The interrelationship between baroreflex sensitivity expressed in ms/mm Hg (BRS) or in Hz/mm Hg (BRSf), carotid wall thickness (IMT), and age was investigated in hypertensive and normotensive subjects with respect to the mean inter-beat interval (IBI) and blood pressure (BP). BP monitoring was performed in 25 treated hypertensives (Hy; 47.4±9.2 years of age) and 23 normotensives (Norm; 44.5±8.1 years). IMT was measured by ultrasonography. BRS and BRSf were determined by the spectral method (five-minute non-invasive beat-to-beat recording of BP and IBI, Finapres, controlled breathing at a frequency of 0.33 Hz). Significant differences between Hy and Norm were detected in IMT (Hy: 0.624±0.183, Norm: 0.522±0.070 mm; p<0.01), BRS (Hy: 3.5±1.6, Norm: 5.7±2.3 ms/mm Hg; p<0.01), BRSf (Hy: 0.005±0.002, Norm: 0.009±0.004 Hz/mm Hg; p<0.01), systolic BP (Hy: 131±21, Norm: 116±17 mm Hg; p<0.01) and diastolic BP (Hy: 77±16, Norm: 64±12 mm Hg; p<0.01). A significant correlation was found between age and IMT (Norm: 0.523, p<0.05; Hy+Norm: 0.419, p<0.01), age and BRS (Norm: -0.596, p<0.01; Hy+Norm: -0.496, p<0.01), age and BRSf (Norm: -0.555, p<0.01; Hy: -0.540, p<0.01; Hy+Norm: -0.627, p<0.01), age and IBI (Hy: 0.478, p<0.05), age and diastolic BP (Hy: -0.454, p<0.05), BRS and IMT (Hy+Norm: -0.327, p<0.05) and BRSf and IMT (Hy+Norm: -0.358, p<0.05). Hypertensive patients have increased IMT and decreased BRS and BRSf. The positive correlation between age and IMT and the negative correlation between age and BRS and BRSf are in agreement with the hypothesis that the age-dependent decrease of baroreflex sensitivity corresponds to the age-related structural changes of the carotid wall. Using two indices of baroreflex sensitivity, BRS and BRSf, we could show that baroreflex sensitivity in hypertensives is lower not only due to thickening of the carotid wall, but also due to aging.
The aim of this study was to analyse the changes of baroreflex sensitivity (BRS) and their relation to changes of heart rate and blood pressure in medical students during moderate psychological stress brought about by oral examination. The changes of BRS during the stress were compared with the changes during light physical exercise. Thirty three students were examined 30 min before and 30 min after the exam. Thirty-nine students of control group were examined at rest and during light exercise. Blood pressure was noninvasively recorded by Peňáz method at rate-controlled breathing (0.33 Hz). The BRS [ms/mm Hg] and BRSf [Hz/mm Hg] were calculated by spectral analysis of spontaneous fluctuations of blood pressure and inter-beat intervals (IBI). BRS before examination (7.12 ms/mm Hg) was significantly lower than after the oral exam (8.77 ms/mm Hg, p<0.05). The difference between BRS in the test group after the oral exam and the control group at rest (10.78 ms/mm Hg) was not significant. BRS during light exercise (7.44 ms/mm Hg) corresponded to the value during psychological stress. The values of BRSf did not change during psychological stress (before: 0.0182 Hz/mm Hg; after: 0.0182 Hz/mm Hg) and exercise (rest: 0.0158 Hz/mm Hg; exercise: 0.0144 Hz/mm Hg). Correlation between BRS or BRSf and blood pressure were not found. A significant negative correlation (r = -0.404, p<0.05) between BRSf and the increase of diastolic blood pressure during stress was observed. It is concluded that BRSf remained constant during psychological stress and exercise, and differed essentially from that in hypertensive subjects.
The spectral analysis technique was applied for noninvasive assessment of heart-rate baroreflex sensitivity (BRS). The coherence between fluctuation of blood pressure and heart rate at 0.1 Hz and at respiratory frequency is high. This fact enables the assessment of BRS by means of calculating the modulus (or gain) of the transfer function between variations in blood pressure and heart rate. The noninvasive continuous blood pressure registration according to Peňáz was used. During voluntarily controlled breathing intervals, the amplitude of 0.1 Hz and respiratory peaks in the spectra of heart rate and blood pressure changed markedly. Nevertheless, the average sensitivity of the baroreflex (modulus) changed insignificantly. This result indicated that the stability of BRS can be advantageous for the use of BRS in clinical practice. The difference between the modulus at 0.1 Hz and at the breathing rate indicates that baroreflex is only one of the factors causing respiratory arrhythmia. We also compared the determination of BRS by spectral analysis with the following alternative method: both lower extremities were occluded for 5 minutes. The release of pressure in the occluding cuffs decreased blood pressure which was followed by a baroreceptor-mediated increase of heart rate. Both methods correlated, but more detailed analysis revealed the role of the low pressure receptors in BRS determined by spectral analysis.
The pulse pressure (PP) is proportional to the preceding interval (T) because of the restitution of contractility and the Starling mechanism, and is inversely proportional to the pre-preceding interval (T-l) because of potentiation of contractility. The aim of the present paper was to find if this relationship can be used for diagnostic purposes. Blood pressure was noninvasively and continuously recorded for 3 minutes (Pen^z method), in 26 healthy subjects, in 13 patients with congestive heart failure (NYHA I,II) and sinusoidal rhythms and in 21 patients with atrial fibrillations. By means of multidimensional regression analysis the coefficient D[T] and D[T-1] were calculated in each subject. D[T] expresses the relative role of the preceding, D[T-1] of the pre-preceding interval. The correlation between PP and T was small in subjects with sinusoidal rhythms. Subjects with particular correlation coefficients between PP and T-l higher than 0.5 were used for further analysis (18 controls, 7 patients). The difference between D[T-1] in controls (0.30 ± 0.20) and in patients (0.48 ± 0.19) was significant (Wilcoxon P<0.05). In subjects with atrial fibrillations both D[T] and D[T-1] were higher in decompensated patients (Wilcoxon P<0.05). The ratio D[T]/D[T-1] was higher in patients with mitral stenosis than in patients with ischaemic heart disease (t-test, P<0.05). The test can be usefully employed as a screening test in medical practice.