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Biomedical subjects

A Malliani

Publications and source records attributed to A Malliani.

At least 127 records · Page 7Linked to original sources
PubMed1991

Sympathovagal interaction during mental stress. A study using spectral analysis of heart rate variability in healthy control subjects and patients with a prior myocardial infarction.

We tested the hypothesis that psychological stress testing in the clinical laboratory provokes changes in the sympathetic and vagal activities regulating heart rate that can be assessed noninvasively using spectral analysis of RR variability. To account for the effects on respiration produced by talking, this study was performed with two different procedures: the I.K.T. (i.e., a computer-controlled mental task that is performed in silence and does not entail human confrontation) and a stressful interview. Finally, we assessed whether ischemic heart disease modifies the spectral changes induced by psychological stress by comparing a group of healthy subjects (age, 38 +/- 2 years) with a group of patients (age, 52 +/- 3 years) recovering from 1-month-old myocardial infarctions. The findings indicate that psychological stress induced marked changes in the sympathovagal balance, which moved toward sympathetic predominance. The low-frequency component of RR variability, a marker of sympathetic activity, increased from 58 +/- 5 normalized units (NU) to 68 +/- 3 NU with the I.K.T. and to 76 +/- 3 NU with the interview. This increase was absent in the group of post-myocardial infarction patients. However, arterial pressure increased significantly in both groups of subjects. The possibility of age playing an important role in determining the differences observed was disproved by the findings of a marked increase in low frequency with mental stimuli in an additional group of borderline hypertensive subjects with ages (55 +/- 2 years) comparable to those of post-myocardial infarction patients.

Adult↗
PubMed1990

Cardiocardiac excitatory reflexes during myocardial ischemia.

Myocardial ischemia represents a stimulus capable of exciting the receptive endings of both the vagal and sympathetic sensory fibers which innervate the heart. As a consequence, multiple and simultaneous reflexes can occur, mediated by the vagal and the sympathetic afferent limbs which, in turn, can modify both the vagal and the sympathetic outflows. Reflexes mediated by vagal afferent fibers are predominantly inhibitory, while those mediated by sympathetic afferent fibers are largely excitatory. In the experimental laboratory the various reflexes can be artificially isolated and analyzed, while in the clinical setting this is not feasible. However, in recent years a computer analysis of cardiovascular short-term variability seems to furnish new indices of vagal and sympathetic modulatory activities. Such analysis in the frequency domain thus seems to provide a tool for both experimental and clinical evaluation of the neural mechanisms accompanying various physiological and pathophysiological events, including acute myocardial ischemia.

Afferent Pathways↗
PubMed1990

Effects of sympathetic activation on heart rate variability in Chagas' patients.

To assess the alterations present in neural control of heart rate in patients with signs of Chagas' disease we studied the spectral components of heart rate variability in 10 Chagas' patients, without cardiac failure, and in 10 control subjects during supine and standing position. Chagas' patients during standing did not present the changes in the spectral components of heart rate variability which normally accompany sympathetic activation and vagal withdrawal.

Arrhythmias, Cardiac↗
PubMed1990

Spectral analysis of sympathetic discharge in decerebrate cats.

To evaluate if the 0.1-Hz low-frequency oscillations of R-R interval are a reflection of rhythmical pattern of discharge of the sympathetic outflow, we analysed in 10 decerebrate cats heart rate and cardiac sympathetic efferent discharge variability. A predominant low-frequency component was present in both signals, thus suggesting that the 0.1-Hz rhythm indeed reflects a rhythmical pattern of discharge of sympathetic outflow.

Animals↗
PubMed1990

Sympathetic activation during treadmill exercise in the conscious dog: assessment with spectral analysis of heart period and systolic pressure variabilities.

We studied in seven conscious dogs the dynamic rearrangements in neural control of heart rate and left ventricular pressure during treadmill exercise as assessed by spectral analysis. The presence, at rest, of a major high-frequency component (HF), an indicator of vagal tone, was reverted during exercise to a major low-frequency component (LF), an indicator of sympathetic activation. These changes were blunted by chronic beta and alpha 1 adrenergic receptor blockade.

Animals↗
PubMed1990

Effects of tilt and exercise on signal-averaged electrocardiogram after acute myocardial infarction.

To determine whether enhanced sympathetic activity could alter a non-invasive index of cardiac instability, we analysed the effects of 90 degrees head-up tilt and submaximal exercise stress test on high amplification signal-averaged electrocardiogram in 64 patients after acute myocardial infarction. At rest, ventricular late potentials were detected in 25% of patients, characterized by a significant prolongation of filtered QRS complex (137 +/- 3 vs 115 +/- 2 ms) and of its components smaller than 40 microV (38 +/- 2 vs 16 +/- 1 ms), as well as by a reduced root mean square voltage calculated for the terminal 40 ms of QRS complex (RMS40 voltage) (19 +/- 1 vs 75 +/- 9 microV) in comparison to patients without micropotentials. Sympathetic activation induced by tilt caused a significant increase in heart rate (from 67 +/- 3 to 79 +/- 3 beats min-1) but did not modify either the incidence of ventricular late potentials or the values of any of the signal-averaged electrocardiogram parameters considered. In 19 patients, recordings were also obtained during a submaximal bicycle exercise stress test at a heart rate of 114 +/- 4 beats min-1 and with systolic arterial blood pressure at 153 +/- 6 mmHg. No effect on signal-averaged electrocardiogram parameters was detectable during this experimental intervention. These data indicate that after myocardial infarction, sympathetic activation does not seem to modify signal-averaged electrocardiogram parameters.

Electrocardiography↗
PubMed1990

Analysis of short-term oscillations of R-R and arterial pressure in conscious dogs.

We studied the neural determinants of the second (i.e., high frequency, HF)- and third-order (i.e., low frequency, LF) spontaneous oscillations of heart period (R-R interval) and arterial pressure (AP) in conscious dogs, with the hypothesis that they might furnish quantitative markers of autonomic controlling activities. Spectral analysis of simultaneous R-R and AP variabilities quantified these oscillations that were also evaluated in units normalized by total power to focus on the balance of these two major components. At rest we observed a prevalent HF component (approximately 0.25 Hz) in R-R and AP variabilities that was synchronous with respiration. This HF component of R-R variability disappeared after atropine infusion and can be considered a marker mostly of vagal activity. When baroreceptor unloading, obtained by moderate hypotension, increased sympathetic activity the LF component increased in R-R, systolic, and diastolic AP variabilities. This increase in LF was not present after ganglionic blockade or after chronic arterial baroreceptor denervation. After chronic bilateral stellectomy, hypotension was not accompanied by an increase in LF component of R-R variability, while LF component remained in AP variability. An increase in LF component of R-R and AP variabilities was observed during transient coronary artery occlusion.

Animals↗
PubMed1990

Continuous 24-hour assessment of the neural regulation of systemic arterial pressure and RR variabilities in ambulant subjects.

In this study, we tested the hypothesis that the neural control of circulation in humans undergoes continuous but in part predictable changes throughout the day and night. Dynamic 24-hour recordings were obtained in two groups of ambulant subjects. In 18 hospitalized patients free to move, direct high-fidelity arterial pressures and electrocardiograms were recorded, and in an additional 28 nonhospitalized subjects, only electrocardiograms were obtained. Spectral analysis of systolic arterial pressure and of RR interval variabilities provided quantitative markers of sympathetic and vagal control of the sinus node and of sympathetic modulation of vasomotor tone. With this approach, the low-frequency (approximately 0.1 Hz) component of RR interval and systolic arterial pressure variabilities is considered a marker primarily of sympathetic activity, whereas the high-frequency (approximately 0.25 Hz) component of RR interval variability, related to respiration, seems to be a marker primarily of vagal activity. We observed a pronounced and consistent reduction in the markers of sympathetic activity and an increase in those of vagal activity during the night. In the invasive studies, while the subjects were still lying in bed after waking up, the markers of sympathetic activity rose rapidly and concomitantly with a simultaneous vagal withdrawal. Noninvasive studies confirmed the early morning rise of the markers of sympathetic activity and the circadian pattern of sympathovagal balance. These data indicate that the ominously increased rate of cardiovascular events in the morning hours may reflect the sudden rise of sympathetic activity and the reduction of vagal tone.

Blood Pressure↗
PubMed1989

Compressed spectral arrays for the analysis of 24-hr heart rate variability signal: enhancement of parameters and data reduction.

Heart rate variability signal in the form of an R-R interval tachogram is detected in Holter type 24-hr ECG recordings. Spectral analysis is carried out over consecutive nonoverlapping records, and the information is displayed in the form of a compressed spectral array through parametric techniques. The trends of spectral parameters such as low-frequency (LF) and high-frequency (HF) powers and central frequencies are also plotted, together with the classical mean R-R value and variance relative to each single spectrum. These parameters quantify the effect of sympatho-vagal balance on heart rate control during the 24-hr period and provide important elements for the diagnostic evaluation of various pathologies, like hypertension. A spectral compression algorithm which checks the position of the poles relative to LF and HF bands inside the unitary circle in the complex zeta-plane is also developed. Applications of this procedure are foreseen in the clinical evaluation of ambulant patients as well as in the study of physical and psychological stress.

Algorithms↗
PubMed1989

Premature ventricular contractions and reflex sympathetic activation in cats.

In 27 decerebrate cats under various experimental conditions, we studied the effects of programmed premature ventricular contractions on the impulse activity of preganglionic sympathetic fibres isolated from the third left thoracic ramus. Single extrastimuli increased the sympathetic discharge by 319(SEM 43)% [from 10.3(1.7) to 36(3.7) imp.s-1, p less than 0.05]. The neural response was significantly enhanced after bilateral vagotomy by 394(34)% [from 12(2.6) to 53.3(9.8) imp.s-1, p less than 0.05], but abolished when the stimuli were delivered during bilateral carotid artery occlusion. No sympathetic reflex response was observed in cats with chronic sino-aortic denervation. In eight cats, during occlusion of the left anterior descending coronary artery, the control sympathetic response was progressively and reversibly attenuated from 239(28)% to 36(14)%, at 90 s from the beginning of the occlusion. After bilateral vagotomy, this inhibitory interaction was no longer present and the sympathetic neural response to programmed stimulation was maintained throughout the occlusion period. The data indicate that the sympathetic reflex response initiated by baroreceptive deactivation could be attenuated by cardiac vagal afferent activity induced by coronary occlusion.

Animals↗
PubMed1989

Spectral analysis of R-R and arterial pressure variabilities to assess sympatho-vagal interaction during mental stress in humans.

We tested the hypothesis that spectral analysis of the R-R interval and systolic arterial pressure variabilities allows assessment of the dynamic changes in neural control of the cardiovascular system in men undergoing mental stress testing. Mental arithmetic increased the low-frequency components of R-R and systolic arterial pressure, i.e. markers of sympathetic activity to the SA node and the vasculature, respectively; it also decreased the high frequency component of R-R variability, a marker of vagal activity. Spectral analysis of R-R and systolic arterial pressure variabilities may be used in the clinic to test the dynamic effects of mental stress on both sympathetic and vagal activities.

Adult↗
PubMed1989

Restraining effect of captopril on cardiovascular sympathetic efferent neural activity.

In 13 decerebrate cats we studied the effects of captopril (10 mg/kg, intravenous bolus) on the background cardiac preganglionic sympathetic discharge and on its responsiveness to brief baroreceptor deactivations induced by premature ventricular contractions. Captopril caused a significant reduction of 57 +/- 7% (from 2.4 +/- 0.4 impulses/0.1s) in sympathetic discharge, with a mean latency of 35 +/- 3 min from the time of drug administration. In addition, the increase in cardiac sympathetic firing during premature ventricular contractions was markedly reduced, from 257 +/- 30% to 70 +/- 17%, before and after administration of captopril. These data indicate that captopril is not only likely to inhibit sympathetic discharge to the heart, but is also likely to restrain the excitatory sympathetic responses to baroreceptor deactivation.

Animals↗