Davis J

Effect of gas density and ventilatory pattern on steady-state co uptake by the lung

The steady-state uptake of carbon monoxide was measured in five normal subjects to study stratified inhomogeneity of gases in the pulmonary airways. An attempt was made to assess the effect of stratified inhomogeneity by varying the physical properties of the inspired gases and the depth and rate of ventilation by the subjects. Twelve different controlled patterns of breathing were followed by each subject on each of three gas mixtures (20% O2 with N2, He and SF6 plus 0.04% CO in each case). The experimental results show that CO uptake was significantly different when breathing the different density gases but that it was always greatest from the most dense gas SF6 and least from He. If the uptake of CO from the inspired gas across the alveolar membrane were controlled by simple molecular diffusion then as gas density decreases uptake would increase. As inspiratory flow rate was increased there was an almost linear increase in CO uptake for each gas mixture with a difference in uptake between the different-density gases which became most marked at the higher flow rates. Flow rate was increased in two ways: by maintaining tidal volume and altering breathing frequency or by maintaining frequency and altering tidal volume. The results for the two extremes, helium and SF6, indicated a difference between these methods of increasing flow rate. In the case of SF6, doubling the flow rate by increasing breathing frequency gave an uptake only marginally lower than doubling the depth of penetration. With helium, however, it was necessary to treble the frequency to obtain the increment of CO uptake achieved by doubling the depth of penetration. The experimental observations are explained by the use of a model based on Taylor dispersion in the conducting airways. The conclusion is that the results confirm the presence of significant stratified inhomogeneity in the airways of the lung.

Effects of particle size and perfusate composition on the uptake of colloidal gold by the rabbit thoracic aorta perfused in situ

The influence has been investigated of particle size on the uptake of radioactive gold colloid by the rabbit thoracic aorta perfused in situ. Particles ranging in diameter from 14 nm to 40 nm were suspended in 0.9% NaCl and infused either at a pressure of 15 mm Hg for times of between 2 1/2 and 60 min or at pressure of between 15 and 160 mm Hg for 5 min. Uptake by the whole intima-media increased with perfusion time and hydrostatic pressure but did not depend on particle size. Radioactive assay of serial sections across the aortic wall also showed that particle size did not influence the distribution of tracer. An effect of perfusate composition on uptake was demonstrated in further experiments in which particles either 14 or 40 nm in diameter were suspended in pooled rabbit serum and infused at pressures of between 15 and 140 mm Hg for 5 min. Uptake and transmural distribution were again independent of particle size, but uptake was 4-5-fold less than when the particles were perfused in saline. Under all perfusion conditions radioactivity fell steeply across the intima and then rose gradually across the media and adventitia. Radioactivity in the outer media and adventitia increased with perfusion time but little change could be detected in intimal activity. In transmission electron micrographs, particles in the intima were not seen to penetrate the internal elastic lamella and in the outer media particles remained extracellular and did not enter collagen bundles. Autoradiographs showed that particles in the intima were uniformly distributed around the circumference of the vessel but in the outer media and adventitia particles usually clustered close to the vasa vasorum.