title: Cardiovascular physiology during supine cycle ergometry and dobutamine stress.
abstract: OBJECTIVE
  This study compared cardiac hemodynamics during supine cycle ergometry and dobutamine stress.
  
  
  METHODS
  Thirty-two healthy volunteers (19 female, 13 male, 23.5 +/- 3.5 yr old) completed respective tests on separate days and in random order. Heart rate, blood pressure, and cardiac output were recorded at baseline and peak stress. Echocardiographic measures included left ventricular end-diastolic dimension, fractional shortening, heart rate corrected velocity of circumferential fiber shortening, end-systolic wall stress, and the difference between measured and predicted fiber shortening for measured wall stress.
  
  
  RESULTS
  Compared with peak exercise, dobutamine infusion resulted in lower cardiac output (12 +/- 2 vs 16 +/- 4 l x min(-1), P < 0.0001), heart rates (163 +/- 7 vs 175 +/- 12 beats x min(-1), P < 0.0001), and systolic blood pressure (160 +/- 22 vs 185 +/- 20 mm Hg, P < or = 0.0001). Echocardiography demonstrated smaller left ventricular end-diastolic dimension (4.2 +/- 0.7 vs 4.5 +/- 0.7 cm, P = 0.013), higher fractional shortening (0.55 +/- 0.07 vs 0.50 +/- 0.06%, P < 0.001), higher VCFc (2.07 +/- 0.36 vs 1.54 +/- 0.20 circs x s(-1), P < 0.001) higher VCFdiff (0.94 +/- 0.35 vs 0.48 +/- 0.20 circs x s(-1), P < 0.001), and lower end-systolic wall stress (25 +/- 11 vs 42 +/- 16 g x cm(-2), P < 0.001). The stress-velocity relationship during dobutamine demonstrated higher y-intercept and steeper slope, indicating greater load-independent contractility.
  
  
  CONCLUSIONS
  The cardiovascular adaptation to exercise and dobutamine stress differ significantly. Cardiac output during peak exercise is greater than during peak dobutamine secondary to increased heart rate and stroke volume. Despite a greater increase in contractility and decrease in afterload, a smaller increase in cardiac output during dobutamine stress may be secondary to limited ventricular preload.
authors.affiliation: Department of Pediatrics, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA. jcnota@wfubmc.edu
authors.forename: James F
authors.initials: JF
authors.lastname: Cnota
authors.forename: Wayne A
authors.initials: WA
authors.lastname: Mays
authors.forename: Sandra K
authors.initials: SK
authors.lastname: Knecht
authors.forename: Shannon
authors.initials: S
authors.lastname: Kopser
authors.forename: Erik C
authors.initials: EC
authors.lastname: Michelfelder
authors.forename: Timothy K
authors.initials: TK
authors.lastname: Knilans
authors.forename: Randal P
authors.initials: RP
authors.lastname: Claytor
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Kimball
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D001794:Blood Pressure; D002302:Cardiac Output; D025401:Echocardiography, Stress; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D011187:Posture; D013318:Stroke Volume; D016277:Ventricular Function, Left