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Biomedical subjects

A Malliani

Publications and source records attributed to A Malliani.

At least 181 records · Page 10Linked to original sources
PubMed1979

Positive feedback sympathetic reflexes and hypertension.

A pressor reflex that can be elicited from the thoracic aorta in conscious dogs is described. Distension of the aorta excites sympathetic afferent fibers and results in an increase in arterial blood pressure because of increased sympathetic outflow to the heart and blood vessels. The reflex center for this positive feedback mechanism is located in the spinal cord and, when the reflex is activated, it can modulate other negative feedback control systems.

Animals↗
PubMed1979

A sympathetic pressor reflex in the conscious dog.

1. The effects of mechanical activation of aortic sympathetic sensory fibres have been studied in conscious dogs. 2. A cannula covered by an inflatable rubber balloon, previously implanted in the descending thoracic aorta, was used to stretch the aortic walls without obstructing blood flow. 3. Aortic stretch significantly increased mean arterial blood pressure and heart rate from control values in the absence of pseudo-affective reactions. 4. This response indicates that positive feedback sympathetic reflexes are operative in the conscious, fully innervated animal.

Animals↗
PubMed1979

Afferent sympathetic unmyelinated fibres with left ventricular endings in cats.

1. We recorded the electrical impulse activity of thirty-three single afferent fibres with left ventricular endings from the third and fourth left thoracic sympathetic rami communicantes of anaesthetized cats. Their conduction velocity ranged from 0.23 to 0.98 m/sec (group C). 2. The endings of each fibre were localized to the left ventricle by mechanical probing performed at the end of the experiment on the non-beating heart. No fibre had multiple sensory fields. 3. The impulse activity (0.95 +/- 0.2 impulses/sec) was spontaneous but most often a fixed temporal correlation between impulses and ventricular dynamics was not detectable. It was increased during occlusion of the thoracic aorta, I.V. administration of isoprenaline or infusion of saline. It was unaffected by asphyxia, haemorrhage and I.V. administration of acetylcholine. It was decreased during occlusion of inferior vena cava. Therefore these ventricular receptors appeared to be mainly sensitive to mechanical events. 4. The fibres were excited during the occlusion of the left main coronary artery, after a latency of 14.5 +/- 1.3 sec. They were also excited during ventricular fibrillation, exhibiting the highest values of impulse activity (2.51 +/- 0.4 impulses/sec). The increase in impulse activity during ventricular fibrillation was sometimes immediate and extreme, with peak frequencies of about 50 impulses/sec. 5. These spontaneously active ventricular receptors with unmyelinated nerve fibres participate in the transmission of the continuous impulse activity which from the cardiovascular system reaches the spinal cord through the sympathetic nerves and which is likely to contribute to the neural control of circulation. Thus the unmyelinated cardiac sympathetic afferents should not be considered as purely nociceptive in function.

Action Potentials↗
PubMed1976

Afferent sympathetic nerve fibres with aortic endings.

1. We recorded the electrical impulse activity of thirty-five single afferent fibres with aortic endings isolated from the third to the sixth left thoracic sympathetic rami communicantes of anaesthetized cats. The endings of each fibre were localized by mechanical probing of the opened aorta at the end of each experiment. 2. Twenty-four fibres had a single aortic receptive field. Eleven fibres had several and distinct receptive fields (from two to four): they were usually located in nearby aortic areas or, in addition, in other proximal portions of the arterial tree or in the adjacent pleura and connective tissue. 3. Twenty-nine fibres had conduction velocities ranging between 5 and 27 m/sec (Group Adelta), while six fibres had conduction velocities between 0-2 and 1-2m/sec (Group C). 4. The spontaneous impulse activity was in phase with the aortic pressure pulse and consisted of not more than one impulse per pressure pulse. It was increased during increases in aortic pressure and, conversely, decreased during decreases in aortic pressure. In vivo and post mortem studies showed that these mechanoreceptors had an impulse activity which rapidly adapted during sustained stimuli. They thus seem to signal pulsatile aortic stretch. 5. These aortic sympathetic afferents are likely to be part of a nervous pathway through which pressor reflexes, exhibiting positive feed-back characteristics, can elicited.

Action Potentials↗
PubMed1976

Reflex sympathetic tachycardia during intravenous infusions in chronic spinal cats.

The reflex tachycardia elicited by rapid intravenous infusions of a blood substitute was studied in 21 chronic cats with spinal sections at C8. All animals could breath spontaneously. The day after section the average resting heart rate (HR) and arterial pressure (AP) were 109 beats/min and 98/67 mmHg, respectively. Vagal blockade with atropine (0.5-0.7 mg/kg iv) was performed prior to each infusion, increasing the average HR To 127 beats/min. In 39 infusions in 21 cats the average increase in HR was 10 beats/min (range from -6 to +22 beats/min). A tachycardia was observed in all but five trials, four of which were obtained in two cats that subsequently responded with a tachycardia. In seven animals the neural circuit mediating the response was partially or totally interrupted by section of several thoracic dorsal roots (T1-T4 or T1-T6) and of the spinal cord at the inferior level of these sections (between T6 and T7). The tachycardia response was progressively reduced and finally abolished by these procedures. These experiments indicate that spinal neural mechanisms are likely to contribute to the phenomenon first described by Bainbridge.

Animals↗
PubMed1976

Mechanical stimuli exciting type A atrial vagal receptors in the cat.

The activity of type A right atrial vagal receptors was recorded from the right cervical vagus in cats anesthetized with sodium pentobarbital, immobilized with gallamine, and with their chests open. Nerve impulses initiated by receptor activation were recorded simultaneously with instantaneous right atrial pressure and dimensional changes under various hemodynamic conditions. Atrial volume changes induced by infusion of saline, bleeding, and occlusion of the inferior vena cava did not alter consistently the systolic activity of the receptors. Electrical stimulation of the right stellate ganglion significantly increased the frequency of discharge during systole, whereas electrical stimulation of the left thoracic vagus significantly reduced the frequency of discharge. These inotropic interventions produced similar effects when the heart was paced at a fixed rate. Pacing the right atrial appendage increased the systolic discharge of the receptors only when at high rates the atrium contracted against closed atrioventricular valves. To investigate the influence of tonic efferent sympathetic activity on spontaneous receptor discharge, three receptors were studied before and after bilateral surgical stellectomy, and in cats with their chest closed three receptors were studied before and after infusion of propranolol. Both of these interventions markedly reduced the systolic activity. In addition to having effects on systolic activity, injection of saline, vagal stimulation, and sympathetic "denervation" always activated the receptors during filling. Our results indicate that: (1) the systolic discharge of type A receptors is a function of the active tension developed by atrial muscle during contraction; and (2) the pattern of discharge of the receptors during the atrial cycle depends on both the degree of atrial distention and the state and extent of contraction.

Animals↗
PubMed1975

Electrical alternation of the T-wave: clinical and experimental evidence of its relationship with the sympathetic nervous system and with the long Q-T syndrome.

In a patient affected by the "long Q-T" syndrome we observed episodes of alternation of the T-wave associated with emotional or physical stresses. In anesthetized and vagotomized cats, we could reproduce both the lengthening of the Q-T interval and episodes of alternation of the T-wave by electrical stimulation of the left stellate ganglion. Our experiments provide further support on the relationships between the "long Q-T" syndrome and the sympathetic nervous system and indicate that alternation of the T-wave may depend on abrupt increases in the sympathetic discharge.

Animals↗
PubMed1975

The long Q-T syndrome.

Recent clinical and experimental data on the long Q-T syndrome (LQTS) are presented and discussed. The pathogenesis of LQTS is dependent on an imbalance between various components of the cardiac sympathetic innervation. A congenital decreased activity through the right cardiac sympathetic nerves seems to be the more likely pathogenetic mechanism for the majority of cases. Other forms of sympathetic imbalance, including left or even right hyperactivity, are, however, possible in isolated cases. Beta-blockers, at full blocking dose, represent the therapy of choice and are greatly effective in reducing the mortality (from 73 per cent to 6 per cent). If syncopal attacks are not eliminated by the medical therapy, the the ablation of the left stellate ganglion along with the first thoracic ganglia is the most rational and specific therapy. The possiblity for the correctly diagnosed and treated patients to escape an otherwise impending death calls urgently for diffusion of the knowledge about the long Q-T syndrome.

Adolescent↗
PubMed1975

Spinal sympathetic reflexes in the cat and the pathogenesis of arterial hypertension.

1. In vagotomized anaesthetized cats with both common carotid arteries occluded, stretch of the thoracic aorta induced reflex increases in arterial blood pressure, heart rate and left ventricular dP/dtmax. Similar responses were obtained in cats with spinal transection at the level of the first cervical nerve roots. 2. The hypothesis is advanced that sympathetic excitatory reflexes may contribute to the maintenance of hypertension through positive feedback.

Animals↗
PubMed1975

Reflex sympathetic changes in aortic diastolic pressure-diameter relationship.

In anesthetized vagotomized cats with the chest opened and artificially ventilated, aortic blood pressure (AP) and external diameter (AD; ultrasound technique) were measured in the proximal third of the descending thoracic aorta. Slow sinusoidal oscillations (0.2-0.3 Hz in aortic volume were produced by a piston pump connected to a femoral artery. Diastolic pressure-diameter relationship (PDR) curves were obtained during control conditions and during stimulation of either the cut central end of the left inferior cardiac nerve (ICN) or the decentralized thoracic sympathetic chain (SC). In six cats with both carotid arteries occluded ICN stimulation reflexly shifted the PDR curves to lower diameters for any given pressure (mean deltaAD 3.2% at control AP). A smaller response to ICN stimulation was obtained in five cats with one patent carotid artery (mean deltaAD 2.3% at control AP). Stimulation of sympathetic efferents to the aorta (SC) caused similar responses in five animals (mean deltaAD 3.4% at control AP). This reflex control of the thoracic aorta may be involved in cardioaortic coupling and may influence the sensitivity of aortic mechanoreceptors.

Animals↗
PubMed1975

Response of type B atrial vagal receptors to changes in wall tension during atrial filling.

In anesthetized curarized cats with their chests open, we recorded the activity of type B right atrial vagal stretch receptors, right atrial pressure, and instantaneous dimensional changes of the right atrium. The nervous activity was analyzed during alterations in atrial dynamics produced by acute volume loading of the right atrium under control conditions and during sympathetic and vagal stimulations. Our results demonstrated that the mean frequency of discharge in the burst was dependent on the absolute tension and the rate of change in tension developed in atrial muscles during filling. The responses of different receptors to changes in atrial dynamics were qualitatively similar but characteristic for each receptor studied. In some experiments nervous activity was recorded after the cats had been killed: static and dynamic changes in atrial tension were then produced by injecting blood into the right atrium. Under these conditions dynamic stimuli always activated the receptors at tensions below the threshold for static stimuli. During dynamic stimuli the instantaneous firing rate was always higher than it was during static stimuli applied at the same level of tension. This study indicates that the nervous activity of type B atrial vagal receptors is closely dependent on static and dynamic changes in atrial wall tension.

Animals↗