Adventitia-dependent mechanical properties of brachiocephalic ovine arteries in in vivo and in vitro studies

Aim: An adventitia dependent regulation of the vascular smooth muscle tone has been described. However, if the adventitia plays an active role on arterial wall biomechanical behaviour and functions remains to be established. Our aim was to characterize the influence of adventitia on arterial wall mechanical properties and the arterial conduit and buffer functions. Methods: Ovine brachiocephalic arteries were studied in vivo (n = 8) and in vitro (with null tone) in a circulation mock (n = 8). Isobaric, isoflow and isofrequency studies were performed. In each segment, pressure and diameter waves were assessed before and after adventitia removal. From the arterial stress–strain relationship, we derived the elastic and the viscous modulus. The buffering and conduit functions were calculated using the Kelvin–Voigt's time constant and the inverse of the characteristic impedance, respectively. Results: In in vivo studies arterial diameter decreased after adventitia removal (P < 0.05). Elastic and viscous modulus in in vivo studies were significantly higher in adventitia‐removed arteries, compared with values in intact vessels (P < 0.05). This behaviour was not observed in in vitro experiments. An impairment of buffer and conduit functions was observed in vivo after adventitia removal (P < 0.05), while both functions remain unchanged in in vitro studies (P > 0.05). Conclusions: Arterial wall viscosity and elasticity were influenced by adventitia removal in in vivo studies, possibly by a smooth muscle‐dependent mechanism, since it was not present in in vitro experiments. Adventitia would be involved in a physiological mechanism of arterial wall viscous and elastic properties regulation, that could influence arterial buffering and conduit functions.