Comparison of arterial wall mechanics using ring and cylindrical segments.

Thin rings and intact cylindrical segments of canine carotid and iliac arteries were used to determine wall mechanics. Measurements of force and length were obtained from the ring segments, whereas measurements of pressure and diameter were obtained from the cylindrical segments under conditions of active (147 mM K+) and passive smooth muscle (Ca2+ free and 2 mM ethyleneglycolbis (beta-aminoethylether)-N,N'-tetraacetic acid). These measurements were normalized to values of segment stress and strain. Under passive conditions stress-strain relations for the rings appeared to be stiffer than those obtained using cylindrical segments. Pressure-diameter curves computed using force-length data from the rings were shifted to higher values of diameter compared with values from the intact segments at all pressure levels. Passive mechanics derived from measurements on ring segments yielded poor estimates of mechanics derived from intact segments. Despite this finding, values of active force development from the two sample geometries were similar. No statistically significant differences were found in values of maximum force development expressed in terms of sample cross-sectional area. Some differences in values of active force development at low values of muscle length were found. The latter were probably related to the differences in passive mechanics and the procedure used to normalize muscle length. Reasonable values of active force development can be obtained from ring segments.