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Biomedical subjects

B C Maciel

Publications and source records attributed to B C Maciel.

At least 37 records · Page 2Linked to original sources
PubMed1992

Myocardial perfusion abnormalities in chronic Chagas' disease as detected by thallium-201 scintigraphy.

Most patients with chronic Chagas' heart disease complain of chest pain. The pathophysiology of this symptom is unknown, although myocardial necrosis and fibrosis are frequent necropsy findings and cardiac autonomic impairment is a prominent feature of the disease. To evaluate the possibility of an ischemic cause for these abnormalities in 23 patients (18 men, aged 32 to 60 years, mean 42) with chronic Chagas' disease complaining of chest pain, thallium-201 myocardial scintigraphy was performed after maximal effort and 4-hour redistribution. Regional wall motion was assessed by radionuclide and contrast angiography. Heart rate responses to sinus respiratory arrhythmia, atropine, phenylephrine and Valsalva maneuver were evaluated in all patients and in 22 normal control subjects. Coronary angiography was performed in 16 patients. Only 1 patient had chest pain and no ischemic electrocardiographic changes occurred in any case during the effort test. Scintigraphic analysis of 7 segments per patient showed perfusion defects in at least 1 segment in all patients. Of 161 myocardial segments 16 showed fixed, 10 reversible, and 22 paradox defects (reverse redistribution). The majority (75%) of the fixed perfusion defects occurred in dyssynergic regions, whereas reverse redistribution predominated in regions with normal wall motion (82%). The reversible defects were present in normal or mildly hypokinetic regions. Markedly impaired parasympathetic cardiac control was present but no significant coronary abnormalities were seen in any of the 16 patients undergoing angiography. It is concluded that whereas fixed defects are likely to correspond to fibrotic or necrotic lesions, reversible and paradox perfusion defects may be caused by regional flow or metabolism derangements, possibly related to abnormal parasympathetic control of the coronary microcirculation.

Adult↗
PubMed1991

Abnormal baroreflex control of heart rate in decompensated congestive heart failure and reversal after compensation.

Congestive heart failure (CHF) causes impairment of baroreflex control of heart rate (HR). To determine if this derangement is reversible, the cardiac chronotropic control was assessed in 10 patients with class IV chronic CHF of various etiologies before and after compensation achieved by bed rest, salt restriction, diuretics and vasodilators. Mean time between the 2 studies was 15 +/- 3 days. The management was modified 3 days before the second autonomic evaluation, so as to reestablish the same diet and pharmacologic conditions of the previous study. Compensation led to significant reduction in symptom-based class, body weight, and pulmonary and systemic congestion. Mean +/- standard error of the mean HR responses (beats/min) before and after compensation were, respectively: (1) to atropine (0.04 mg/kg): 10 +/- 2 and 27 +/- 2 (p less than 0.01); (2) to handgrip (30% maximum capacity, 1 minute): 9 +/- 2 and 19 +/- 3 (p less than 0.005); (3) to headup tilt (5 minutes): 4 +/- 3 and 20 +/- 4 (p less than 0.005). Mean +/- standard error of the mean baroreflex sensitivity (ms/mm Hg) of RR responses to phenylephrine and amyl nitrate-induced changes in systolic pressure was, respectively, in each condition: phenylephrine, 0.9 +/- 0.2 and 8 +/- 2.3 (p less than 0.05); amyl nitrate, 0.3 +/- 0.2 and 4.1 +/- 1.1 (p less than 0.05). A significant correlation between improvement in HR responses to atropine and tilt and changes in body weight was obtained. These findings show a reversible component of impaired baroreflex control of HR in severe CHF, possibly due to its congestive effects.

Adaptation, Physiological↗
PubMed1991

High output failure in patients with peripartum cardiomyopathy: a comparative study with dilated cardiomyopathy.

Although few studies have reported on relatively preserved ventricular function in patient with peripartum cardiomyopathy, the condition is usually believed to have the typical low-output congestive hemodynamic pattern of the dilated congestive cardiomyopathies. Two groups of patients, 14 with peripartum cardiomyopathy and 12 with dilated congestive cardiomyopathy who were matched for gender and age, were studied. They had normal blood pressure and similar New York Heart Association functional class, nutritional status, thyroid function and routine laboratory evaluation. All patients were catheterized during stable in-hospital compensation of heart failure, which was achieved by bed rest, sodium restriction, and administration of digoxin and diuretics long (more than 3 months) after delivery. Significant differences (p less than 0.05) between patients with peripartum cardiomyopathy and those with dilated congestive cardiomyopathy were observed in regard to: (1) cardiac index: 3.34 +/- 1.36 L/min/m2 versus 2.24 +/- 0.72 L/min/m2, (2) systemic vascular resistance: 1713 +/- 567 dynes.sec.cm-5 versus 2194 +/- 603 dynes.sec.cm-5, (3) right ventricular stroke work index: 8.6 +/- 4.2 g.M/m2 versus 14.8 +/- 8.2 g.M/m2 in the peripartum cardiomyopathy and the dilated congestive cardiomyopathy groups, respectively. Three of the patients with peripartum cardiomyopathy had resting cardiac index values that were even higher than the normal upper limit for our laboratory (4.5 L/min/m2): 4.80, 5.70, and 5.63 L/min/m2. They also had nearly normal left ventricular ejection fractions: 0.68, 0.41, and 0.51, respectively. These results indicate that, unlike the common dilated cardiomyopathy, the hemodynamic pattern in patients with peripartum cardiomyopathy is not homogeneous, and some patients have high-output failure and near normal left ventricular function.

Adult↗
PubMed1991

A new method for noninvasive estimation of ventricular septal defect shunt flow by Doppler color flow mapping: imaging of the laminar flow convergence region on the left septal surface.

An accurate but simple and noninvasive method for quantifying flow across a ventricular septal defect has yet to be implemented for routine clinical use. A region of flow convergence is commonly imaged by Doppler color flow mapping on the left septal surface of the ventricular septal defect, appearing as a narrowed region of laminar flow with aliased flow velocities entering the orifice. If the first aliasing region represents a hemispheric isovelocity boundary of a surface of flow convergence and all flow at this surface crosses the ventricular septal defect, the flow through the defect can be estimated by using the radius (R), measured from the first alias to the orifice, and the Nyquist limit (NL) velocity (the flow velocity at the first alias). Doppler color flow imaging was performed in 18 children with a single membranous ventricular septal defect undergoing cardiac catheterization at a mean age of 29.8 months (Group I). Indexes of maximal flow rate across the defect were developed from either the radius or the area, obtained by planimetry, of the first alias, based on Doppler color flow images. All indexes were corrected for body surface area and compared with shunt flow (Qp-Qs) and pulmonary to systemic flow ratio (Qp/Qs) determined at cardiac catheterization. Doppler color flow indexes derived from images of flow convergence in both the long-axis (n = 15) and oblique four-chamber (n = 10) views correlated closely with Qp/Qs (r = 0.71 to 0.92) and Qp - Qs (r = 0.69 to 0.97).(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1991

Effects of pressure and volume of the receiving chamber on the spatial distribution of regurgitant jets as imaged by color Doppler flow mapping. An in vitro study.

Regurgitant jet dimensions imaged by color Doppler flow mapping have been used to evaluate the severity of valvular insufficiency in clinical studies. To study the effect of pressure and volume within the receiving chamber on the magnitude of spatial distribution of regurgitant jets assessed by color Doppler techniques, we designed a simple constant-flow model in which a jet was driven through a known orifice (1.5 mm2) into a compliant receiving chamber by a steady-flow pump. A distal tube at the outflow closed the system and maintained the volume of the chamber constant during pump operation. We varied flow rate from 60 to 270 ml/min into elastic balloons with different static compliances of 1, 2, 4.5, and 9 ml/mm Hg (pressures of 57, 28, 18, and 8 mm Hg, respectively); the balloons served as receiving chambers at the constant volume of 150 ml. We also evaluated the effect of different volumes of a receiving chamber (110, 130, and 150 ml and pressures of 5, 15, and 24 mm Hg) with a static compliance of 2 ml/mm Hg over the same range of flow rates. For each of the different balloons, jet area correlated linearly with the jet velocity across the orifice (r = 0.98, 0.99, 0.98, and 0.97) and also with flow rate (r = 0.97, 0.99, 0.98, and 0.99). At the same flow rate and volume of receiving chamber, however, the jet area imaged by color Doppler decreased as the pressure in the receiving chamber increased, although receiving-chamber volume was constant.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1990

[Hemodynamic study of peripartum cardiopathy following compensation of heart failure].

PURPOSE: To assess hemodynamic characteristics of patients with peripartum cardiomyopathy under standardized conditions of clinical compensation of heart failure, and more than 3 months after the end of the gravidic period. PATIENTS AND METHODS: Fourteen patients with peripartum cardiomyopathy underwent left and right cardiac catheterization, under rest condition. Cardiac output was measured by the Fick method, left ventricular ejection fraction determined by contrast ventriculography, and the coronary circulation was studied angiographically. RESULTS: The hemodynamic pattern observed was variable, with 28% of the cases showing low right and left ventricular filling pressures, normal LV ejection fraction, and normal or even elevated cardiac output, with low pulmonary and systemic vascular resistance. CONCLUSION: Although the mechanisms responsible for such peculiar hemodynamic characteristics, have not been elucidated, it is likely that they are associated with more benign prognosis, as compared to other patients with peripartum cardiomyopathy, who show the low-output failure commonly seen in cases of dilated cardiomyopathy.

Adolescent↗
PubMed1990

Depressed respiratory sinus arrhythmia: additional evidence for impairment of vagal activity in human hyperthyroidism.

The efferent activity of the parasympathetic component of the autonomic nervous system was evaluated by measuring the magnitude of the respiratory sinus arrhythmia in 3 female patients with hyperthyroidism (Basedow-Graves' disease) before and after treatment. The heart rate variations induced by the test increased in all patients after treatment of thyrotoxicosis (from 15 +/- 2.9 to 28.3 +/- 6.6 beats/min; mean +/- SEM) with propylthiouracil (600 mg/day). This result confirms our previous observations indicating an important and reversible impairment of the efferent vagal activity in human hyperthyroidism.

Arrhythmia, Sinus↗
PubMed1989

Evaluation of the autonomic nervous system of the heart in male patients with mitral valve prolapse syndrome using respiratory sinus arrhythmia and dynamic exercise.

The autonomic nervous system of the heart was evaluated in two male groups composed of 11 patients with mitral valve prolapse and of 10 normal subjects, using the heart rate response in two types of tests: respiratory sinus arrhythmia at rest and dynamic exercise. Sinus arrhythmia was of higher magnitude in patients with mitral valve prolapse when compared to the control group; however, the differences reached statistical significance only at a respiratory frequency of 7 cycles/min. With respect to dynamic exercise (25, 50, 100, 150 W during 4 min), the heart rate response, either in terms of the early, vagus-dependent fast tachycardia (first 10 s), or the late, sympathetic-dependent tachycardia (1-4 min) was normal in both groups studied, the same occurring with aerobic exercise capacity evaluated by measurement of the anaerobic threshold. Thus, our results show that in the group of male patients with mitral valve prolapse studied here, the parasympathetic abnormalities, if present, are of questionable physiological significance and do not affect the sympathetic and parasympathetic control of heart rate during dynamic exercise.

Adult↗
PubMed1989

Sympathetic and parasympathetic changes in heart rate control during dynamic exercise induced by endurance training in man.

1. Seven healthy young men of sedentary habits were submitted to a 10-week period of endurance physical training on a cycle ergometer. The training program caused a 15% increase in maximal oxygen consumption (VO2max) and a 16% reduction in resting heart rate (HR). Before and after training, these volunteers performed dynamic exercise (DE) on a cycle ergometer at loads of 25, 50, 75, 100 and 150 w for 4 min at each level. The same exercise protocol was applied to 13 sedentary individuals and to 7 athletes (medium distance runners) who showed a VO2max of 39.4 and 53.8 ml/kg, respectively. HR was continuously monitored throughout the period of effort at each workload. 2. During the first 10 s of DE, a period when tachycardia is mediated almost exclusively by vagal withdrawal, the athletes presented a more rapid increase in HR than sedentary subjects. The same tendency was observed in the sedentary individuals after the training period, although of a lesser magnitude. 3. During the DE phase in which sympathetic mediation plays an important role (between 30 s and 4 min), the athletes presented a lower HR increase than the sedentary individuals, and the same response pattern was observed in the group submitted to physical training. Total HR increase (from 0 to 4 min) induced by DE was lower in athletes than in sedentary subjects and was not changed by training of the sedentary subjects. 4. These results suggest that aerobic training decreases the slow sympathetic and increases the fast parasympathetic contribution to HR during dynamic exercise at the same absolute workloads. 5. These functional changes in the autonomic control of HR may or may not be associated with modifications of absolute HR values which increase from rest to the end of exercise. In contrast to what happens in athletes, the autonomic adaptations observed after short-term aerobic training may occur during DE without changes in the total HR response.

Adaptation, Physiological↗
PubMed1989

[Ventricular function in mitral valve prolapse: effects of beta adrenergic blockers with and without intrinsic sympathomimetic activity].

A corollary of the "cardiomyopathy therapy" implies that mitral valve prolapse may cause intrinsic myocardial depression. The impairment of ventricular function may not be detected in basal conditions, but could be unmasked by superimposing depressant factors. The use of beta-blockers constitutes the first choice treatment for the symptomatic management of patients with mitral valve prolapse. Therefore, we tested the hypothesis that myocardial depression could be shown during beta-blockade in the uncomplicated primary form of mitral valve prolapse. The results of echocardiographic and radionuclide angiographic evaluation of left ventricular function during basal conditions, as well as under beta-blockade with propranolol and pindolol, do not lend support to the cardiomyopathy hypothesis of the pathogenesis of primary mitral valve prolapse. However, significant decreases of heart rate, left ventricular ejection fraction and peak velocity of left ventricular systolic emptying were seen with propranolol, but not with pindolol. Beta-blockade with intrinsic sympathomimetic activity may be preferable therapeutic option for patients with mitral valve prolapse.

Adolescent↗
PubMed1989

Leg endurance training has no effect on the autonomic control of heart rate during isometric exercise.

1. Heart rate (HR) response to isometric exercise (handgrip) was investigated in 7 normal males of sedentary habits before and after endurance training involving the muscles of the lower limbs. Thirteen additional sedentary individuals and 7 middle-distance runners were also studied. Isometric exercise was performed at 100, 75 and 50% of maximum voluntary contraction (MVC) during 10, 20 and 40 s, respectively. Training produced a 15.6 +/- 1.4% (mean +/- SEM) increase in VO2max and a reduction in resting HR from 69 +/- 1.9 to 58 +/- 1.7 bpm. HR was monitored throughout each period of isometric exercise. 2. The pattern of HR response to static effort performed by untrained muscles was comparable before and after training as well as in athletes and sedentary individuals during the first 10 s of contraction, a period during which tachycardia is mainly mediated by vagal release. After the first 10 s, when the sympathetic influence on tachycardia becomes evident, athletes and trained individuals showed a slight but nonsignificant tendency toward lower HR increases. 3. These results do not demonstrate any appreciable alteration in the efferent activity of autonomic components induced by aerobic training of the leg muscles when isometric exercise is performed with untrained muscles.

Adaptation, Physiological↗
PubMed1988

Cardiovascular effects of berberine in patients with severe congestive heart failure.

Berberine, an alkaloid of the protoberberine family, has been shown to have strong positive inotropic and peripheral resistance-lowering effects in dogs with and without heart failure. To determine the acute cardiovascular effects of berberine in humans, 12 patients with refractory congestive heart failure were studied before and during berberine intravenous infusion at rates of 0.02 and 0.2 mg/kg per min for 30 minutes. The lower infusion dose produced no significant circulatory changes, apart from a reduction in heart rate (14%). The 0.2 mg/kg per min dose elicited several significant changes: (a) Decreases in systemic (48%, p less than 0.01) and pulmonary vascular resistance (41%, p less than 0.01), and in right atrium (28%, p less than 0.05) and left ventricular end-diastolic pressures (32%, p less than 0.01). (b) Increases in cardiac index (45%, p less than 0.01), stroke index (45%, p less than 0.01), and LV ejection fraction measured by contrast angiography (56%, p less than 0.01). (c) Increases in hemodynamic and echocardiographic indices of LV performance: peak measured velocity of shortening (45%, p less than 0.01), peak shortening velocity at zero load (41%, p less than 0.01), rate of development of pressure at developed isovolumic pressure of 40 mmHg (20%, p less than 0.01), percent fractional shortening (50%, p less than 0.01), and the mean velocity of circumferential fiber shortening (54%, p less than 0.01). (d) Decrease of arteriovenous oxygen difference (28%, p less than 0.05) with no changes in total body oxygen uptake, arterial oxygen tension, or hemoglobin dissociation properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

The use of isometric exercise as a means of evaluating the parasympathetic contribution to the tachycardia induced by dynamic exercise in normal man.

Fourteen normal subjects were submitted to isometric exercise (IE), dynamic exercise (DE) and a combination of the two (IE + DE). The main purpose of the present study was to use IE as a means of evaluating the mechanism of the heart rate (HR) increase induced by DE. To this end, the magnitude of the IE (handgrip) was standardized so as to cause an elevation of HR almost exclusively by vagal withdrawal: IE was performed using a dynamometer strain-gauge system with a linear response at 75% of maximum voluntary contraction (MVC) for 10 s, repeated at 1 min intervals. The change in HR evoked by IE under control conditions was compared with that evoked during DE, and during the corresponding recovery period. DE was performed by the legs, with the subject in the seated position for 4 min, at workloads of 55 and 105 watts, separated by a rest period. In the combined protocol, IE was performed at the beginning of DE, as well as at 1, 2 and 3 min during DE, and at 0, 1, 2, 3 and 5 min during recovery period. The following results were obtained: (1) IE associated with DE always induced smaller increase in heart rate than IE alone, and this effect was more marked at 105 than at 55 W; this finding suggested a workload-dependent vagal withdrawal at the very beginning of DE that was sustained until the end of effort.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Autonomic control of heart rate during dynamic exercise in human hyperthyroidism.

1. The relative contribution of the sympathetic and parasympathetic components of the autonomic nervous system to the regulation of the chronotropic response to dynamic exercise was evaluated indirectly in nine patients with thyrotoxicosis and in seven normal volunteers. All subjects were women, with equivalent ages in both groups. Six of the nine patients with hyperthyroidism were reevaluated after clinical compensation of the disease with propylthiouracil. 2. Heart rate responses were evaluated during discontinuous dynamic effort maintained for 4 min on a bicycle ergometer at levels of 5, 15, 25 and 50 W, and also of 75 W in normal individuals. The study was also performed under conditions of sympathetic pharmacological blockade with propranolol (0.2 mg/kg body weight). 3. Even though the magnitude of the total increase in heart rate evoked by each level of dynamic exercise was equivalent in normal and hyperthyroid patients, the tachycardiac response occurring at the beginning of the exercise, which depends on a predominantly vagal mechanism, was substantially different from that observed after 30 s of effort, when sympathetic contribution becomes more important. The hyperthyroid patients showed considerably lower increases in heart rate than the normal individuals during the initial 30 s of effort, with the opposite occurring from this moment onward. 4. In the hyperthyroid patients, beta-adrenergic blockage depressed tachycardia after 30 s of effort at the 15 and 50 W levels, whereas in normal individuals this effect was only manifested at 50 and 75 W. 5. The patients who obtained clinical compensation showed a pattern of chronotropic response which tended to be close to that shown by normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Autonomic Nervous System↗
PubMed1988

Limitations of facial immersion as a test of parasympathetic activity in man.

1. The heart rate response to immersion of the face in water, as an isolated manoeuvre or in combination with apnoea, was studied in eight normal volunteers to establish the conditions under which it could be used as a standardized, simple, non-invasive and reproducible test of parasympathetic activity. 2. The following procedures were evaluated: (a) 10 s apnoea in air at different lung volumes; (b) facial immersion in water for 2 min at various temperatures (5, 15 and 25 degrees C), with respiration maintained through a closed circuit; (c) combination of immersion and apnoea at different lung volumes. Three volunteers were re-evaluated after pharmacological blockade with atropine sulphate (0.04 mg/kg body weight). 3. The results showed that: (a) apnoea in air triggered lung volume-dependent heart rate responses; (b) facial immersion in water induced transient bradycardia which was maximum between 20 and 30 s of immersion; (c) there was no appreciable difference in the bradycardia evoked by immersion at different temperatures; (d) the combination of immersion and apnoea caused heterogeneous heart rate responses with no potentiation of bradycardia in relation to each manoeuvre as performed separately; (e) atropine did not reduce the magnitude of bradycardia induced by immersion in two of the subjects studied. 4. The variability of responses observed in the present study was probably due to the multiple receptors and afferent pathways that are simultaneously excited during these manoeuvres. As a consequence, the autonomic efferent response will depend on the unpredictable net effect of interaction of these mechanisms. This is a limiting factor for the standardization of this test as a simple and reproducible method for the assessment of parasympathetic activity. 5. Furthermore, the results obtained under pharmacological blockade indicate that the vagal efferent mechanism is not the only factor responsible for the bradycardia caused by facial immersion without apnoea.

Adult↗