Non-invasive assessment of pulse wave velocity in mice by means of ultrasound images

Objective: Pulse wave velocity (PWV) is considered as a surrogate marker of arterial stiffness and could be useful for characterizing cardiovascular disease progression even in mouse models. Aim of this study was to develop an image process algorithm for assessing arterial PWV in mice using ultrasound images only and test it on the evaluation of age-associated differences in abdominal aorta PWV. Methods: Ultrasound scans were obtained from ten adult (mean age: 5.5 months) and nine old (mean age: 15.5 months) wild type male mice (strain C57BL6) under gaseous anesthesia. For each mouse, instantaneous values of diameter and flow velocity were obtained from abdominal aorta B-mode and PW-Doppler, respectively. Single-beat mean diameter and velocity were calculated providing the velocity-diameter (lnD-V) loop. PWV values for both the early systolic phase (aaPWV) and the late systolic one (aaPWVls) were obtained from the slope of the corresponding linear parts of the loop. Relative distension (relD) was calculated from the mean diameter signal. Results: aaPWV values for adult mice (1.91 ± 0.44 m/s) were significantly lower (p < 0.01) than those obtained for older ones (2.71 ± 0.63 m/s) and the same result was found for aaPWVls (2.68 ± 0.68 vs 3.67 ± 0.95 m/s; p < 0.05). relD measurements were significantly higher (p < 0.01) in adult (22.7% ± 5.2%) compared with older animal evaluations (15.8% ± 3.9%). Conclusions: The proposed system discriminates well between age groups and supplies a non-invasive evaluation of anatomical and functional parameters of the mouse abdominal aorta. Since it provides a non-invasive PWV assessment from ultrasound (US) images only, it may offer a simple and useful system for evaluation of local vascular stiffness at other arterial site in the mouse, such as the carotid artery.