Effect of changing afterload and inotropic states on inner and outer ventricular wall thickening.

Effect of changing afterload and inotropic states on inner and outer ventricular wall thickening. Am. J. Physiol. 263 (Heart Circ. Physiol. 32): H109-H116, 1992.--To study the differing behaviors of the inner (IH) and outer halves (OH) of the left ventricular (LV) free wall during an increasing afterload and changing inotropic states, we determined the LV pressure (LVP) and transmural (TM) and OH wall thickness (WTTM and WTOH) by sonomicrometry in 11 anesthetized dogs. The percent systolic wall thickening (% delta WT) and the fractional contribution (FC) were calculated. At rest, % delta WT of TM, IH, and OH were 22 +/- 1 (mean +/- SE), 33 +/- 3, and 13 +/- 2 (P less than 0.01 vs. IH), respectively. The FC of IH and OH were 74 +/- 5 and 29 +/- 4% (P less than 0.01 vs. IH), respectively. During increasing afterload by aortic constriction (AC) without drugs, % delta WT in IH was reduced to 22 +/- 2%, associated with unchanged % delta WT in OH (12 +/- 3%), whereas the FC of IH and OH were not altered from resting values. During AC with dobutamine infusion (3 micrograms.kg-1.min-1), the % delta WT and FC in each layer were not reduced from resting values. On the other hand, during AC with propranolol (2 mg bolus iv), the reduction of % delta WT in IH was greater (from 29 +/- 4 to 15 +/- 6%, P less than 0.01) than that in OH (from 11 +/- 2 to 10 +/- 3%; P less than 0.01 vs. IH). The FC in the IH was decreased (56 +/- 16%) by AC with propranolol, so that the difference in FC between IH and OH became insignificant (FCOH 40 +/- 13%, P greater than 0.1 vs. FCIH).(ABSTRACT TRUNCATED AT 250 WORDS)