HEART RATE-DEPENDENCE OF ARTERIAL DISTENSIBILITY IN-VIVO

Objectives Viscous and inertial components contribute to arterial dist ensibility and compliance in vitro. The purpose of our study was to de termine whether this phenomenon is of relevance in vivo, namely, wheth er arterial compliance is altered by an increase in heart rate. Design Arterial diameter was assessed by an echo-Doppler device in a common carotid and femoral artery, namely, in a large elastic and a muscle ar tery. The studies were performed in 12-week-old pentobarbitone-anaesth etized Wistar-Kyoto rats subjected to atrial pacing via a transjugular unipolar catheter at five different randomly sequenced rates (280, 31 0, 340, 370 and 400 beats/min), After each stage, spontaneous sinus rh ythm was allowed to return, Blood pressure was measured via a catheter inserted into the carotid or femoral artery contralateral to the vess els in which the diameter was measured, Arterial compliance and disten sibility values were derived according to the Langewouters formula. Re sults A progressive increase in heart rate caused by pacing was accomp anied by progressive and marked reductions in carotid artery complianc e and distensibility, When quantified by the area under the distensibi lity-pressure or compliance-pressure curve the reduction was in the ra nge 15-43%. Although a tendency to a similar phenomenon was observed i n the femoral artery, in the latter vessel the reduction in distensibi lity and compliance was less marked and statistically insignificant. C onclusions In the anaesthetized rat acute increases in heart rate are accompanied by reductions in arterial compliance and distensibility. T he effect is greater in elastic than in muscle arteries.