Intrapulmonary gas mixing and dead space in artificially ventilated dogs.

In this study we have investigated the effects of breath holding and of the physical properties of gases on four different respiratory dead spaces (VD): the Fowler, the physiological, the washout and the inert gas dead space. The experiments were performed with dogs which were ventilated artificially with breathing patterns with different post-inspiratory breath holding times (ta) of 0, 0.5, 1.0 and 2.0 s. Tracer amounts of acetone, ether and enflurane were infused continuously into a peripheral vein and a bolus of a mixture of krypton, Freon12 and SF6 was introduced into the peritoneal cavity. After reaching steady state, samples of arterial blood, mixed venous blood and mixed expired air were taken simultaneously. From the partial pressures (Pa, PV and PE respectively) we determined the excretion (E = PE/PV), retention (R = Pa/PV) and the physiological dead space fraction (VD,phys/VT = (1- PE/Pa)) for each gas, where VT is tidal volume. Further, we recorded the expirograms of the six tracer gases and of CO2 from which the Fowler dead space fractions (VD,Fowler/VT) of the different gases were determined. Also the washout dead space fractions (VD,washout/VT) for He and SF6 were determined as well as the inert gas dead space fraction (VD,MIGET/VT) with the use of the multiple inert gas elimination technique (MIGET). With the exception of VD,phys/VT for SF6, all dead space fractions decreased with increasing ta. VD,phys/VT for the poorly soluble gas SF6 was considerably larger than VD,phys/VT for the remaining gases. For the highly soluble acetone VFowler/VT was considerably smaller than VD,Fowler/VT for the other gases. VD,washout,SF6/VT was always larger than VD,washout,He/VT and VD,Fowler,SF6/VT. Further, VD,phys/VT was larger than VD,Fowler/VT for SF6 and acetone. However, for gases with intermediate solubility in blood VD,phys/VT tended to be smaller than VD,Fowler/VT. We conclude that the respiratory dead spaces are affected by the breathing pattern and by the physical properties of gases, i.e. their diffusivity in alveolar gas and their solubility in blood or lung tissue.

Intrapulmonary gas mixing and pulmonary gas exchange in artificially ventilated dogs.

To investigate the effect of incomplete gas mixing between tidal air and residual gas on pulmonary gas exchange, anaesthetized dogs were ventilated artificially with breathing patterns with different durations of the post-inspiratory apnoea (ta = 0, 0.5, 1.0 and 2.0 s), where tidal volume, breathing frequency, inspiratory and expiratory flow patterns were kept constant. We determined the alveolar ventilations (VA) of He and SF6 from the product of end-expiratory lung volume (VL,E') and specific ventilation (VA/VL,E'). VL,E' was determined by the dilution technique and the specific ventilations of the two gases were obtained from their multiple-breath washout. Further, tracer amounts of acetone, ether and enflurane were infused continuously into a peripheral vein and a bolus of a gas mixture of krypton, Freon12 and SF6 was introduced into the peritoneal cavity. We determined the Excretion (E) and Retention (R) of these six gases according to the multiple-inert-gas-elimination technique (MIGET). VA increased with increasing ta, where VA,He was about 14% larger than VA,SF6. For both gases, however, the increase in VA relative to control (VA for ta = 0) was virtually the same: 9, 11 and 19% (mean values) for ta = 0.5, 1.0 and 2.0 s respectively. For all dogs the E/R curve shifted to larger E values with increasing ta. E for the most soluble tracer gas (acetone) increased by 11, 21 and 25% for ta = 0.5, 1.0 and 2.0 s respectively. VA, determined with MIGET from the ventilation/perfusion distribution, increased by almost the same percentages.(ABSTRACT TRUNCATED AT 250 WORDS)

The excretion of highly soluble gases by the lung in man.

The excretion (E) of inert gases by the lung depends on, among other things, their blood-gas partition coefficients (lambda). According to conventional gas exchange models, E should increase with increasing lambda. However, recent models that take into account the tidal character of breathing and the buffering capacity of lung tissue predict that E will show a minimum in the range of large lambda values (lambda greater than 10). Further, this local minimum should shift to larger lambda values in exercise conditions as compared to rest conditions. The aim of this study is to verify this predicted behaviour of E. The experiments were carried out with seven healthy subjects at rest and at three work loads (50 W, 100 W and 150 W) on a bicycle ergometer. The behaviour of E was determined from the results of a simultaneous washin of four tracer gases: ethyl acetate (lambda approximately 75), acetone (lambda approximately 330), ethanol (lambda approximately 2000) and acetic acid (lambda approximately 20000). The washin lasted 4 min, and E was calculated from E = 1 - PE-/PI, where PI and PE- are the partial pressures of the tracer gas in inspired and mixed expired gas determined from the recordings obtained during the last minute of washin. PI and PE- were measured with a mass spectrometer. Comparison of the E values of the four gases shows that at rest a minimum value for E is found for acetone. In exercise conditions, however, the smallest E value is found for the more soluble ethanol or acetic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

The sloping alveolar plateau of tracer gases washed out from mixed venous blood in man.

We have investigated the slope of the alveolar plateau for inert tracer gases that were washed out from mixed venous blood. Two pairs of tracer gases were used (He, SF6) and (C2H2, Freon 22). The gases of each pair share almost the same blood-gas partition coefficient but they have different diffusive properties in the gas phase. The experiments were performed in healthy subjects at rest and at three levels of exercise (75, 150, 225 W). Each experiment started with the alveolar washin of the tracer gases by adding these gases to inspired air. This washin was continued for several minutes in order to dissolve sufficient amounts of the tracer gases in the body tissues. Subsequently, the tracer gases were washed out. In this paper, the slopes of the alveolar plateaus are defined as the relative increase of the concentration per second. Steeper slopes were found for the heavier gases (SF6 and Freon 22) in comparison with those for the lighter gases of the two pairs (He and C2H2). This finding may be ascribed to the contribution of diffusion-limited gas mixing in the lung to the slope of the alveolar plateau. For each gas, the slope for the first expiration during washout (alveolar washout) was considerably smaller than that for the later part of washout (mixed venous washout), and the difference amounts to about 56% and 76% of the slope during mixed venous washout at rest and at the highest level of exercise, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Diffusion-limited gas mixing in the lung and its consequences for transpulmonary gas transport.

The ratio of alveolar ventilations of He and SF6 (VA,He/VA,SF6) was determined in 7 healthy male subjects at rest and at three different levels of exercise on a bicycle ergometer (75, 150 and 225 W). This ratio was calculated from the ratio of the specific ventilations for these gases which were obtained from the decay of the end-tidal partial pressures of He and SF6 during a simultaneous, multiple-breath washout. In all experiments, VA for He was larger than VA for SF6. On the average, VA,He/VA,SF6 was equal to 1.09, and the mean values of this ratio at rest and at the three levels of exercise were not significantly different. Therefore, the difference in VA for He and SF6 (VA,He-VA,SF6) increased with increasing work load. Further, we used the mean value obtained for VA,He/VA,SF6 to calculate the ratio of excretion values (E1/E2) for pairs of hypothetical tracer gases with equal blood-gas partition coefficients and with different diffusivities in the gas phase. E1/E2 ranged from unity for lambda = 0 to about 1.08 for lambda = 10. At a given lambda, E1/E2 decreased with increasing ventilation-perfusion ratio of the lung. Thus, the difference between the excretion values of light and heavy tracer gases will be most pronounced under rest conditions and for gases that are well soluble in blood.

Uptake of highly soluble gases in the epithelium of the conducting airways.

Short duration washin and washout experiments were carried out with the gases ether (diethyl ether), ethyl acetate and acetone in order to study the excretion behaviour in the lung of gases highly soluble in blood and tissues. Carbon dioxide (CO2) was analyzed as a reference gas during the washout. The excretion values for acetone were generally the lowest, those for ether the highest, and intermediate ones were obtained for ethyl acetate. These results are in accord with the experimental data of others. Analysis of the washout curves shows that for acetone the volume of gas expired before the beginning of phase II is considerably smaller than found for CO2 and ether. During washout, the slope of the alveolar plateau for acetone is negative for the first few breaths and becomes positive thereafter; however, it remains lower than the slopes for CO2 and ether, which are always positive. These two phenomena occurring during washout clearly demonstrate that the acetone in the expired air must originate from the epithelial tissue lining the conducting airways. We conclude, therefore, that, in terms of gas transport, the conducting airways behave differently for poorly and highly soluble gases and this provides a physiological basis for the deviating excretion behaviour of highly soluble gases.

Plasma renin activity and plasma catecholamines in intact and splenectomized running and swimming beagle dogs.

The influence of splenectomy in the dog on plasma catecholamine levels and plasma renin activity during treadmill running and swimming was investigated. Plasma catecholamines were measured by a radioenzymatic assay and plasma renin activity by a radioimmunoassay. Exercise consistently increased plasma catecholamine levels before and after splenectomy (range of increase:3--38 pmol X ml-1). Swimming, however, was a stronger stimulus than running. No change in the ratio between noradrenaline and adrenaline was found. In intact dogs exercise results in a marked increase in hematocrit due to splenic contraction (range of increase 3--8 volume %), while renal blood flow and plasma renin activity remain virtually constant. In splenectomized dogs, exercise has been reported to induce a decrease in renal blood flow. In contrast to this known effect on renal blood flow, splenectomy did not affect plasma renin activity in treadmill running dogs. In swimming dogs, however, plasma renin activity was increased after splenectomy (range of increase 3.3--6.9 ng X Ang I X ml-1 X h-1). Possibly, a threshold in sympathetic tone is required to increase renin release in the dog.