Distal projection of insufflated gas during tracheal gas insufflation.

Tracheal gas insufflation (TGI) flushes expired gas from the ventilator circuitry and central airways, augmenting CO2 clearance. Whereas a significant portion of this washout effect may occur distal to the injection orifice, the penetration and mixing behavior of TGI gas has not been studied experimentally. We examined the behavior of 100% oxygen TGI injected at set flow rates of 1-20 l/min into a simulated trachea consisting of a smooth-walled, 14-mm-diameter tube. Models incorporating a separate coaxial TGI injector, a rough-walled trachea, and a bifurcated trachea were also studied. One-hundred percent nitrogen, representing expiratory flow, passed in the direction opposite to TGI at set flow rates of 1-25 l/min. Oxygen concentration within the "trachea" was mapped as a function of axial and radial position. Three consistent findings were observed: 1) mixing of expiratory and TGI gases occurred close to the TGI orifice; 2) the oxygenated domain extended several centimeters beyond the endotracheal tube, even at high-expiratory flows, but had a defined distal limit; and 3) more distally from the site of gas injection, the TGI gas tended to propagate along the tracheal wall, rather than as a central projection. We conclude that forward-directed TGI penetrates a substantial distance into the central airways, extending the compartment susceptible to CO2 washout.     

Correction of inert gas washin or washout for gas solubility in blood

We show that when an inert gas is washed into the lungs its retention in the blood during any one breath is approximately proportional to its solubility. This relationship makes possible the correction of washin or washout data for blood uptake or release, provided that two gases of different solubility are used simultaneously. The method automatically allows for the characteristics of an individual washin or washout and for the occurrence of recirculation within a fairly short washin or washout period. It has been tested in models with nonuniform ventilation and perfusion and closely approximates the behavior of a truly insoluble gas. In the derived ventilation distribution, gas solubility appears as ventilation to units of low turnover. In the case of N2 this effect is small but causes appreciable overestimation of lung volume. The recovered dead space and main alveolar distribution are insignificantly affected.     

High-temperature gas chromatography and gas chromatography-mass spectrometry of glycoprotein and glycosphingolipid oligosaccharides

High-temperature gas chromatography and gas chromatography-inass spectrometry for the analyses of oligosaccharides derived from glycoproteins or glycosphingolipids has been developed. Pcrmethylatcd oligosaccharides with up to about 12 sugar residues and masses up to 2500 Daltons can be analyzed. This approach is discussed and exemplified.     

Effect of increased gas density on pulmonary gas exchange in man.

Pulmonary gas exchange was measured in seven resting supine subjects breathing air or a dense gas mixture containing 21% O2 in sulfur hexafluoride (SF6). The mean value of the alveolar-arterial oxygen difference (AaDO2) decreased from 12.4 on air to 7.0 on SF6 (P less than 0.01), and increased again to 13.4 when air breathing resumed (P less than 0.01). No differences occurred between gas mixtures for O2 consumption, respiratory quotient, minute ventilation, breathing frequency, heart rate, or blood pressure, and the improved oxygen transfer could not be attributed to changes in cardiac output or mixed venous oxygen content in the one subject in which they were measured. These results are best explained by an altered distribution of ventilation during dense gas breathing, so that the ventilation-perfusion ratio (VA/Q) variance was reduced. Of several considered mechanisms, we favor one in which SF6 promotes cardiogenic gas mixing between peripheral parallel units having different alveolar gas concentrations. This mechanism allows for observed increases in arterial carbon dioxide tension and dead space-to-tidal volume ratio during dense gas breathing, and suggests that intraregional VA/Q variance accounts for at least one-half of the resting AaDO2 in healthy supine young men.     

The influence of gas exchange on lung gas concentrations during air breathing

A model study is made of the contribution that continuing respiratory gas exchange makes to the alveolar plateau slope for O₂ during air breathing. Calculations in the model of the O₂ concentration appearing at the mouth during expiration, are performed for single breaths of air at constant flow rates 18 litres/min and 120 litres/min. At 18 litres/min the breathing period is 5 sec, the initial lung volume is 2300 ml, and the O₂ uptake rate is 300 ml STPD/min; whereas at 120 litres/min these parameters are 4 sec, 1200 ml, and 1800 ml STPD/min respectively. In each case the initial lung O₂ tension is taken to be 98 mm Hg. It is found that at 18 litres/min, the O₂ concentration difference on the alveolar plateau over the last second of expiration is 0.4 mm Hg when gas exchange is omitted and 1.2 mm Hg when gas exchange is included in the model. At 120 litres/min, this difference is zero and 5.0 mm Hg respectively. The gas exchange component predicted from a corresponding well-mixed compartment model is the same at 18 litres/min (0.8 mm Hg) but is 6.0 mm Hg at 120 litres/min.     

Ventilation-perfusion inhomogeneity increases gas uptake: theoretical modeling of gas exchange.

Ventilation-perfusion (VA/Q) inhomogeneity was modeled to measure its effect on gas exchange in the presence of inspired mixtures of two soluble gases using a two-compartment computer model. Theoretical studies involving a mixture of hypothetical gases with equal solubility in blood showed that the effect of increasing inhomogeneity of distributions of either ventilation or blood flow is to paradoxically increase uptake of the gas with the lowest overall uptake in relation to its inspired concentration. This phenomenon is explained by the concentrating effects that uptake of soluble gases exert on each other in low VA/Q compartments. Repeating this analysis for inspired mixtures of 30% O(2) and 70% nitrous oxide (N(2)O) confirmed that, during "steady-state" N(2)O anesthesia, uptake of N(2)O is predicted to paradoxically increase in the presence of worsening VA/Q inhomogeneity.