Power spectral analyses of systemic arterial pressure and Heart Rate (HR) during central hypovolemia: Effect of age

The purpose of this study was to test the hypothesis that low-frequency (LF) oscillation of systolic arterial pressure (SP) during central hypovolemia was less resposive with aging. Beat to beat SP (intra-arterial catheter or Finapres) and HR in 9 young (Y ≤30yrs) and 7 older (O ≥60yrs) healthy subjects were collected during supine resting, lower body negative pressure (LBNP) -15 & -40 torr for 10 min. A section of 6-min stationary data was selected and resampled at 2 Hz after time binding for the analyses of SP and HR power density (Welch method) and their transfer function gain (calculated using DADiSP software) at high-frequency (HF, 0.15-0.35Hz) and LF (0.04-0.15 Hz). There was no age-related difference in baseline HR or SP. The reflex tachycardia at -40 torr LBNP was significantly greater in Y than O subjects, whereas the SP decrease was similar between the groups. LF power of SP was augmented by LBNP in both groups and this response tended to be greater (P=0.07) in O compared to Y subjects (see table). Group Young Older LBNP torr 0 -15 -40 0 -15 -40 HR bpm 60±3 64±5 76±5*† 55±2 56±2 60±1* SP mmHg 122±4 120±4 113±4* 126±7 116±4* 119±6* HF mmHg² 2.06±0.43 3.28±0.71 1.82±0.24 1.21±0.30 1.29±0.34 2.32±0.58 LF mmHg² 3.41±1.24 3.84±0.85 5.50±1.92* 4.83±0.84 4.62±0.31 9.05±1.37* *indicates a significant change. †denotes a significant difference between the groups. We concluded that a sympathetically mediated vasomotor modulation was not diminished in healthy older subjects during central hypovolemia.