Effects of aging on cardiovascular responses to parasympathetic withdrawal

Objectives The study was done to determine whether the effects of parasympathetic withdrawal on heart rate, blood pressure (BP), and systolic and diastolic function are altered with normal aging. Background Cardiac responses to beta-adrenergic sympathetic stimulation decline with aging as does the heart rate response to parasympathetic withdrawal, but the extent to which other responses to parasympathetic withdrawal decrease is less clear. Methods Heart rate, BP, systolic function, and diastolic filling responses to parasympathetic withdrawal induced by atropine (0.02 mg/kg) were compared in 50 healthy subjects, 28 older (ages 65 to 80 years, mean 70 years; 18 females all on estrogen) and 22 young (age 18 to 32 years, mean 26 years; 12 females) subjects, using radionuclide angiography. Results Parasympathetic withdrawal in the older group caused less of an increase in heart rate (+33 vs. +48 beats/min), cardiac index (+0.6 vs. +1.5 l/m2), systolic blood pressure (−1 vs. +7 mm Hg), and early diastolic filling rate (+1.7 vs. +2.4 end-diastolic volumes/s) (all p ≤ 0.01). At similar declines in the diastolic filling period, end-diastolic volume index (EDVI) fell substantially more in the older group (−11.6 vs. −2.4 ml/m2, p < 0.001). The only gender difference was in diastolic filling rate, which was similar in the young males and females, but significantly less in older males than in older females. Conclusions The responses to parasympathetic withdrawal as well as sympathetic stimulation decline with aging, and both contribute to the reduced cardiovascular responses to stress with advancing age.