Low-frequency oscillations in R-R interval and blood pressure across the continuum of cardiovascular risk

The purpose of this study was to assess the power and the frequency of low-frequency (LF; 0.04-<0.15 Hz) oscillations in systolic blood pressure (SBP) and R-R interval (RRi) across the continuum of risk of cardiovascular disease, including age. A potential confound in such determinations is low spontaneous breathing frequency in some individuals. We measured beat-to-beat SBP, RRi and respiration in healthy YOUNG (33±3 years) and OLDER subjects (62±5 years) and older patients with hypertension (HT, 61±5 years), coronary artery disease without (CAD, 62±5 years) and with type 2 diabetes (CAD+DM, 62±4 years, n=28 for all groups) during spontaneous breathing at supine rest. Power (Power(LF)) and median frequency (Med(LF)) of LF oscillations were calculated by power spectral analysis after removing respiratory effects by least-mean-square adaptive filtering. OLDER had higher Power(LF-SBP) (5.5±3.0 vs. 3.4±2.5 mmHg(2), p=0.002) and lower Power(LF-RRi) than YOUNG (339±460 vs. 575±422 ms(2), p=0.001) whereas neither variable differed between OLDER and patient groups. Med(LF-SBP) (0.072±0.009 vs. 0.080±0.011 Hz, p=0.005) and Med(LF-RRi) (0.072±0.010 vs. 0.079±0.013 Hz, p=0.027) were lower in OLDER compared with YOUNG. Compared with OLDER, Med(LF-RRi) was lower in CAD (0.065±0.006 Hz, p=0.015) and CAD +DM (0.066±0.008 Hz, p=0.012); whereas CAD+DM had also lower Med(LF-SBP) (0.065±0.006 Hz, p=0.012). No differences were observed between OLDER and HT and between CAD and CAD+DM in these variables. We concluded that age is major determinant of the power of LF oscillations in SBP and RRi at rest, whereas the median frequency of these oscillations is altered also by coronary artery disease.