title: Changes in regional myocardial function and external work in exercising dogs with ischemia.
abstract: Changes in regional myocardial work of the nonischemic wall and left ventricular (LV) asynchrony of the nonischemic wall during exercise-induced ischemia were examined in seven conscious dogs instrumented with a micromanometer for LV pressure measurement and sonomicrometers for control and ischemic wall thickness and LV external short and long axes. Ischemia was produced during steady-state exercise by a pneumatic constrictor on the left circumflex coronary artery. Time difference between peak thickening of control (anterior) and ischemic (posterior) walls was measured as an index of LV asynchrony. LV pressure-wall thickness loop area of both the control wall (LVP-CW loop) and ischemic wall was calculated as an index of regional myocardial external work. With ischemia during exercise, peak LV pressure decreased by 11%, and time difference of peak thickening in the two walls increased, accompanied by marked deformation of the LVP-CW loop during early relaxation, which was related to protodiastolic thickening of the ischemic wall. Thus, despite a significant increase in percent systolic thickening during exercise, loop area of control wall was not enhanced. These changes of the LVP-CW loop were confirmed by calculation of stress-strain loop areas as an additional index of regional myocardial external work but having true dimensions of work. Stress-strain loop area in the control wall during ischemic exercise showed a similar value to that during control exercise, thereby confirming lack of compensatory increase. Thus, during exercise-induced ischemia, regional myocardial external work in the normal region does not increase despite an increase in systolic wall thickening.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Division of Cardiology, University of California, San Diego 92093.
authors.forename: S
authors.initials: S
authors.lastname: Miyazaki
authors.forename: Y
authors.initials: Y
authors.lastname: Goto
authors.forename: B D
authors.initials: BD
authors.lastname: Guth
authors.forename: T
authors.initials: T
authors.lastname: Miura
authors.forename: C
authors.initials: C
authors.lastname: Indolfi
authors.forename: J
authors.initials: J
authors.lastname: Ross
mesh_terms: D000818:Animals; D003327:Coronary Disease / Q000209:etiology / Q000503:physiopathology*; D004285:Dogs; D006321:Heart / Q000503:physiopathology*; D006439:Hemodynamics; D005082:Physical Exertion; D011312:Pressure; D013997:Time Factors; D016277:Ventricular Function, Left