To determine whether significant regional differences in shortening exist in the canine left ventricle, the shortening characteristics of small segments of the circumferentially oriented hoop axis fibers and the more longitudinally oriented fibers near the epicardium were examined using pairs of ultrasound crystals placed at three levels of the left ventricular free wall in the open-chest dog. Mean control shortening of the hoop axis fibers near the apex of the left ventricle averaged 20% of the end-diastolic length, significantly greater than shortening at the midventricular (13%) or basal (14%) levels. During transient periods of aortic constriction, end-diastolic length increased significantly and the extent of shortening was maintained for the hoop axis fibers at the apical and midventricular levels; end-diastolic length did not change and shortening decreased at the basal level. The epicardial fibers shortened an average of 5.6% of their end-diastolic length during control conditions at all three sites and showed small, parallel changes in shortening and end-diastolic length during aortic constriction. We conclude that significantly greater hoop axis shortening occurs near the apex of the left ventricle and that at this level a uniformly contracting model is inappropriate. In addition, the response of the hoop axis fibers to increased aortic impedance is not homogeneous, with a significant reduction in shortening occurring only at the base of the left ventricle where end-diastolic length does not increase.

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One hundred twenty eight cervical carotid arteriograms were twice viewed by three readers for the evaluation of atherosclerotic disease at the carotid bifurcation. Stenoses were estimated using calipers to the nearest 5% and lesions were qualitatively characterized as smooth, irregular, or ulcerated. The intraobserver correlation coefficient between estimates of percent stenosis was .94 overall and .98 for the internal carotid artery. The average intraobserver variability in estimating percent stenosis was 5.23% for all vessels and 6.04% with a standard deviation of 8.09% for the internal carotid artery. The intraob server percent agreement at a fixed stenosis is denned as the percent of the time one reader on two readings would read at least the fixed percent stenosis among cases that might be read as having the fixed percent stenosis. The intraobserver percent agreement rate for the internal carotid artery was 95.9% at > 0% stenosis, 90.4% for 50% or greater stenosis, and 96.8% for 100% stenosis (total occlusion). The interobserver correlation coefficient between readers was .92 overall and .97 for the internal carotid artery. The absolute difference in percent stenosis between readers was 7.21% for all vessels and 8.64% for the internal carotid artery with a standard deviation of 9.5%. The interobserver agreement rate for the internal carotid artery at > 0% stenosis was 93.0%, 85.4% for 50% or greater stenosis and 96.8% at 100% stenosis. The addition of oblique views had no statistical effect on estimates of percent stenosis but increased the frequency with which irregularity and ulceration were diagnosed in the internal carotid artery.