Regional work of the ventricle: wall tension--area relation

We clarified that the set of the isotropic component (T) of wall tension and the area (A) of a selected region of the left ventricular wall expresses the regional work with sufficient accuracy. The area surrounded by the locus of the T-A relation in the T-A plane is approximately equal to the real work done by that region. The behavior of the T-A loop was studied in nine anesthetized dogs under various conditions. The regional area and diameter of the left ventricle were measured with ultrasonic crystal pairs. The wall tension was calculated from measured left ventricular pressure and diameter by a generalized Laplace's equation for a thick-walled model. During volume loading, administration of methoxamine, and aortic constriction, the regional work per stroke increased with the increase in end-diastolic regional area, which is considered to be the regional Frank-Starling mechanism. With the development of ischemia, the T-A loop for the ischemic region shifted to the right and the work done by that region decreased. After a certain stage in the development of ischemia, the work done by the ischemic region became negative. When only one of the segmental lengths, rather than the area, is measured, difficulty arises in the physical interpretation of pressure-length or tension-length data in some cases. The T-A loop diagram resolves such difficulty by defining the regional work correctly. We conclude that the T-A loop diagram is a useful tool for analyzing the regional ventricular function.