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Biomedical subjects

F Costa

Publications and source records attributed to F Costa.

At least 91 records · Page 5Linked to original sources
PubMed1997

An improved flow evaluation scheme in orifices of different aspect ratios.

An accurate and reliable method of regurgitant flow calculation is currently unavailable. The goal of this study was to define a new general method of flow calculation for orifices of different aspect ratios. The success of the method relies on matching the imaged flow field distribution obtained by color flow mapping (CFM) to a three-dimensional (3D) numerical flow field distribution of known geometry. The flow field in three orifices of identical cross-sectional area with aspect ratios of 1 (circular), 2 and 4 (elliptical) was evaluated by: (a) CFM, (b) 3D echocardiographic imaging, and (c) 3D finite element modeling (FEM). The orifice shape and size were accurately estimated by 3D echocardiographic imaging. FEM showed that the normalized centerline velocity profile of the flow field depends on the orifice aspect ratio. CFM provided a good description of the centerline profile for each case. For a given distance from the orifice center, the equivelocity contour surface area increases with increasing aspect ratio. A simple flow calculation scheme was developed to calculate regurgitant flow independent of orifice shape. This improved method showed better results than previous studies and may prove to be advantageous when analyzing in vivo flow fields with complex geometries.

Computer Simulation↗
PubMed1997

The hypertension of autonomic failure and its treatment.

We studied the incidence and severity of supine hypertension in 117 patients with severe primary autonomic failure presenting to a referral center over a 9-year period. Patients were uniformly characterized by disabling orthostatic hypotension, lack of compensatory heart rate increase, abnormal autonomic function tests, and unresponsive plasma norepinephrine. Fifty-four patients had isolated autonomic impairment (pure autonomic failure). Sixty-three patients had central nervous system involvement in addition to autonomic impairment (multiple-system atrophy). Patients were studied off medications, in a metabolic ward, and on a controlled diet containing 150 mEq of sodium. Fifty-six percent of patients had supine diastolic blood pressure > or =90 mm Hg. The prevalence of hypertension was slightly greater in females (63%) than in males (52%). Potential mechanisms responsible for this hypertension were investigated. No correlation was found between blood volume and blood pressure. Similarly, plasma norepinephrine (92+/-15 pg/mL) and plasma renin activity (0.3+/-0.05 ng/mL per hour) were very low in the subset of patients with pure autonomic failure and supine hypertension (mean systolic/diastolic pressure, 177 +/- 6/108 +/- 2 mm Hg, range 167/97 to 219/121). Supine hypertension represents a challenge in the treatment of orthostatic hypotension. We found these patients to be particularly responsive to the hypotensive effects of transdermal nitroglycerin. Doses ranging from 0.025 to 0.1 mg/h decreased systolic blood pressure by 36+/-7 mm Hg and may effectively treat supine hypertension overnight, but the dose should be individualized and used with caution.

Aged↗
PubMed1997

Malignant vagotonia due to selective baroreflex failure.

Baroreflex failure is characterized by dramatic fluctuations of sympathetic activity and paroxysms of hypertension and tachycardia. In contrast, unopposed parasympathetic activity has not been described in patients with baroreflex failure because of concurrent parasympathetic denervation of the heart. We describe the unusual case of a patient with baroreflex failure in a setting of preserved parasympathetic control of HR manifesting episodes of severe bradycardia and asystole. Thus, parasympathetic control of the HR may be intact in occasional patients with baroreflex failure. Patients with this selective baroreflex failure require a unique therapeutic strategy for the control of disease manifestations.

Baroreflex↗
PubMed1997

Effects of differing antecedent hypoglycemia on subsequent counterregulation in normal humans.

The aim of the study was to determine the effects of specific levels of antecedent hypoglycemia on subsequent autonomic, neuroendocrine, and metabolic counterregulatory responses. Eight healthy, overnight-fasted male subjects were studied during 2-day protocols on four separate randomized occasions separated by at least 2 months. On day 1, insulin was infused at a rate of 9 pmol x kg(-1) x min(-1) and 2-h clamped euglycemia (plasma glucose 5.2 +/- 0.2 mmol/l) or differing hypoglycemia (plasma glucose 3.9 +/- 0.1, 3.3 +/- 0.1, or 2.9 +/- 0.1 mmol/l) was obtained during morning and afternoon. The next morning after an evening meal and 10-h overnight fast, each subject underwent a 2-h hyperinsulinemic (9 pmol x kg(-1) x min[-1]) hypoglycemic (2.9 +/- 0.1 mmol/l) clamp study. Despite equivalent day 2 plasma glucose and insulin levels, differing levels of antecedent hypoglycemia produced specific blunting of subsequent counterregulatory responses. Day 1 hypoglycemia of 3.9 mmol/l resulted in significantly (P < 0.01) blunted epinephrine, muscle sympathetic nerve activity, and glucagon responses. Day 1 hypoglycemia of 3.3 mmol/l resulted in additional significant blunting (P < 0.01) of pancreatic polypeptide, norepinephrine, growth hormone, endogenous glucose production, and lipolytic responses. Deeper day 1 hypoglycemia of 2.9 mmol/l produced similar day 2 counterregulatory failure as day 1 hypoglycemia of 3.3 mmol/l. In summary, in healthy overnight-fasted men, mild antecedent hypoglycemia of 3.9 mmol/l significantly blunts sympathoadrenal and glucagon, but not other forms of neuroendocrine counterregulatory responses, to subsequent hypoglycemia. Antecedent hypoglycemia of 3.3 mmol/l resulted in additional significant blunting of all major neuroendocrine and metabolic responses to subsequent hypoglycemia. We conclude that in normal humans, there is a hierarchy of blunted counterregulatory responses that are determined by the depth of antecedent hypoglycemia.

Adult↗
PubMed1996

Role of cortisol in the pathogenesis of deficient counterregulation after antecedent hypoglycemia in normal humans.

The aim of this study was to determine the role of increased plasma cortisol levels in the pathogenesis of hypoglycemia-associated autonomic failure. Experiments were carried out on 16 lean, healthy, overnight fasted male subjects. One group (n = 8) underwent two separate, 2-d randomized experiments separated by at least 2 mo. On day 1 insulin was infused at a rate of 1.5 mU/kg per min and 2 h clamped hypoglycemia (53 +/- 2 mg/dl) or euglycemia (93 +/- 3 mg/dl) was obtained during morning and afternoon. The next morning subjects underwent a 2-h hyperinsulinemic (1.5 mU/kg per min) hypoglycemic (53 +/- 2 mg/dl) clamp study. In the other group (n = 8), day 1 consisted of morning and afternoon 2-h clamped hyperinsulinemic euglycemia with cortisol infused to stimulate levels of plasma cortisol occurring during clamped hypoglycemia (53 mg/dl). The next morning (day 2) subjects underwent a 2-h hyperinsulinemic hypoglycemic clamp identical to the first group. Despite equivalent day 2 plasma glucose and insulin levels, steady state epinephrine, norepinephrine, pancreatic polypeptide, glucagon, ACTH and muscle sympathetic nerve activity (MSNA) values were significantly (R < 0.01) blunted after day 1 cortisol infusion compared to antecedent euglycemia. Compared to day 1 cortisol, antecedent hypoglycemia produced similar blunted day 2 responses of epinephrine, norepinephrine, pancreatic polypeptide and MSNA compared to day 1 cortisol. Antecedent hypoglycemia, however, produced a more pronounced blunting of plasma glucagon, ACTH, and hepatic glucose production compared to day 1 cortisol. We conclude that in healthy overnight fasted men (a) antecedent physiologic increases of plasma cortisol can significantly blunt epinephrine, norepinephrine, glucagon, and MSNA responses to subsequent hypoglycemia and (b) these data suggest that increased plasma cortisol is the mechanism responsible for antecedent hypoglycemia causing hypoglycemia associated autonomic failure.

Adrenocorticotropic Hormone↗
PubMed1996

Temporal and geographical trends of anti-HIV-1 antibodies screening among newborns in Italy, 1990-1993. Italian Collaborative Study Group for HIV Prevalence in Newborns.

To describe the dynamic of HIV-1 prevalence in Italian childbearing women and to estimate the future incidence of pediatric AIDS due to vertical transmission, dried-blood specimens collected from a consecutive sample of newborns in all Italian regions were examined for the presence of anti-HIV-1 antibodies (HIV-Ab) after the routine neonatal screening program was completed. Of 555,722 blood samples collected and examined for HIV-Ab between 1990 and 1993, 550 (0.099%) were positive. Nationwide, the HIV seroprevalence decreased between 1990 and 1992 (0.124% in 1990, 0.100% in 1991, 0.085% in 1992), and increased, as compared with that in the previous year, in 1993 (0.096%). In an univariate analysis, HIV seroprevalence was positively was positively associated with being born in regions having higher AIDS cumulative incidence and in metropolitan areas, but negatively associated with year of delivery. In a multiple logistic regression analysis, only the AIDS cumulative incidence level of the delivery area and being born in a metropolitan area remained independently associated with HIV seroprevalence. Our results show significant geographical variation in the spread of HIV infection among childbearing women in Italy and provide useful indications to target prevention and care strategies for HIV-infected women and their children and to estimate the potential impact of implementing programs aimed at preventing vertical transmission of HIV infection.

Adult↗
PubMed1996

Artificial urinary sphincter implantation for neurogenic bladder: a multi-institutional study in 107 children.

OBJECTIVES: To evaluate the outcome of implantation of the AMS 800 artificial urinary sphincter in children with neurogenic bladder. PATIENTS AND METHODS: The records of 107 children (74 boys and 33 girls) treated for neurogenic urinary incontinence by implantation of the AMS 800 artificial sphincter between 1983 and 1993 were reviewed retrospectively. The underlying cause of incontinence in 92 patients was spina bifida, the mean age at implantation was 13.7 years and 30 patients had undergone previous bladder neck surgery. Implantation was carried out in combination with another surgical procedure in 24.3% of patients. The mean follow-up was 61 months (minimum 12). RESULTS: The mean operational life of the sphincter was 56 months. No deaths occurred but removal of the artificial sphincter was necessary in 20 patients (19%). Surgical revision was not required in 44 patients (41%) but at least one revision was performed in 63 and more than one in 42. There were 21 mechanical failures, 40 surgical complications and 39 cases involving changes in the dynamics of bladder function. Of the 87 children (81%) in whom the device is still in place, 72 are completely continent (83%), 10 are slightly wet, and five are incontinent. The overall success rate was 77%. CONCLUSIONS: The results emphasize that for successful implantation of an artificial urinary sphincter in children, the pre-operative bladder capacity must be sufficient and previous surgery should not have been performed on the bladder neck, the site of choice for implantation in children. Sphincterotomy is not always necessary in paediatric patients. Children and parents should be informed of the high complication rate and the need for long-term follow-up.

Adolescent↗
PubMed1996

Zygomatic leiomyoma. Case report.

Leiomyoma is a benign tumor that originates from the smooth muscle. If often develops in the uterus and in organs rich of smooth muscle like bowel and subcutaneous tissue. It is infrequently observed in the oral nasal cavities or in paranasal sinuses. The authors, after an accurate revision of the literature, present their first case of zygomatic leiomyoma. They underline the diagnostic aspects in relationship to histologic and immunohistochemical examinations, for surgical therapy.

Adult↗
PubMed1995

Effect of neurovestibular stimulation on autonomic regulation.

Conditions associated with nausea and vomiting, such as motion sickness or side effects of medications, are commonly associated with a clinical picture consistent with parasympathetic activation and sympathetic withdrawal. It can be postulated, therefore, that vestibular stimulation contributes to sympathetic withdrawal. To test this hypothesis five normal volunteers, 24-33 years old, were studied during caloric vestibular stimulation while monitoring muscle sympathetic nerve activity directly through a needle electrode placed in a peroneal nerve. The ear was irrigated with water at a flow rate of 450 ml/min and 37 degrees C. The water temperature was sequentially lowered by 7 degree C intervals until intolerable side effects developed or a temperature of 16 degrees C was reached. Nystagmus was induced in all subjects, but heart rate, blood pressure, muscle sympathetic nerve activity and plasma norepinephrine levels did not change significantly during or after caloric stimulation, even when the subjects felt dizzy and nauseated. No evidence of sympathetic withdrawal was observed in any subject either by muscle sympathetic nerve activity or plasma norepinephrine measurements. In conclusion, we have found that selective vestibular stimulation is not accompanied by significant changes in the sympathetic nervous system function. In particular, no sympathetic withdrawal was observed. It could be argued that lack of sympathetic stimulation is an inadequate response to the symptoms associated with caloric stimulation.

Adult↗
PubMed1995

Wall thickening of common carotid arteries in patients affected by noninsulin-dependent diabetes mellitus: relationship to microvascular complications.

This study evaluates the wall thickness of common carotid arteries and the atherosclerotic involvement of the carotid bifurcations in patients with noninsulin-dependent diabetes mellitus (NIDDM), with and without microvascular complications. Seventy subjects affected by NIDDM, and 17 healthy controls were evaluated by means of high-resolution echo-Doppler scan. Twenty-six diabetics (Group A) and complications (overnight proteinuria > 500 mg, background retinopathy, sensory neuropathy), while 44 (Group B) had no complications. The two groups were comparable for age, sex, plasma lipid profile, and smoking habit. Arterial hypertension was present in 15 of 26 (58%) complicated patients (Group A) and in 18 of 44 (41%) uncomplicated patients (Group B). None of the patients had a history of cerebrovascular disease. The authors found that the wall thickness of the common carotid artery was greater and atherosclerotic lesions of the carotid bifurcation were more frequent in diabetic patients with microvascular complications than in uncomplicated diabetics (who had a similar distribution of other risk factors for atherosclerosis) and in nondiabetic controls. These data on the one hand confirm the role of diabetes as an independent risk factor for carotid atherosclerosis and, on the other hand, indicate a correlation between microvascular lesions and early atherosclerosis in diabetes.

Arteriosclerosis↗
PubMed1995

[Gallbladder motility following intake of mineral bicarbonate-alkaline water. Ultrasonographic assessment].

Sonographic measurement of gallbladder volume has allowed us to assay the influence of many substances (hormones, drugs, etc.) on gallbladder kinetics playing a pivotal role in digestive mechanisms. The aim of the present study has been to evaluate the effect of an alkaline bicarbonate water (Donata) on gallbladder emptying. The study was performed in cross-over. Ten healthy volunteers randomly assumed alkaline bicarbonate water or saline (400 ml). Gallbladder volumes were measured by ultrasonography, according to ellipsoid method, before and 15', 30', 45', 60', 90', 120' after water or saline intake. A week later the test was repeated. Gallbladder kinetics was evaluated referring to fasting volume, residual volume, absolute emptying and maximum percent emptied. Student's "t" test for paired data was used for statistical evaluation of the results. Gallbladder volumes were significantly reduced 15', 30', 45' and 60' after alkaline bicarbonate water administration, whereas saline did not induced gallbladder emptying. The present results suggest that Donata water may be employed in order to ameliorate dyspepsia due to biliary dyskinesia, moreover it may play a complementary role in the prevention and in the medical treatment of biliary lithiasis.

Adult↗
PubMed1994

Plasma zinc response to a breakfast meal or fasting in elderly women.

The aim of this study was to determine whether the postprandial decline in plasma zinc concentration is altered by aging. Eleven women, between the ages of 65 and 82 yr, participated in two separate experimental protocols: a high carbohydrate breakfast trial and a fasting trial. Plasma zinc concentrations were measured from blood samples obtained at 8:00 AM (baseline fasting) and at 30-min intervals until 1:00 PM during each trial. Following the breakfast meal, plasma zinc concentrations declined 14% from 75 +/- 1 to 65 +/- 2 micrograms/dL (p < 0.05), reaching a nadir 2.7 +/- 0.2 h after the meal. This decline was significantly (p < 0.0001) greater than the 3.6% fall observed during the fasting trial. Postprandial changes in the plasma zinc concentrations were correlated with postprandial changes in serum glucose (r = -0.43, p < 0.001), serum insulin (r = -0.17, p < 0.01), and serum phosphorus (r = 0.32, p < 0.005). These data show that plasma zinc concentrations decline following food intake in elderly women in the same manner as previously described for younger adult women.

Aged↗
PubMed1994

Role of adenosine in the sympathetic activation produced by isometric exercise in humans.

Isometric exercise increases sympathetic nerve activity and blood pressure. This exercise pressor reflex is partly mediated by metabolic products activating muscle afferents (metaboreceptors). Whereas adenosine is a known inhibitory neuromodulator, there is increasing evidence that it activates afferent nerves. We, therefore, examined the hypothesis that adenosine stimulates muscle afferents and participates in the exercise pressor reflex in healthy volunteers. Intraarterial administration of adenosine into the forearm, during venous occlusion to prevent systemic effects, mimicked the response to exercise, increasing muscle sympathetic nerve activity (MSNA, lower limb microneurography) and mean arterial blood pressure (MABP) at all doses studied (2, 3, and 4 mg). Heart rate increased only with the highest dose. Intrabrachial adenosine (4 mg) increased MSNA by 96 +/- 25% (n = 6, P < 0.01) and MABP by 12 +/- 3 mmHg (P < 0.01). Adenosine produced forearm discomfort, but equivalent painful stimuli (forearm ischemia and cold exposure) increased MSNA significantly less than adenosine. Furthermore, adenosine receptor antagonism with intrabrachial theophylline (1 microgram/ml forearm per min) blocked the increase in MSNA (92 +/- 15% vs. 28 +/- 6%, n = 7, P < 0.01) and MABP (38 +/- 6 vs. 27 +/- 4 mmHg, P = 0.01) produced by isometric handgrip (30% of maximal voluntary contraction) in the infused arm, but not the contralateral arm. Theophylline did not prevent the increase in heart rate produced by handgrip, a response mediated more by central command than muscle afferent activation. We propose that endogenous adenosine contributes to the activation of muscle afferents involved in the exercise pressor reflex in humans.

Adenosine↗