Spectral analysis of heart rate dynamics in elderly persons with postprandial hypotension

Abstract

Prior studies suggest that postprandial hypotension in elderly persons may be due to defective sympathetic nervous system activation. We examined autonomic control of heart rate (HR) after a meal using spectral analysis of HR data in 13 old (89 ± 6 years) and 7 young (24 ± 4 years) subjects. Total spectral power, an index of overall HR variability, was calculated for the frequency band between 0.01 and 0.40 Hz. Relatively low-frequency power, associated with sympathetic nervous system and baroreflex activation, was calculated for the 0.01 to O.15 Hz band. High-frequency power, representing parasympathetic influences on HR, was calculated for the O.15 to 0.40 Hz band. Mean arterial blood pressure declined 27 ± 8 mm Hg by 60 minutes after the meal in elderly subjects, compared with 9 ± 8 mm Hg in young subjects (p ≤0.0001, young vs old). The mean change in low-frequency HR power from 30 to 5O minutes after the meal was +19.4 ±25.3 U in young subjects versus −0.1 ± 1.5 U in old subjects (p ≤0.02). Mean change in total power was also greater in young (19.0 ± 26.6 U) subjects compared with old subjects (0.0 ± 1.6 U, p ≤0.02). Mean ratio of low:high-frequency power increased 3.1 ± 3.3 U in young subjects vs O.5 ± 2.7 U in old subjects (p ≤0.01). The increase in low-frequency HR power and in the low:high frequency band ratio in young subjects is consistent with sympathetic activation in the postprandial period. Absence of this finding in elderly subjects with postprandial hypotension is consistent with defective baroreflex compensation after a meal.