A retrospective method for pulse-wave velocity measurement in the mouse

Abstract

The pulse-wave velocity (PWV) is inversely related to arterial compliance, and provides a useful measure of vascular function. In this study, the PWV was measured non-invasively in the mouse carotid artery using the time-delay (TD) and flow-area (QA) methods. The TD technique determines the distributed PWV from the time-delay between Doppler-derived upstrokes at two locations a known distance apart. The QA method estimates the local PWV as the ratio between the change in volume flow and the change in cross-sectional area during the reflection-free period of the cardiac cycle. Our new QA approach measures the cross-sectional area and flow through the vessel using a high- frame-rate retrospective colour flow imaging (RCFI) technique. The cross-sectional area is determined by integrating over the region of flow in each frame of the RCFI dataset, while the volume flow is calculated by averaging the velocities over the vessel in each frame and multiplying by the corresponding area. The TD method was compared with the flow-area method in the carotid artery of 7 young CD-1 mice, anesthetized with isoflurane. The average TD PWV was found to be 3.03±0.17 m/s. The average QA PWV was found to be 2.97±0.18 m/s. The TD method was found to correlate well with the QA method (r=0.91, p<0.001). The mean difference between the TD method and the QA method was 0.06±0.08 m/s, and 95% of the differences fell within ±0.41±0.20 m/s of the mean difference. These results indicate that the QA method should be capable of distinguishing between changes to PWV caused by vascular disease. It was found that the QA method permits the measurement of the local PWV. The TD method offered superior reliability to the QA method for PWV determination in the mouse carotid artery because it was affected by fewer contextual factors. However, the QA method is useful for situations in which the TD method is unsuitable due to the geometry of the vessel. In this study, we compared a QA method of measuring the PWV with an image-guided TD method in the carotid artery of seven CD-1 mice. The TD technique was used to measure a distributed PWV over the carotid artery from the aortic arch to the bifurcation. The QA method was applied to determine the local PWV at the midsection of the carotid. The objective of this study was to assess the potential of the QA method against the TD method and to demonstrate a simple image-based methodology for performing PWV measurements. Determination of the most reliable PWV estimation method will be useful in a future longitudinal study of vascular development in transgenic mice.