SHORT-TERM VARIATION IN THE ELASTIC PROPERTIES OF A MUSCULAR ARTERY IN HUMANS

1. Information on the interaction between mechanical strain and the elastic properties of large arteries could give insight to the origin of haemodynamic vascular injury, possibly resulting in formation of atherosclerotic plaques. Intra-individual variation in the elastic properties of muscular arteries measured using non-invasive techniques has been observed. This variation could be due to changes in blood pressure, since the elastic properties of muscular arteries are strongly non-linear. 2. The objective of the present study was to evaluate variability in the elastic properties of a muscular artery over a time period of up to Ih. Furthermore, the relation between changes in elastic properties and alterations in blood pressure was studied. With a noninvasive high-resolution ultrasound technique, the diameter and distension of the femoral artery were assessed by repeated measurements in 10 healthy subjects (mean age 27 +/- 2.9 years) under resting conditions over 40-60 min. Intra-arterial blood pressure of the contralateral common femoral artery and heart rate were recorded simultaneously. From the distension and pulse pressure, the distension/pressure ratio was calculated, a measure of the compliance. For each parameter the variation coefficient was computed. 3. In all subjects a considerable variation was found in distension (mean variation coefficient 14.8%) but not in pulse pressure (mean variation coefficient 3.7%). The expected positive correlation between pulse pressure and distension was absent in eight subjects. As a consequence, large intra-individual variation was found in the distension/pressure ratio (mean variation coefficient 15.3%). When plotted as function of time, gradual fluctuations in the distension/pressure ratio were observed. 4. In the majority of the subjects no correlation between diastolic pressure and diameter was observed. Therefore the non-linear relation between diastolic diameter and distension cannot explain the observed variation in the distension/pressure ratio. A possible explanation might be a modification of the elastic properties of this large muscular artery by vasoactive substances and the central nervous system. 5. Under resting conditions, the elastic properties of the femoral artery in humans show large intra-individual variation with time. This variation cannot be explained by alterations in diastolic diameter, suggesting that active vessel wall behaviour is responsible for the variability. Due to the variability of the distension/pressure ratio in this large artery, a single measurement cannot give a proper characterization of the elastic properties.