Aortic wave intensity analysis of ventricular-vascular interaction during incremental dobutamine infusion in adult sheep

Abstract

This study undertook a detailed examination of the ventricular-vascular interaction of the predominant beta-adrenergic agonist dobutamine using wave intensity analysis. Eight anesthetized open-chest ewes were instrumented with an aortic micromanometer to measure central aortic blood pressure (P) and an ultrasonic flow probe to obtain ascending aortic blood velocity (U). Hemodynamics were recorded during incremental dobutamine infusion (0.5, 1, 2.5, 5, 7.5, and 10 microg.kg(-1).min(-1)). Wave intensity (dI(W)) was calculated as the product of the rates of change of P and U with customized software using ensemble-averaged signals. Forward and backward components of dI(W), P, and U were determined after calculation of wave speed. As well as the typical initial forward compression wave (FCW), midsystolic backward compression wave (BCW), and late-systolic forward expansion wave (FEW(es)), two minor and previously unheralded waves were also detectable in the wave intensity profile at baseline. The first was an early systolic backward expansion wave (BEW), which reduced P but increased peak U. The second was a mid-systolic forward expansion wave (FEW(ms)), which reduced P and U. During dobutamine infusion FCW dI(W) increased 18-fold (P < 0.001), but BCW dI(W) rose 12-fold (P < 0.001) while FEW(es) dI(W) fell by 70% (P < 0.001). However, the latter changes were accompanied by a 44-fold increase in BEW dI(W) (P = 0.005) that augmented the initial aortic forward flow and a >100-fold rise in FEW(ms) dI(W) (P < 0.001) that produced earlier and enhanced aortic blood deceleration. These findings provide new insights into the ventricular-vascular interaction of dobutamine.

Wave intensity amplification and attenuation in non-linear flow: Implications for the calculation of local reflection coefficients

“…Wave intensity represents the summation of infinitesimal wavelets and was initially defined (Parker et al, 1988;Parker and Jones, 1990) as dP dU, where dP and dU are incremental changes in P and U over one sample interval; however timecorrected wave intensity WI ¼ (dP/dt)(dU/dt), employed in this study, is increasingly being used (Jones et al, 2002;Niki et al, 2002;Penny et al, 2008;Smolich et al, 2008) since it is independent of sample rate.…”

“…It has long been recognised that the pressure and flow waves generated during ventricular systole are partially reflected from the vasculature and that these reflections make a significant contribution to ventricular afterload and overall haemodynamics (Brin and Yin, 1984;O'Rourke and Kelly, 1993;Duan and Zamir, 1995;Koh et al, 1998;Penny et al, 2008). Moreover, accurate quantitation of the degree of wave reflection is important in view of the increasing use of indices based on this measure in the management of clinical conditions such as hypertension (Nichols et al, 2008;Weber et al, 2007).…”

“…Under normal conditions, the initial ventricular impulse produces a large forward compression wave (FCW) in early systole, which accelerates blood and increases pressure. Subsequently, a forward expansion wave (FEW) generated in late-systole reduces pressure and flow before valve closure (Parker et al, 1988;Penny et al, 2008). The FCW is often followed by a smaller backward compression (BCW) and/or a backward expansion wave (BEW), which arise from downstream reflection of FCW (Hollander et al, 2001;Khir et al, 2001;Khir and Parker, 2005;Zambanini et al, 2005;Penny et al, 2008).…”

“…With the remaining approaches, R is calculated directly from the wave magnitude, which can be quantified by peak WI (Jones et al, 1992(Jones et al, , 2002Bleasdale et al, 2003;Fujimoto et al, 2004;Khir and Parker, 2005;Penny et al, 2008;Smolich et al, 2008) or the wave area (termed 'cumulative intensity') Penny et al, 2008;Smolich et al, 2008). Thus, R has been calculated from the ratio of the cumulative intensities of backward (CI À ) and forward (CI + ) waves (Hollander et al, 2001;Hobson et al, 2007;Penny et al, 2008;Smolich et al, 2008):…”

“…Thus, R has been calculated from the ratio of the cumulative intensities of backward (CI À ) and forward (CI + ) waves (Hollander et al, 2001;Hobson et al, 2007;Penny et al, 2008;Smolich et al, 2008):…”