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Biomedical subjects

G Vacca

Publications and source records attributed to G Vacca.

At least 91 records · Page 5Linked to original sources
PubMed1987

The effect of beta-blockade on the transient increase in coronary vascular resistance resulting from haemorrhage.

Abrupt reduction in aortic blood pressure by haemorrhage in the anaesthetized dog has previously been used to assess the effect of elastic recoil and myogenic properties of the coronary vascular wall on diastolic coronary resistance. Using such assessments this study examines whether beta-blockade influences the magnitude of the effect of the vessel wall on coronary resistance. In two groups of dogs abrupt reduction in aortic blood pressure caused by haemorrhage resulted in an initial increase in diastolic coronary resistance, followed by its decline to the control value. In the first group with intact vagi, beta-blockade resulted in a greater initial increase in resistance and attenuation of its subsequent decline. Vagotomy in the second group did not abolish the effect of beta-blockade on diastolic coronary resistance. The findings suggest that during abrupt reduction in perfusion pressure, beta-blockade and reduction in heart rate and coronary blood flow resulted in a greater elastic recoil of the coronary vascular wall associated with an initial increase in diastolic coronary resistance and attenuation of myogenic properties related to return of diastolic coronary resistance to the control level.

Animals↗
PubMed1986

The effect of the coronary vascular wall on the changes in the coronary vascular resistance during a sudden reduction and recovery of the aortic blood pressure.

To demonstrate the effect of elastic and myogenic properties of the vessel wall on the mean coronary vascular resistance during ventricular diastole (m.d.c.r.), this resistance was assessed in twenty dogs anaesthetized with sodium pentobarbitone during a 10 s period of arterial haemorrhage and 20 s of recovery from this haemorrhage. In a first stage of the study ten dogs were investigated following sectioning of the vagal nerves in the neck, beta-blockade, and ligation of the carotid arteries. During haemorrhage and reduction in aortic blood pressure (A.B.P.) in these dogs, there was an initial rise (at 2 s after the start of the haemorrhage) in m.d.c.r. which quickly decreased to a value similar to that obtained during the control period. After the abrupt cessation of haemorrhage, and a rise in A.B.P., there was an initial decrease in m.d.c.r. which eventually increased to the control levels. In the second stage of study identical patterns of changes were obtained in a group of five dogs in which the cervical vagi were not sectioned and beta-blocking agents not given. In another group of five dogs, during infusion of dipyridamole to force maximal coronary vasodilation, the increase in m.d.c.r. was maintained throughout the period of haemorrhage and reduction in A.B.P., and m.d.c.r. did not decrease below the control values following the abrupt cessation of haemorrhage and a rise in A.B.P. The findings in the dogs without dipyridamole infusion suggested that the pattern of changes in m.d.c.r. was due to changes in the perfusion pressure and their effect on the elasticity and myogenic properties of the coronary vascular wall. This suggestion was supported in the second stage of the study, when the reductions in m.d.c.r. were abolished by forcing coronary vasodilation using the infusion of dipyridamole.

Animals↗
PubMed1984

The effect of gaboon viper (Bitis gabonica) venom on cardiac stroke work in the anaesthetized rabbit.

The effect of Bitis gabonica venom administered intravenously in the rabbit at the dose of 0.125 mg/kg (approximately 10% of LD50) has been studied. Venom caused marked changes in cardiovascular parameters principally a precipitous but transient fall in total peripheral resistance and arterial blood pressure. Furthermore in the period occurring between 5 and 30 min after the injection of venom, a transient increase in stroke work was observed as a result of the ejection of an increased stroke volume against a blood pressure which had already returned to normal. Such a transient inotropic effect has also been observed in other small mammals and could be attributed to an adrenergic mechanism.

Animals↗
PubMed1984

Sarcoidosis of the peripheral nerve: clinical, electrophysiological and histological study of two cases.

Two cases of sarcoid polyneuropathy were diagnosed by histological examination of the nerve biopsy. The electrophysiological findings in both patients suggested a neuropathy of axonal type, confirmed by a morphological study of a sural nerve biopsy by light microscopy and on teased-fiber preparations. The sarcoid granulomas were multiple, especially in case 2; they were sparse in the epineurial and perineurial spaces and absent in the endoneurium, whose interstitial component contained cellular infiltrations of scattered macrophages. Blood vessel changes were a constant morphological feature. The mechanisms that possibly contribute to the pathogenesis of the sarcoid neuropathy are discussed in relation to previous reports.

Aged↗
PubMed1983

Cardiac performance in the rabbit as affected by the venom of bitis gabonica. (A preliminary report).

The effect of the venom of Bitis gabonica administered intravenously in the rabbit at the dose of 0.125 mg/kg has been compared with that produced by the same dose of the compound in the dog. In the rabbit the effect on total peripheral resistance, aortic blood pressure and stroke volume is less marked and shorter than in the dog. Furthermore in a period included between 5 and 30 min after the injection, in the rabbit a transient increase of stroke work is observed as a result of the ejection of an increased stroke volume against a blood pressure which has already returned to normal. Such a transient inotropic effect of the venom was also observed in other small mammalians and might be attributed to an adrenergic mechanism.

Animals↗
PubMed1983

Changes in aortic blood pressure and cardiac output curves as induced by stenosis of the descending thoracic aorta.

In 9 anaesthetized open chest rabbits cardiac output and aortic blood pressure were recorded. Cardiac output was obtained by means of an electromagnetic blood flow transducer placed around the ascending aorta. When a 10 sec stenosis of the descending thoracic aorta was produced, an increase of mean, systolic, diastolic and pulse pressure was observed above the stenosis, with a remarkable delay of the peak systolic pressure with respect to the peak velocity of ventricular ejection. Moreover, it is note worthy that during the stenosis the deceleration phase of the ventricular ejection showed a slackening which was responsible for a longer ejection time. Owing to such a longer ejection time, in 4 experiments stroke volume and cardiac output increased above the control in spite of a high aortic impedance. It is probably that the changes observed in the contour of the ventricular ejection curve, depend on modifications of the gradient between left ventricle and aortic blood pressure as well as on the combined effects of the Starling's law and of the afterload.

Animals↗
PubMed1983

Autoregulation of the coronary vascular resistance after beta-adrenergic receptor blockade.

It was previously observed that at the beginning of a 10 sec multiple arterial haemorrhage, vascular elasticity induces an increase of coronary vascular resistance, which in the late part of the haemorrhage is counteracted by the relaxation of the vascular smooth muscle fibres. In the present study the effect of multiple arterial haemorrhage on the coronary vascular resistance was studied after beta-adrenergic receptor blockade. The results suggest that also in these circumstances an elastic mechanism precedes a myogenic mechanism in the regulation of coronary vascular resistance.

Adrenergic beta-Antagonists↗
PubMed1983

The effect of Bitis gabonica (Gaboon viper) snake venom on external iliac and mesenteric arterial circulation in the dog.

The effects of Gaboon viper (Bitis gabonica) venom on external iliac and mesenteric arterial blood flow and resistance were investigated in eight anaesthetized, close-chest dogs. Venom doses in the range 0.125-0.5 mg/kg produced a profound fall in external iliac and mesenteric arterial resistance, which recovered to control values after 30 min. After a third dose of venom, the mean arterial blood pressure failed to recover and the animals died after a period of severe hypotension. External iliac arterial blood flow rose concomitantly with the fall in external iliac resistance and decreased to a value significantly below control after 30 min. Paradoxically, mesenteric blood flow fell during the period of vasodilation. The results suggest that widespread vasodilation of muscle vascular beds (of which the external iliac circulation is representative) leads to shunting of blood away from the less-dilated mesenteric circulation. Venom-induced peritoneal haemorrhage caused a fall in blood volume and increase in viscosity. These undoubtedly contributed to the severe haemodynamic deterioration of the preparations after the third injection of the venom.

Animals↗