J. P. Siche

Association between high heart rate and high arterial rigidity in normotensive and hypertensive subjects.

Background The dynamic elastic modulus of central arteries is very frequency-dependent. Although resting heart rate is a potent independent risk factor for morbidity and mortality both from cardiovascular and from noncardiovascular disease, no link between tachycardia and arterial stiffness has ever been established. Objective To relate arterial stiffness to heart rate in a population with relatively low cardiovascular risk. Methods Pulse-wave velocity measurements and highresolution echo-tracking techniques were used to determine the degree of arterial distension (of carotid and femoral arteries, and terminal aorta) and the velocity of the pulse wave (aorta and upper and lower limbs) at the same time as heart rate, in members of a large population of normotensive and hypertensive subjects in a multicenter study in Paris, Fleury-Merogis and Grenoble (France). Results A high heart rate was strongly associated with reduced distension and elevated pulse-wave velocity, even after adjustment for age and blood pressure. A high aortic pulse-wave velocity was also negatively associated with a low baroreflex sensitivity. The most significant associations between high heart rate and high arterial rigidity were found for the carotid artery, the thoracic aorta, and the lower limbs, but there was no significant result for the terminal aorta and the arm arteries. Conclusion This study demonstrates that there is a statistically significant positive link between high heart rate and high arterial stiffness measured at the site of central and lower limb arteries. Since an elevated heart rate has been shown to be associated with cardiovascular risk, such findings may be relevant for future cardiovascular studies in epidemiology.

Arterial mechanics predict cardiovascular risk in hypertension

Systolic and diastolic blood pressures are the exclusive mechanical factors considered as predictors of cardiovascular risk for members of populations of normotensive and hypertensive subjects. However, if hypertension is considered as a mechanical factor acting on the arterial wall with deleterious consequences, the totality of the blood pressure curve should be considered in order to investigate the risk. The purpose of this review is to show that in addition to systolic and diastolic blood pressures, other hemodynamic indexes with particular relevance for cardiac complications and that originate from pulsatile pressure should be taken into account, namely brachial pulse pressure, pulse pressure amplification, early wave reflections, and pulse wave velocity.

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.

Left ventricular hypertrophy and arterial hypertrophy.

In the most recent WHO recommendations of 1996 it was reiterated that the classification of HT still remains based on the actual BP figures but also on the importance of target organ lesions. Thus the study of cardiac and vascular function and in particular the presence of hypertrophy or remodeling is of importance. A limited number of studies have examined the prevalence, the association and the correlation between modifications and remodeling in the heart and in the vasculature. It is important to distinguish compliance vessels such as the carotid from resistance vessels such as the radial. For compliance vessels the prevalence of cardiac and vascular hypertrophy are nearly identical being around 5% for normotensive subjects and around 12% for hypertensive subjects. This prevalence of thickening in the intima-media is more evident in subjects with left ventricular hypertrophy (LVH). The left ventricular geometric pattern is also an element to take into account. The presence of concentric remodeling of the left ventricle without LVH has already been associated with an increase in intima-media thickness (IMT). When there is an LVH this IMT is similar in severity to the LVH and in particular concentric. For resistance vessels such as the radial artery the number of studies is limited but a significant correlation between left ventricular mean wall thickness and common carotid artery distensibility and compliance has been found. There is also a significant correlation between the radial median lumen ratio and the relative wall thickness but this correlation disappears when age and systolic BP are taken into account. Thus for this type of vessel it is too early to conclude the elements contributing to structural changes. The determinant factors for these structural changes in the heart and the carotid arteries associated with hypertension are certainly multiple be they haemodynamic, hormonal or genetic. The observation establishing an association between anomalies at cardiac and vascular level may have undoubted diagnostic, prognostic and therapeutic implications which are all intimately related and which require refinement and confirmation.

Diagnostic and prognostic value of exercise testing.

Summary: Measuring blood pressure during exercise under a standard protocol could be a useful diagnostic method in high‐risk patients and in borderline hypertensive subjects. It may also serve as an adapted test for hypertensive subjects undergoing physical activity at work or at leisure time with a particular cardiovascular work load. It can be used as a method of assessment to confirm the efficacy of an antihypertensive drug, and for prognostic evaluation of cardiovascular risk in terms of morbidity and mortality. An exercise blood pressure profile does not provide information about blood pressure during activities of daily living. For this purpose, ambulatory blood pressure measurement appears to be more relevant. Résumé: La mesure de la pression artérielle à l’effort dans le cadre d’un protocole standardisé apparait être un examen complémentaire important lors de l’étude de certains sujets: sur le plan diagnostique chez les sujets à “haut risque” et les hypertendus limites; sur un plan d’aptitude et d’orientation, chez les sujets hypertendus dont les activités professionnelles ou extra‐professionnelles impliquent une contrainte cardiovasculaire importante; sur un plan thérapeutique pour affirmer l’efficacité d’un médicament; et sur un plan pronostique, pour anticiper les facteurs de risque en terme de morbidité et de mortalité. Encore faut‐il bien réaliser que ces tests d’effort ne permettent pas d’apprécier les contraintes de la vie quotidienne, leur type, leur intensité et leur durée. C’est dans ce cadre que des mesures en ambulatoire paraissent se justifier.

Use of Ambulatory Blood Pressure Monitoring in the Management of Antihypertensive Therapy

SummaryThe recent development of ambulatory blood pressure (ABP) monitoring techniques has improved recording of blood pressure in therapeutic trials and in the clinical setting. The application of ABP differs according to which of these 2 applications is being considered.In therapeutic trials, a placebo control is required. The large quantity of precise data acquired with ABP monitoring allows the study of a limited number of patients; it also allows individual study of patients with a ‘white coat’ response (i.e. elevated blood pressure in response to examination by the clinician). Analysis of data from ABP monitoring may include the following: comparison of mean blood pressure values over 24 hours, daytime or night-time, or over any other selected time period; 24-hour blood pressure profiles, or analysis hour-by-hour, giving true chronotherapy, and providing data regarding the wearing-off of a drug effect or loss of therapeutic control; analysis of blood pressure at particular times, such as on waking; or specific examination of nonresponders.In individual patients, ABP monitoring should be reserved for specific indications. It can be used before initiation of treatment to confirm the necessity for treatment, especially in the context of hypertension at rest or the ‘white coat’ effect. With established treatment, ABP monitoring can be used in patients with resistant hypertension, in severe hypertension to examine loss of blood pressure control over time or inversion of the day/night cycle, and in patients with a specific illness, e.g. diabetes, in order to obtain the lowest blood pressure readings possible.Examination of these factors assists clinicians to accurately decide upon the timing and frequency of antihypertensive therapy.

Circadian Changes of Left Ventricular Ejection Fraction in Normal Subjects

Sleep has a specific physiology with related cardiovascular changes. We have previously found in respiratory patients [chronic obstructive pulmonary disease (COPD) and sleep apnea syndrome (OSAS)] an unexpected decrease in left ventricular ejection fraction (LVEF) at waking in the morning when compared with the rest period during the day. Whether this observation was linked to the consequences of the respiratory abnormalities or reflected physiological fluctuations related to the changes in autonomic nervous system tone remained unknown. Thus, we have set out to analyze the changes in LVEF with sleep in normal individuals. Eight healthy young men had LVEF measured before and after submaximal exercise, at rest before bedtime, and on waking in the morning. Technetium-99m with in vivo red cell labelling was used. Sleep parameters were assessed using classical polysomnography. In order to detect any influence of autonomic nervous system stimulation on LVEF, sympathovagal tone (SVT) was also assessed during night-time LVEF measurements using spectral analysis of RR intervals. LVEF at rest was within the normal limits for all the subjects (range 51-62%). On submaximal exercise, the LVEF increased in four subjects, was unchanged in two, and decreased in two. The main result concerns the changes in LVEF overnight. In the morning, LVEF decreased dramatically in three subjects and reached a level of < 30% in four. These decreases in LVEF were not related to changes in SVT or sleep structure. LVEF values returned to normal in 30 min. The LVEF changes during exercise are in accordance with previous data in the literature. The dramatic decrease in LVEF observed in the morning could be related either to vascular resistance changes or to nocturnal variations in cardiac contractility, which both need further studies to be established.

Second-generation calcium antagonists and ambulatory blood pressure monitoring.

Ambulatory blood pressure monitoring (ABPM) is a particularly useful method for evaluating the effects of antihypertensive drugs. ABPM allows the therapeutic effect of an agent to be assessed continually by a large number of measurements, and the greater number of readings contributes to the higher degree of reproducibility associated with ABPM compared to other methods for measuring blood pressure. ABPM also enable measurements to be taken in “real-life” situations and removes the problem of observer bias. The number of patients required for clinical studies can be significantly reduced by using ABPM. It is still essential, however, to identify “white coat” subjects, placebo responders, and patients who do not respond to the treatment. ABPM studies have demonstrated that the novel dihydropyridine calcium antagonist, lacidipine, significantly reduces both systolic and diastolic blood pressures over a 24-h period, both during the day and at night. Furthermore, although the trough-to-peak ratios of many calcium antagonists have been shown to fall below the recommended level of 50%, lacidipine has a ratio above 60%. Other ABPM studies have also shown that lacidipine can correct the ‘early morning increase’ in blood pressure without effecting the 24-h nyethemeral profile.

Cardiac and vascular remodelling: effect of antihypertensive agents.

The 1996 World Health Organization (WHO) recommendations for mild hypertension stressed the need to evaluate target-organ lesions as treatment criteria. The effects of both vascular and heart remodelling on hypertension must to be taken into account, as they adversely influence the prognosis of patients with hypertension. It was previously demonstrated that at least three classes of antihypertensive agents were able to decrease morbidity and mortality in patients with hypertension. Meta-analyses have shown that angiotensin-converting enzyme inhibitors seem to have a marked effect on regression of left ventricular hypertrophy (LVH). However, the relationship between drug-induced LVH regression and reduced morbidity and mortality remains to be confirmed. The effect of antihypertensive agents on vascular hypertrophy, as assessed by intima-media thickness, and their involvement in reducing morbid events, also have to be determined at the vascular level. As experimental data have highlighted the involvement of angiotensin II in animal models of LVH and vascular hypertrophy development, the role of angiotensin II AT1 receptor blockers should also be assessed in this indication.

Relationship between low-frequency oscillations of blood pressure and changes in arterial diameter

Aim To study spontaneous variations in radial artery compliance. Methods Compliance was evaluated non-invasively by an echo-tracking system, and variations in sympathovagal tone were analysed by a spectral analysis of continuous blood pressure recordings using a Fast Fourier algorithm. We studied 23 healthy volunteers, aged 25 ± 4 years (mean ± SD), at rest, on two occasions at least one day apart (5 ± 3 days). Results There were no significant differences between the means of the arterial compliance measurements and those of the corresponding spectral analysis. However, the magnitude of change in the low-frequency periods (4–66 mHz) was significantly related (P<0.01) to a significant and inverse change in compliance for the same level of blood pressure. Conclusions While it is possible to use spectral analysis to measure the effect of autonomic nervous regulation on radial artery properties, low-frequency periods cannot be safely ascribed to sympathetic effects alone. Other effects must also be taken into account in measurements of radial artery distensibility.