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

1. Information on the interaction between mechanical strain and the el astic properties of large arteries could give insight to the origin of haemodynamic vascular injury, possibly resulting in formation of athe rosclerotic plaques. Intra-individual variation in the elastic propert ies of muscular arteries measured using non-invasive techniques has be en observed. This variation could be due to changes in blood pressure, since the elastic properties of muscular arteries are strongly non-li near. 2. The objective of the present study was to evaluate variabilit y in the elastic properties of a muscular artery over a time period of up to Ih. Furthermore, the relation between changes in elastic proper ties 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 health y subjects (mean age 27 +/- 2.9 years) under resting conditions over 4 0-60 min. Intra-arterial blood pressure of the contralateral common fe moral artery and heart rate were recorded simultaneously. From the dis tension and pulse pressure, the distension/pressure ratio was calculat ed, a measure of the compliance. For each parameter the variation coef ficient was computed. 3. In all subjects a considerable variation was found in distension (mean variation coefficient 14.8%) but not in puls e pressure (mean variation coefficient 3.7%). The expected positive co rrelation between pulse pressure and distension was absent in eight su bjects. As a consequence, large intra-individual variation was found i n the distension/pressure ratio (mean variation coefficient 15.3%). Wh en plotted as function of time, gradual fluctuations in the distension /pressure ratio were observed. 4. In the majority of the subjects no c orrelation between diastolic pressure and diameter was observed. There fore the non-linear relation between diastolic diameter and distension cannot explain the observed variation in the distension/pressure rati o. A possible explanation might be a modification of the elastic prope rties of this large muscular artery by vasoactive substances and the c entral nervous system. 5. Under resting conditions, the elastic proper ties of the femoral artery in humans show large intra-individual varia tion with time. This variation cannot be explained by alterations in d iastolic diameter, suggesting that active vessel wall behaviour is res ponsible 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.