Using angiocardiographic data from 50 human subjects, a comparison was made of calculations of circumferential wall stress in the left ventricle based on the thin-walled ellipsoidal model of Sandier and Dodge and the thickwalled ellipsoidal model of Wong and Rautaharju. The Sandier and Dodge formula consistently overestimated mean stress as determined from the Wong and Rautaharju model. The degree of overestimation in terms of percent error usually varied between 5% and 15% and overall averaged about 10% at endsystole as well as at end-diastole. Analysis of the various factors influencing the discrepancy between calculations indicated that the expected increase in error associated with an increase in wall thickness during systole tended to be mitigated by a concomitant change in chamber geometry, specifically, an increase in the ratio of major to minor semiaxis. This study, then, offers an estimate of the error introduced by employing the Sandier and Dodge or similar thin-walled ellipsoidal models for computation of mean circumferential stress.

The coupled or equivalent exchange of the cations and anions of 11 salts, chiefly alkali metal and alkaline earth chlorides, with surface Hf and OH-of a commercial a-basic aluminum oxide was studied. Adsorption equilibrium constants and reaction site densities are reported. These site densities and those for two salts with other aluminas are low, so that the area per site is of the order of 1-10 X lo2suggesting the reaction is very specific.In three other systems which are a t least partially irreversible (where the salts are LiC1, XiC12, or Cu(N03)*) the total amount of reaction with the surface is much greater. Here, there are probably both exchange reactions, which are partially irreversible, and equivalent exchange reactions.Site density depends upon both anion and cation.