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Biomedical subjects

G Parati

Publications and source records attributed to G Parati.

At least 91 records · Page 5Linked to original sources
PubMed1996

Effects of sino-aortic denervation on spectral characteristics of blood pressure and pulse interval variability: a wide-band approach.

Sino-aortic denervation (SAD) is employed in cats to evaluate the baroreflex influence on blood pressure (BP) and pulse interval (PI) spectral components from 0.00008 to 0.9 Hz as assessed by FFT wide-band spectra and their 1/f modelling; and the linear coupling between BP and PI and between systolic and diastolic BP as assessed by coherence analysis. Specific procedures have been developed to obtain an effective smoothing of spectra and coherence functions. SAD induced an increase in BP powers from 0.03 to 0.0006 Hz and a power reduction of most of the remaining BP components; a reduction of PI powers at all frequencies; marked deviations of BP spectra from the 1/f trend; a reduction of the coherence between BP and PI from 0.12 to 0.5 Hz and a coherence enhancement at lower frequencies. These findings indicate that the arterial baroreflex modulates both fast and slow spectral components of BP and PI; homogeneously enhances PI fluctuations at all frequencies; produces differentiated effects on BP fluctuations along the frequency axis; and at low frequencies exerts the buffering action on BP through strategies which reduce the BP-PI linear link.

Animals↗
PubMed1996

Finapres tracking of systolic pressure and baroreflex sensitivity improved by waveform filtering.

OBJECTIVE: Arterial pressure waveforms distort between brachial and finger arteries, causing differences mainly in systolic pressure. Distortion, reportedly, can be removed by applying a waveform filter to the finger pressure. DESIGN: We analysed the data from two studies that detected discrepancies in systolic tracking between Finapres and brachial pressures. The first set comprised waveforms of seven volunteers during incremental bicycle exercise to exhaustion and the second set comprised waveforms of eight volunteers during increasing phenylephrine infusion. METHODS: We applied the filter and compared 1 min averaged unfiltered and waveform-filtered finger and brachial pressures. RESULTS: During exercise, finger systolic pressure overestimated brachial increasingly, from 7(SD 10) mmHg at rest to 27(17) mmHg at maximal exertion. Differences were reduced by waveform filtering from 3 (SD 9)mmHg at rest to 1 (SD 15)mmHg at maximal exertion. During phenylephrine infusion finger systolic pressure overestimated brachial pressure, but the magnitude of the overestimate decreased from 14 (SD 15)mmHg at baseline to -1(SD 16)mmHg at maximal rate. After waveform filtering overestimation was an almost constant 6(SD 11)mmHg. Median baroreflex sensitivities from brachial, unfiltered and waveform-filtered finger pressure were 5.8, 7.5 and 5.3 ms/mmHg and correlation increased after filtering. The results indicate improved systolic pressure tracking after waveform filtering. CONCLUSIONS: Finger pressure distortion follows a general pattern correctable by waveform filtering. Waveform filtering allows a 'brachial' view to be obtained from Finapres data.

Adolescent↗
PubMed1996

Difference between office and ambulatory blood pressure and response to antihypertensive treatment.

OBJECTIVE: To investigate whether a clinic-ambulatory blood pressure difference persists with time under active drug treatment or placebo and to determine whether and how it interferes with the evaluation of the efficacy of antihypertensive treatment. DESIGN AND METHODS: In 382 mild or moderate essential hypertensive patients (mean age +/- SD 51.5 +/- 9.2 years) clinic and ambulatory (SpaceLabs 90207 device) blood pressures were measured twice, under baseline conditions and after 4-8 weeks of antihypertensive treatment by calcium antagonists or angiotensin converting enzyme inhibitors (n = 266) or of placebo administration (n = 116). In each patient the difference between clinic and daytime average blood pressure was taken as a surrogate measure of the magnitude of the 'white-coat effect', separately for systolic and diastolic blood pressures. The changes in this difference induced by treatment and by placebo and the relationship between the blood pressure changes induced by drug treatment and by placebo and the magnitude of the difference before and during treatment or placebo, respectively, were computed. RESULTS: Before drug treatment, the difference was 16.6 +/- 13.6 and 10.1 +/- 7.9 mmHg for systolic and diastolic blood pressures, respectively. During treatment the corresponding values were 11.9 +/- 14.2 and 6.8 +/- 9.2 mmHg; both of the reductions were statistically significant. Both for systolic and for diastolic blood pressure, the reduction in clinic blood pressure caused by treatment was directly related to the clinic-ambulatory difference before treatment, but inversely related to the magnitude of that difference persisting during treatment. The clinic-ambulatory blood pressure difference observed before placebo was attenuated during placebo, the magnitude of the attenuation being similar to that found under drug treatment. No significant difference between clinic and daytime average heart rate was ever observed before and during active treatment or placebo. CONCLUSIONS: A considerable clinic-ambulatory blood pressure difference persists during several weeks of antihypertensive treatment, but its magnitude is significantly attenuated. This leads to an overestimation of the effectiveness of antihypertensive treatment when this is assessed by clinic blood pressure measurements only. This overestimation is greater in subjects with an initially greater difference because in these subjects the subsequent attenuation is greater. Because similar phenomena are observed with placebo, the attenuation in the difference during drug treatment is likely to reflect merely habituation to clinic blood pressure measurements with time.

Ambulatory Care↗
PubMed1996

Ambulatory blood pressure monitoring.

PREDICTIVE VALUE OF 24-H AMBULATORY BLOOD PRESSURE MONITORING: Average 24-h blood pressure values are more closely related to the target-organ damage of hypertension than are clinic blood pressure readings. Preliminary evidence from longitudinal studies suggests that ambulatory blood pressure is also superior to isolated clinic readings in the prognostic evaluation of hypertensive patients. This is supported by the demonstration that in hypertensive patients with left ventricular hypertrophy, regression of cardiac hypertrophy following treatment was better predicted by the drug-induced reduction in 24-h average blood pressure than clinic blood pressure. BLOOD PRESSURE VARIABILITY: Also, 24-h blood pressure variability seems to be involved in the genesis of hypertension target-organ damage, while the clinical value of specific components of the 24-h blood pressure profile, such the nocturnal blood pressure fall, is still a matter of debate. Similar caution is needed in approaching the clinical significance of white coat hypertension, the definition of which is still affected by important methodological problems.

Blood Pressure↗
PubMed1996

Conventional and ambulatory blood pressure measurement in older patients with isolated systolic hypertension:second progress report on the ambulatory blood pressure monitoring project in the Syst-Eur trial.

OBJECTIVES: To compare clinic and ambulatory blood pressure measurement and the reproducibility of these measurements in older patients with isolated systolic hypertension.PATIENTS: A total of 477 patients aged >/= 60 years with isolated systolic hypertension on clinic measurement were monitored during the placebo run-in phase of the Syst-Eur trial. METHODS: The time-weighted 24 h blood pressure, clock time day and night blood pressure, the cumulative sum-derived crest and trough blood pressure and the high and low blood pressure levels of the square-wave model were computed. The daily alteration between the high and low blood pressure spans was quantified using the clock time day-night difference, the cumulative sum-derived circadian alteration magnitude, the Fourier amplitude and the difference between the high and low blood pressure levels of the square-wave model. RESULTS: The daytime ambulatory systolic blood pressure was, on average, 21 mmHg lower than the clinic blood pressure, whereasthe diastolic blood pressure was, on average, similar with both techniques of measurement. In the 132 patients who underwent repeat measurements, clinic blood pressure levels and the parameters describing the difference betgween the daily high and low blood pressure spans were equally reproducible. However, both were less reproducible than the ambulatory blood pressure levels. The repeatability coefficients, expressed as percentages of near maximum variation, were 50 and 51% for the clinic systolic and diastolic blood pressures, 30 and 33% for the mean 24 h systolic and diastolic blood pressures and between 44 and 54% for the parameters describing the daily alteration between the high and low blood pressure spans. CONCLUSION: In older patients with isolated systolic hypertension, clinic and ambulatory systolic blood pressure may differ greatly; the prognostic significance of this difference remains to be elucidated. Furthermore, the level of blood pressure in these patients is more reproducible by ambulatory measurement than it is by clinic measurement.

Journal Article↗
PubMed1996

Reproducibility of blood pressure measurements.

Clinic blood pressure readings are less reproducible than 24 h and daytime average ambulatory blood pressures. This may depend on (1) the continuous and spontaneous variability which characterizes daily life blood pressure, (2) the well-known 'white-coat' effect and (3) other methodological problems affecting traditional sphygmomanometric readings, such as the observer's bias and digit preference. The higher reproducibility of average 24 h and daytime blood pressures is also, at least in part, a function of the greater number of blood pressure readings available. On the other hand, the various components of the 24 h blood pressure profile appear, in general, to be less reproducible than the 24 h average value. This is the case for hourly values, for the day-night blood pressure difference and for a number of statistical parameters employed for modelling the 24 h blood pressure curve. An alternative and simple way to obtain reproducible blood pressure values, without making use of ambulatory blood pressure monitoring techniques, may be offered by the average of 20-25 blood pressure readings obtained automatically or semi-automatically under standardized conditions in outpatient clinics. The implications of these findings for clinical trials aimed at evaluating the features of the effects of antihypertensive drugs on 24 h blood pressure are discussed.

Journal Article↗
PubMed1996

Lessons to be learned from 24-hour ambulatory blood pressure monitoring.

A number of cross sectional studies have shown that both the 24-hour average blood pressure value and the degree of 24-hour blood pressure variability bear a significant relation with the end organ damage of hypertension. Although longitudinal evidence of the clinical relevance of 24-hour ambulatory blood pressure monitoring data are scanty, the results of a recent prospective study have clearly shown the superiority of average 24 hour, daytime and nighttime blood pressure values over clinical readings in predicting the regression of left ventricular hypertrophy in treated hypertensive patients. Ambulatory blood pressure monitoring may also be useful in the evaluation of antihypertensive treatment, although the problem of whether ambulatory blood pressure is "normalized" by treatment remains still to be properly addressed. Moreover, currently employed discontinuous ambulatory blood pressure monitoring devices cannot adequately clarify the ability of antihypertensive drugs to buffer blood pressure variability. This interesting issue needs to be assessed in a more analytical fashion by means of recently developed beat-to-beat non-invasive ambulatory blood pressure recorders coupled with wide-band spectral analysis techniques.

Animals↗
PubMed1996

Baroreflex modulation of the cardiovascular system: new insights from the joint analysis of blood pressure and heart rate signals.

This paper focuses on a number of methods for the analysis of the relationship between the arterial baroreflex and different components of blood pressure and heart rate variability. Broad-band spectral analysis techniques have allowed us to obtain experimental evidence that the arterial baroreflex exerts its influence not only on fast but also on slow components of blood pressure and heart rate, i.e., on components with periods longer than 60 sec. Focusing on faster changes in blood pressure and heart rate, both time domain and frequency domain techniques have been developed to track the sensitivity of baroreflex heart rate modulation over time, either in laboratory or in daily life conditions. These approaches have considerably broadened our understanding of the role of baroreflex modulation of the heart and peripheral circulation in a number of pathological and physiological conditions.

Animals↗
PubMed1995

Blood pressure variability and reflex control in the elderly.

Several lines of experimental and clinical evidence collected over the past ten years suggest that the aging process is characterized not only by profound structural cardiovascular alterations, but also by marked functional changes in the reflex mechanisms involved in the homeostatic control of the circulation. This paper will examine how aging affects baroreceptor control of the heart and sympathetic nerve traffic, providing evidence that while the former is markedly impaired in the elderly, the latter is virtually preserved. It will also discuss the age-related alterations in cardiopulmonary receptor function that, under physiological conditions, tonically inhibit sympathetic vasoconstriction tone and renin release from the kidney. Finally, evidence will be provided showing that short- and long-term blood pressure variabilities (and the different components of blood pressure variability) over 24 hours undergo major changes in the elderly. All these alterations in neural cardiovascular control mechanisms have clearcut clinical implications representing a potential marker of the increased cardiovascular risk which characterizes elderly people.

Aged↗
PubMed1995

Lack of placebo effect on ambulatory blood pressure.

Several studies have reported that, at variance with clinic blood pressure, ambulatory blood pressure is not reduced by treatment with placebo. However, this evidence has usually been obtained in small groups of subjects and no data are available from a larger sample of patients. To address this issue we have analyzed data from 116 outpatients involved in placebo-controlled studies on antihypertensive treatment. The patients were studied before and at the end of a 6- to 8-week period of placebo. In all patients, blood pressure was measured by sphygmomanometry and over the 24 h by automatic ambulatory monitoring. Administration of placebo was accompanied by a significant reduction in systolic and diastolic clinic blood pressure (-5.3 +/- 1.1 and -4.4 +/- 0.6 mm Hg, respectively; P < .01), but not in 24-h, daytime and nighttime blood pressure. Hourly systolic and diastolic blood pressure profiles were virtually superimposable in the two different periods, except for the first 4 h, in which systolic blood pressure was slightly but significantly lower during than before placebo (149.5 +/- 1.2 v 146.4 +/- 1.2 mm Hg; P < .05). These results provide a large database indicating that 24-h average blood pressure is not reduced by placebo, thus it is not necessary to include a placebo control group in antihypertensive drug studies in which ambulatory blood pressure monitoring is employed. A small placebo effect occurs, however, in the first hours of ambulatory monitoring. This may lead to a slight overestimation of the peak blood pressure effect of a drug and an underestimation of its trough-to-peak ratio if placebo correction of the data is not made or if the first part of ambulatory blood pressure monitoring is not excluded from data analysis.

Blood Pressure↗
PubMed1995

Calculation of trough:peak ratio of antihypertensive treatment from ambulatory blood pressure: methodological aspects.

OBJECTIVE: To address several methodological questions related to calculation of trough:peak ratio from 24 h ambulatory blood pressure (BP) recordings. METHODS: Data from patients with mild essential hypertension who were included in parallel group (n = 280) or cross-over studies (n = 39) were pooled. 24 h ambulatory BP recordings were available after 2- to 4-week washout from treatment and at the end of a 4- to 8-week period of treatment with calcium antagonists (n = 143), angiotensin converting enzyme inhibitors (n = 103) or placebo (73 patients from parallel group studies and 39 from a cross-over study). Each recording started between 0900 and 1000 h, immediately after the drug or placebo intake during the treatment phase. BP was measured at 15 min intervals during the day and at 15-20 min intervals during the night. Peak changes were calculated from systolic BP and diastolic BP 2-8 h after drug intake, and trough changes from readings taken during the last 4 h of the 24 h. RESULTS: Peak changes induced by drug treatment were progressively reduced when data were averaged over 1, 2, 4 and 6 h. BP reproducibility showed a concomitant increase and the best compromise between correct estimate of peak changes and reproducibility was the average of the adjacent 2 h with the maximal BP fall. Peak and trough (average of last 2 h) changes showed a normal distribution, whereas trough:peak ratios showed non-normal distributions, large scatters and many individual values with no pharmacodynamic significance (namely, much above unity and below zero). Selecting responders to treatment reduced the dispersion and made the trough:peak ratio distribution normal. There was no correlation between trough:peak ratios and changes in BP variability (standard deviation of 24 h mean) induced by treatment. Placebo administration caused no trough but a modest peak fall. Peak changes during placebo also showed a wide scatter and a non-normal distribution, which makes correction with respect to average peak placebo data inappropriate in parallel-group studies. However, placebo correction may be performed for each subject in cross-over studies, leading to a reduction in peak changes and an increase in trough:peak ratio values. CONCLUSIONS: When the trough:peak ratio is assessed from ambulatory BP, peak and trough changes should preferably be computed over a 2 h time window. To remove values with no pharmacodynamic significance, the analysis should preferably be conducted only in responders to treatment at peak. Although placebo is accompanied by some peak effect, placebo correction might be appropriate only for individual subjects in cross-over studies.

Antihypertensive Agents↗
PubMed1995

Blood pressure variability, cardiovascular risk and antihypertensive treatment.

TWENTY-FOUR HOUR BLOOD PRESSURE PARAMETERS: The use of ambulatory blood pressure monitoring techniques has shown clearly that 24-h average blood pressure is more closely related to the end-organ damage of hypertension than isolated office blood pressure readings. It has also provided evidence that the degree of blood pressure variability over a 24-h period may be independently related to the cardiovascular complications of hypertension. However, all the available data on this issue come from cross-sectional studies, and prospective evidence on the actual prognostic value of 24-h blood pressure parameters has only recently been provided for daytime blood pressure variability. There is still no prospective evidence concerning overall 24-h blood pressure variability. ANTIHYPERTENSIVE AGENTS AND BLOOD PRESSURE VARIABILITY: Available antihypertensive agents are unable to effectively buffer blood pressure variability. However, drugs with a long-lasting antihypertensive effect and an optimal trough: peak ratio may at least prevent further iatrogenic increases in the amplitude of blood pressure fluctuations. BEAT-TO-BEAT BLOOD PRESSURE MONITORING: The ability of antihypertensive agents to actually reduce 24-h blood pressure variability needs to be demonstrated in future studies, using beat-to-beat blood pressure monitoring which is now possible by means of non-invasive techniques.

Antihypertensive Agents↗
PubMed1995

Blood pressure variability over 24 hours: its different components and its relationship to the arterial baroreflex.

This paper describes several different methods for the analysis of blood pressure and heart rate variability over the 24 hours, both in the time and in the frequency domain. The mechanisms possibly involved in the genesis of the variations in blood pressure and heart rate which occur over a 24-hour period are also discussed. Finally, new approaches to the dynamic evaluation of the sensitivity of baroreflex control of heart rate and of its changes over the 24 hours in daily life conditions, based on computer analysis of the interaction between fluctuations in blood pressure and heart rate, are described. Data obtained by applying these methods in different clinical conditions (normotensive vs. hypertensive subjects, young vs. elderly individuals and pure autonomic failure patients) are presented.

Journal Article↗
PubMed1995

Effects of aging on 24-h dynamic baroreceptor control of heart rate in ambulant subjects.

The effects of aging on the dynamic modulation of baroreflex sensitivity over 24 h was assessed in eight elderly (mean age +/- SD, 63.9 +/- 3.2 yr) and in eight young (23.9 +/- 6.1 yr) mild or moderate essential hypertensive patients, who were subject to a 24-h intra-arterial (Oxford technique) blood pressure recording in ambulatory conditions. The sensitivity of baroreflex control of the heart rate was dynamically assessed by quantifying 1) the slope of the regression line between pulse interval (the reciprocal of heart rate) and systolic blood pressure changes over spontaneously occurring hypertension-bradycardia or hypotension-tachycardia sequences (time domain analysis) and 2) the ratio between spectral-powers of pulse interval and systolic blood pressure around 0.1 Hz (alpha-coefficient: frequency domain analysis). The 24-h average sequence slope was lower in old than in young individuals (4.4 +/- 0.5 vs. 9.9 +/- 1.3 and 4.8 +/- 0.7 vs. 8.4 +/- 1.4 ms/mmHg for hypertension-bradycardia and hypotension-tachycardia sequences, respectively; P < 0.05 for both). Similar results were obtained by using the alpha-coefficient approach. The marked nighttime increase in baroreflex sensitivity observed in young individuals was much less evident in the elderly. Thus 24-h baroreflex sensitivity is markedly impaired by aging. The impairment becomes manifest also as an inability to increase baroreflex sensitivity at night.

Aged↗
PubMed1995

Spectral analysis of blood pressure and heart rate variability in evaluating cardiovascular regulation. A critical appraisal.

Blood pressure variability includes rhythmic and nonrhythmic fluctuations that, with the use of spectral analysis, appear as clear peaks or broadband power, respectively. This review offers a concise and critical description of the spectral methods most commonly used (fast Fourier transform versus autoregressive modeling, time-varying versus broadband spectral analysis) and an evaluation of their advantages and disadvantages. It also provides insight into the problems that still affect the physiological and clinical interpretations of data provided by spectral analysis of blood pressure and heart rate variability. In particular, the assessment of blood pressure and heart rate spectra aimed at providing indexes of autonomic cardiovascular modulation is discussed. Evidence is given that multivariate models--which allow evaluation of the interactions between changes in blood pressure, heart rate, and other biological signals (such as respiratory activity) in the time or frequency domains--offer a more comprehensive approach to the assessment of cardiovascular regulation than that represented by the separate analysis of fluctuations in blood pressure or heart rate only.

Autonomic Nervous System↗