Wave intensity analysis of left atrial mechanics and energetics in anesthetized dogs

Abstract

Hobson TN, Flewitt JA, Belenkie I, Tyberg JV. Wave intensity analysis of left atrial mechanics and energetics in anesthetized dogs. Am J Physiol Heart Circ Physiol 292: H1533-H1540, 2007. First published November 17, 2006; doi:10.1152/ajpheart.00837.2006The left atrium (LA) acts as a booster pump during late diastole, generating the Doppler transmitral A wave and contributing incrementally to left ventricular (LV) filling. However, after volume loading and in certain disease states, LA contraction fills the LV less effectively, and retrograde flow (i.e., the Doppler Ar wave) into the pulmonary veins increases. The purpose of this study was to provide an energetic analysis of LA contraction to clarify the mechanisms responsible for changes in forward and backward flow. Wave intensity analysis was performed at the mitral valve and a pulmonary vein orifice. As operative LV stiffness increased with progressive volume loading, the reflection coefficient (i.e., energy of reflected wave/ energy of incident wave) also increased. This reflected wave decelerated the forward movement of blood through the mitral valve and was transmitted through the LA, accelerating retrograde blood flow in the pulmonary veins. Although total LA work increased with volume loading, the forward hydraulic work decreased and backward hydraulic work increased. Thus wave reflection due to increased LV stiffness accounts for the decrease in the A wave and the increase in the Ar wave measured by Doppler.hemodynamics; left atrium; A wave; Ar wave; Doppler echocardiography THE LEFT ATRIUM (LA) functions as a booster pump during late diastole, contributing ϳ20% to left ventricular (LV) filling (32). Doppler echocardiography has shown that there can be retrograde flow (i.e., the atrial reversal or Ar wave) into the pulmonary veins (PV) as blood is propelled forward into the LV during atrial systole (i.e., the transmitral A wave) (30). Analysis of the A and Ar waves may be useful in the assessment of various cardiac conditions (11,12,30,33).Previous studies have demonstrated an inverse relationship between LV end-diastolic pressure (P LVED ) and forward flow during atrial systole (16, 25,31). Increased LV operative stiffness, which is related to the increase in P LVED , is recognized as one mechanism responsible for diminished atrial contribution to LV filling (32, 45) and augmented reversed flow into the PV (2,22,24,32,41). Although it is intuitive that such a relationship would exist, the fundamental mechanisms have not been studied.Wave intensity analysis (WIA) (34,35,43) can be used to discriminate between the effects of upstream and downstream events at a specific location and provides a means of quantifying the energy carried by waves traveling through the heart and vasculature. A wave [i.e., a "propagated disturbance" (26)] changes both pressure (P) and blood velocity (U); wave "intensity" is an instantaneous function of the incremental changes in P and U and is expressed as power normalized by cross-sectional area (W/m 2 ). Waves are considered ...

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

“…In prior studies (Koh et al, 1998;Hollander et al, 2001;Hobson et al, 2007;Penny et al, 2008;Smolich et al, 2008), it has been implicitly assumed that waves propagate along an arterial segment without changing size, where 'size' refers to the peak WI (magnitude) or cumulative intensity (wave area). However, Jones et al (1992) noted that peak FCW became greater while peak FEW became smaller with measurements taken at progressively more distal aortic sites, a finding which is predicted by the model used in this study.…”

“…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):…”

Genesis of the characteristic pulmonary venous pressure waveform as described by the reservoir‐wave model

“…; Hobson et al . ). The rise in pressure observed with the c wave is a result of a BCW arising from LV contraction and the process of mitral valve closure, including the potential bulging of the leaflets into the LA.…”

Wave intensity analysis in the great arteries – What has been learnt during the last 25 years? Part 1

“…It was shown that as the la contracts, it generates a FCW (FCWla) that travels towards the lV and also a BCW (BCWla) that travels towards the pVs 70 . The FCWla tends to accelerate flow into the lV, but gets partially reflected at the mitral orifice, giving rise to a second BCW in the la (BCWla_2).…”

“…Both BCWla and BCWla_2, once transmitted into the pVs, tend to decelerate pV flow in late diastole. The size of the reflected wave was augmented as lV stiffness was acutely increased, and resulted in higher retrograde flow through the pVs 70 .…”