Biomedical subjects

Alberto Porta

Publications and source records attributed to Alberto Porta.

26 records · Page 2Linked to original sources

PubMed2003

Assessing autonomic disturbances of hypertension in the general practitioner's office: a transtelephonic approach to spectral analysis of heart rate variability.

OBJECTIVES: Spectral analysis of heart rate variability (HRV) provides potentially useful information on autonomic disturbances of human hypertension. However, its practical use outside the clinical laboratory is largely unexplored. The aim of this study was to test the feasibility of assessing HRV from the general practitioner's (GP's) office, using a novel transtelephonic approach. DESIGN: Parallel study on two similar groups: 150 subjects (100 hypertensives and 50 normotensives) studied in our hospital clinic and compared with 150 subjects studied in an out-of-hospital practice (100 hypertensive subjects from GPs' surgeries and 50 normotensive subjects participating in a multinational company's health maintenance programme). METHODS: Spectral analysis of RR interval variability was used to assess autonomic regulation of the sino-atrial (SA) node, both at rest and during standing. For the out-of-hospital practice, strings of continuous electrocardiograms (ECGs), recorded with a microminiature instrument, were fed, off line, through standard telephone lines to our laboratory for subsequent spectral analysis. RESULTS: RR spectral profiles obtained from healthy controls or hypertensive patients examined in their GPs' surgeries were similar to those obtained in a hospital clinic, both at rest and when standing up. CONCLUSIONS: The present study shows the feasibility of using a transtelephonic approach to perform spectral analysis of heart rate variability from physicians' surgeries. This method could favour a more widespread use of autonomic assessment in the clinical management of hypertension.

Adult↗

PubMed2002

Power-law behavior of heart rate variability in Chagas' disease.

Beta slope is a nonlinear index derived from the power-law analysis of 24-hour heart rate variability (HRV); in healthy subjects, the beta index is typically near -1, suggesting a fractal behavior of HRV. There is scarce data on HRV in Chagas' disease. This transversal study intends to describe power-law and linear HRV patterns in different forms of Chagas' disease. Patients and healthy controls (n = 26) without other diseases were submitted to a standardized protocol, including electrocardiography, echocardiography, and 24-hour Holter monitoring. Patients with Chagas' disease were divided into groups according to their left ventricular (LV) systolic function: normal (group 1, n = 85), segmental abnormalities (group 2, n = 49), and reduced ejection fraction (group 3, n = 26). The temporal series were carefully processed to obtain the HRV indexes and beta slope. Despite the differences in the LV systolic function, the 3 groups were comparable in terms of long-term HRV index values. After adjustment for covariates, short-term HRV index values were consistently reduced in the Chagas' disease groups. The beta-index values were also diminished in Chagas' disease groups (group 1: -1.09 +/- 0.03, group 2: -1.11 +/- 0.06; group 3: -1.14 +/- 0.03; and controls: 0.95 +/- 0.03, p <0.001). This breakdown of fractal long-range correlation of RR interval dynamics, a strong predictor of mortality in other cardiomyopathies, may reflect cardiac dysautonomia that may have gone undetected in long-term time-domain analysis. This abnormality may explain the increased risk for arrhythmic sudden death found in Chagas' disease even in the absence of signs of LV dysfunction.

Adult↗

PubMed2002

Intravenous amiodarone modifies autonomic balance and increases baroreflex sensitivity in conscious rats.

Amiodarone is an antiarrhythmic agent commonly used to treat cardiac arrhythmias. This study was designed to investigate the effects of intravenous amiodarone on the neural control of heart rate and arterial pressure and spontaneous baroreflex sensitivity (BRS). Experiments were carried out on conscious freely moving normotensive Wistar (WR) and spontaneously hypertensive rats (SHR). Arterial pressure was continuously monitored before and after amiodarone (50 mg/kg i.v.) or vehicle for 30 min. Heart rate (expressed as the pulse interval, PI) and systolic arterial pressure (SAP) variabilities were assessed using autoregressive spectral analysis. BRS was calculated as the alpha-index (the square root of the ratio between the PI and SAP powers). Amiodarone induced bradycardia and hypotension in both strains, with these effects being more intense in SHR. The variability profile of PI was characterized by a significant reduction of normalized low frequency (LF) and LF/HF ratio, while the high frequency (HF) component both in absolute and normalized units (nu) was increased in both WR and SHR strains. A significant decrease in SAP variance and its LF oscillation was observed. In addition, BRS was also increased in both groups, being more intense in SHR. In both WR and SHR, intravenous amiodarone had a considerable effect on heart rate variabilities (HRV), shifting cardiac sympathovagal balance toward a sympathetic inhibition and/or vagal activation, which were associated with an increase in spontaneous BRS. Decreases of SAP variance and LF(SAP) suggest sympatholytic effects on peripheral vessels. Besides the direct ion channel effects, these changes in the autonomic balance could contribute to the antiarrhythmic action of the intravenous amiodarone.

Amiodarone↗

PubMed2002

Effects of cardiac rehabilitation and exercise training on autonomic regulation in patients with coronary artery disease.

BACKGROUND: Although cardiovascular rehabilitation and exercise training have substantial benefits in various ischemic heart disease (IHD) risk factors and subsequent prognosis after major IHD events, there is a paucity of information about its effects on autonomic regulation (such as heart rate variability [HRV] and baroreflex gain), particularly considering its arterial and cardiopulmonary components. METHODS: We studied 40 patients (aged 60 +/- 6 y) after major IHD events, including 29 who underwent a comprehensive phase II cardiac rehabilitation and exercise training program and 11 controls who did not attend cardiac rehabilitation. Specifically, we determined whether active training improves prognostic indices of autonomic regulation of the SA node and whether changes in baroreflex gain could be ascribed to the arterial or to the cardiopulmonary component of the overall arterial pressure/heart period baroreflex. RESULTS: Only patients with IHD undergoing active rehabilitation demonstrated a significant increase in R-R interval, in its variance, in overall gain of arterial pressure/heart period baroreflex (7.44 +/- 1.20 ms/mm Hg to 12.12 +/- 1.48 ms/mm Hg, P <.001) and in peak oxygen consumption (Delta = 2.45 mL/kg/min, P <.001). Separate examination of the selective arterial and cardiopulmonary components showed that only the latter increased significantly (6.17 +/- 1.09 ms/mm Hg to 10.62 +/- 1.56 ms/mm Hg; P <.01). CONCLUSIONS: Cardiac rehabilitation is associated with significant improvements in autonomic markers of neural regulation of the SA node, such as increases in R-R variance and the gain of the overall spontaneous baroreflex, with specific improvements in the cardiopulmonary component as opposed to the arterial baroreflex component of this system. These improvements may further explain the reduction in morbidity and mortality noted after formal cardiac rehabilitation and exercise training programs.

Angioplasty, Balloon, Coronary↗

PubMed2002

Noninvasive quantification of respiratory modulation on left ventricular size and stroke volume.

To noninvasively explore the complex interactions between heart rate, left ventricular (LV) stroke volume (SV) and respiration, different techniques were proposed and applied to the beat-to-beat measurements of end-diastolic (ED), end-systolic (ES) volumes and SV, obtained from echocardiographic acoustic quantification LV volume signal. Data were obtained from eight patients with dilated cardiomyopathy (DCM, age 60 +/- 2, mean +/- SE), and from 11 age-matched healthy volunteers (N, age 63 +/- 2). Spectral analysis showed an increase in HF power in DCM, both in ED (in ml2, 58 +/- 18 versus 19 +/- 5 in N) and in SV (in ml2, 55 +/- 12 versus 17 +/- 5 in N), together with an increase in total power (in ml2, ED: 119 +/- 31 in DCM versus 48 +/- 9 in N; SV: 88 +/- 17 in DCM versus 31 +/- 8 in N). Folded scattergrams evidenced higher amplitude oscillations in DCM (in ml, ES: 7.93 +/- 1.29; ED: 7.94 +/- 1.59; SV: 7.27 +/- 0.91) compared to N (in ml, ES: 4.08 +/- 0.64; ED: 3.56 +/- 0.65; SV: 3.63 +/- 0.43). Moreover, the prevalent effect of increased afterload generating SV reduction during inspiration was pointed out in N, while an intersubject dispersion in the relation between respiratory phase and LV dimension changes was found in DCM. Black-box model identification summarized these mechanisms by means of a few quantitative parameters.

Cardiomyopathy, Dilated↗

PubMed2002

Evidence of unbalanced regulatory mechanism of heart rate and systolic pressure after acute myocardial infarction.

The interactions between systolic arterial pressure (SAP) and R-R interval (RR) fluctuations after acute myocardial infarction (AMI) were investigated by measures of synchronization separating the feedback from the feedforward control and capturing both linear and nonlinear contributions. The causal synchronization, evaluating the ability of RR to predict SAP (chi(s/t)) or vice versa (chi(t/s)), and the global synchronization (chi) were estimated at rest and after head-up tilt in 35 post-AMI patients, 20 young and 12 old. Significance and nonlinearity of the coupling were assessed by surrogate data analysis. Tilting increased the number of young subjects in which RR-SAP link was significant (from 17 to 19) and linear (from 11 to 18). In AMI, both significance and linearity of the coupling were low at rest (26 significant and 24 nonlinear) and further reduced after tilt (17 significant and 16 nonlinear). Old subjects showed a partial recovery of linearity after tilt (rest: 1 linear of 7 significant; tilt: 5 linear of 8 significant). In young subjects, the causal synchronization indexes were balanced and increased from rest (chi(t/s) = 0.072 +/- 0.037 and chi(s/t) = 0.054 +/- 0.028) to tilt (chi(t/s) = 0.125 +/- 0.071 and chi(s/t) = 0.108 +/- 0.053). On the contrary, in old subjects and AMI patients, the feedforward was prevalent to the feedback coupling at rest (old: chi(t/s) = 0.041 +/- 0.023 and chi(s/t) = 0.069 +/- 0.042; AMI: chi(t/s) = 0.050 +/- 0.030 and chi(s/t) = 0.089 +/- 0.053). Tilting blunted the unbalance in old subjects (chi(t/s) = 0.065 +/- 0.052 and chi(s/t) = 0.069 +/- 0.044) but not in AMI patients (chi(t/s) = 0.040 +/- 0.019 and chi(s/t) = 0.060 +/- 0.040). Thus, after AMI, nonlinear mechanisms are elicited in RR-SAP interactions. Furthermore, the neural regulation of the cardiovascular system resulted in imbalance as a consequence of impaired feedback and enhanced feedforward control mechanisms.

Adult↗

PubMed2002

Opposite effects of iv amiodarone on cardiovascular vagal and sympathetic efferent activities in rats.

It is unknown whether amiodarone exerts a direct central action on the cardiovascular autonomic nervous system. This study was designed to evaluate the effects of acute amiodarone administration on vagal and sympathetic efferent nerve discharges. Experiments were carried out in 25 decerebrate unanesthetized rats. In one group, vagal activity was recorded from preganglionic fibers isolated from the cervical vagus nerve. In another group, sympathetic recordings were obtained from fibers isolated from the cervical sympathetic trunk in intact conditions or after barodenervation. Recordings were performed before and for 60 min after amiodarone (50 mg/kg iv) administration. In all groups, amiodarone induced bradycardia and hypotension. Vagal activity increased immediately, reaching a significant difference after 20 min (260 +/- 131% from 16.4 +/- 3.3 spikes/s) and was unmodified by the barodenervation. At difference, sympathetic activity after an initial and short-lasting increase (150 +/- 83% from 24.8 +/- 5.7 spikes/s) began to decrease significantly after 20 min (36 +/- 17%) throughout the experiment. The initial increase in sympathetic activity was not observed in barodenervated animals. These changes in vagal and sympathetic activity could play an important role in contributing to the antiarrhythmic action of amiodarone.

Amiodarone↗

PubMed2002

Biomedical signal processing and modeling in cardiovascular systems.

This article revisits the subject of short-term heart-rate and arterial-pressure variability from the perspective of model structures that can be useful in defining signal processing algorithms. We draw a general scheme of the oscillation sources and interactions that contribute to cardiovascular control mechanisms and highlight the elements that were considered in different modeling works. The origin, superposition, and interaction of respiratory high-frequency (HF) and vasomotor low-frequency (LF) rhythms is presented as the integration of supraspinal and spinal circuits, vasomotor activity, and pressure control loops. We analyze in detail the necessity of considering all relevant interactions for the algorithms designed to estimate the baroreflex sensitivity. We also pinpoint the components of cardiorespiratory coupling in relation to the analysis of data from the acoustic quantification of the left ventricular volume. Finally, we analyze the tendency to produce complex behaviors even in extremely simplified systems involving interactions between oscillatory mechanisms.

Animals↗