Arteriolar dimensions from unanesthetized rabbits

Arteriolar dimensions were determined during vasodilated states of natural vasomotion in unanesthetized rabbits using the ear chamber technique. Analysis of 383 arteriolar segments were made in 16 New Zealand white rabbits, 8-9 weeks after implantation of the ear chamber under the conditions of 25.5 +/- 0.5 degrees C (room temperature), 33.6 +/- 1.4 degrees C (ear surface temperature), 38.3 +/- 0.5 degrees C (rectal temperature), 66.5 +/- 3.2 mmHg (aortic mean blood pressure) and 238.6 +/- 33.0 beats/min (heart rate). Inside diameter (ID) and outside diameter were measured by closed circuit television microscopy using a Vista model 308 video image splitter. Wall thickness (WT) vs. ID, wall-to-lumen ratio (W/L) vs. ID and cross-sectional wall area (CSWA) vs. ID were fitted to the formulae: WT = 0.14 X ID + 3.8 (r = 0.76, p less than 0.001), W/L = 4.23 divided by ID + 0.12 (r = 0.84, p less than 0.001) and CSWA = 0.57 X ID2 + 11.0 X ID + 93.7 (r = 0.93, p less than 0.001), respectively. W/L increased rapidly in precapillary arterioles, especially below 30 micron ID, since WT has a finite size while ID does not. This structural property of resistance vessels is important in regulating peripheral resistance, blood flow, and downstream capillary density.