To test the hypothesis that cardiac autonomic function was compromised with aging, we compared the heart rate variability (HRV) during lower body negative pressure (LBNP) induced central hypovolemia in 12 young (27±1yr) and 12 older (65±2yr) healthy subjects. Frequency domain of HRV (correlogram) was assessed from 8-min record of beat-to-beat HR during breathing at 0.25Hz. The power at low frequency (LF, 0.04-0.15Hz) and high frequency (HF, 0.15-0.40Hz) was extracted and the normalized changes in HF (HF/(LF+HF)) and LF (LF/HF) were calculated as the index of the cardiac parasympathetic (Rp) and sympathetic (Rs) responses, respectively. There was no age-related difference in the baseline HR (young vs. older: 58±2 vs. 60±2bpm) or blood pressure (Finapres), nor in the normalized HF (0.32±0.06 vs. 0.28±0.06) or LF (5.1±1.7 vs. 6.9±2.3). LBNP significantly decreased pulse pressure (PP, P<0.001) in both young and older subjects (baseline: 59±3 and 65±4mmHg), and this decreased PP appeared to be greater (P<0.04) in the older group (see table). However, the significant changes in the cardiac autonomic responses at high levels of Young Older LBNPtorr 0 -15 -30 -40 -15 -30 -40 Rp (%) 100 101±16 70±9 45±7* 90±14 95±13 72±12 Rs(%) 0 132±28 202±34* 279±53** 161±33 140±27 160±28 ΔHRbpm 0 +0.9±2 +7.2±2**~ +9,3±2** +1.2±1 +3.1+1 +8.7±4* ΔPPmmHg 0 -5±2 -7±2* -9±7* -8±3* -13±2* -15±5* * ** indicate significant different from the baseline & baseline and -15 torr N=5 at -40 torr in both groups. LBNP were observed only in young group. We concluded that aging compromised both cardiac sympathetic activation and vagal withdrawal during LBNP induced central hypovolemia.
|State||Published - 1 Dec 1997|