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Biomedical subjects

A Malliani

Publications and source records attributed to A Malliani.

At least 109 records · Page 6Linked to original sources
PubMed1993

[The effects of chronic cilazapril treatment on sympathetic vasomotor tonus: a spectral analysis study of pressure variability].

Animal experiments suggest that an important component of the antihypertensive effects of ACE inhibitors might derive from an inhibition of the sympathetic vasomotor tone. We addressed this problem on 22 mildly hypertensive subjects (48 +/- 2 years; arterial pressure 151 +/- 3/95 +/- 1 mmHg), in whom sympathetic vasomotor tone was non invasively inferred by the power of the low frequency component (0.1 Hz) of the spontaneous oscillations of systolic arterial pressure (LFSAP), during placebo and after 4 weeks of treatment with a new ACE inhibitor, cilazapril, 5 mg per os oid. LFSAP was computed at rest and during physical (active orthostatism) and mental (computerized attentional test and mental arithmetic) stimuli capable of enhancing sympathetic drive. Cilazapril treatment reduced resting arterial pressure to 128 +/- 3/80 +/- 2 mmHg, without affecting heart rate (78 +/- 2 and 74 +/- 2 b/min, respectively). The increases in LFSAP produced by standing were significantly greater during placebo than during active treatment (delta LFSAP = 10 +/- 3 and 5 +/- 2 mmHg2, respectively). These data suggest that an important reduction of sympathetic vasomotor tone accompanies the antihypertensive effects of chronic ACE-inhibitor treatment.

Blood Pressure↗
PubMed1992

Circadian variation of spectral indices of heart rate variability after myocardial infarction.

The circadian variations of spectral indices of heart rate variability were analyzed in 20 patients 4 weeks after a first and uncomplicated myocardial infarction (MI) and in 20 control subjects. R-R interval and variance showed a characteristic day-night pattern with a significant reduction of the latter parameter in patients after MI (10,967 +/- 1109 msec2 vs 16,860 +/- 2132 msec2). Control subjects were characterized by a predominance of low-frequency (approximately 0.1 Hz) component during the day and of high-frequency (approximately 0.25 Hz) component during the night, which reflected the expected 24-hour pattern of variation of sympatho-vagal balance. A 24-hour elevation (64 +/- 3 normalized units [nu] vs 56 +/- 2 nu; p less than 0.05) of the low-frequency component and a smaller (23 +/- 2 nu vs 32 +/- 2 nu; p less than 0.05) high-frequency component during the night differentiated patients after MI from subjects. The difference between the two groups was even more evident when the 24-hour sympatho-vagal balance was assessed with the low frequency/high frequency ratio. Thus spectral analysis of heart rate variability indicates that in patients after MI there is an alteration of neural control mechanisms as indicated by the presence of signs of sympathetic activation and by the attenuation of the nocturnal increase in vagal tone.

Aged↗
PubMed1992

Spectral analysis of sympathetic discharge, R-R interval and systolic arterial pressure in decerebrate cats.

In 19 decerebrate and artificially ventilated cats, we analyzed, with a power spectral methodology, the variability simultaneously present in R-R interval and in thoracic preganglionic sympathetic outflow. R-R interval was characterized, as already described in humans and other experimental preparations, by two rhythmic components occurring at a frequency of about 0.1 Hz (low-frequency, LF) and at one corresponding to respiratory rate (high-frequency, HF) which, in these experiments, was set at 0.32 Hz. Two similar rhythmic components were also present in the sympathetic discharge. Arterial pressure changes were produced by aorta or vena cava flow obstruction in order to produce reflex responses in sympathetic activity. Reflex sympathetic excitations induced an increase in the LF component of both R-R interval and sympathetic discharge variabilities, while the HF components were simultaneously reduced. In contrast, reflex sympathetic inhibitions were accompanied by a decrease in LF components of both variability signals, while the HF components were simultaneously increased. A significant and positive correlation was found between changes in impulse activity and the amplitude of LF component of either R-R interval or sympathetic discharge variabilities. These data support the hypothesis that the low-frequency component of R-R variability can be used as a marker of sympathetic modulation.

Animals↗
PubMed1992

Effects of chronic cilazapril treatment on cardiovascular control: a spectral analytical approach.

In 11 subjects with mild hypertension (sitting arterial pressure of 146 +/- 5/97 +/- 2 mm Hg), the effects of chronic angiotensin-converting enzyme (ACE) inhibition (cilazapril, 5 mg p.o. once daily for 4 weeks) were studied at rest and during active standing by means of spectral analysis. Sympathetic vascular control was inferred from the power of the low-frequency (LF) component of the systolic arterial pressure (SAP) variability, assessed noninvasively with a plethysmographic technique. Simultaneously, quantitative indices of neural control of the sinoatrial (SA) node were obtained with the power of the LF and of the high-frequency (respiration linked) component of R-R variability. Before treatment, active standing produced a clear increase in the LF components of R-R and SAP variabilities. At the end of the 4 weeks of cilazapril treatment, the LF component of SAP variability during standing was significantly lower than prior to treatment, while the increase in the LF component of R-R variability was left unchanged. These findings suggest an inhibitory effect of chronic ACE inhibition upon vasomotor sympathetic control, as assessed non-invasively by this technique.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Analysis of neural mechanisms accompanying different intensities of dynamic exercise.

The neural mechanisms accompanying dynamic exercise of different intensities were analyzed in dogs and human subjects by means of autoregressive spectral analysis of heart period and arterial pressure variabilities. In the animal experiments, 8 conscious dogs were examined after implanting a solid state pressure gauge in the left ventricle. Animals were examined at rest and during a treadmill run, at 4 km/h, and 0 degrees incline. The experiments were repeated after chronic alpha 1-adrenoreceptor blockade. During the treadmill run, heart rate and systolic left ventricular pressure increased significantly. Simultaneously, the low frequency (LF, 0.1 Hz) component of pulse interval and of systolic pressure variabilities, ie, markers, respectively, of sympathetic modulation of the SA node and of vasomotor activity, increased significantly (evaluated respectively, in normalized and absolute units). After chronic alpha 1-adrenoreceptor blockade, the increase in LF component of systolic pressure variability was prevented, while that observed in R-R interval variability was maintained. Human studies were carried out with either invasive or noninvasive techniques. In the former approach already described, performed in young hypertensive subjects, arterial pressure was recorded with a high fidelity technique. In the second approach applied to young champion swimmers, only the variability of the R-R interval was examined. In both studies, moderate levels of exercise were accompanied by an increase in the LF component of the spectrum: in the case of arterial pressure variability, this increase was detectable both in absolute and normalized units; vice versa, in the case of R-R variability, since physical exercise is accompanied by a marked abatement of the variance, normalized units had to be used in order to evaluate the shift of the sympathovagal balance in favor of sympathetic overactivity.

Adolescent↗
PubMed1992

[A noninvasive assessment of the gain in baroceptor control of the heart rate in man].

In this study we addressed the problem of the noninvasive evaluation of the overall gain of baroreceptor control of heart period. We studied a population of healthy controls (n = 49, age 30 +/- 2 years, systolic arterial pressure [by Finapres] 114 +/- 1 mmHg) and a group of mild hypertensive subjects (n = 14, age 51 +/- 2 years, systolic arterial pressure 151 +/- 5 mmHg). Subjects were studied at rest both in absence and in presence of chronic beta-adrenergic receptor blockade (atenolol: controls 50 mg po oid x 4 days; hypertensives 100 mg po oid x 2 weeks). Spectral analysis of RR interval and of systolic arterial pressure variabilities provided noninvasive markers of autonomic control of the SA node and of the vasculature. The index alpha, obtained from bivariate cross spectral and spectral analysis provided a quantitative assessment of the closed loop gain of baroreceptor control of the heart period. The index alpha resulted more elevated in the normotensive than in the hypertensive group. Additionally it appeared significantly increased at the end of the treatment with the beta-adrenergic blocking drug atenolol. Furthermore, alpha appeared significantly and negatively correlated with age, systolic arterial pressure and, although weakly, with low frequency; it was positively correlated with the average RR interval. In conclusion, this study suggested an important link between the average level of sympathetic activity and baroreceptor control of heart rate in normotensive and mild hypertensive subjects. The clinical importance of this sympathetic modulation of the gain of the heart period/arterial pressure relationship can now be assessed with this noninvasive approach.

Adult↗
PubMed1992

[The role of mitral regurgitation in the neurovegetative regulation of mitral valve prolapse].

To define the role of mitral regurgitation (MR) on sympatho-vagal balance in mitral valve prolapse (MVP) patients, we analyzed 41 ambulatory MVP symptomatic patients. Twenty-seven patients (4 males, 23 females, aged 34 +/- 3 years) had significative MR assessed color Doppler, while 14 patients (5 males, 9 females, aged 29 +/- 3 years) had no MR; 36 age- and sex-matched subjects were studied as controls (C). Spectral analysis of heart rate variability (HRV) was performed at rest and during sympathetic activation (tilt). In the whole group of MVP patients spectral components did not differ significantly from C at rest and during tilt. When patients were subdivided in relation to the presence (+) or absence (-) of MR, HRV revealed in MR+ patients at rest an increased high frequency (HF) and a diminished low frequency (LF) component (47 +/- 5 and 41 +/- 5 normalized units, nu) with respect to C (34 +/- 3 and 54 +/- 3 nu, p < 0.05, respectively). Viceversa during tilt, in MR+ patients it was possible to observe a LF increase greater than in C (delta LF: 36 +/- 4 versus 25 +/- 3 nu, p < 0.05). As HF component is currently interpreted as a marker of vagal modulation of HRV, our results suggest an increased vagal tone associated with MR possibly due to stimulation of atrial vagal receptors; moreover, an increased sympathetic responsiveness to tilt seems to characterize MR+ patients.

Adult↗
PubMed1992

Power spectral analysis of RR variability.

The analysis of beat-to-beat spontaneous oscillations of heart rate variability is a recent and noninvasive approach capable of providing important information on neural mechanisms controlling cardiovascular function. In particular, with spectral analysis of RR variability, two major components can be detected at low (LF, approximately 0.1 Hz) and high (HF, approximately 0.25 Hz) frequency. They have been demonstrated to be appropriate indices of, respectively, sympathetic and parasympathetic modulations of heart period. In control subjects, at rest, LF is slightly predominant over HF. In post myocardial infarction patients there is a predominant LF and a diminished HF that suggests an alteration of sympatho-vagal balance with a predominance of sympathetic tone. This approach, by providing indices of sympathetic and vagal neural regulatory outflows, appears adequate to evaluate several pathophysiological conditions such as ischemic heart disease, hypertension or congestive heart failure, which are characterized by important alterations of neural regulatory mechanisms.

Electrocardiography↗
PubMed1991

Impaired heart rate variability in patients with chronic Chagas' disease.

Spectral analysis of heart rate variability was used to investigate the possible alteration in sympathovagal control of heart rate in patients with Chagas' disease. The study included 31 subjects, divided into three groups: controls, Chagas' 1 (subjects with only positive serology for Chagas' disease) and Chagas' 2 (subjects with positive serology and electrocardiographic abnormalities that are usually found in this disease). The subjects were studied during rest, while standing, and during handgrip exercise. With this approach, the low frequency (approximately 0.1 Hz) spectral component of R-R interval variability is considered to be a marker primarily of sympathetic activity, whereas the high frequency (approximately 0.25 Hz) component, which is related to respiration, seems mainly to reflect vagal activity. We observed significant (p less than 0.05) differences among the three groups during standing: although in the control subjects the low-frequency component increased (delta = 30 +/- 5 normalized units, nu), there was no increase in Chagas' 1 (delta = -1 +/- 8 nu) and Chagas' 2 (delta = -2 +/- 8 nu) patients. During handgrip exercise, another test that is capable of exciting sympathetic outflow, there was an increase of low frequency only in control subjects. These results confirm the occurrence of quantitative and assessable abnormalities in the neural control of heart rate variability in Argentinian patients with chronic Chagas' disease, even in the absence of heart failure.

Chagas Disease↗
PubMed1991

Assessment of the neural control of the circulation during psychological stress.

In this study, we used spectral analysis of short-term R-R and systolic arterial pressure (SAP) variabilities to estimate the changes in neural control of the circulation produced by psychological stress. The 0.1 Hz low-frequency (LF) component of R-R and SAP variabilities provided a quantitative index of the sympathetic activity controlling heart rate and vasomotion. Conversely the high-frequency (HF) respiratory component of R-R variability provided an index of vagal tone. In conscious dogs we used the seemingly stressful situation of being accompanied for the first time to the experimental laboratory as a stimulus. In human subjects we used mental arithmetic. In both cases LF of R-R and SAP variabilities increased significantly suggesting enhanced sympathetic activity both to the SA node and the vasculature. In man, the index alpha, a measure of the overall gain of baroreceptor mechanisms, was found to be reduced during mental arithmetic. Spectral analysis of cardiovascular variabilities thus suggests that in man and in conscious dogs psychological challenges induce a profound re-arrangement of neural control of the circulation, which appears to be characterised by sympathetic predominance and which can be monitored by this technique.

Adult↗
PubMed1991

Altered pattern of circadian neural control of heart period in mild hypertension.

We addressed the problem of the circadian changes in neural control of heart period in ambulant hypertensive subjects. A running spectral analysis of R-R variability from Holter tapes provided markers of sympathetic, i.e. low-frequency component (LF) almost equal to 0.10 Hz, and vagal, i.e. high-frequency component (HF) almost equal to 0.25 Hz, controlling activities for the 24-h period of the recording. Significant circadian differences were observed in LF between the two groups of subjects: during night-time rest (0300-0400 h), LF was greater in hypertensives than in normotensives (56 +/- 2 and 48 +/- 2 nu, respectively; P less than 0.05). Furthermore, the difference between daytime and night-time LF values was progressively reduced with increasing severity of the hypertensive state, as assessed by resting arterial pressure levels. Spectral analysis of R-R variability suggests that essential hypertension may be characterized by a reduced day-night oscillation in sympathetic activity than can be quantified non-invasively using this approach.

Adult↗
PubMed1991

Cardiovascular neural regulation explored in the frequency domain.

A consistent link appears to exist between predominance of vagal or sympathetic activity and predominance of HF or LF oscillations, respectively: RR variability contains both of these rhythms, and their relative powers appear to subserve a reciprocal relation like that commonly found in sympathovagal balance. In this respect, it is our opinion that rhythms and neural components always interact, just like flexor and extensor tones or excitatory and inhibitory cardiovascular reflexes, and that it is misleading to separately consider vagal and sympathetic modulations of heart rate. In humans and experimental animals, functional states likely to be accompanied by an increased sympathetic activity are characterized by a shift of the LF-HF balance in favor of the LF component; the opposite occurs during presumed increases in vagal activity. In addition, LF oscillation evaluated from SAP variability appears to be a convenient marker of the sympathetic modulation of vasomotor activity. Although based on indirect markers, the exploration in the frequency domain of cardiovascular neural regulation might disclose a unitary vision hard to reach through the assemblage of more specific but fragmented pieces of information.

Animals↗
PubMed1991

[The excitatory effect of adenosine on the discharge activity of the afferent cardiac sympathetic fibers].

Recent clinical observations suggest that adenosine may produce cardiac pain; even though the mechanisms involved still need defining, one of the most convincing hypotheses seems to be a direct adenosine stimulation of the sympathetic nerve endings present in the myocardium. In 10 decerebrate and artificially ventilated cats, single sympathetic afferent fibres innervating the left ventricle were isolated from the third white thoracic ramus communicans of the left sympathetic chain. After locations of the fibre receptor field on the cardiac surface, we evaluated the effects of the local epicardial application of adenosine (0.1, 1 and 10 mg/ml) on the nervous discharge activity. These results were compared with those obtained by application of bradykinin, a potent natural algogenic substance which activates sympathetic afferents, and by a mechanical stimulus such as a slight increase of systolic arterial pressure (46 +/- 6% from 113 +/- 18 mmHg) induced by partial occlusion of the thoracic aorta. In particular, adenosine (1 mg/ml) elicited a significant increase in impulse activity (from 0.11 +/- 0.02 to 0.36 +/- 0.06 imp/0.1 s) with a latency of 16 +/- 2 s. Bradykinin application (20 micrograms/ml), in the same way, produced a significant increase in impulse activity (from 0.11 +/- 0.01 to 0.86 +/- 0.16 imp/0.1 s) with a latency of 8 +/- 1 s. Neither situation showed significant hemodynamic changes. An increased neural discharge (from 0.11 +/- 0.02 to 0.26 +/- 0.04 imp/0.1 s) was also observed during aortic occlusion. After purinergic receptor blockade by aminophylline (5 mg/kg, iv), the response to adenosine was no longer observed, while responses to bradykinin and aortic occlusion were unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗