title: Load dependence of the single beat maximal pressure (stress)/volume ratios in humans.
abstract: To determine whether the slopes of the single beat maximal pressure (stress)/volume ratios are sensitive to changes in loading conditions in humans, 16 patients without cardiac disease were studied with simultaneous micromanometer-determined left ventricular pressures and biplane contrast cineangiograms under control conditions and during methoxamine and nitroprusside infusions. Left ventricular volumes were calculated with use of a Simpson's rule algorithm, wall thickness was obtained iteratively, and both midwall circumferential and meridional stresses were computed frame by frame. The maximal pressure/volume and both circumferential and meridional maximal stress/volume ratios were calculated using a single beat from each loading condition assuming a zero volume-axis intercept. Mean left ventricular systolic pressure increased 47% during the methoxamine infusion and decreased 22% during the nitroprusside infusion compared with control (p less than 0.001 for both). Despite these changes in left ventricular systolic pressure, heart rate was eliminated as a confounding variable by right atrial pacing; and mean maximal rate of change of left ventricular pressure [(+)dP/dtmax] and rate of change at developed pressure 40 mm Hg [(+)(dP/dt) per DP40] values did not differ significantly. Mean single beat maximal pressure/volume ratios also did not differ significantly among the three loading conditions. In contrast, mean single beat circumferential and meridional maximal stress/volume ratios were 3.15 +/- 1.83 and 1.40 +/- 0.82 g/cm2 per ml at control; they increased to 4.47 +/- 2.44 and 2.21 +/- 1.25 g/cm2 per ml during the methoxamine infusion (p less than 0.001 for both), and they decreased during the nitroprusside infusion to 2.58 +/- 1.47 and 1.14 +/- 0.57 g/cm2 per ml (p less than 0.05 and p less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: University of Michigan, Department of Internal Medicine, Ann Arbor.
authors.forename: M R
authors.initials: MR
authors.lastname: Starling
authors.forename: D G
authors.initials: DG
authors.lastname: Montgomery
authors.forename: R A
authors.initials: RA
authors.lastname: Walsh
mesh_terms: D000328:Adult; D000465:Algorithms; D002304:Cardiac Pacing, Artificial; D002932:Cineangiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008729:Methoxamine; D008875:Middle Aged; D009200:Myocardial Contraction; D009599:Nitroprusside; D012044:Regression Analysis; D013318:Stroke Volume
chemical_list: D009599:Nitroprusside; D008729:Methoxamine