Cardiovascular autonomic modulation in essential hypertension: Effect of tilting

Abstract

To better understand the role played by the autonomic nervous system in essential hypertension, we used autoregressive power spectrum analysis to study the noncasual oscillations in RR interval, blood pressure, and skin blood flow in 40 subjects with mild to moderate hypertension and in 25 age- matched control subjects at low frequency (index of sympathetic activity to the heart and the peripheral circulation) and high frequency, respiratory related (index of vagal tone to the heart). RR interval, respiration, noninvasive systolic blood pressure, and skin arteriolar blood flow were simultaneously and continuously recorded with subjects in the supine position and immediately after tilting. The low-frequency component was not significantly different in the two groups either at the cardiac level (control versus hypertensive subjects: 39.1±4.3 versus 39.9±3.7 normalized units [NU]) or at the vascular level (1.52±0.17 versus 1.69±0.13 ln mm Hg2). After head-up tilting, the RR interval fluctuations were less in hypertensive subjects (low-frequency components from 39.9±3.7 to 48.4±4.1 NU, P