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M Di Rienzo

Publications and source records attributed to M Di Rienzo.

At least 37 records · Page 2Linked to original sources
PubMed1998

Early and late sympathetic activation in hypertension.

In several experimental animal models of hypertension, sympathetic factors have been shown to be involved in the development and/or maintenance of high blood pressure. Although the information available on this issue in man is more scarce, recent evidence clearly indicates the participation of adrenergic mechanisms in the early and late phases of the hypertensive process. In addition, several cardiovascular risk factors frequently associated with hypertension, such as obesity, insulin-resistance, cigarette smoking, and the atherogenic process, are also characterized by alterations in sympathetic cardiovascular drive. This contributes to a further activation of the sympathetic nervous system thus favoring the development of the end organ damage (e.g. cardiac and vascular hypertrophy) associated with the hypertensive state.

Animals↗
PubMed1998

Methods to quantify sympathetic cardiovascular influences.

This paper will critically review the main features of the various techniques (plasma noradrenaline assay, noradrenaline spillover technique, microneurographic recording of postganglionic muscle sympathetic nerve and power spectral analysis of blood pressure and heart rate signals in specific bands) currently employed to assess sympathetic cardiovascular control in humans. After highlighting the advantages and limitations of each approach, the paper will describe some of the results obtained by employing the above mentioned techniques to detect abnormalities in sympathetic cardiovascular tone in physiological and pathological conditions.

Arousal↗
PubMed1998

Clinical relevance blood pressure variability.

Blood pressure fluctuates continuously over time, either spontaneously or in response to a variety of external stimulations. The occurrence of these continuous and often marked blood pressure variations is not only of pathophysiologic interest, but it may also have a clinical relevance. Indeed, it has been shown that the occurrence of pronounced blood pressure changes at the time of the physician's visit may introduce errors in the diagnosis of hypertension and in the assessment of the efficacy of antihypertensive treatment. Moreover, several studies have reported that the end-organ damage of hypertension is significantly and independently related to the degree of blood pressure variability during the day and night. This was shown by reports that assessed blood pressure variability by a variety of different methods, i.e. by computing the 24 h or daytime blood pressure standard deviation, the degree of morning blood pressure rise or that of night-time blood pressure fall, the frequency of blood pressure peaks over the 24 h, and the blood pressure increases under stressful conditions or during physical exercise. Results from a recent follow-up study have provided evidence that the degree of blood pressure variability may also have prognostic relevance in hypertensive patients. Thus, optimal antihypertensive treatment might also need to reduce the degree of blood pressure fluctuations together with the 24 h average blood pressure levels. Until recently, however, available antihypertensive drugs have been ineffective in buffering blood pressure variability or have even been responsible for an increase in the degree of blood pressure fluctuations. Further studies are needed to assess whether recently developed antihypertensive agents, and in particular those able to induce a smooth reduction in blood pressure over the 24 h or to modulate the sympathetic influences exerted on the cardiovascular system, may represent better tools to reduce the magnitude of an enhanced blood pressure variability in hypertensive patients over the 24 h. Recent progress in technology has offered us more powerful tools to address this issue. They include devices for continuous noninvasive ambulatory blood pressure monitoring (Portapres, TNO), and techniques for a more comprehensive analysis of all components which contribute to overall blood pressure variability (broad-band spectral analysis).

Blood Pressure↗
PubMed1997

Time and frequency domain estimates of spontaneous baroreflex sensitivity provide early detection of autonomic dysfunction in diabetes mellitus.

Diabetic autonomic dysfunction is associated with a high risk of mortality which makes its early identification clinically important. The aim of our study was to compare the detection of autonomic dysfunction provided by classical laboratory autonomic function tests with that obtained through computer assessment of the spontaneous sensitivity of the baroreceptor-heart rate reflex (BRS) by time domain and frequency domain techniques. In 20 normotensive diabetic patients (mean age +/- SD 41.9 +/- 8.1 years) with no evidence of autonomic dysfunction on laboratory autonomic testing (D0) blood pressure (BP) and ECG were continuously monitored over 15 min in the supine position. BRS was assessed as the slope of the regression line between spontaneous increases or reductions in systolic BP and linearly related lengthening or shortening in RR interval over sequences of at least 4 consecutive beats (sequence method), or as the squared ratio between RR interval and systolic BP spectral powers around 0.1 Hz. We compared the results with those of 32 age-matched normotensive diabetic patients with abnormal autonomic function tests (D1) and with those of 24 healthy age-matched control subjects with normal autonomic function tests (C). Compared to C, BRS was markedly less in D1 when assessed by both the slope of the two types of sequences (data pooled) and by the spectral method (-71.3% and -60.2% respectively, both p < 0.01). However, BRS was consistently although somewhat less markedly reduced in D0, the reduction being clearly evident for all the estimates (-57.0% and -43.5%, both p < 0.01). The effects were more evident than those obtained by the simple quantification of the RR interval variability. These data suggest that time and frequency domain estimates of spontaneous BRS allow earlier detection of diabetic autonomic dysfunction than classical laboratory autonomic tests. The estimates can be obtained by short non-invasive recording of the BP and RR interval signals in the supine patient, i.e. under conditions suitable for routine outpatient evaluation.

Adult↗
PubMed1997

Dynamic detection of rhythmic oscillations in heart-rate tracings: a state-space approach based on fourth-order cumulants.

This paper presents a new procedure specifically aimed at providing a dynamical detection of the oscillations occurring in long-term heart-rate (HR) tracings. The procedure is based on a time-variant state-space modelling of the fourth-order cumulants of the HR signal. The state-space estimator was selected because of its demonstrated capability to distinguish between deterministic and stochastic components of the signal, while the fourth-order cumulants of the signal were used as input of the model to further reduce adverse effects of coloured, white and l/f Gaussian noise possibly present in the input data. The procedure was tested by the analysis of simulated signals and its performance was compared with the results obtained by state-space modelling applied directly on the test signals (instead of on the fourth-order cumulants of the signals) and by the more traditional auto-regressive modelling. The comparison has shown a clear superiority of the proposed procedure over the other techniques in discriminating deterministic oscillations from coloured noise. Finally, the applicability of the procedure to biological data was verified by analysing five experimental HR tracings recorded in normal subjects during laboratory and daily life conditions.

Electrocardiography↗
PubMed1997

Autonomic cardiac regulation in obstructive sleep apnea syndrome: evidence from spontaneous baroreflex analysis during sleep.

OBJECTIVE: To assess spontaneous baroreceptor-heart rate reflex sensitivity during sleep in patients with obstructive sleep apnea syndrome, a condition associated with increased cardiovascular morbidity and mortality and characterized by marked sympathetic activation, which is believed to originate from hypoxic chemoreceptor stimulation, although little is known of other possible mechanisms such as baroreflex impairment. DESIGN AND METHODS: In 11 patients with severe obstructive sleep apnea syndrome (mean+/-SD age 46.8+/-8.1 years, apnea/hypopnea index 67.9+/-19.1 h), who were normotensive or borderline hypertensive during wakefulness by clinic blood pressure measurements, finger blood pressure was monitored beat-by-beat non-invasively (Finapres) at night during polysomnography. Periods of wakefulness and sleep were identified based on electroencephalographic recordings. Baroreflex sensitivity was assessed by the sequence technique, as the slope of the regression line between spontaneous increases or reductions in systolic blood pressure (SBP) and the related lengthening or shortening in the RR interval, occurring over spontaneous sequences of four or more consecutive beats. The number of these sequences was also computed, as an additional index of baroreflex engagement by the spontaneous blood pressure fluctuations. The controls were age-related normotensive or borderline hypertensive subjects without sleep apnea who had been investigated in previous studies; in these subjects blood pressure was recorded intra-arterially over 24 h in ambulatory conditions and spontaneous baroreflex sensitivity was assessed by the sequence technique. RESULTS: In our patients the lowest nocturnal arterial oxygen saturation was 78.6+/-12.1% (mean+/-SD). During sleep, the number of pooled +RR/+SBP and -RR/-SBP sequences per hour was 20.3+/-2.7 per h in patients with sleep apnea and 27.1+/-2.1 /h in controls (means+/-SEM). The average baroreflex sensitivity during sleep periods was 7.04+/-0.8 ms/mmHg in sleep apnea patients and 10.05+/-2.1 ms/mmHg in controls. Both the pooled number of sequences and baroreflex sensitivity values of the sleep apnea patients were significantly (P < 0.01) less than the corresponding night values of control subjects. In the sleep apnea patients, at variance from controls, baroreflex sensitivity did not show any increase during sleep compared with its values during wakefulness (6.9+/-1.0 ms/mmHg). CONCLUSIONS: Our data provide evidence that spontaneous baroceptor reflex sensitivity is depressed in severe obstructive sleep apnea syndrome. This suggests that in such patients baroreflex dysfunction and not only chemoreceptor stimulation by hypoxia may be involved in the sympathetic activation which occurs during sleep. Such dysfunction may contribute to the higher rate of cardiovascular morbidity and mortality reported in these patients.

Adult↗
PubMed1997

Smoking impairs baroreflex sensitivity in humans.

In 10 healthy smokers, finger blood pressure was recorded continuously for 1 h in a supine control condition and for 1 h while smoking four cigarettes, one every 15 min. Smoking increased average systolic blood pressure (+19%, P < 0.01) and its variability and reduced pulse interval (reciprocal of heart rate, -22%, P < 0.01) and its variability. Baroreflex sensitivity, as assessed by the slope of spontaneous hypertension/bradycardia or hypotension/tachycardia sequences and by the alpha-coefficient (squared ratio between pulse interval and systolic blood pressure spectral powers at 0.1 Hz) was significantly decreased (P < 0.01) during smoking, whereas there were no effects of smoking on the reflex changes in pulse interval induced by carotid baroreceptor stimulation through a neck suction device. Sham smoking by a drinking straw had no effects on any of the above parameters. Thus, when assessed in the absence of laboratory maneuvers in daily life conditions, baroreflex sensitivity is markedly impaired by smoking. This impairment may contribute to the smoking-induced increase in blood pressure and heart rate as well as to the concomitant alterations in their variability.

Adult↗
PubMed1997

Modulation of pulmonary arterial input impedance during transition from inspiration to expiration.

We investigated whether respiration influences pulmonary arterial input impedance during transition from inspiration to expiration in five anesthetized, spontaneously breathing dogs. Impedance (Z) was separately assessed for heart beats occurring in inspiration, in expiration, and during the transition from inspiration to expiration (transitional beat). Transitional beats were scored by the ratio between the fraction of beat falling in expiration and the total beat duration [expiratory fraction (Efr)] to quantify their position within the transition. In transitional beats, input resistance linearly increased with Efr; Z modulus at the heart-rate frequency (fHR) decreased up to -50% for Efr = 50%. Z phase at fHR was greater than in inspiration for Efr <40% and lower for Efr >50%. Unlike blood flow velocity, mean value and first harmonic of pulmonary arterial pressure were correlated to Efr and paralleled the changes of input resistance and Z at fHR. This indicates that respiration influences Z through modifications in arterial pressure. The evidence of important respiratory influences on Z function may help the pathophysiological interpretation of dysfunctions of the right heart pumping action, such as the so-called cor pulmonale.

Animals↗
PubMed1997

Broadband spectral analysis of blood pressure and heart rate variability in very elderly subjects.

Systolic blood pressure (SBP) variability is increased and R-R interval variability is reduced in the elderly. Little is known, however, about how SBP and R-R interval variabilities change in the very elderly. More important, however, it is not known which frequency components of SBP and R-R interval variability are affected significantly. We addressed this issue in subjects older than 70 years by broadband spectral analysis, which allows all variability components from the lowest to the highest frequency to be considered. In 20 very elderly normotensive subjects (mean +/- SD age, 78.1 +/- 6.8 years) and 28 normotensive adult subjects (36.1 +/- 7.1 years), noninvasive finger blood pressure and R-R intervals were recorded continuously for 30 minutes in the supine position and 15 minutes in the upright position. SBP and R-R interval power spectral densities were computed over the entire frequency region between 0.005 Hz (0.007 Hz in the upright position) and 0.5 Hz. Overall SBP variability (SD) was greater and overall R-R interval variability was less in very old subjects than in adult subjects. All spectral R-R interval powers were reduced significantly in very elderly individuals. The spectral SBP powers were greater in the very elderly group than in the adult group only in the very-low-frequency range (<0.04 Hz). This was true in the supine and the standing positions. With subjects in the standing position, the shape of the broadband spectra differed in the very old and adult subjects because in the former group the increase in SBP and R-R interval power around 0.1 Hz that was seen in the latter was blunted. Therefore, in very elderly subjects a reduction in overall R-R interval variability is accounted for by a reduction in all of its frequency components. The accompanying increase in overall BP variability, however, results from a nonhomogeneous behavior of its frequency components, which consists of an increase in the very low frequency and a concomitant reduction in the higher frequency powers. The mechanisms responsible for these changes may be complex, but at least they may in part reflect the baroreflex impairment and autonomic dysfunction that characterize aging.

Adult↗
PubMed1997

Sympathetic activity, blood pressure variability and end organ damage in hypertension.

Animal studies have provided clearcut evidence that sympathetic factors are involved in the development and maintenance of high blood pressure (BP). This also appears to be the case in humans, in which sympathetic activation, detected through plasma noradrenaline measurement, noradrenaline spillover technique and direct recording of muscle sympathetic nerve activity, has been shown to characterize the early phases of the hypertensive state and parallel its severity. Sympathetic factors also play in a variety of pathophysiological states frequently associated with hypertension, such as obesity, insulin resistance and atherosclerosis. In addition evidence has been collected that adrenergic factors represent one of the mechanisms involved in determining BP variability, which is strictly associated with end organ damage. Taken together these findings underline the importance that the therapeutical approach to hypertension is aimed not only at lowering BP but also at reducing sympathetic activity.

Animals↗
PubMed1997

Critical appraisal of indices for the assessment of baroreflex sensitivity.

The sequence technique and the spectral estimation of the alpha coefficient are currently employed for the assessment of "spontaneous" baroreflex sensitivity (BRS). The comparison of performance and effectiveness of these techniques is obtained by the analysis of systolic blood pressure (SBP) and pulse interval (PI) tracings recorded in conscious cats before and after baroreceptor denervation. Results indicate that (1) the average BRS estimates obtained by the sequence technique and by the alpha coefficient at the respiratory frequency are similar, (2) the alpha coefficients computed at the respiratory frequency tend to be higher than alpha coefficients estimated at 0.1 Hz, and (3) in spite of what is traditionally claimed, the PI-SBP coherence does not seem to represent a reliable parameter to enhance the specificity of the spectral estimate, because coherence values often remain above the 0.5 threshold also after baroreceptor denervation.

Animals↗
PubMed1997

Clinical value of blood pressure variability.

Blood pressure (BP) is known to continuously fluctuate over time and both the amplitude and frequency of these changes have been reported to be clinically relevant. Indeed, it has been shown that the occurrence of pronounced BP changes at the time of the physician's visit may introduce errors in the diagnosis of hypertension and in the assessment of the efficacy of antihypertensive treatment. Moreover, several studies have provided evidence that the end organ damage of hypertension is not only more closely related to 24h average BP values than to casual BP readings, it is also significantly and independently related to the degree of BP variability during the day and night. Results from a recent follow-up study support the possibility that the degree of BP variability may also have prognostic relevance in hypertensive patients. Recent progress in technology has offered us non-invasive techniques for the assessment of beat-to-beat finger blood pressure variability and for the detailed quantification of all its frequency components from the fastest to the slowest ones. Their role as additional surrogate endpoints in essential hypertension needs to be addressed in future studies.

Blood Pressure↗
PubMed1996

Neural cardiovascular regulation and 24-hour blood pressure and heart rate variability.

The availability of ambulatory intraarterial blood pressure monitoring techniques offers a deeper insight into the features of blood pressure variability over 24 hours and allows better understanding of the mechanisms responsible for the continuous and marked blood pressure changes that occur throughout the day and at night. Among these mechanisms, central and reflex neural influences play a major role. This has led to the development of techniques for the assessment of 24-hour "spontaneous" baroreflex sensitivity through combined computer analysis of blood pressure and heart rate variations in the time or frequency domain. The recent introduction of continuous noninvasive ambulatory blood pressure monitors offers the unique possibility of obtaining dynamic information on neural cardiovascular control in clinical conditions in which the assessment of autonomic cardiovascular regulation may have diagnostic and prognostic implications.

Blood Pressure↗
PubMed1996

Blood pressure and heart rate variability in autonomic disorders: a critical review.

Spectral analysis (SA) of blood pressure (BP) and heart rate (HR) fluctuations has been proposed as a unique approach to obtain a deeper insight into cardiovascular regulatory mechanisms in health and disease. A number of studies performed over the last 15 years have shown that autonomic influences are involved in the modulation of fast BP and HR fluctuations (with a period <1 min), particularly at frequencies between 0.2 and 0.4 Hz [high frequency (HF) region or respiratory frequency] and around 0.1 Hz [mid frequency (MF) region]. In patients with secondary or primary autonomic dysfunction, SA of BP and HR signals recorded at rest or during orthostatic challenge in a laboratory environment have shown the occurrence of a reduction in the power of MF and/or HF, BP and HR components. Such a reduction is associated or may even precede the clinical manifestation of autonomic neuropathy. However, the above results collected in standardized laboratory conditions cannot reflect the features of neural cardiovascular control during daily life in ambulant individuals with autonomic failure. To investigate this issue, SA techniques have been applied to 24 h beat-to-beat intra-arterial and non-invasive finger BP recordings obtained in elderly subjects and in pure autonomic failure patients, respectively. In these conditions, HR powers displayed a reduction over a wide range of frequencies (from 0.5 to below 0.01 Hz). Conversely, BP powers underwent a complex rearrangement characterized by a reduction in the power around 0.1 Hz and by an increase in the powers at the respiratory frequency and at frequencies below 0.01 Hz. Dynamic quantification of the sensitivity of the baroreceptor-heart rate reflex by combined analysis of systolic BP and pulse interval (i.e. the interval between consecutive systolic peaks) powers around 0.1 Hz (alpha technique) has shown that in elderly subjects, and even more so in pure autonomic failure patients, baroreflex sensitivity is markedly reduced over the 24 h, and is no longer characterized by its physiological day-night modulation. In conclusion, although in some instances SA of cardiovascular signals may fail to fully reflect the features of autonomic cardiovascular control, the evidence discussed clearly demonstrates that this approach represents a promising tool for a dynamic assessment of the early impairment of neural circulatory control in autonomic failure. This is particularly the case when these analyses are performed on 24 h continuous BP and HR recordings in ambulant subjects.

Autonomic Nervous System Diseases↗
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

Does spontaneous respiration alter pulmonary artery input impedance?

The aim of this study was to determine whether spontaneous respiration influences pulmonary artery input impedance, a question that has received little attention in the literature. Impedance values were assessed during three different phases of the respiratory cycle, namely inspiration, expiration and postexpiration (i.e. the null respiratory flow period between expiration and the next inspiration) in five anaesthetized spontaneously breathing dogs. Firstly, impedance values during postexpiration were taken as the reference baseline, and compared with values obtained during inspiration and expiration. Then, differences between values in inspiration and in expiration were tested, taking impedance during inspiration as the baseline. Differences with respect to postexpiration were found for three parameters of input impedance: input resistance, characteristic impedance, and the frequency at the first zero-crossing of the impedance phase from negative to positive values (f(cross)). Input resistance was significantly lower in inspiration (85% of the baseline), characteristic impedance was significantly greater in inspiration and in expiration (112 and 119% respectively), and f(cross) was significantly lower in expiration (89%). By contrast, only input resistance differed significantly when inspiration was compared to expiration. Therefore, spontaneous respiration was shown to influence input impedance significantly. The observed changes in characteristic impedance and f(cross) might be explained by a stiffening of the pulmonary artery wall, due to neural and/or mechanical factors, during inspiration and expiration.

Animals↗