Submitted on August 3, 2006
Accepted on November 9, 2006
Wave Intensity Analysis of Left Atrial Mechanics and Energetics in Anesthetized Dogs
Tracy Hobson1, Jacqueline Flewitt2, Israel Belenkie1, and John V. Tyberg3*
1 Medicine, University of Calgary, Calgary, Canada
2 Cardiac Sciences, Physiology and Biophysics, University of Calgary, Calgary, Canada
3 Medical Physiology, University of Calgary, Calgary, Canada
* To whom correspondence should be addressed. E-mail: jtyberg{at}ucalgary.ca.
The left atrium (LA) acts as a booster pump during late diastole, generating the Doppler transmitral A wave and contributing incremently 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.
