Abstract
The effects of inotropic interventions upon the maximal rate of change of left ventricular (LV) wall thickness and internal diameter during early diastole were measured in nine open-chest dogs by ultrasonic-dimension gauges. Isoproterenol increased the maximal rate of wall thickening during systole from 28 +/- 3 to 48 +/- 5 (SE) mm/s (P less than 0.001), whereas it had no effect on the maximal rate of wall thinning during early diastole, 40 +/- 4 vs. 42 +/- 4 mm/s [not significant (NS)]. Isoproterenol also increased the maximal rate of reduction of the LV diameter during systole from 87 +/- 6 to 125 +/- 8 mm/s (P less than 0.001), whereas it had little effect on the maximal rate of increase of the diameter during early diastole, 79 +/- 6 vs. 87 +/- 4 mm/s (NS). Similarly, propranolol had a direct effect on the maximal rate of wall thickening and LV diameter reduction during systole, but it had little or no effect on their counterparts during early diastole. These observations support the concept that alterations of the contractile state need not be accompanied by a concomitant effect on relaxation.
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