Biomedical subjects

M N Alçada

Publications and source records attributed to M N Alçada.

5 recordsLinked to original sources

PubMed1999

A tinnitus objectivization: how we do it.

The medical therapy of tinnitus should be oriented by objective measurement of the disorder. Preferably, it should be qualitative, indicating the exact neural mechanism to be neuromodulated by neuroprotective medication. The neurophysiological approach in objectivization of tinnitus is presented by means of auditory brainstem response and middle latency response. These tests could be applied in functional follow-up of medical therapy, as these are more sensitive and harmless methods as compared to standard morphological methods.

Adult↗

PubMed1998

A study of auditory afferent organization in children with dyslalia.

The auditory afferent (AA) control is an important feedback mechanism in the speech generation. A different organization of AA pathways in children with speech alterations is suggested. In order to investigate this possibility we recorded the auditory brainstem responses (ABR) and middle latency responses (MLR) on monoaural and binaural click stimulation in a group of 17 normal children with no alteration of the speech (N) and in 16 children with dyslalia (eight with systematic (S) and eight with non-systematic errors of the speech (NS)). All of children were normal hearing, with normal ORL and neurological status, right-handed and with the age approximately 7 years old. A lateralization effect was found in the S group. Normally, it was only found for wave I. The efficiency of both AA pathways was the same in NS group, indicating a more effective right pathway in more rostral areas. A prolonged latency (X = 0.25 ms) of wave III was registered on the right side in the NS group compared to normals, as well for wave V (X = 0.175 ms) with increased sweep rate (21 vs. 51 and 71). The effect of sweep rate augmentation was also studied (21-51-71) on latency values and inter-wave differences in these groups. A successive latency prolongation (X = 2.97 ms) of MLR wave Na was registered between the N-S-NS groups. In the S group a latency binaural interaction (BI) of MLR left wave Na was prolonged for 3.52 ms and in the NS group for a further 1.32 ms compared to normals. Only in the NS group was a prolongation of the BI of the right wave Pa detected (6.76 ms) compared to normals. Results suggest a different AA organization in children with dyslalia. Possible locations of alterations in functioning could be pons, and thalamocortical projections. ABR and MLR could evaluate the auditory-speech capability of children.

Auditory Pathways↗

PubMed1997

Prevention by a somatostatin analogue of the hypertensive and cardiovascular structural changes induced by blockade of adenosine receptors.

1. Long-term administration of the adenosine receptor antagonist, 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), causes arterial hypertension and cardiovascular hypertrophic and hyperplastic changes (Matias, Albino-Teixeira, Polónia & Azevedo, 1991). As somatostatin is a repressor of cell growth, and adenosine is a potent inducer of the somatostatin gene, we investigated the putative involvement of somatostatin in the cardiovascular effects of DPSPX. 2. DPSPX (90 micrograms kg-1 h-1, i.p.) or saline and the somatostatin analogue, octreotide (75 micrograms kg-1 day-1, s.c.), or saline were infused through Alzet minipumps to Wistar rats. Blood pressure was measured with the tail-cuff technique. Seven days after implantation of the minipumps the rats were killed and the tissues prepared for microscopy. 3. DPSPX induced arterial hypertension and cardiovascular hypertrophic and hyperplastic changes as previously described (Matias et al., 1991). Treatment of the rats with octreotide alone had no effect either on blood pressure or in blood vessel morphology. However, octreotide prevented both the hypertensive and the cardiovascular morphologic effects of DPSPX. 4. The results are compatible with the involvement of somatostatin in the long-term cardiovascular effects of adenosine.

Animals↗

PubMed1995

FIA titrations of ephedrine in pharmaceutical formulations with a PVC tetraphenylborate tubular electrode.

A flow injection system for the titration of ephedrine in pharmaceutical products with potentiometric detection was developed. For this purpose a tetraphenylborate tubular electrode was constructed. The electrode was prepared without inner reference solution and with a PVC membrane based on tetrapentylammonium tetraphenylborate as ion exchanger and 2-nitrophenylphenyl ether as mediator solvent. Its operational characteristics were evaluated in a low dispersion manifold and compared with more conventionally shaped electrodes using the same sensor. In the pH range 2.5-11.5, the electrodes showed linear response between 3.8 x 10(-6) and 0.1 M with a slope of -56.4 mV/log[BPh4]. Ephedrine determinations in pharmaceutical products were carried out in a single channel manifold with a mixing chamber incorporated and using the tubular electrode as detector. Recovery rates of 98.6 +/- 2.5% were obtained in the analysis of tables, nasal drops and syrups with a sampling rate of about 60 h-1.

Electrodes↗

PubMedDate not supplied

PVC membrane electrode without inner reference solution for the direct determination of ephedrine in pharmaceutical preparations.

A PVC membrane electrode, without inner reference solution, based on an ion association extraction system responding to ephedrine is described. It incorporates an ephedrine-tetrakis (4-chlorophenyl)borate ion-pair complex in 2-nitrophenyloctyl ether. The prepared electrode exhibits a near Nernstian response (57.5 mV per decade) over the concentration range of 2 x 10(-5)-10(-1) M ephedrine in solutions of pH 2.5-9. The reproducibility of the electrode potentials were +/- 1 mV by day during at least 6 months. Response time was about 6 s for ephedrine concentrations between 10(-5) and 10(-1) M. Determinations of ephedrine in pharmaceutical preparations (tablets, nasal drops and syrups) by direct potentiometry gave an average recovery of 99.1% (w/w) and a mean standard deviation of 1.9% (w/w).

Chemistry, Pharmaceutical↗