sn during a MBNW is diffusion independent and may constitute a sensitive index of convection-dependent inhomogeneity (CDI). Subtraction of this component from the first breath suggests that Sn in a single-breath washout is largely due to a diffusion-dependent mechanism. The latter may reflect an interaction of convection and diffusion within the lung periphery, whereas CDI may comprise ventilation inequality among larger units, subtended by more centrally located branch points.

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To study the relationship between bronchomotor tone, static mechanical properties of the lung, and ventilation distribution, we measured the pressure-volume (P-V) curve of the lung and several ventilatory indexes before and after intravenous atropine in eight normal subjects. The indexes of ventilation distribution were derived from multiple breath N2 washouts by a recently developed analysis (7,8). The latter not only provides a sensitive measure of overall ventilation inhomogeneity but distinguishes between the convection-dependent inhomogeneity (CDI) among larger lung units and that due to the interaction of convection and diffusion (DCDI) within the lung periphery. Atropine decreased lung elastic recoil but distensibility, as defined by the exponent (K) in the monoexponential analysis of the P-V data, was unchanged. The overall ventilation inhomogeneity increased by 37% after atropine (P less than 0.02) due to an increase in the CDI component. More importantly, there was a significant correlation between the loss of lung recoil (but not K) and each of the indexes of CDI among the subjects. There was no correlation between the changes in lung recoil and in DCDI. Our findings indicate that normal bronchomotor tone contributes to the elastic recoil of the lung. Furthermore, the tone is distributed in a way that enhances the uniformity of ventilation distribution among diffusion-independent lung units. Presumably this is achieved by minimizing interacinar intrinsic inequalities in static mechanical properties.

By using the potentiometric titration method, acidity constants in the polar aprotic solvent acetonitrile (in the form of pK a AN values) of cations obtained by protonation of 13 substituted 4-nitropyridine N-oxides and cationic homoconjugation constants (K BHB + ) of the cationic acids conjugated with the N-oxides studied have been determined. A correlation has been established between the tendency toward cationic homoconjugation (expressed as log K BHB + ) and the basicity of the N-oxides in acetonitrile (pK a AN ). Further, by using ab initio methods at the RHF and MP2 levels utilizing the Gaussian 6-31G* basis set, energies and Gibbs free energies have been determined of protonation and formation of homocomplexed cations stabilized by O‚‚‚H‚‚‚O bridges in the gas phase. The calculated protonation energies, ∆E prot , and Gibbs free enthalpies, ∆G prot , in vacuo have been found to correlate well with the acid dissociation constants (expressed as pK a AN values) of protonated N-oxides, whereas the calculated energies, ∆E BHB + , and Gibbs free energies, ∆G BHB + , of homoconjugation do not correlate with the cationic homoconjugation constant values determined in acetonitrile.

This paper investigates the tribochemical reactions of n-hexadecane proceeding i n a tribosystem lubricated by n-hexadecane at ambient and elevated temperatures. It is hypothesised that, at ambient temperature, reactions are mostly initiated by the mechanical action of the system, and at elevated temperature (200°C) thermochemical reactions should be dominant. An experimental study was performed using a ball-on-disc machine with steel-on-steel mating elements. To analyse wear tracks, Fourier transform infrared microspectrophotometry (FTIRM) and electron spectroscopy for chemical analysis (ESCA IXPS) were used. To investigate chemical changes in the bulk lubricant, gas chromatography coupled with mass spectrometry (GCIMS) was applied. The results provide clear evidence for the hypothesis that two types of oxygenation processes of n-hexadecane under boundary lubrication conditions should be considered. The first, at ambient temperature, is controlled by the mechanical action and the second is clearly controlled by temperature. The analytical techniques applied gave evidence of the formation of some reaction products from hexadecane under boundary lubrication conditions. These products include compounds having Fe-0 bonding (salts and chelates), carbonyl compounds, and iron carbide.