Aging Diminishes Dynamic Function Cardiovascular Regulation

Introduction
Age related arterial blood pressure (ABP) instability occurs more significantly during lower body negative pressure
(LBNP) challenge, which appears to be associated with a diminished vagal cardiac function (1,2). However, it remained
unknown whether the relationship between ABP and heart rate (HR) variability was modified as a result of aging. The
purpose of this study was to assess the effect of aging on dynamic baroreflex control of HR function.

Methods
Eight elderly (71±2 yr) and seven 7 young (27±2 yr old) men and women participated in the study. After 6-min baseline
data collection, LBNP was applied at -15, -30, and -50 Torr, respectively. HR (electrocardiograph) and ABP (Colin
Tonometer) were continuously recorded at 400Hz. A section of 5-min steady-state data was selected from each
condition. Transfer function between mean ABP (MAP) and HR was calculated by Welch spectral estimator (3, 4, 5).
Low-frequency (LF: 0.04-0.14 Hz) and high-frequency (HF: 0.15-0.30 Hz) cross-spectral power was extracted. SAS
software was used for t test and ANOVA.

Results
Body weight and height were statistically similar between elderly (73.5±5.5kg and 168±3cm) and young (70.5±5.7kg
and 174±3cm) group. Baseline MAP, systolic/diastolic ABP were significantly higher in elderly (92±3, 132±4/73±4
mm Hg) than in young (81±2, 117±3/63±2 mm Hg) group, whereas HR was not different between two groups (elderly
vs young: 59±4 vs 62±3 bpm). LBNP -50 Torr only decreased systolic ABP in elderly subjects (122±6 mm Hg) without
significant effect in young group (114±4 mm Hg). Table 1 summarizes that the coherence and the gain of the transfer
function between MAP and HR signals were significantly lower in elderly than young group.

Discussion / Conclusions
This study was among the first to document the impact of human aging on dynamic control of cardiovascular function.
Our data suggested that the dynamic variability between ABP and HR was dissociated in elderly subjects as indicated
by the overall lower coherence (<0.5) of transfer function. Besides, the magnitude of the gain was significantly smaller
in elderly than young group, indicating a diminished dynamic baroreflex function. This aging related cardiovascular
dysfunction could be a responsible mechanism to explain a greater decrease in ABP observed in elderly.

References
[1]. Shi X. et al. (2003). Gerontology, 49, 279-286.
[2]. Shi X. et al (2000). Am J Physiol, 279, H1548-H1554.
[3]. Saul J. et al. (1991). Am J Physiol, 261, H1231-H1245.
[4]. Zhang R. et al. (1998). J Appl Physiol, 85, 1113-1122.
[5]. Wray W. et al. (2001). Am J Physiol, 281, H1870-H1880.

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