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Biomedical subjects

G Vacca

Publications and source records attributed to G Vacca.

At least 73 records · Page 4Linked to original sources
PubMed1994

The effect of distension of the stomach on coronary blood flow in anaesthetized pigs.

The present study was undertaken in anaesthetized pigs to determine whether distension of the stomach reflexly affects coronary blood flow. Experiments were performed on 17 pigs anaesthetized with ketamine and sodium pentobarbitone and artificially ventilated. Coronary blood flow was measured with an electromagnetic flowmeter positioned around the origin of the left circumflex coronary artery. The stomach was distended by injecting 0.8l warm Ringer solution into a balloon positioned within the stomach (mean gastric transmural pressure of about 13 mm Hg). Changes in aortic blood pressure and heart rate were prevented by a pressurized reservoir connected to the left femoral artery and by atrial pacing respectively. Distension of the stomach always caused a decrease in mean coronary blood flow. In five pigs, the magnitude of the decrease in coronary blood flow was graded by step increments in the gastric distending volume from 0.6l to 1l. The response of coronary blood flow was not affected by the administration of atropine (12 pigs), while it was abolished by the administration of bretylium tosylate (eight pigs) and by bilateral vagotomy (eight pigs; four cervical, four subdiaphragmatic vagotomy). These results show that innocuous distension of the stomach in anaesthetized pigs reflexly decreases coronary blood flow. This reflex response is mediated by sympathetic effects and its afferent limb involves the vagal nerves.

Anesthesia, Intravenous↗
PubMed1994

The effect of distension of the stomach on plasma renin activity in the anesthetized pig.

It has recently been shown that distension of the stomach in anesthetized pigs causes reflex hemodynamic responses through efferent sympathetic mechanisms. The present study was undertaken to investigate whether these mechanisms include activation of the renin-angiotensin system. In twelve anesthetized pigs, intragastric balloons were distended for periods of 30 minutes by 0.81 of warm Ringer solution (mean gastric transmural pressure of about 12 mmHg). Changes in arterial blood pressure and heart rate were respectively prevented by a pressurized reservoir connected to the left femoral artery and by atrial pacing. Plasma renin activity was measured during the last minute of distension by radioimmunoassay of angiotensin I. In each of the twelve pigs distension of the stomach caused an increase in plasma renin activity. In five pigs, this response was graded with step increments of the distension. The increase in plasma renin activity to gastric distension was abolished by bilateral subdiaphragmatic vagotomy (six pigs) and by bilateral section of the renal nerves (six pigs). The present study showed that innocuous distension of the stomach in the anesthetized pig reflexly increased plasma renin activity. The afferent limb of the reflex was in the vagal nerves and the efferent limb involved renal nerves.

Animals↗
PubMed1993

The primary reflex effects of distension of the stomach on heart rate, arterial pressure and left ventricular contractility in the anaesthetized pig.

The present study was planned to investigate whether distension of the stomach primarily affects the heart rate, arterial blood pressure and left ventricular inotropic state and to explore the reflex mechanisms involved. In 16 anaesthetized pigs, distension of gastric balloons with 0.81 of Ringer solution (gastric transmural pressure of about 13 mmHg) without controlling any haemodynamic variable caused an increase in arterial blood pressure. When this response was prevented, an increase in heart rate was obtained in each animal. In five pigs, the increase in heart rate was graded by step increments of distension. No significant changes in maximum rate of change of left ventricular pressure were observed in the sixteen pigs during gastric distensions performed whilst preventing changes in heart rate and arterial blood pressure. The responses of arterial blood pressure and heart rate were not influenced by the administration of atropine (four and six pigs respectively), while they were abolished by the administration of bretylium tosylate (ten pigs) and by bilateral vagotomy (six pigs; three cervical, three subdiaphragmatic). The present study showed that gastric distension which was likely to be innocuous in the anaesthetized pig reflexly increased arterial blood pressure and heart rate. The afferent limb of the reflex was in the vagal nerves and the efferent limb involved sympathetic pathways.

Anesthesia↗
PubMed1993

Peripheral blood flows during colorectal distension in anaesthetised dogs.

Distension of the descending colon elicits reflex cardiovascular responses, including increases in heart rate and arterial blood pressure. To study the relative contribution of vasoconstriction in individual vascular beds to this reflex response, experiments were performed on seven dogs anaesthetised with chloralose and instrumented with electromagnetic flowmeters around the superior mesenteric, the left renal and the left external iliac arteries. The colorectal portion of the intestine was distended at constant pressure (36.6 mm Hg, 4.9 kPa mean; range 25-50 mm Hg, 3.3-6.7 kPa) with warm Ringer solution for periods of 2 min. After a set of control distensions, the experiments were performed whilst the reflex rise in arterial pressure was prevented by removal of blood from the arterial tree. In control distensions arterial pressure increased by 11.3 +/- 1.5 mm Hg, 1.51 +/- 0.12 kPa (mean +/- SEM). In distensions at constant arterial pressure, peripheral blood flows were altered to different extents in the three territories studied: vascular resistance increased by 30.8 +/- 5.6% (P < 0.01) in the mesenteric, by 4.1 +/- 1.5% (P < 0.03) in the renal, and by 15.2 +/- 6.8% (NS) in the external iliac bed. We conclude that colorectal distension may reflect activation of a function-specific pathway of the sympathetic nervous system, which leads to much greater vasoconstriction in the splanchnic circulation than in renal or musculocutaneous circulations.

Analysis of Variance↗
PubMed1992

Haemodynamic effects of distension of the descending colon in anaesthetized dogs.

1. This study was undertaken to determine whether distension of the descending colon in anaesthetized dogs reflexly affects the heart rate, arterial blood pressure or the left ventricular inotropic state. 2. Experiments were performed on twenty-six dogs, which were anaesthetized with sodium pentobarbitone and artificially ventilated. A segment of the distal descending colon was isolated and was distended with warm Ringer solution at a steady intraluminal pressure. 3. In each animal, distension of the colon caused an increase in heart rate and aortic blood pressure. The response of an increase in heart rate was augmented by preventing changes in aortic blood pressure, and was graded in seven dogs by step increments in the distending pressure. In the same animals, distension of the colon always caused a small increase in left ventricular (dP/dt)max at constant heart rate and aortic blood pressure. 4. In four of the twenty-six dogs, cutting the pelvic nerves did not abolish the observed responses to the distension. In seven of the twenty-six dogs, which included the four animals with sectioned pelvic nerves, cutting the hypogastric nerves completely abolished all the observed responses. 5. In thirteen of the twenty-six dogs, propranolol or bretylium tosylate completely abolished the reflex increases in heart rate and left ventricular (dP/dt)max, and phentolamine or bretylium tosylate abolished the reflex increase in aortic blood pressure. 6. These results showed that distension of the colon reflexly increased the heart rate, arterial blood pressure and left ventricular inotropic state. These reflex responses were mediated by sympathetic effects and their afferent limb involved the hypogastric nerves.

Animals↗
PubMed1992

Efferent limb of the coronary vasoconstrictor reflex elicited by distension of the descending colon in anesthetized dogs.

Distension of the descending colon elicits reflex coronary vasoconstriction. To study the efferent branch of this reflex, experiments were performed on 5 dogs anesthetized with pentobarbitone. A pouch was formed from the distal 15 cm of the descending colon and distended at constant pressure (54 +/- 8.9 mmHg) with warm Ringer solution from a pressurized bottle. During distensions of the colon, arterial blood pressure and heart rate were kept constant by the withdrawal of blood and pacing of the heart, respectively. Experiments were performed before and after intravenous bretylium tosylate (10 mg/kg), a compound which prevents the outflow of catecholamines from the sympathetic postganglionic neurons. Before chemical sympathectomy, colon distension at constant heart rate and blood pressure caused a decrease in mean coronary blood flow by 7 +/- 3.3% (mean +/- SD, p less than 0.0005). This response was abolished after the administration of bretylium (-0.07 +/- 0.95%, p greater than 0.40). We conclude that the efferent branch of the reflex coronary vasoconstriction elicited by colon distension is through sympathetic nerves.

Animals↗
PubMed1991

The effect of distension of the urinary bladder on coronary blood flow in anesthetized dogs.

To determine whether distension of the urinary bladder reflexly affects coronary blood flow, experiments were performed in eleven dogs anaesthetized with sodium pentobarbitone. Both ureters were cannulated and the urinary bladder was distended with warm Ringer solution at a steady intravesical pressure. Arterial blood pressure was prevented from changing by a pressurized reservoir of warm Ringer solution connected to the femoral arteries. Coronary blood flow was measured with an electromagnetic flowmeter positioned around the origin of the left circumflex coronary artery. When the reflex increase in heart rate was prevented by atrial pacing in seven dogs, distension of the urinary bladder always caused a decrease in mean coronary blood flow. Similar results were obtained in all eleven dogs after administration of propranolol. The decrease in mean coronary blood flow was significantly reduced by atropine or bilateral cervical vagotomy, and was abolished by bretylium tosylate. The results showed that distension of the urinary bladder reflexly decreased mean coronary blood flow, a response involving efferent cardiac vagal and sympathetic pathways.

Animals↗
PubMed1991

The efferent mechanisms of reflex hemodynamic responses to distension of the descending colon in anesthetized dogs.

We have recently shown that distension of the descending colon in anesthetized dogs causes reflex increases in heart rate, aortic blood pressure and the maximal rate of rise of left ventricular pressure, involving afferent pathways in the hypogastric nerves. In this study we have examined the efferent mechanisms involved in those responses. The descending colon was distended using Ringer solution at constant pressure in 13 anesthetized dogs. As previously shown, distension of the colon caused an increase in aortic blood pressure, heart rate and the maximal rate of rise of left ventricular pressure. The increase in the aortic blood pressure was abolished by either bretylium tosylate or phentolamine. Propranolol or bretylium tosylate abolished the increases in heart rate when changes in the aortic blood pressure were prevented, and abolished the increases in the maximal rate of rise of left ventricular pressure when the increases in heart rate were also prevented. These results indicate that the reflex increases in heart rate, arterial blood pressure and the maximal rate of rise of left ventricular pressure involved efferent sympathetic pathways.

Animals↗
PubMed1991

Reflex effects of descending colon distension on coronary blood flow in anesthetized dogs.

To find out whether distension of the descending colon reflexly affects coronary blood flow, experiments were performed in nine dogs anesthetized with pentobarbitone. The descending colon was isolated between ligatures and distended with warm Ringer solution at a steady intraluminal pressure. Arterial blood pressure was prevented from changing by withdrawing blood from the left femoral artery. In two of the nine dogs the arterial blood pressure was also kept constant by tightening a plastic snare round the thoracic aorta. The reflex increase in heart rate was prevented by atrial pacing. Distension of the descending colon at constant heart rate and arterial blood pressure always caused a decrease in mean coronary blood flow, amounting to 2.44 +/- 1.8 ml/min (mean +/- SD), equal to a percent decrease of 14.3 +/- 10.5. This response was completely abolished by section of the hypogastric nerves, thus demonstrating that a reflex mechanism is involved.

Animals↗
PubMed1990

The effect of distension of the urinary bladder on left ventricular inotropic state in anesthetized dogs.

To decide whether distension of the urinary bladder reflexly affects the left ventricular inotropic state, experiments were performed in eight dogs anesthetized with pentobarbitone. After cannulation of both ureters the urinary bladder was repeatedly distended through a urethral catheter with warm Ringer solution at a steady intravesical pressure. The maximal rate of rise of left ventricular pressure (dP/dtmax) obtained at constant heart rate and cardiovascular pressures was used to assess changes in left ventricular inotropic state. Arterial blood pressure was prevented from changing by a pressurized reservoir containing warm Ringer solution and connected to the femoral arteries. Following prevention of the reflex increase in heart rate by atrial pacing, distension of the urinary bladder always increased the maximal rate of rise of left ventricular pressure in the eight dogs. There were no significant changes in left ventricular systolic or end-diastolic pressures. The increase in maximal rate of rise of left ventricular pressure was abolished following the administration of propranolol. The results indicate that a reflex increase in left ventricular inotropic state occurred in response to distension of the urinary bladder. This reflex response involved beta-adrenergic stimulation.

Animals↗
PubMed1989

Efferent limb of the atrial receptor reflex decrease in plasma renin activity in anaesthetized dogs.

The efferent limb of the reflex response of a decrease in plasma renin activity in response to stimulation of atrial receptors was examined in two groups of experiments in anaesthetized dogs. The atrial receptors were discretely stimulated by distension of small balloons in the left pulmonary vein-atrial junction and in the atrial appendage. In the first group, in which the responses of tachycardia and natriuresis were blocked, the diuretic response was accompanied by decreases in plasma renin activity. This decrease was abolished in the second group by renal denervation. The results have shown that the efferent limb of the response of a decrease in plasma renin activity involved the renal nerves.

Animals↗
PubMed1989

The effect of distension of the urinary bladder on activity in efferent renal fibres in anaesthetized dogs.

1. To test whether distension of the urinary bladder causes a consistent change in activity in efferent renal nerve fibres, bladder distension was performed in anaesthetized dogs. The carotid sinuses were vascularly isolated and perfused with blood at constant flow. Both ureters were cannulated and the urinary bladder was distended with warm Ringer solution at a steady intravesical pressure. 2. In a first series of experiments all twenty-six renal nerve fibres in eleven dogs which responded to changes in carotid sinus pressure and changes in the nature of the blood perfusing the carotid sinuses also responded to distension of the bladder. 3. In a second series of experiments, graded bladder distension over a range of pressure of 0-9.2 kPa led to a graded increase in activity in thirteen efferent renal fibres in six dogs. The magnitude of the renal nerve response was greater at low than at high carotid sinus pressure. Over a range of carotid sinus pressure of 9-30 kPa, the greatest renal nerve activity was obtained at the lower end of this range in the presence of bladder distension. 4. Thus distension of the urinary bladder resulted in the response of a consistent increase in efferent renal nerve activity, which could be graded according to intravesical pressure. The magnitude of the responses to bladder distension was affected by carotid sinus pressure.

Action Potentials↗
PubMed1989

EEG and spectral analysis in HIV immunocompetent patients free from clinical CNS impairment. A follow-up study in 20 cases.

Twenty HIV immunocompetent subjects without neurological symptoms were studied by EEG and spectral EEG analysis over a period of 6-16 months. 40% of them showed mild diffuse changes in background activity on basal evaluation, but the appearance of neurological symptoms and the evolution of clinical picture seemed unrelated to the presence of aspecific EEG and spectral analysis changes. As most of them were oppiate abusers, these findings could be ascribed to the long-term drug use.

AIDS Dementia Complex↗
PubMed1988

Effect of tachycardia and constriction of left circumflex artery on coronary flow and pressure in anaesthetized dogs.

1. The effect of graded changes in heart rate between 100 and 160 beats/min and constriction of the left circumflex coronary artery which reduced coronary blood flow was examined in seven anaesthetized and artificially ventilated dogs in the absence of significant changes in aortic blood pressure. Mean diastolic coronary blood flow, and the difference between the mean diastolic pressures in the coronary artery and the left ventricle were related to the increase in heart rate. 2. In all seven dogs diastolic coronary blood flow showed linear increases with heart rate increments with and without coronary narrowing which averaged 70 and 82% respectively. 3. A significant shift to the right in the relation between heart rate and mean diastolic coronary blood flow occurred with each grade of coronary constriction. Coronary blood flow became lower at any given heart rate. 4. The shift to the right in the relation between heart rate and coronary blood flow was associated with decreases in the difference between the mean diastolic pressures in the coronary artery and the left ventricle which accompanied the increase in heart rate. 5. The results suggest that increases in heart rate can enhance diastolic coronary blood flow despite coronary narrowing which reduced flow, possibly through dilatation in myocardial blood vessels.

Anesthesia, General↗
PubMed1987

Simple physical model of coronary vasodilation.

The coronary diastolic pressure-flow relationship was studied in two groups of dogs; in one group coronary circulation was characterized by normal tone of vascular smooth muscle, while in the other group, complete relaxation of smooth muscle fibres was produced by intravenous infusion of dipyridamole. The coronary flow (CF) was measured in both groups for several values of mean aortic blood pressure (ABP), the variations being obtained by means of a 10 s arterial haemorrhage. The measured CF versus ABP data were found to be well represented by best fit curves calculated by power regression methods. These curves were quite different in the presence and absence of dipyridamole infusion. A simple physical model is proposed for analysis of these curves; the model is based on the Poiseuille equation, modified to take into proper account the variations of the vessel radii under different ABP values during ventricular diastole. These variations are expressed by means of Laplace and Hooke's laws by equating wall tension due to APB, to the sum of tensions due to elastic and smooth muscle forces. Analysis of CF versus APB curves, performed on the basis of this model, shows that to account for the large change of coronary bed conductance observed under dipyridamole infusion one must assume not only that the smooth muscle tone is absent but also that some relevant variations occur in the whole coronary bed, thus pointing to possible recruitment of new blood vessel paths.

Animals↗