REDUCED PARASYMPATHETIC CARDIAC CONTROL IN PATIENTS WITH HYPERTENSION AT REST AND UNDER MENTAL STRESS

The neurogenic component in the pathogenesis of essential hypertension has predominantly been analyzed with regard to the sympathetic part of the autonomous nervous system; the parasympathetic branch has largely been neglected. We investigated whether 54 normotensive (mean casual blood pressure [cBP]: 125 +/-: 6/82 +/- 4 mm Hg), 41 borderline hypertensive (cBP: 134 +/- 8/90 +/- 5 mm Hg), and 34 hypertensive men (cBP: 152 +/- 13/101 +/- 5 mm Hg) without secondary target organ damage differed in parasympathetic cardiac control. Parasympathetic cardiac control was assessed via the amount of fast fluctuations (0.15 to 0.40 Hz; vagus band) and by the amount of respiratory-linked fluctuations (mean respiratory frequency +/- 0.03 Hz) in the power spectra of continuously registered interbeat intervals under the following conditions: mean of three rest phases with 10, 5, and 5 minutes' duration (REST); mean of two modes of a reaction time task with 10 and 5 minutes' duration (RTT); mean of 5 minutes' mental arithmetic plus noise (MA). Analysis of variance (ANOVA) shows that spectral energy in the so-called vagus band reveals the most prominent differences between blood pressure groups under all conditions: REST = normotensive, 2.70 +/- 0.31; borderline hypertensive, 2.55 +/- 0.33; and hypertensive, 2.43 +/- 0.43 (F[2.126] = 6.19; p< 0.01). RTT = normotensive, 2.41 +/- 0.35; borderline hypertensive, 2.19 +/- 0.33; and hypertensive, 2.17 +/- 0.46 (F[2.126] = 6.04; P < 0.01); MA = normotensive, 2.69 +/- 0.34; borderline hypertensive, 2.52 +/-: 0.33; and hypertensive, 2.38 +/- 0.46 (F[2.126] = 7.04; p< 0.01). The ratio between the midfrequency band around 0.10 Hz and the vagus band, tentatively representing sympathovagal balance, is increased in both nonnormotensive groups, indicating a relative preponderance of sympathetic efferents. The results demonstrate that a reduction in parasympathetic cardiac control significantly contributes to a disturbance in Sympathetic and parasympathetic cardiovascular control in hypertension.