title: The effect of aging on phenylephrine response in normal subjects.
abstract: BACKGROUND
  With aging, cardiac responses to β-adrenergic stimulation decline but the responses to α1-stimulation are less clear. Moreover, whether aging, in the absence of disease, influences the left ventricular response to an increase in afterload is unclear. This study examined the effect of aging on heart rate (HR), blood pressure (BP), cardiac index (CI) and several left ventricular contractility measurements during α 1-stimulation with a phenylephrine infusion.
  
  
  METHODS
  Subjects were rigorously screened to be normal by history, physical, blood tests, ECG, ETT and echocardiogram. Twelve young (mean 26 years, all male) and 15 aged (69 years, 11 males) subjects were studied during 10 minute infusions of phenylephrine at 0.5 and 1.0 mcg/ kg/min. HR, BP and radionuclide ventriculographic cardiac volumes were measured.
  
  
  RESULTS
  Systolic BP increased more in the aged than in the young (22 vs. 13%, p=0.003), while heart rate (16 vs. 21%, p=0.05) fell less. Contractile responses to phenylephrine, including EF, stroke volume index (SVI), stroke work index and left ventricular contractility index were not altered with aging. Systemic vascular resistance (SVR) was higher at baseline and at each infusion rate, but there was no age-associate change in the response to PE.
  
  
  CONCLUSIONS
  In a healthy normal aged population, a preserved SVI response in the setting of a higher baseline SVR results in an increased SBP response to α1-stimulation. Contractile responses to increased afterload are not altered with aging. Age-associated differences in the response to α1-stimulation are small and are explained by altered baroreflex sensitivity and a stiffer vasculature.
authors.affiliation: Division of Cardiology, Department of Medicine, Seattle Veterans Affairs Medical Center and University of Washington, Seattle, Washington ; Division of Nuclear Medicine, Department of Radiology, Seattle Veterans Affairs Medical Center and University of Washington, Seattle, Washington ; Department of Geriatric Medicine, Vancouver Hospital and Health Science Center, S124-2211 Westbrook Mall, Vancouver, BC Canada V6T 2B5.
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Madden
authors.forename: Wayne C
authors.initials: WC
authors.lastname: Levy
authors.forename: Arnold
authors.initials: A
authors.lastname: Jacobson
authors.forename: John R
authors.initials: JR
authors.lastname: Stratton