Study of arterial blood pressure by a Windkessel-type model: influence of arterial functional properties.

OBJECTIVE: To analyse the performance of a Windkessel blood pressure (BP) modeling of arterial compliance adjusted in a dynamic fashion according to a non-linear relationship between the arterial compliance (AC) and BP. Non invasive measurements of the radial BP waveform (MILLAR tonometry) were compared to those constructed by an electric simulator reproducing the model in a symmetrical network subdivided into 121 segments. We introduced at cardiac level the aortic stroke volume (Doppler echocardiography) and the dynamic values of compliance (relation of compliance-to pressure, constant or variable) whether the model was linear or non linear, measured by high resolution Doppler (NIUS 02) for each subject. RESULTS: At the radial artery segment the modelled BP obtained by the non linear model of AC was not significantly different from the measured BP wave, while in the linear model (AC constant at mean BP level) the systolic BP was significantly underestimated. (*P < 0.05). CONCLUSION: This work shows the limits inherent in simplification of arterial compliance in the Windkessel model using constant parameters. This demonstrates the influence of the dynamic properties of the arterial wall in a conduction artery on the level of systolic and diastolic BP.

[Models of arterial pressure using a Windkessel type model: role of the functional arterial properties]. / Modélisation de la pression artérielle par un modèle de type Windkessel. Influence des propriétés fonctionnelles artérielles.

UNLABELLED: The Windkessel model is a linear model which does not take into account the structural and functional variations of the arteries related to the pulsatility of the blood pressure (BP) and its variations between systole and diastole. OBJECTIVE: To analyse the performance of a BP modelisation where the parameters of AC are adjusted in a dynamic fashion according to a curvilinear relationship of the arterial properties (compliance) in relationship to the BP between systole and diastole. DESIGN AND METHODS: 9 control subjects (age 25 +/- 3). The non invasive measures of the radial BP waveform (Millar tonometry) was compared to that constructed by an electric simulator reproducing the model in a sysmetrical network subdivised into 121 segments where we introduced for each subject: at cardiac level, the aortic stroke volume (Doppler echocardiography), and at the radial level, the dynamic values of compliance and diameter according to an arc-tangent model (measured by arterial echography NiUS02). RESULTS: The BP obtained by the adjusted model, where the AC parameter follows the curvilinear, relationship dV/dP measured experimentally, was not significantly different from the experimental, while in the constant model (AC at mean BP level) the systolic BP was different. CONCLUSION: This work shows in an experimental way the limits inherent in simplification in the Windkessel modelisation of the vascular system with constant parameters. It shows in a conduction artery the influence of the functional properties of the arterial wall on the level of systolic and diastolic BP.

Individual smoothing of blood pressure profiles to define responders or non-responders to drugs.

OBJECTIVE: To compare different methods of individual therapyh efficacy assessment in order to define responding subjects. METHODS: Hypertensive patients were included in three double-blind clinical trials (placebo versus bisoprolol, lisinopril and amlodipine) and ambulatory blood pressure measurements (four per hour) were performed at the end of each month. We analysed the effect of therapy (placebo minus treatment) according to the following criteria: type of model (hourly mean, moving average, fast Fourier analysis), determination of the time to the peak effect (the lowest value of the modelled blood pressure) and the sampling time around this peak (1, 2,., 24 h). RESULTS: Regardless of the type of model, the level of individual therapy efficacy is significantly higher than that of the overall subjects (group efficiency), when the sampling time around this peak decreases. The proportion of responders decreases as the sampling time used to calculate the drop in blood pressure increases, whatever the kind of model and the threshold used to define responders (5 or 10 mmHg in systolic blood pressure). CONCLUSION: By this method, it is possible to appreciate the percentage of subjects considered individuallyas responders according to the time around the peak. This evaluation complements information given by the trough: peak ratio.

Non-invasive ambulatory blood pressure variability and cardiac baroreflex sensitivity.

AIM: The objective of this study was to evaluate the relationship between non-invasive ambulatory blood pressure variability and cardiac baroreflex sensitivity in hypertensive patients. SUBJECTS AND METHODS: Ambulatory blood pressure measurements (15-min intervals for 24 h) and continuous blood pressure measurements (Finapres, 20 min at rest after a 10-min resting period) were performed in 123 untreated hypertensives (resting diastolic blood pressure > or = 90 mmHg; 80 males, 43 females; mean +/- SD age 49 +/- 12 years, range 19-73). Fourier series were used to model 24-h blood pressure profiles (four harmonics). Ambulatory blood pressure variability was assessed by determination of the residuals in each 24-h blood pressure profile (measured minus predicted pressures). Resting blood pressure variability was defined as the SD of the mean Finapres value. Baroreflex sensitivity was evaluated by automatic detection of blood pressure and pulse interval sequences of > or = 3 beats when systolic blood pressure and pulse interval sequences changed in the same direction (increase or decrease: 1 mmHg for systolic blood pressure and 4 ms for RR interval), and was assessed as the slope of the regression line for each sequence. RESULTS: Ambulatory systolic blood pressure variability increased with age (r = 0.28*) and systolic pressure (r = 0.44**). Baroreflex sensitivity (increasing systolic pressure/pulse interval) decreased significantly with age (r = -0.48**) and systolic pressure (r = -0.23**), and was significantly related to increased ambulatory blood pressure variability (r = -0.33**). In a multivariate stepwise analysis the relationship between ambulatory blood pressure variability and baroreflex sensitivity (increasing systolic pressure/pulse interval) was statistically independent of age and systolic pressure (R = 0.55, P<0.001); this relationship was not observed with the corresponding decreasing sequence. CONCLUSIONS: This study shows that in uncomplicated hypertension, ambulatory blood pressure variability is related to baroreflex sensitivity independently of the blood pressure level. This finding has prognostic implications for this non-invasive measurement, which needs to be confirmed by large longitudinal studies.

[Baroreflex sensitivity and vascular involvement in hypertension]. / Sensibilité baroréflexe et retentissement vasculaire chez l'hypertendu.

UNLABELLED: Relationships between baroreflex sensitivity (BRS) and arterial distensibility are evaluated by continuous measurement of blood pressure (Finapres) and carotid-femoral pulse wave velocity measurement (PWV); 73 subjects are recruited on WHO criteria (age: 48 +/- 13). An ambulatory measurement of BP is also performed to evaluate the mean BP 24 level. The BRS is evaluated at rest during 20 min of acquisition data in a lying position, using a dedicated software [(automatic detection by of BP sequences were 3 or more systolic BP and RR interval increased of 1 mmHg for SBP and 4 ms for RR (PS+/RR+) or decreased (PS-/RR-)]. The BRS is the slope of the regression line between SBP and RR interval of each sequences (if correlation coefficient > 0.95). RESULTS: resting BP: SBP/DBP = 170 +/- 12 mmHg. HR 72 +/- 15 batt/min, PWV = 10.8 +/- 3.2 m/s. Mean BRS is 8.2 +/- 3.8 for PS+/RR+ and 8.7 +/- 3.8 ms/mmHg PS-/RR-. The coefficient of correlation (Pearson) between PWV and BRS is -0.59* for PS+/RR+ and -0.41* for PS-/RR- (*: p < 0.01). In multivariate analyses, these relations were statistically independent of age and BP for the sequences PS+/RR+ but not for the sequences PS-/RR- suggesting a predominant vagal alteration in hypertensive subjects associated with the alteration of carotido-femoral pulse wave velocity.

Examination of variability in arterial blood pressure at rest using spectral analysis in hypertensive patients.

INTRODUCTION: We hypothesize that in essential hypertension sympathetic nervous activity is related to the development of left ventricular hypertrophy, which can be regarded as a measure of the severity of hypertension. METHODS: Using spectral analysis, we studied the short-term variability in resting blood pressure and heart rate in essential hypertensive subjects. We measured blood over 10 min using a Finapres in 88 subjects after 20 min rest. We performed echocardiography to evaluate left ventricular hypertrophy and thereby identified three groups: 23 control subjects (group I), 29 hypertensive subjects (World Health Organization criteria) without left ventricular hypertrophy (group II) and 36 hypertensive subjects with left ventricular hypertrophy (group III). None had been treated for hypertension before the study. RESULTS: The variability in blood pressure over a low-frequency period considered to be a marker of sympathetic activity was significantly increased in group II compared with groups I and III (analysis of covariance taking into account blood pressure and age). The variability in heart rate was similar in groups II and III, but both groups had a significantly reduced variability in heart rate compared with group I. CONCLUSION: These data, which examine globally, using a non-invasive method, all neurohormonal factors associated with the development of left ventricular hypertrophy, demonstrate that, in the time course of hypertension, low-frequency oscillations in blood pressure and heart rate are shifted to a lower level, presumably reflecting altered function of the sympathetic nervous system. We suggest that spectral analysis of blood pressure at rest in hypertensive patients can lead to complementary information to single measures of blood pressure and detect differences in the cardiovascular regulatory system.

[Left ventricular hypertrophy and blood pressure variability during rest and ambulatory monitoring in the hypertensive patient]. / Hypertrophie ventriculaire gauche et variabilité de la pression artérielle au repos et en ambulatoire chez l'hypertendu.

To study the relationship between assessment of blood pressure (BP) variability measured by continuous measurement (Finapres) or discontinuous ambulatory (ABPM Spacelabs) in 70 untreated essential hypertensive subjects (mean age 51 +/- 12) and their relationship with the development of left ventricular hypertrophy (LVH). There is no relationship between the BP variability measurements either by Finapres nor by ABPM. Multiple regression analysis show that ambulatory systolic BP variability (standard deviation) and resting BP variability (spectral analysis of SBP in the medium frequency band 0.1 Hz) are related to LVH index when we take into account age and BP difference (to explain LVH) (p < 0.001) ABPM SBP variability increase with LVH, while resting SBP measurement of BP variability (Mayer waves) significantly decreased. The study points to the different role of BP variability measurements in the mechanisms related to left ventricular hypertrophy and to the interest of continuous BP resting spectral analysis measurements.

[Blood pressure variability during rest and left ventricular hypertrophy in the hypertensive patients. A spectrum analytic approach]. / Variabilité de la pression artérielle au repos et hypertrophie ventriculaire gauche chez l'hypertendu. Approche par analyse spectrale.

OBJECTIVE: To study the relationship between spectral analysis measurement of blood pressure (BP) and heart rate (HR) at rest, in untreated essential hypertension, and their relationship with the development of left ventricular hypertrophy (LVH). DESIGN AND METHODS: 41 untreated hypertensives (25M/16W, age 50 +/- 12, range 23-73) were measured at rest (WHO criteria DBP > 90 mmHg) by digital continuous photoplethysmography (Finapres 2300 (F), 6 mn of measurement in the dorsal decubitus position and standing up). Measurement of LVH (Devereux criteria, left ventricular mass index LVMI, g/m2) to analyse two groups (LVMI+: LVMI > 107 if women and 120 if men; n = 19; LVMI = 137 +/- 25), and (LVMI-; n = 22; LVMI = 92 +/- 17). The overall variability is standard deviation (SD), spectral analysis variability (SA) is FFT of 256 points over 3 periods low (LF: 0.004-0.07Hz), medium (MF: 0.07-0.13Hz), high (HF: 0.13-0.5Hz). Comparisons by Wilcoxon test and Anova (age, sex) (* p < 0.05, ** p < 0.01). RESULTS: By WHO criteria, the SBP was significantly lower in the LVMI-group (153 +/- 10 vs 165 +/- 18**), the DBP was not significantly different (94 +/- 6 vs 96 +/- 10). By continuous measure (F) at rest there was no significant difference for SBP or DBP. On standing up the SBP was significantly lower in the LVMI-group (148 +/- 20 vs 162 +/- 22**). The SD of the DBP at rest was more elevated in the LVMI-group (3.34 vs 3.06*), but not significantly different standing up. There was no significant difference in SBP at rest (6.7 vs 6.32) or standing (9.13 vs 11.5). The Spectral analysis of the MF was significantly elevated in the LVMI-group at rest for SBP (3.56 vs 3.01*), DBP (1.99 vs 1.19*), and HR (1.79 vs 1.77*). This was not significantly different in the LF and HF for SBP, DBP, HR. CONCLUSION: These results are different from those obtained by invasive ambulatory measures. The spontaneous variability in BP and HR at rest is increased when there is no cardiac effect (LVMI-). SA gives additional information in showing that the increase in variability is due to an increase in the Mayer waves, suggesting the existence of an elevation in adrenergic tone in hypertensive patients not having LVH.

[Baroreflex regulation and blood pressure variability during rest in the hypertensive patient]. / Régulation baroréflexe et variabilité tensionnelle au repos chez l'hypertendu.

The object of this study was to compare the variability of blood pressure measured non-invasively with the Finapres under resting conditions in hypertensive patients with non-hypertensive subjects matched for age, and to evaluate the relationship between resting blood pressure, i.e. without any stimulation, and the sensitivity of the baroreflex evaluated by crossed spectral analysis (SA). Thirty-four hypertensives (WHO criteria) untreated for three weeks, with a mean age of 50 +/- 7 years, were compared with 60 control subjects with a mean age of 50 +/- 9 years. The blood pressure and heart rate were measured continuously in the dorsal decubitus and standing positions. The direct and crossed SA was undertaken by a specific programme using the fast Fourier method. The average blood pressure of controls differed significantly from that of the hypertensive population (118 +/- 15/65 +/- 10 mmHg vs 157 +/- 20/86 +/- 11 mmHg). The mean heart rate of the hypertensives was faster: 76 +/- 11 vs 67 +/- 10 beats/min (p < 0.001). Under basal conditions, there was greater absolute variability in the hypertensive subjects but the relative variability and heart rate were the same as those of the controls. Direct SA provided additional data by showing that this variability was due to LF oscillations. Crossed SA showed a change in the sensitivity of the slope of regulation of the baroreflex in hypertensives, 7.35 vs 8.68 ms/mmHg (p < 0.05). These results show that, under basal conditions, it is possible to demonstrate an increase in the absolute variability in blood pressure in hypertensive patients.(ABSTRACT TRUNCATED AT 250 WORDS)

[Evaluation of the aging change in cardiac autonomic nervous system by automated clinical measurement]. / Evaluation de l'altération du système nerveux autonome cardiaque avec l'âge par mesure clinique automatisée.

The object of this study was to establish normal values for age of clinical tests of autonomic nervous system activity based on an automatic measuring system. Ninety-seven subjects (50 M/47 F) aged 20 to 85 years (average 45 +/- 13 years) with a normal clinical examination and no medication were included in the study. The blood pressure (BP) and heart rate (HR) were measured continuously with the Finapres system. After a resting period, the BP and HR were measured continuously in 5 different situations: dorsal decubitus position for 7 minutes; on getting up actively in less than 3 seconds and for 9 minutes in the upright positions, during deep breathing at 6c/min and Valsalva manoeuvre during a handgrip test at 30% of maximal voluntary strength for 3 minutes. A specific programme (ISN-CNRS) initiated the calculations of the test and performed direct and crossed spectral analysis in the lying and standing positions. The average BP was 120 +/- 18/66 +/- 11 mmHg and HR was 67 +/- 9 b/min. A negative linear correlation was observed with age with respect to the 3 tests investigating vagal activity: 30/15 ratio, spontaneous variations of respiration and HR, ratio of HR at the end of Valsalva with r = -0.43, r = -0.60, r = -0.34 (p < 0.001). The other two tests: variation of systolic BP 1 min 30 after standing and variation of diastolic BP during the handgrip did not change with age.(ABSTRACT TRUNCATED AT 250 WORDS)