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Biomedical subjects

A Malliani

Publications and source records attributed to A Malliani.

At least 145 records · Page 8Linked to original sources
PubMed1988

Parameter extraction from heart rate and arterial blood pressure variability signals in dogs for the validation of a physiological model.

The paper describes an automatic procedure for improving the extraction of parameters in heart rate (HR) and arterial blood pressure (ABP) beat-to-beat variability signals. Auto- and cross-spectral analysis of such signals is carried out through parametric models and the distribution of the power of the spectra and the phase relationships are compared in various physiological situations induced in the dogs via drug infusion or surgical interventions which do influence the control mechanisms of HR and ABP. This "black-box" approach allows the obtention, directly from the processing of the above-mentioned signals, of the estimation of parameters relative to cardiovascular models, as the ones described by simple equations (Windkessel and Starling laws are introduced as examples). These parameters seem to validate significantly the capability of such models to describe the physiological interactions existing between the two considered signals. Applications may be foreseen both for research and clinical purposes.

Algorithms↗
PubMed1988

Spectral analysis of heart rate variability in the assessment of autonomic diabetic neuropathy.

We studied heart rate variability in 49 uncomplicated diabetics (27 with insulin therapy; 22 with oral hypoglycemic agents) and in 40 age-matched controls. An automatic autoregressive algorithm was used to compute the power spectral density (PSD) of beat by beat RR variability derived from the surface ECG. The PSD contains two major components (a low frequency approximately 0.1 Hz (LF) and a high frequency, respiratory linked, approximately 0.25 Hz (HF] that provide, respectively, quantitative markers of sympathetic and vagal modulatory activities and of their balance. As compared to controls, in diabetics, besides a reduced RR variance at rest (2722 +/- 300 and 1436 +/- 241 ms2, respectively), we observed during passive tilt an altered response of spectral indices of sympathetic activation and vagal withdrawal, suggestive of a complex modification in the neural control activities. In addition, we compared this approach to the commonly used clinical tests score, and observed that the latter provides overall results similar to those obtained with spectral changes induced by tilt (r = 0.42; P less than 0.01). Of potential clinical importance is that the data obtained with spectral analysis appear more thoroughly quantifiable and do not require the active collaboration of the patients.

Adolescent↗
PubMed1988

Sympathetic predominance in essential hypertension: a study employing spectral analysis of heart rate variability.

In this study on 91 subjects we tested the hypothesis of an enhanced sympathetic activity in uncomplicated essential hypertension employing spectral analysis of heart rate variability. With this technique the tonic sympathetic and vagal activities and their changes are respectively assessed by the power of approximately 0.1 Hz (low frequency, LF) and approximately 0.25 Hz (respiratory linked, high frequency, HF) components of the spectrum of the beat by beat variability of RR interval. When comparing the 40 subjects with diastolic blood pressure consistently greater than 95 mmHg (hypertensives, Ht), with 35 age-matched controls (diastolic arterial pressure less than 90 mmHg, Nt), we observed that LF was greater and HF smaller in Ht as compared to Nt, thus suggesting an enhanced sympathetic activity and a reduce vagal activity in Ht. Additionally, passive tilt, which in Nt enhances LF [delta = 26 +/- 2 normalized units (nu)] and reduces HF (delta = -22 +/- 2, nu), produced smaller (P less than 0.05) changes in Ht (delta LF = 6.3 +/- 2.7 and delta HF = -7.5 +/- 2.3 nu). Furthermore, the values of LF at rest and the altered effects of tilt on LF and HF were significantly correlated with the degree of the hypertensive state. Chronic beta-adrenergic blockade (atenolol 100 mg once daily for 2 weeks, n = 13) reduced heart rate and blood pressure (from 162/103 to 136/88 mmHg) together with a significant diminution of LF and an increase of HF. Thus, spectral analysis of RR variability appears to be a convenient non-invasive technique to follow the progressive alterations in sympatho-vagal balance present in essential hypertension.

Adult↗
PubMed1988

Changes in autonomic regulation induced by physical training in mild hypertension.

The adaptive effects of physical training on cardiovascular control mechanisms were studied in 11 subjects with mild hypertension. In these subjects we assessed the gain of the heart period-systolic arterial pressure relationship in the unfit and the fit state by using 1) an open loop approach, whereby the gain is expressed by the slope of the regression of heart period as a function of systolic arterial pressure, during a phenylephrine-induced pressure rise and 2) a closed loop approach with proper simplification, whereby the gain is expressed by the index alpha, obtained through simultaneous spectral analysis of the spontaneous variabilities of heart period and systolic arterial pressure. Both methods indicated that training significantly increased the gain of the relationship between heart period and systolic arterial pressure at rest and reduced arterial pressure and increased heart period significantly. This gain was drastically reduced during bicycle exercise both in the unfit and fit state. In a second group of normotensive (n = 7; systolic pressure, 133 +/- 3 mm Hg) and hypertensive (n = 7; systolic pressure, 180 +/- 10 mm Hg) subjects undergoing 24-hour diagnostic continuous electrocardiographic and high fidelity arterial pressure monitoring, the index alpha was significantly reduced in the hypertensive group at rest. Furthermore, when analyzed continuously over the entire 24-hour period, this index underwent minute-to-minute changes with lower values during the day and higher values during the night. We propose the index alpha as a quantitative indicator of the changes in the gain of baroreceptor mechanisms occurring with physical training in mild hypertension and during a 24-hour period in ambulatory subjects.

Adult↗
PubMed1988

Automatic assessment of the interaction between respiration and heart rate variability signal.

The present paper introduces an original method of processing heart rate variability (HRV) and respiration signals as detected respectively through chest electrodes and thoracic belt in dogs under different experimental conditions. Signals are processed as time series synchronous with the occurrence of QRS complexes on ECG signal and auto and cross spectra are accordingly calculated. Two particular bands appear mainly of interest on the spectrum of HRV signal: one in correspondence with the respiration rate and another one at a lower frequency value. Values of power at these frequency bands together with coherence and phase between HRV signal and respiration complete the parameters which try to quantify a few aspects of the complex dynamic relationships between the original signals. In particular, controlled respiration in dogs was studied through the connection with an automatic ventilator, as well as the effects of drugs which interact with the neural regulatory systems (i.e. sympathetic and parasympathetic nervous system). Gain and phase relationships between heart rate variability and respiration, obtained with spectral analysis, could be used to provide a better understanding of the neural control mechanisms linking heart rate and respiration in various experimental conditions. The method described in this study is to be used both in physiological and clinical research.

Animals↗
PubMed1987

Heart rate variability as an index of sympathovagal interaction after acute myocardial infarction.

By analysis of spectral components of heart rate variability, sympathovagal interaction was assessed in patients after acute myocardial infarction (AMI). At 2 weeks after AMI (n = 70), the low-frequency component was significantly greater (69 +/- 2 vs 53 +/- 3 normalized units [NU], p less than 0.05) and the high-frequency component was significantly smaller (17 +/- 1 vs 35 +/- 3 NU) than in 26 age-matched control subjects. This difference was likely to reflect an alteration of sympathovagal regulatory outflows with a predominance of sympathetic activity. At 6 (n = 33) and 12 (n = 29) months after AMI, a progressive decrease in the low- (62 +/- 2 and 54 +/- 3 NU) and an increase in the high-frequency (23 +/- 2 and 30 +/- 2 NU) spectral components was observed, which suggested a normalization of sympathovagal interaction. An increase in sympathetic efferent activity induced by tilt did not further modify the low-frequency spectral component (78 +/- 3 vs 74 +/- 3 NU) in a subgroup of 24 patients at 2 weeks after AMI. Instead, 1 year after AMI, this maneuver was accompanied by an increase in the low-frequency component (77 +/- 3 vs 53 +/- 3 NU, p less than 0.05) of a magnitude similar to the one observed in control subjects (78 +/- 3 vs 53 +/- 3 NU). These data indicate that the sympathetic predominance that is detectable 2 weeks after AMI is followed by recovery of vagal tone and a normalization of sympathovagal interaction, not only during resting conditions, but also in response to a sympathetic stimulus.

Adult↗
PubMed1987

Heart rate variability signal processing: a quantitative approach as an aid to diagnosis in cardiovascular pathologies.

The heart rate variability (HRV) signal carries important information about the systems controlling heat rate and blood pressure, mainly elicited by autonomic nervous system (sympathetic and parasympathetic) controls. The present paper illustrates methods of HRV signal processing by using autoregressive (AR) modeling and power spectral density estimate. The information enhanced in this way seems to be particularly sensitive in discriminating various cardiovascular pathologies (hypertension, myocardial infarction, diabetic neuropathy, etc.). This method provides a simple non-invasive analysis, based on the processing of spontaneous oscillations in heart rate. Particular emphasis is directed to the algorithms used and to their direct application by using proper computerized techniques: only a few paradigmatical examples will be illustrated as preliminary results.

Cardiovascular Diseases↗
PubMed1987

Attenuation of baroreceptive mechanisms by cardiovascular sympathetic afferent fibers.

By sectioning spinal dorsal roots from C8 to T6, we analyzed the contribution of sympathetic cardiovascular afferent fibers to the reflex bradycardia induced by arterial pressure rises in 24 anesthetized and in 21 decerebrate cats. In anesthetized cats, the reflex bradycardia was obtained in 16 animals with occlusions of the thoracic aorta and in 8 animals with phenylephrine injections (25-75 micrograms/kg). In both experimental conditions, the dorsal root section enhanced the bradycardia response, which thus increased from 15 +/- 3 to 20 +/- 3% during aortic constrictions and from 11 +/- 3 to 19 +/- 6% during phenylephrine injections (P less than 0.05). The enhancement, after rhizotomy of the reflex bradycardia during aortic occlusion, was more pronounced in eleven decerebrate cats as it increased from 21 +/- 4 to 34 +/- 4%, P less than 0.05. In five vagotomized and decerebrate cats, the reflex bradycardia was also increased after rhizotomy despite the overall reduction of the reflex response. In five decerebrate cats with beta-adrenergic receptor blockade (propranolol 0.2-0.4 mg/kg iv), aortic occlusion resulted in a small reduction in heart rate which was not significantly affected by dorsal root section. Our data indicate that excitatory reflexes mediated by dorsal roots are likely to modulate the inhibitory supraspinal reflexes that determine the heart rate reduction during acute rises in arterial blood pressure.

Adrenergic beta-Antagonists↗
PubMed1986

Spectral and cross-spectral analysis of heart rate and arterial blood pressure variability signals.

A parametric method for autoregressive (AR) auto- and cross-spectral analysis is presented for the contemporaneous processing of heart rate and arterial blood pressure variability signals. In particular, the introduced bivariate spectral analysis (phase and coherence spectra) provides quantitative and objective means which are useful to measure the role played by the neural controlling systems (sympathetic and parasympathetic systems) on the cardiovascular signals under different pathophysiological conditions. Algorithmic aspects, connected to the way of processing discrete numerical series synchronized to single cardiac beats, are particularly stressed. Important applications are foreseen both in physiological studies and in clinical practice as an aid to the detection of various relevant cardiovascular pathologies such as hypertension and diabetes.

Blood Pressure↗
PubMed1986

Continuous recording of direct high fidelity arterial pressure and electrocardiogram in ambulant patients.

A system providing high quality direct arterial blood pressure recordings and electrocardiograms in ambulatory patients was devised using a modified commercially available Holter type magnetic tape recorder together with a microminiature Millar (3F) tip transducer. This system did not require a perfusion line and solved the major drawbacks of other available systems. Pressure and electrocardiographic data were fed directly from the playback unit into a minicomputer for automatic beat to beat waveform analysis. Thus the blood pressure and RR interval variability signals could be simultaneously analysed with autoregressive modelling techniques to provide a quantitative estimate of sympathovagal balance in ambulant patients. The system was reliable, simple, and safe to use.

Ambulatory Care↗
PubMed1986

Effects of propranolol on the impulse activity of cardiovascular sympathetic afferent fibers.

The influence of beta-adrenergic receptor blockade on the impulse activity of 21 cardiovascular sympathetic afferent nerve fibers (11 from the thoracic aorta, 10 from the pulmonary veins), isolated from the left sympathetic rami communicantes T-3 and T-4 was studied in anesthetized, vagotomized cats. Aortic pressure, heart rate, and neural discharge were recorded during control conditions and during brief aortic occlusions of comparable amplitude and duration. Administration of dl-propranolol (0.2-0-4 mg/kg) did not modify aortic pressure or neural discharge of the fibers during control conditions, although, as expected, heart rate was diminished. dl-Propranolol administration did change the response of cardiovascular sympathetic afferents to similar aortic pressure increases. Before drug administration, aortic occlusion caused a significant increase in neural discharge of both aortic and pulmonary vein sympathetic afferent fibers, from 0.52 +/- 0.12 to 1.64 +/- 0.31 and from 0.67 +/- 0.10 to 2.08 +/- 0.25 impulses/sec, respectively (p less than 0.05). After dl-propranolol administration, comparable increases in aortic pressure resulted in slight but not significant increases in neural discharge of aortic and pulmonary vein fibers. Administration of d-propranolol (0.4-0.6 mg/kg), which possesses only membrane-stabilizing properties, did not modify the firing rate of four pulmonary sympathetic afferents, which subsequently decreased their response to pressure rises after administration of dl-propranolol. These results indicate that beta-adrenergic receptor blockade reduces the responsiveness to hemodynamic stimuli of sympathetic cardiovascular afferent fibers that are capable of mediating excitatory pressor reflexes.

Animals↗
PubMed1986

Circulatory markers of nervous activation during myocardial ischemia.

In man, electrocardiographic changes typical of transient myocardial ischemic episodes can be accompanied by increases in arterial pressure and heart rate or, at the opposite side of the spectrum, by decreases in arterial pressure and heart rate. It has been clearly proved that all of these changes can occur independently of the perception of pain. Transient ischemic episodes associated with hypotension and bradycardia or hypotension without the tachycardia that could be expected from a baroreceptive mechanism, are likely to reflect a depressor reflex mediated by cardiac vagal afferent fibers. It is a clinical and experimental working hypothesis that these depressor reflexes would characterise more severe episodes of ischemia: in clinics, those accompanied by signs of acute ventricular failure; in the laboratory, those induced by "global" ischemia. On the other hand, ischemic episodes associated with hypertension and tachycardia, usually thought to depend on a pain mechanism, are likely to reflect a pressor reflex mediated by cardiac sympathetic afferent fibers. It is our hypothesis that these pressor reflexes from the heart are the most frequent companions of less severe ischemic episodes, whether or not signalled by anginal pain. In the laboratory, a pressor reflex can be constantly obtained with a limited "regional" ischemia. These neural mechanisms, that should be analyzed independently of any teleologic reasoning, may be of paramount importance not only in determining the hemodynamic profile accompanying ischemic episodes, but in inducing those local changes in visceral neural activity that an increasing evidence indicates as crucial factors in arrhythmias and coronary death.

Angina Pectoris↗