3.5 NON-INVASIVE US-BASED WAVE INTENSITY ANALYSIS IN MICE

Abstract

Wave Intensity Analysis (WIA) can provide information about the interaction between vascular and cardiac system. WIA-derived indexes have quantitative physiological meaning. We investigated age-associated changes in WIA-derived parameters in mice and correlated them with biomarkers of cardiac function. Sixteen wild-type male mice (strain C57BL6) were imaged with high-resolution ultrasound (Vevo 2100) at 8 weeks (T0) and 25 weeks (T1) of age. Carotid pulse wave velocity (PWV) was calculated from B-Mode and PW-Doppler images using the lnD-V loop and employed to evaluate WIA: amplitudes of the first (W1) and the second (W2) local maxima and minimum (Wb) were assessed. Reflection index (RI) was assessed as Wb/W1. Cardiac output (CO), ejection fraction (EF) fractional shortening (FS) and stroke volume (SV) were evaluated strain analysis provided strain and strain rate values for longitudinal, radial and circumferential directions (LS, LSR, RS, RSR, CS, CSR). Isovolumetric relaxation time (IVRT) was calculated from mitral inflow PW-Doppler images and normalized for cardiac cycle length. W1(T0:4.42e-07±2.32e-07m2/s T1:2.21e-07±9.77e-08m2/s), W2(T0:2.45e-08±9.63e-09m2/s T1:1.78e-08±7.82e-09m2/s), Wb(T0:-8.75e-08±5.45e-08m2/sT1:-4.28e-08±2.22e-08m2/s), CO(T0:19.27±4.33ml/min T1:16.71±2.88ml/min), LS(T0:17.55±3.67% T1:15.05±2.89%), LSR(T0:6.02±1.39s-1 T1:5.02±1.25s-1), CS(T0:27.5±5.18% T1:22.66±3.09%) and CSR(T0:10.03±2.55s-1 T1:7.50±1.84s1) significantly reduced with age. W1 was significantly correlated with CO(R=0.58), EF(R=0.72), LS(R=0.65), LSR(R=0.89), CS(R=0.61), CSR(R=0.70) at T0; correlations were not significant at T1.! The decrease in W1 and W2 suggests a reduction in cardiac performance, while that in Wb, in view of unchanged RI, can be associated with a reduction in the total energy carried by the wave. The loss of correlation between WIA-derived parameters and cardiac biomarkers might reflect an age-associated alteration in cardio-vascular coupling.