Early return of augmented wave reflection impairs left ventricular relaxation in aged Fisher 344 rats

Left ventricular (LV) relaxation is influenced by vascular loads imposed on the heart. The current study investigated the influence of the timing and magnitude of arterial wave reflection on LV isovolumic pressure relaxation, with a specific focus on the aging process. Fisher 344 rats aged 6, 18, and 24 months were anesthetized and thoracotomized. Arterial wave reflection was characterized by wave transit time (τ(w)) and wave reflection factor (R(f)) using the impulse response of the filtered aortic input impedance spectra. Indices of LV pressure relaxation included peak -dP(LV)/dt and the isovolumic relaxation time constant (τ(e)). The vascular dynamic condition in the rats was characterized by (1) a progressive increase in R(f) and decrease in τ(w) associated with age, especially at 24 months; and (2) a decline in aortic compliance (C(m)). Changes in LV relaxation consisted of a fall in peak -dP(LV)/dt and a rise in LV τ(e) with age. Taking LV τ(e) as the dependent variable and arterial R(f) and τ(w) as the two independent variables, multiple linear regression was employed to fit the data. The correlation among the three parameters reached significance (τ(e) =11.885+5.350×R(f)-0.213×τ(w); r=0.5823, p<0.05). This finding indicated that as arterial τ(w) shortened and arterial R(f) was augmented with age, LV τ(e) became more prolonged and late pressure relaxation slowed. Thus, the heavy reflection intensity with early return of the pulse wave reflection might account for the age-related deterioration in LV isovolumic pressure decay.