New Insight into the Mechanism of Cardiovascular Dysfunction in the Elderly: Transfer Function Analysis:

This study sought to test the hypothesis that alterations in the relationships between (i) mean arterial pressure (MAP) and heart rate (HR), (ii) cardiac output (CO) and MAP, and (Hi) total Peripheral resistance (TPR) and MAP variability contribute to the diminished dynamic control of cardiovascular function with advanced age. Six-minute hemodynamic data were continuously recorded in 11 elderly (70 ± 2 years) and 11 young (26 ± 1 year) healthy volunteers under supine resting condition and during lower body negative pressure–induced orthostatic challenge. The data were converted using fast Fourier transform, and the ratio of cross-spectra to auto-spectra between two signals (i.e., MAP-HR, CO-MAP, TPR-MAP) was computed for transfer function analysis. In the low-frequency ranges (LF; 0.04–O.14 Hz) and high-frequency ranges (0.15–0.30 Hz), the gain and coherence of the transfer function describing the relationship between MAP-HR signals were significantly greater in younger than in older adults. The phase deg...