Mechanical and inotropic reserve in conscious dogs with left ventricular hypertrophy.

We studied the left ventricular (LV) responses to infusions of norepinephrine and prenalterol, a specific beta 1-adrenergic receptor agonist, in conscious, chronically instrumented adult dogs with severe LV hypertrophy. The goal of this study was to determine the extent of compensation induced by LV hypertrophy in an animal model in which the pressure overload was gradually increased, as occurs in human pathological states. One to 2 yr after banding the ascending aorta of puppies, six dogs with severe LV hypertrophy (LV free-wall weight-to-body weight ratio 7.0 +/- 0.4 g/kg), and nine sham-operated littermates (LV free-wall weight-to-body weight ratio 4.0 +/- 0.2 g/kg) were studied. The dogs were instrumented with ultrasonic dimension crystals (to measure LV short-axis diameter and wall thickness), miniature LV pressure transducers, and LV and aortic catheters. In the control dogs norepinephrine (0.4 micrograms X kg-1 X min-1) increased LV systolic/diastolic pressure from 121 +/- 2/9 +/- 1 to 177 +/- 9/20 +/- 2 mmHg, mean arterial pressure from 97 +/- 2 to 143 +/- 9 mmHg, LV dP/dt from 3,363 +/- 123 to 5,174 +/- 343 mmHg/s, and mean systolic wall stress from 194 +/- 14 to 299 +/- 22 g/cm2, while mean velocity of circumferential fiber shortening (Vcf), (dD/dt/D)max, and heart rate did not change from base line. In dogs with LV hypertrophy norepinephrine increased LV pressure from 224 +/- 16/11 +/- 1 to 305 +/- 22/19 +/- 1 mmHg, mean arterial pressure from 90 +/- 2 to 132 +/- 4 mmHg, LV dP/dt from 3,246 +/- 156 to 5,619 +/- 345 mmHg/s, and mean systolic wall stress from 224 +/- 11 to 307 +/- 24 g/cm2.(ABSTRACT TRUNCATED AT 250 WORDS)