Fig. 1.

(A) Chronically instrumented, conscious monkeys were connected to a tether, but otherwise unrestrained in their cage during recording. (B) The aorta was instrumented with descending thoracic aortic catheters for measurement of aortic pressure and ultrasonic dimension crystals on opposing surfaces of the thoracic and abdominal aorta for measurement of aortic diameters. Examples of responses to acute phenylephrine induced hypertension are shown in a young monkey (C) and in and old monkey (D). Stiffness reflected by reduced aortic diameter excursion was increased more in old monkeys with phenylephrine than in young monkeys.