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Biomedical subjects

F Magrini

Publications and source records attributed to F Magrini.

At least 55 records · Page 3Linked to original sources
PubMed1992

Prolonged water immersion. Effects on blood pressure maturation in normotensive rats.

The purpose of this experiment was to study the impact of simulated microgravity and of chronic removal of hydrostatic pressure gradients on blood pressure maturation and body growth in rats. A special device was developed in our laboratory to transfer prolonged "dry" water immersion (a technique that has been used for training astronauts under hypogravic conditions) to six Sprague-Dawley test rats (immersion-G group). The time course of heart rate, systolic blood pressure, urinary output, and body weight was monitored from weaning to maturity and then compared with those responses from six sex- and age-matched Sprague-Dawley rats grown in a gravity environment (group G). A downward shift in systolic blood pressure and body weight maturation curves was observed in immersion-G rats from the age of 60 days. Cessation of dry water immersion produced a gradual, significant rise in systolic blood pressure but not in body weight to control values. No marked changes in heart rate and urinary output between G and immersion-G rats were noticed throughout the investigation. Our results provide indirect evidence that an interference in the natural history of blood pressure maturation was introduced by immersion, which dissociated the effects of body weight increase during growth from the effects of ageing per se. It is concluded that the physiological increase in systolic blood pressure during growth is partly gravity-dependent.

Animals↗
PubMed1992

Acute effects of cilazapril on coronary hemodynamics in patients with renovascular hypertension.

The effects of converting enzyme inhibition on coronary and systemic hemodynamics in the presence of a chronically activated renin-angiotensin system were investigated in five renovascular hypertensive patients with no ECG/echocardiographic evidence of left ventricular hypertrophy. Coronary blood flow (CBF, thermodilution technique), intra-arterial blood pressure, AVO2 difference (coronary sinus), heart rate, and coronary vascular resistance were measured at rest, during isometric exercise (handgrip to 50% of maximal effort for 3 min) before and 60 min after 2.5 mg of oral cilazapril. The drug induced a prompt, significant decrease in mean arterial pressure and a sustained increase in CBF. The performance of handgrip after cilazapril resulted in higher increases in CBF for a given increase in myocardial oxygen requirements. These observations suggest that angiotensin II (Ang II) maintains the ability to alter the control mechanisms of CBF even under long-term conditions and that converting enzyme inhibition reverses the Ang II-induced effects on coronary hemodynamics.

Adult↗
PubMed1989

A percutaneous approach to cardiac haemodynamics in anaesthetised rats.

Established methods for evaluating cardiac function in small animals involve surgical manoeuvres. We describe a method for evaluating left ventricular volume (LVV) and pressure (LVP) in anaesthetised adult rats. Under fluoroscopic control a 23 G needle was inserted into the left ventricular cavity of anaesthetised normotensive WKY rats. LVV was determined by biplane angiography and LVP was measured directly. Surface electrocardiograms were recorded throughout the procedure. In 8 animals the study was repeated three times, one week apart. Animals were then sacrificed and tissues harvested for histological examination. In 8 rats, the technique was found to be reproducible and there was no evidence of functional (ECG) or pathological myocardial damage following repeated measurements. In conclusion this technique provides a reproducible method of measuring LVV and LVP, allowing longitudinal haemodynamic studies in anaesthetised rats.

Anesthesia, Intravenous↗
PubMed1989

Cardiac responses to head up tilt during early extrauterine life: relevance of active acquisition of erect posture.

Mammals must adapt to gravity on passing from the intrauterine to the extrauterine environment. In order to evaluate the cardiovascular effects of gravity in the first phases of extrauterine life, the effects of passive orthostatism on the cardiac filling volume were investigated through longitudinal haemodynamic studies in 14 normal healthy males before (6 months) and after (18 months) acquiring the ability to stand. Left ventricular diameter (by echocardiographic measurement), arterial blood pressure (by sphygmomanometry) and heart rate were measured in the supine and upright position at both ages. At 6 months the left ventricular end diastolic volume was not modified by a change in posture [supine 6(SEM 3) ml, upright 6(3) ml], so heart rate was minimally altered [supine 128(9), upright 130(11) beats.min-1] and blood pressure remained stable [supine 74(6), upright 73(5) mm Hg]. After the acquisition of the erect posture (18 months) left ventricular end diastolic volume was reduced [supine 14(3), upright 8(2) ml], heart rate increased [supine 110(11), upright 127(12) beats.min-1] and blood pressure remained constant [supine 80(6), upright 79(7) mm Hg]. The assumption of the erect posture therefore represents a phase when, for the first time in the natural history of the cardiovascular system, translocation of intravascular volume from the cardiopulmonary area to the periphery stimulates nervous and humoral responses to control the dynamics of body fluids and arterial blood pressure in a gravitational environment.

Adaptation, Physiological↗
PubMed1989

Marked blood pressure fluctuations during narcoleptic attacks alternating with abnormal wakefulness: effects of treatment with clonidine.

A middle-aged man was admitted to our department because of sleep-wake cycle disorders (alternating hypersomnia and sleeplessness), bipolar behavioural disturbances and marked fluctuations in blood pressure and heart rate. Neither evident precipitating stimuli nor an obvious cause for his illness were found. When tests that normally activate intrinsic autonomic responses were performed, two distinct circulatory patterns were recognized. During hypersomnia (phase A), cardiovascular reflex activity was blunted or abolished and orthostasis could not be maintained. The clinical, biochemical, behavioural pictures and the observed decrease in sympathetic outflow resembled the effects of clonidine administration. On the contrary, during sleeplessness (phase B) the autonomic pathways were functionally integral and orthostatic hypotension was not detected. The clinical, biochemical, behavioural features and cardiovascular overactivity closely mimicked the abrupt withdrawal syndrome encountered with clonidine. Three hypothetical mechanisms are advanced to explain this intriguing case as well as the acute and chronic relief of our patient's clinical problem following institution of clonidine therapy (phase C). The role played by central alpha adrenoceptors in integrating sleep-wake, cardiovascular and behavioural functions is also suggested.

Blood Pressure↗
PubMed1989

The effects of a microgravitational environment on the blood pressure maturation curve in normotensive rats.

In order to determine whether gravity influences the growth of terrestrial mammals, systolic blood pressure, heart rate, urinary output and body weight were measured at 10-day intervals from the age of 30 days (weaning) to 150 days in 12 male Sprague-Dawley rats. Six rats were grown in a gravitational environment. 'Dry' water immersion was used to subject six rats to a microgravitational environment between the ages of 30 and 90 days. A downward shift in systolic blood pressure and body weight maturation curves was observed in the microgravitational group from the age of 60 days. After the 'dry' water immersion was stopped, the fully developed rats showed a significant increase in systolic blood pressure, which returned to control values, but not in body weight. We conclude that the physiological increase in systolic blood pressure taking place in rats during growth is partly dependent on gravity.

Animals↗
PubMed1988

Effects of angiotensin and angiotensin blockade on coronary circulation and coronary reserve.

Angiotensin is a potent coronary vasoconstrictor, but little is known of the effects of long-term activation of the renin-angiotensin system on coronary reserve in humans. The effects of exercise on coronary hemodynamics were determined in eight patients with mild essential uncomplicated hypertension, before and after treatment with furosemide (50 mg, to ensure activation of the renin-angiotensin system). Coronary sinus blood flow was measured by thermodilution technique, intra-arterial blood pressure was measured from the ascending aorta, and plasma renin activity was determined by radioimmunoassay. Oxygen supply and demand were derived (using coronary sinus blood flow multiplied by the arteriovenous oxygen difference to equal oxygen supply and heart rate multiplied by the mean systolic blood pressure to equal oxygen demand) both at rest and during isometric exercise (handgrip to 50 percent of maximal effort for three minutes). The study was a single-blind crossover (furosemide versus placebo) design. Furosemide produced a significant reduction in coronary sinus blood flow, associated with an increase in coronary vascular resistance. Changes in mean arterial pressure and heart rate were insignificant. Slight reductions in plasma volume and mean right atrial pressure were observed. During isometric exercise, the increase in oxygen supply for a given increment in oxygen demand was attenuated by furosemide. The contribution of the renin-angiotensin system to this effect was determined by the short-term administration of 25 mg of the angiotensin converting enzyme inhibitor captopril. Forty-five minutes after oral captopril, coronary reserve was restored to pretreatment values. In conclusion, furosemide modulates coronary reserve, and it is likely that this is because furosemide mediates activation of renin-angiotensin system, thus reducing the vasodilatory capacity of the coronary arteries.

Adult↗
PubMed1988

Cardiogenic hypertension in maturing dogs.

The purpose of this study was to evaluate whether the heart can induce high blood pressure by maintaining an inappropriately elevated cardiac output/body weight ratio during growth. Direct (femoral artery) mean arterial pressure (MAP), heart rate, cardiac output/body weight ratio (as defined by M-mode echocardiography), and total peripheral vascular resistance were measured and calculated every 2 months in nine conscious dogs during development from 2 to 10 months of age. In four dogs a J-shaped catheter for atrial pacing was chronically implanted at the age of 3 months, and their hearts were permanently paced at 130 beats/min until maturity. The aim of atrial pacing was to prevent the natural slowing of the heart rate and, consequently, to maintain a cardiac output/body weight ratio that was inappropriately high in relation to age during growth. Five dogs were studied as controls. No hemodynamic differences were observed until the age of 4 months. From the age of 5 to 10 months heart rate was kept at 130 beats/min by atrial pacing in the atrially paced group, and the mean cardiac output/body weight ratio did not decrease (196 +/- 24 vs 191 +/- 34 [SE] ml/min/kg). MAP rose from 62 +/- 4 to 116 +/- 8 mm Hg, and total peripheral resistance increased from 0.34 +/- 0.07 to to 0.61 +/- 0.09 mm Hg/ml/min/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1987

Human renovascular effects of dopexamine hydrochloride: a novel agonist of peripheral dopamine and beta 2-adreno-receptors.

The effects of dopexamine on the renal circulation have been examined to show whether any augmentation of renal blood flow (RBF) was secondary to the effect of the drug on cardiac output (CO) or whether it had any additional direct renal vasodilator activity. Eight male patients with mild to moderate hypertension, who were undergoing renal vein catheterization for renin estimation, were studied. Dose related increments in RBF (baseline (B) = 504 ml X min-1; after treatment (D) = 605 ml X min-1), CO (B = 5.9 l X min-1; D = 6.7 l X min-1), heart rate (B = 77 beats/min; D = 100 beats/min) and systolic blood pressure (B = 143 mmHg; D = 166 mmHg) were observed on administration of dopexamine 3 micrograms X kg-1 X min-1, with insignificant changes in diastolic blood pressure (B = 84.4 mmHg; D = 90 mmHg) and total peripheral resistance (B = 17.85; D = 17.25 Units). There was a slight but significant reduction in renal vascular resistance (B = 20.59, D = 18.75). The ratio of RBF to CO (%) confirmed that the increase in RBF due to dopexamine hydrochloride was greater that attributable to the increase in CO or perfusion pressure alone (RBF/CO B = 8.5%, D = 9%), consistent with selective renal vasodilatation. The fall in renin activity and lack of systemic vasodilatation suggest that this was a DA1-receptor mediated effect.

Adrenergic beta-Agonists↗
PubMed1987

Converting-enzyme inhibition and coronary blood flow.

The effects of converting-enzyme inhibition (25 mg oral captopril) on coronary hemodynamics in the presence and absence of activation of the renin-angiotension system were studied in 10 patients with mild essential hypertension with no evidence of ischemic heart disease. Coronary blood flow was determined by thermodilution before and after 1 week of diuretic therapy in six patients and before and after placebo in four patients. The diuretic (50 mg/day furosemide) reduced coronary blood flow and increased coronary vascular resistance; in these same patients, captopril reduced mean arterial pressure and the rate-pressure product but increased coronary flow significantly. There was no change in any of these variables after captopril in the placebo group. Similar results were obtained in normotensive rats treated with hydrochlorothiazide; the increase in coronary flow after captopril correlated significantly with the control plasma renin activity. These results in hypertensive humans and normotensive experimental animals indicate that diuretic therapy reduces coronary blood flow significantly, and angiotensin can play a significant role in modulating coronary vascular resistance under conditions associated with activation of the renin-angiotensin system.

Adult↗
PubMed1983

Hemodynamic effects of massive peripheral edema.

The possibility that noncardiac massive peripheral edema reduces venous distensibility was investigated in eight patients in the supine and 80-degree head-up tilt position before and after diuretic therapy. After clearance of the edema with diuretic therapy, total blood volume (TBV) was not significantly decreased; therefore, in the supine position the significant (2p less than 0.001) decrease of right atrial pressure, stroke volume, cardiac output, and cardiopulmonary blood volume (CBV) by the diuretics was due to an improvement in venous compliance which resulted in peripheral redistribution of CBV since the ratio CBV/TBV was decreased during diuretic therapy (2p less than 0.001). Furthermore, before diuretic therapy, tilt significantly decreased right atrial pressure, stroke volume, cardiac output, CBV, and the ratio CBV/TBV; but after diuretic therapy, the decrease of the same variables during tilt was significantly (2p less than 0.001) greater. These results indicate that marked peripheral edema considerably decreases venous compliance which can be improved with diuretic therapy.

Adult↗
PubMed1982

Hemodynamic effects of diuretics in patients with marked peripheral edema and mild hypertension.

Hypertension develops in about 10% to 50% of patients with nephrosis or cirrhosis and peripheral edema, but the hemodynamic mechanism of the hypertension and its reversal by diuretic therapy has not been elucidated. In eight patients with marked edema and mild hypertension, diuretics (furosemide and spironolactone) decreased mean arterial pressure because of concurrent decrease in cardiac output and total peripheral resistance. Neither total blood volume nor plasma volume were decreased by the diuretics and the decrease in body weight was therefore attributed to the decrease in interstitial fluid volume. This, in turn, resulted in increased venous capacitance (as can be judged from the diuretic-induced decrease in the ratio of cardiopulmonary blood volume/total blood volume).

Adult↗
PubMed1982

A critical improvement of the local thermodilution method for measuring renal blood flow in man.

A new catheter with a "pig tail" shaped end has been used for renal venous blood outflow measurement by the local thermodilution method. Left and right renal blood flow were measured in nine hypertensive patients with monolateral renal artery stenosis (previously documented by selective renal angiography). Percutaneous introduction and positioning of the "pig tail" catheter in the renal veins was performed without complications. In all cases no deformities in the dilution curves due to: a) contact of the thermistor with the vessel walls; b) shifting baseline during injection; or c) variable and in homogeneous mixing, were observed. Mean percentage variation of five consecutive renal blood flow determinations was 6% in a flow range 154 to 718 cm3 . min-1. We conclude that the use of "pig tail" catheters represents a critical improvement of the local thermodilution method for measuring renal blood flow.

Adult↗
PubMed1981

Circulatory and renin responses in man to unilateral reduction of the renal perfusion pressure.

This study is concerned with the mechanisms of human renovascular hypertension. Unilateral partial occlusion of a renal artery was accomplished using a balloon-tipped catheter for occlusive angiography in seven normotensive and 17 primary hypertensive subjects. The renin and circulatory responses were studied during a 60 min reduction of the renal perfusion pressure (RPP) by 50% of control. This stimulus was considered to be safe and strong enough to produce a three to four-fold rise in plasma renin activity. It was observed that: a) systemic (arterial) renin was significantly raised at 5 min, reached a peak at 15 min and continued to be significantly higher than the baseline until the occlusion was removed; b) venous renin and venous arterial difference on the occluded side became elevated after the stimulus and remained so for the duration of the occlusion; c) renin release from the contralateral kidney became partially inhibited; d) in no case did systemic arterial pressure, heart rate or cardiac output change during the studies; e) renin and circulatory patterns were similar in normotensive and hypertensive subjects. It is concluded that in humans unilateral RPP reduction duplicates the renin pattern of the Goldblatt kidney, but does not duplicate the circulatory response. This evidence applies to a 1 h renal artery occlusion and does not exclude the possibility that renin may have a role in a rise in blood pressure following renal artery stenosis of longer duration.

Blood Pressure↗
PubMed1979

Echocardiographic and hemodynamic correlates in Prinzmetal angina pectoris: a case report.

In a patient suffering from Prinzmetal angina pectoris, ischemic attacks of the anterior left ventricular wall were associated with the following changes: fall in cardiac output; increased left ventricular diastolic pressure (LVDP) and volume; flattening of the septal motion; marked reduction of the mitral valve early diastolic amplitude and rate of opening; and marked reduction of the systolic closure velocity. It is suggested that LVDP rise depends, at least in part, on variations in left ventricular diastolic volume and segmental wall motion, and that disruption of the mitral valve motion derives from changes in LVDP and flow through the mitral orifice.

Angina Pectoris↗