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Biomedical subjects

O Costa

Publications and source records attributed to O Costa.

At least 37 records · Page 2Linked to original sources
PubMed1996

[Neurocardiogenic syncope: its pathogenesis, diagnosis and treatment].

Neurocardiogenic syncope seems to be the most common cause of syncope. It is believed to be triggered by paradoxical autonomic reflexes, beginning in the ventricular mechanoreceptors of the heart, modulated by the brain stem and terminating in the autonomic efferent pathways (parasympathetic stimulation with bradycardia or asystole and sympathetic inhibition with severe hypotension). Tilt test has been used recently, as a safety and effective tool to identify subjects prone to syncope. Although the pathophysiology of this syndrome is not completely understood, pharmacological therapeutics seems very effective in resolving symptoms.

Autonomic Nervous System↗
PubMed1996

[Basic concepts on the assessment of arterial baroreceptor sensitivity with non invasive methods. Estimate of the spontaneous gain of the arterial baroreceptor].

Arterial baroreceptors are sensitive to variation in both blood and pulse pressure. When there is an increase in those pressures, the baroreceptors increase the rhythm in which electric impulses are discharged. The impulses are transmitted by the receptors to the nervous centres of the brainstem. Once processed, these signals turn into sympathetic and vagal impulses. The vagal efferents control heart rate and the sympathetic efferents control heart rate, myocardial contractility and peripheral resistance. If there is an increase in blood pressure, then there will be a reflex decrease in the sympathetic activity and an increase in the parasympathetic one. The cardiac cronotropic response to blood pressure variation is very fast-with a delay of one or two beats. The amplitude of the response is a sigmoidal function. The greatest inclination of the response curve, that is to say, the area of greatest variation of the RR interval per unit of pressure, characterises the gain of the baroreceptors. The traditional method for obtaining the gain of the baroreceptor is a pharmacological one. Generally, the patient is given phenilephrine intravenously, in bolus and then the correlation between heart rate and the increase in intra-arterial blood pressure (reflex bradycardia) is calculated. Lately, it has been used the calculation of the spontaneous gain of the baroreceptor starting from a study carried out on the normal fluctuations in blood pressure and in the pulse interval both in time and frequency domain. The first case deals with the calculation of the gain of the function of transfer between the variations both in blood pressure and the RR intervals in the LF and the HF bands. The second case deals with the analysis of the occurrence of sequences of three beats with successive increases or decreases in blood pressure and in the RR interval. The gain is obtained from the linear regression of all the sequences. The application of these techniques to the recordings of blood pressure obtained by non-invasive methods (Finapress) makes possible that this procedure be followed under real conditions since it requires no previous stimulation of the cardiovascular system, which would probably interfere with the mechanisms to be evaluated, and requires no equipment in the condition which is normally required by experimental methodology.

Blood Pressure↗
PubMed1995

[The spectral analysis of heart rate variability. A comparative study between nonparametric and parametric spectral analysis in short series].

OBJECTIVE: to compare parametric (AR) and non parametric (FFT) spectral analysis results obtained in 512 beats series. INTERVENTIONS: 104 healthy subjects with normal physical examination and electrocardiogram were studied. The Ecg was recorded at rest, with controlled breathing at 15 cycles/min., and sampled at 300 Hz. The spectral VLF, LF and HF were calculated with FFT algorithm. For the same series, an auto-regressive analysis (AR) with optimized choice of the order of the model (AIC criterion) have been computed, VLF, LF and HF components were identified by AR spectral decomposition. RESULTS: In both groups, athletes and sedentary, there were no statistically differences between VLF, LF, HF and LF/HF spectral indices computed by the two methods. CONCLUSION: the results suggest that with controlled breathing it does not seems to exist any advantage in the use of AR spectral analysis to compute spectral components of heart rate variability, which is much more laborious that fixed bands non parametric FFT analysis.

Adolescent↗
PubMed1995

Clear-cell sarcoma of tendons and aponeuroses studied by immunoscintigraphy.

Clear-cell sarcoma is a rare tumor that arises in association with tendons and aponeuroses. Although it shares with malignant melanoma several histologic and ultrastructural features, it has a clinical course different from that of conventional melanomas. A case of clear-cell sarcoma studied by immunoscintigraphy with 99mTc-labeled F(ab')2 fragments of the monoclonal antibody 225.28 S is reported.

Adenocarcinoma, Clear Cell↗
PubMed1994

Neuronal regulation of cochlear blood flow in the guinea-pig.

1. Previous studies have shown that electrical stimulation (ES) of the guinea-pig cochlea causes a neurally mediated increase in cochlear blood flow (CBF). It is known that the centrifugal neuronal input to the cochlea comes through the perivascular sympathetic plexus from the cervical sympathetic chain and along the vestibular nerve (VN) from the periolivary area of the brainstem. Both of these neuronal systems are distributed topographically in the cochlea. 2. In order to study the neural origins of ES-evoked CBF increase, laser Doppler flowmetry was used to test the following hypotheses. (a) The response is regional, that is, limited to the area of the cochlea stimulated. To test this we performed differential ES of the cochlear turns. CBF was measured from either the third or the first turn. (b) The response is mediated via autonomic receptors within the cochlea. To study this, we applied atropine, succinylcholine and idazoxan locally to the cochlea. (c) The response is influenced by neuronal input via the sympathetic cervical chain (SC) and components of the VN. We stimulated and sectioned the SC, and sectioned the VN, to test this hypothesis. 3. We observed that the CBF response was topographically restricted to the stimulated region. Locally applied muscarinic or nicotinic antagonists (atropine and succinylcholine respectively) did not affect the response. However, local idazoxan (an alpha 2-blocker) eliminated the response. Locally applied adrenaline and SC stimulation modified the dynamic range of the response. SC sectioning enhanced the responsiveness of the cochlear vasculature to ES. The VN section caused a temporary decrease in CBF and elimination of the ES-evoked CBF response. 4. We conclude that the release of dilating agents is topographical with respect to ES current flow, the ES-evoked CBF increase is peripherally mediated via alpha 2-receptors, and the response is influenced by input via the SC. The elimination of the response by VN sectioning proximal to the brainstem indicated that fibres of the VN mediate the CBF increase during direct cochlear ES. The data suggest that these fibres may be the efferent limb of a neural loop involved with the regulation of CBF. Such a system could provide a mechanism for the rapid increase in CBF with organ stress.

Adrenergic alpha-Antagonists↗
PubMed1994

Heart rate variability in 24-hour Holter recordings. Comparative study between short- and long-term time- and frequency-domain analyses.

Mean hourly parameters obtained from all beats (long series) were compared with those obtained from a sample of 512 beats extracted each hour (short series) in nine presumably normal subjects. For both the short and long series, the spectral components, very low frequency, (VLF), low frequency (LF), and high frequency (HF), and time-domain indices (such as the Ewing statistic [PNN50] and RR standard deviation [SD-RR]), have been estimated. The spectral components LF and HF, estimated from the short and long series, were not significantly different, whereas significant differences were found between VLF, SD--RR, and PNN50. In both the short and long series, a strong correlation was found between LF and SD-RR and between HF and PNN50. The results suggest that, over a period of 24 hours, hourly LF and HF spectral components can be obtained using a single series of 512 beats every hour, with a great advantage over the evaluation of the mean hourly parameters. This method would be particularly useful in the study of circadian heart rate spectral analysis in Holter recordings with multiple artifacts or ectopic beats, and in general, when analysis of the entire 24-hour series is not feasible.

Adult↗
PubMed1994

[The ambulatory recording of the long-term electrocardiogram].

In the past 5 years, a new approach was developed to evaluate the patient with sporadic symptoms as is the patient with syncope--the long-term ambulatory loop electrocardiogram monitoring. This method allow to assure the heart rate and rhythm at the moment of the symptoms hardly to be able with the other diagnostic tools disposable. The long-term ambulatory loop electrocardiogram monitoring was not to replace the actual tools, but complement them. Newer devices are smaller and too light, and have the ability of registry some minutes before and after the symptom. In the near future, the devices will be able to detected and store arrhythmias and to possess an easy and accessible management. With continued and profitable work that has been done in this area, a large proportion of patients with the diagnosis of "syncope of unknown etiology" can have a diagnostic and specify therapeutic and we will be able to assert with more strictness if the symptoms related by the patient are or not of cardiovascular origin.

Arrhythmias, Cardiac↗
PubMed1994

[Sudden death in athletes].

Identifying all athletes at risk for exercise-related sudden death is difficult because systematic reliable screening is expensive. Nevertheless, if a perfect screening method existed, an appreciable number of athletes at increase risk for sudden death would not be identified. We think that a careful history designed to identify symptomatic athletes and a rigorous family history of congenital heart disease may be the most practical screening method.

Adolescent↗
PubMed1994

[Syncope: how to deal with it?].

Syncope is a frequent symptom, with an expensive protocol of difficult evaluation in face of its diverse causes. The authors describe the proper use of the tests available, particularly the tilt test, and conclude that nowadays only few syncopal episodes would remain unexplained.

Diagnosis, Differential↗
PubMed1993

Middle cerebral artery occlusion increases cerebral capillary permeability.

One hour after middle cerebral artery occlusion, the regional blood to brain transfer coefficient of alpha-aminoisobutyric acid was determined in eight barbiturate anaesthetized rats. The transfer coefficient (microliter/min-1/g-1) was significantly higher in the ischaemic cortex (10.6 +/- 2.3) than in the contralateral cortex (6.5 +/- 1.0). Cerebral regional capillary surface area was determined in another group of twelve rats using an alkaline phosphatase stain for the total capillary bed and fluorescein isothiocyanate-dextran to visualize the perfused capillaries. Perfused capillary surface area (cm2/cm3) was lower in the ischaemic cortex (141 +/- 31) than in the contralateral cortex (426 +/- 32). Using these values for the transfer coefficient, surface area and our previously published data of regional cerebral blood flow after middle cerebral artery occlusion, we calculated the extraction fraction of alpha-aminoisobutyric acid, the permeability-surface area product and the permeability of cerebral regional capillary beds. Although, there are numerous reports of permeability-surface area product of brain capillaries, to our knowledge, the permeability has never been determined before. The calculated extraction fraction ratio for alpha-aminoisobutyric acid for ischaemic cortex/contralateral cortex was 3.1. Similar ratios for permeability-surface area product and capillary permeability were 1.6 and 4.4, respectively. Thus, there was a more than four fold increase in capillary permeability to small molecules in the ischaemic cortex one hour after middle cerebral artery occlusion.

Aminoisobutyric Acids↗
PubMed1993

[Malignant vasovagal syncope: a case of prolonged asystole induced by the "tilt" test and aggravated by therapy with a beta blocker (a clinical case and diagnostic, physiopathologic and therapeutic review)].

The authors describe a case of a middle-age male with recurrent syncope, in whom the tilt test was useful in the diagnosis and therapeutic evaluation. Malignant criteria of vasovagal syncope were established and the beta blocking worsening effect was documented, in spite of the general agreement of the first choice drug.

Adult↗
PubMed1993

Spectral analysis of heart rate variability in athletes.

The objectives of the study were to characterize power spectrum pattern of the heart rate variability and assessment of the relative contributions of sympathetic and parasympathetic cardiac nervous system control in athletes. Thirty-three male athletes, swimming (1), canoeing (10), cycling (6), athletics (4), football (3), roller-skating (2) and volleyball (7) aged 23.4 +/- 5.5 years, with a mean athletic level of 18 hours/week (8-45) and 33 sedentary healthy control subjects were included. Ecg signals were recorded after a period of 15 minutes in supine rest with controlled breathing at 15 cycles/min. Signal acquisition was done at 300 samples/sec. From 512 consecutive heart beats, we calculated mean average, standard deviation, maximum and minimum R-R intervals and, after computing the fast Fourier transform, total spectrum power, low frequency (LF), high frequency (HF) components and its ratio (LF/HF). The average R-R interval was 987.7 +/- 168.8 ms and 762.7 +/- 125.3 ms, the variance was 5.44 and 2.51 ms2 and ratio of R-R interval maximum/minimum (E/I ratio) 1.53 +/- 0.16 and 1.41 +/- 0.16, respectively for athletes and control group. Differences between groups were significant (p < 0.01) for all parameters, with higher variability in the athletes. Both spectral bands (LF and HF) had higher power in athletes (LF = 925 +/- 920 and HF = 2258 +/- 2349 ms2) than in the control group (LF = 442 +/- 446 and HF = 1179 +/- 1542 ms2) (p < 0.01). There were no significant differences for LF/HF ratio, or normalized LF (LF%) or normalized HF (HF%) between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

[Evaluation of the aerobic capacity of blind people, by direct VO2 maximal measurement].

Physical activity is the basic factor to the human being in order to assume his place in society. Blind persons are often sedentary, which compromises its physical capacity. The present work evaluates the blind person's physical capacity, analysing possible differences related to sex, age and life time blindness. The sample was constituted by 27 blind (congenital and noncongenital), 18 male and 9 female, aged between 17 and 37 years old. To evaluate previous physical activity, a questionnaire, was answered which showed a dominant sedentary population. The maximum oxygen uptake was determined in a treadmill test using standard procedures (Bruce protocol). Medium results for boys were 45.85 +/- 8 ml/kg/min and for girls were 34.46 +/- 3.8 ml/kg/min. The difference between congenital and acquired blindness on the VO2max values was 2.9 ml/kg/min, not statistically significant (p = 0.468). Those findings lead us to consider that aerobic capacity mostly depends on type and intensity of physical exercise which may be temporary related to the onset of blindness and visual impairment degree.

Adolescent↗
PubMed1991

[Study of the autonomous nervous system with heart rate spectral analysis in acute myocardial infarction].

OBJECTIVES: Characterize power spectrum pattern of heart rate variability (HRV) and assessment of relative cardiac nervous system in patients with acute myocardial interaction of sympathetic and parasympathetic infarction. We also compared the spectral power with some known prognostic risk variables. STUDY DESIGN: Study of patients with acute myocardial infarction (AMI) and sedentary healthy subjects sex matched. SUBJECT AND METHODS: 19 postinfarction patients aged 55.7 +/- 10.5 years and 19 healthy subjects controls aged 53.9 +/- 11.0. ECG signals were recorded after 15 minutes of supine rest with controlled breathing at 15 cycles/min. Signal acquisition was done at 300 samples/sec. From 512 consecutive sinus beats, we calculated the average, standard deviation, maximum and minimum values and rate between the longest and shortest R-R interval (E/I). We also calculated, after computing the fast Fourier transform, the total spectrum power, low frequency component (LF, from 0.01 to 0.15 Hz), high frequency component (HF, from 0.15 to 0.50 Hz) and its ratio (LF/HF). Thereafter, we correlated these results with radionuclide ejection fraction, duration of treadmill test, Holter ventricular premature complex and localization of infarction. RESULTS: The average R-R interval was 757.9 +/- 116.3 and 850.9 +/- 133.9 msec (p less than 0.05), the R-R corrected standard deviation was 15.3 +/- 6.0 and 38.2 +/- 8.5 msec (p less than 0.001) and ratio E/I was 1.13 +/- 0.06 and 1.32 +/- 0.09 (p less than 0.001) in AMI and control group, respectively. In AMI group, low frequency spectral band was very decreased (LF = 0.03 +/- 0.02 sec2) and high frequency was virtually absent (HF = 0.01 +/- 0.01 sec2) compared with control group (LF = 0.13 +/- 0.06 and HF = 0.14 +/- 0.15 sec2), p less than 0.001; ratio LF/HF was increased in AMI group. There were no significant differences between groups for normalized LF (LF%) and HF (HF%). CONCLUSIONS: These results showed that spectral pattern in AMI patients had very low LF and HF power density. Decreased HRV in that group was mainly due to diminished parasympathetic influence in cardiac regulation; nevertheless ratio LF/HF was increased which represents an imbalance of sympatho-vagal activity with predominance of sympathetic tone. We found poor correlation between frequency domain indices and other risk variable; best correlation was between total spectral power and radionuclide ejection fraction (r = 0.642, p less than 0.01), which could express independent prognostic value in AMI patients risk stratification.

Autonomic Nervous System↗
PubMed1991

[Spectrum analysis of the variability of heart rate in athletes].

OBJECTIVES: Characterize power spectrum pattern of the heart rate variability and assessment of the relative contributions of sympathetic and parasympathetic cardiac nervous system control in athletes. STUDY DESIGN: Prospective study of athletes and sedentary healthy control group sex and age matched. SUBJECT AND METHODS: 8 athletes, 3 female and 5 male, swimming (4), canoeing (2) and cycling (2), aged 17.4 +/- 3.6 years, and 8 sedentary healthy controls. ECG signals were recorded after a period of 15 minutes in supine rest with controlled breathing at 15 cycles/min. Signal acquisition was done at 300 samples/sec. From 512 consecutive heart beats, we calculated the average, the standard deviation, the maximum and the minimum values and the rate between the longest and the shortest R-R interval (E/I). We also calculated, after computing the fast Fourier transform, the total spectrum power, the low frequency component (LF, from 0.01 to 0.15 Hz) and the high frequency component (HF, greater than 0.15 Hz) and its ratio (LF/HF). RESULTS: The average R-R interval was 921 +/- 154.2 msecs and 673.2 +/- 98 msecs, the standard deviation was 72.5 and 29.4 msecs and the ratio E/I 1.63 +/- 0.14 and 1.28 +/- 0.08, respectively for athletes and control group. Differences between groups were significant (p less than 0.01) for all parameters, with higher variability in the athletes. Both spectral bands (LF and HF) and higher power in athletes (LF = 0.54 +/- 0.23 and HF = 0.76 +/- 0.14) than in the control group (LF = 0.14 +/- 0.10 and HF = 0.18 +/- 0.15) (p less than 0.001). There were no significant differences for LF/HF ratio, or normalized LF (LF%) or normalized HF (HF%) between groups. CONCLUSIONS: The present results indicates higher power of both spectral bands (LF and HF) and higher amplitude of the respective peaks in athletes when compared with healthy sedentary, with a clear predominance of the HF band in the total spectral power density, which suggest that the higher heart rate variability observed in athletes reveals the predominance of parasympathetic activity, without reduction of the sympathetic tone.

Adolescent↗
PubMed1991

[High resolution electrocardiogram and late potential monitoring].

The signal-averaged ECG became an important noninvasive method for identifying life-threatening ventricular arrhythmias. It is most accurate in patients with coronary artery disease and can be helpful in predicting whether a patient with an unexplained syncope or nonsustained VT is at risk of developing sustained ventricular tachycardia or not. A patient with an entirely normal signal-averaged ECG is at very low risk of sustained VT. In contrast, an abnormal signal-averaged ECG should raise suspicion about VT, and prompt further studies, including electrophysiological testing. Signal-averaged ECG can also be used repeatedly with acceptable reproducibility. Technological advances and improvements in the frequency analysis of the averaged signal may increase the predictive accuracy of the technique and consequently enhance its clinical applications.

Electrocardiography↗
PubMed1990

Age-dependent LH and FSH effect on the proliferation of women's peripheral blood lymphocytes in vitro.

Pituitary gonadotropic hormones (LH and FSH) were found to induce an age-dependent proliferation of women's peripheral blood lymphocytes (PBL). Results showed that PBL of elderly women gave a higher gonadotropic response than those of younger donors and that the number of responders to the mitogenic stimulus of the hormones was always more important in older than in younger women. A negative correlation between the mitogenic effect of FSH (10(-9) g/ml) and the level of plasma concentration of some steroid hormones (17-beta-estradiol or both 17-beta-estradiol and progesterone) was observed in younger donors. It was also found that physiological concentrations of LH and FSH can either increase or decrease the Concanavalin A (Con A)-induced proliferation in vitro of PBL taken from both young or postmenopausal women. In certain elderly women (4/9) a synergistic effect of Con A and LH, giving rise to high levels of thymidine incorporation similar to those achieved by Con A-stimulated PBL of young women, was observed. The possible physiological significance of these results is discussed.

Adult↗