The effect of aging on phenylephrine response in normal subjects

Area of Science:

• Cardiology
• Gerontology
• Physiology

Background:

• Cardiac responses to beta-adrenergic stimulation decrease with age.
• The impact of aging on alpha-1 adrenergic stimulation and left ventricular response to increased afterload remains unclear.

Purpose of the Study:

• To investigate the effects of aging on heart rate, blood pressure, cardiac index, and left ventricular contractility during alpha-1 stimulation with phenylephrine.

Main Methods:

• Studied 12 young (26 years) and 15 aged (69 years) healthy males.
• Administered phenylephrine infusions (0.5 and 1.0 mcg/kg/min) for 10 minutes.
• Measured heart rate, blood pressure, and cardiac volumes using radionuclide ventriculography.

Main Results:

• Aged individuals showed a greater systolic blood pressure increase (22% vs. 13%) and less heart rate fall (p=0.05) during phenylephrine infusion.
• Left ventricular contractile responses (EF, SVI, stroke work index) were not altered by aging.
• Systemic vascular resistance was higher in aged subjects but the response to phenylephrine was similar.

Conclusions:

• In healthy aging individuals, preserved stroke volume index response with higher baseline systemic vascular resistance leads to increased systolic blood pressure response to alpha-1 stimulation.
• Contractile responses to increased afterload are maintained with aging.
• Age-associated differences in alpha-1 stimulation response are minimal, attributed to altered baroreflex sensitivity and vascular stiffness.