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Biomedical subjects

M Velasco

Publications and source records attributed to M Velasco.

At least 163 records · Page 9Linked to original sources
PubMed1989

Intracranial studies on potential generators of some vertex auditory evoked potentials in man.

Potential generators for surface brain stem (ABSP), P200 and P300 auditory evoked potentials have been localized in patients with implanted electrodes used as an electrophysiological procedure for surgical treatment. Results suggest that surface SP and SN1-2 and components V, VI and VII of ABSP and component P3 and P300 result from specific auditory system activation, while components N1-P2 of P200 and N2-N4 of P300 result from nonspecific systems. Two subcortical generators were localized related to surface ABSP-one at the medial geniculate thalamic region (MG) related to SP and SN1 and V, VI, VII potentials, the other near the hippocampal region related to SN2. One subcortical generator related to surface N1-P2 of P200 was found near the caudal mesencephalic reticular formation, and the other two subcortical generators related to surface N2-P4 and P3 of P300 were found at the subthalamic and MG regions, respectively. Reverse polarity of some bipolar responses and lack of amplitude-latency gradients of some referential potentials at the gyrus orbitalis, rostral thalamus and anterior commissure, suggest the existence of other additional potential generators more rostrally located.

Brain↗
PubMed1989

Topographical analysis of subcortical vertex-like activities evoked by ipsi- and contralateral multimodal sensory stimulation in man.

A topographical analysis of the mesencephalic, thalamic and forebrain vertex-like activities evoked by ipsi- and contralateral somatic (SVA), visual (VVA) and auditory stimuli (AVA) was made in patients with electrodes implanted for diagnoses and treatment. Typical SVA, VVA and AVA recorded from a nonspecific polysensory system (NSS) were mainly bilateral and with similar latencies. Typical AVA to only contralateral stimuli were frequent at the ventrolateral thalamus and striatum level. In contrast, bilateral VA with different latencies and VA evoked only by ipsilateral stimuli were rare and mainly localized at the edge of the NSS. Within the NSS, typical VA to ipsi- and contralateral stimuli showed different cerebral distribution patterns according to the sensory modality stimulated, i.e. SVA showed amplitudes in response to contralateral stimuli smaller than to ipsilateral stimuli at the mesencephalic level, larger amplitudes in response to contralateral than to ipsilateral stimuli at the thalamic level and had equal amplitudes in response to contralateral and ipsilateral stimuli in the forebrain regions. VVA showed amplitudes in response to contralateral stimuli equal to those in response to ipsilateral stimuli at the mesencephalic, thalamic and forebrain levels. AVA showed amplitudes in response to contralateral stimuli equal to those in response to ipsilateral stimuli at the mesencephalic level, had amplitudes of contralateral responses larger than those of ipsilateral responses at the thalamic level and showed different amplitude combinations in the forebrain regions.

Brain↗
PubMed1989

Wakefulness-sleep modulation of the surface and depth auditory evoked potentials in man.

Amplitude and latency changes of early and late components of surface and depth auditory evoked potentials were determined during wakefulness-sleep steady state shifts in epileptic patients, with implanted electrodes used as an electrophysiological procedure for surgical treatment of temporal lobe seizures. Early surface (I and V) and depth (N8 and N15) components of the auditory brainstem potentials and late surface (P2 and N2) and depth (B and C) components of the auditory evoked potentials were produced by either 8/s or single clicks, delivered monoaurally and simultaneously recorded from the vertex and contralateral thalamic (lateral geniculate thalamic nucleus) and frontotemporal (amygdala, hippocampus and orbitofrontal cortex) regions, while patients spontaneously shifted from initial wakefulness (W1) to slow wave sleep (SWS I, II and IV), to paradoxical sleep (PS) and to final wakefulness (W2). Amplitude of late surface (P2 and N2) and depth (B and C) components significantly decreased when patients shifted from SWS IV to PS and increased from PS to W2. Latency of components P2 and B increased while that of components N2 and C decreased from SWS IV to PS. No latency changes in late components were found from PS to W2. In addition, amplitude and latency of P2 and B components significantly decreased while those of N2 and C increased from W1 to SWS IV. Polarity of all late components remained unchangeable during all wakefulness-sleep state shifts, with the exception of that of component C which reversed from W1 to SWS IV. In contrast, early surface (I and V) and depth (N8 and 15) components showed no systematic changes in amplitude and latency during all consecutive wakefulness-sleep shifts, with the exception of a significant increase amplitude but no latency of component V from PS to W1.

Epilepsy, Temporal Lobe↗
PubMed1989

[T-lymphocyte subpopulations in acute viral hepatitis].

The variability of the clinical course in viral hepatitis depends more on the immune response of the host that on the type of virus involved. Inductors/helpers (LT4) or cytotoxic/suppressors (LT8) T-lymphocytes regulate the immune response which can be modified during infection or in homosexuals who are at high risk for viral infection. We studied 45 males with viral hepatitis (25 B, 13 A, and 7 non A-non B hepatitis), 20 normal and 20 homosexual subjects. LT4, LT8 and B lymphocytes were determined by immunofluorescence in peripheral blood. A significant and transient decrease in levels of LT4 was found in A and B hepatitis (670 and 591 per ml vs 873 for normals). In some hepatitis B cases this decrease persisted until the HB serum antigen disappeared. Increased levels of LT8 were found in asymptomatic or hepatitis B infected homosexuals (682 and 782 respectively vs 506 per ml in normals). No difference from normals were found in non A-non B hepatitis. B lymphocytes were normal in all groups. Serum factors acting as immunoregulators of suppressors of LT4 function may be involved in the delayed synthesis of anti-HB serum antibody.

Acute Disease↗
PubMed1989

[Subjects infected with human immunodeficiency virus: serological markers of prognostic value].

Three stages in the course of acquired immunodeficiency syndrome (AIDS) have been recognized: asymptomatic, AIDS related complex (AIDS-RC) and clinical AIDS. In contrast to asymptomatic patients, subjects with clinical AIDS show HIV antigens in serum and a disappearance of antibodies against the main viral core (anti-P24). In 31 subjects infected with HIV we measured serum HIV antigens and anti-P24 antibodies (ELISA). Twelve were asymptomatic, 7 had AIDS-RC and 12 were patients with clinical AIDS. HIV antigens were positive in 9 of 11 AIDS cases but only in 1 AIDS-RC and 1 asymptomatic patient. Anti-P24 were present in only 3 AIDS cases and in the majority of asymptomatic and AIDS-RC cases. The only asymptomatic patient with HIV antigen positive and anti-P24 negative serum developed polyarthritis, fever and salmonellosis 3 years later. One patient with AIDS-RC and similar serologic findings remains stable and all patients with clinical AIDS have died. Determination of these serum markers may be helpful in establishing a prognosis in HIV infected patients.

AIDS Serodiagnosis↗
PubMed1989

[Cutaneous metastasis in gastric cancer].

We report 3 patients operated on for gastric cancer who developed skin metastasis proven by biopsy. Within a year of this complication 2 patients had died, confirming the bad prognosis associated to this finding. No estimates of the frequency of this complication are available in Chile.

Adult↗
PubMed1988

A multicenter study of doxazosin in the treatment of severe essential hypertension.

The antihypertensive efficacy and safety of doxazosin, a selective alpha 1-inhibitor, were assessed in 33 severely hypertensive patients. The study involved three phases: a 1-day baseline period, a 32-day period in which patients received doxazosin, 1 to 16 mg, once daily, and a 4-week maintenance period. All patients were considered therapy successes (sitting diastolic blood pressure either less than or equal to 90 mm Hg or greater than or equal to 10 mm Hg reduction) at a mean daily dose of 8.1 mg. Twenty-seven patients (82%) achieved good blood pressure control (sitting diastolic blood pressure less than or equal to 90 mm Hg) at a mean dose of 6.7 mg once daily. By the final treatment visit, mean systolic/diastolic blood pressures in the sitting and supine positions were significantly reduced by 40/29 and 37/28 mm Hg from a mean baseline of 180/121 and 181/121 mm Hg to final visit values of 140/91 and 144/92 mm Hg, respectively (p less than 0.05). Eleven patients experienced one or more side effects that were mild or moderate and disappeared or were tolerated with continued therapy. During the study no abnormal laboratory test findings were identified by the investigators. The investigators' global assessment of the efficacy and toleration of once-daily doxazosin therapy was excellent or good for 31 (94%) patients and fair for the remaining two patients.

Adolescent↗
PubMed1987

Kindling-like convulsive activities in the isolated ileum of the guinea pig. I. Electrical stimulation.

A kindling-like convulsive activity model produced by subthreshold, iterative electrical stimulation of the isolated male guinea pig ileum is described. In this model, the mechanical activity of the longitudinal muscular fibers of the ileum was systematically quantified in terms of the basic frequency, tonus, amplitude, and transient amplitude increments (A, n spikes/20 min) of "normal" contractions and presence of high-amplitude, paroxysmal, "epileptiform" contractures (B, n spikes/20 min). Changes in these parameters were statistically compared through consecutive stages of the same stimulated male ileum (I = initial activation, II = initial inhibition. IIIA = late activation, and IV = late inhibition) and equivalent stages of stimulated female and nonstimulated male ilea where "kindling-like" activities were only occasionally observed. Basic tonus, amplitude, and number of A spikes showed significant changes through consecutive stimulated male ileum "kindling" stages: increased from baseline to stage I, decreased from I to II, increased from II to III and from III to IIIA, and decreased from IIIA to IV. The number of B spikes significantly increased from II to III, III to IIIA, and IIIA to IV. No significant changes in baseline frequency were found through all stages nor in tonus, amplitude, A and B spikes between stage IV and the self-sustained activity observed 120 min after stimulation. In addition, there were significant correlations between B spikes vs. basic tonus and amplitude and A spikes when the stimulated male ileum shifted from stage II to IIIA (positive correlations) and from IIIA to IV (negative correlations). Basic tonus during stage I, basic amplitude during IIIA, A spikes during self-sustained activity and B spikes during III, IIIA, IV, and self-sustained activity were in the stimulated male ileum larger than those in both the stimulated female and the nonstimulated male ilea. Tonus and A spikes during III and IIIA in the stimulated male ileum were larger than in the nonstimulated, whereas tonus during IV and self-sustaining activity and amplitude during II in the stimulated male ileum were smaller than in the female stimulated ileum.

Animals↗
PubMed1987

Emphysematous pyelonephritis.

A case of emphysematous pyelonephritis which was diagnosed by conventional radiology and confirmed by ultrasonography, computed tomography, and surgery is described. The etiology and pathogenesis of this severe infection are discussed, and the usefulness of the various noninvasive radiologic methods for the diagnosis and management of the infection is reviewed.

Emphysema↗
PubMed1987

Effect of prazosin and propranolol on lipoproteins of hypertensive patients.

A comparative study between prazosin and propranolol with twenty male patients with mild to moderate essential hypertension was used to study the effects of these antihypertensive agents on plasma lipoproteins, and more specifically high density lipoproteins-2 and Apo A-I. After 4 weeks on placebo, the patients were randomly assigned to prazosin therapy (Group A) and other ten patients to propranolol therapy (Group B) for 8 weeks. Doses required for normalization of blood pressure ranged between 1 to 8 mg/day for prazosin and 20 to 240 mg/day for propranolol. The mean blood pressure was lowered to normal by both drugs. The results indicate that prazosin has no adverse effects on plasma lipids and lipoproteins separated by density gradient centrifugation. In contrast, propranolol increased total plasma triglycerides and decreased high density lipoprotein-2 apoprotein A-I and cholesterol levels by 50% in the group of ten patients. Since low levels of high density lipoproteins have been found to be associated with an increased incidence of coronary artery disease, the data obtained suggest that propranolol may induce significant, potentially atherogenic changes on lipid metabolism in hypertensive patients.

Adult↗
PubMed1987

Antihypertensive properties of tiapamil (RO 11-1781)--a new calcium antagonist--in patients with mild and moderate essential hypertension.

An open, non-comparative study, with a new calcium antagonist-tiapamil, was undertaken in 22 patients with mild and moderate essential hypertension (stage I-II WHO). After a two-week placebo period, patients were treated with tiapamil, 300-600 mg twice daily during a period of six weeks (Dose-finding period). Thereafter patients were continued on tiapamil during a 54 week period (Long-term follow-up). In some patients it was necessary to add the diuretic hydrochlorothiazide to obtain adequate control of the arterial hypertension. Monotherapy with tiapamil normalized supine diastolic blood pressure after the first six weeks in 17 of the 21 evaluable patients, and reduced it by greater than or equal to 10 mmHg (1.3 kPa) from baseline without normalization in two patients. In the two remaining cases the decrease was less than 10 mmHg. The optimal dose administered at six weeks in those patients who responded to treatment (normalization or decrease by greater than or equal to 10 mmHg.) was 600 mg/day in 32% of the cases, 750-900 mg/day in 47% and more than 900 mg/day in 21%. After completion of the dose-finding part, 19 patients continued treatment for a further 54 weeks. In 16 out of 19 patients hydrochlorothiazide was added to enhance the antihypertensive effect. All three patients who received tiapamil monotherapy throughout the trial, had normalized supine diastolic blood pressure on completing the study. In the 16 patients with the combination therapy, the addition of hydrochlorothiazide led in two patients to no further decrease in supine diastolic blood pressure, to an additional decrease by less than 10 mmHg in ten patients and by greater than or equal to 10 mmHg in four in comparison with the values obtained before starting combination therapy. At the end of the study 11 of these 16 patients had normalized supine diastolic blood pressure. The mean daily dose was 900 +/- 45 mg of tiapamil and 39 +/- 4 mg of hydrochlorothiazide. Both monotherapy and the combination regimen were well tolerated, and no effects attributable to drug interactions were observed. It may be concluded that tiapamil in oral doses of 300-600 mg twice daily is an effective antihypertensive agent with an excellent tolerance when administered for a period of 54 weeks.

Adolescent↗
PubMed1987

Electroencephalographic characteristics of children with learning disabilities.

Normal, borderline and abnormal EEG findings were investigated in 122 children with no evidence of active neurological or psychiatric disorder, or perceptual or behavioral alterations. All children had a normal IQ. Sixty-one children had a good academic achievement (Controls) and 61 were considered as learning disabled (LD). The great majority of the children had pathological antecedents considered as risk factors for brain damage. The main findings observed were: Abnormal signs were significantly more frequent in LD than in control children. Atypical high amplitude alpha, and abnormal focal paroxysmal and nonparoxysmal activities were found only in LD children with risk factors. No significant differences in the resting EEG were found between presence or absence of pathological antecedents, or between males and females, when the children were compared as a group against the 4 EEG categories. Paroxysmal reactivity to eye-closure was only observed in children with a pathological history. Excessive response to hyperventilation (Grades II and III) was found significantly more frequently in girls than in boys.

Brain Damage, Chronic↗
PubMed1986

Effects of prazosin and propranolol on blood lipids and lipoproteins in hypertensive patients.

Prazosin and propranolol were compared in an open, crossover study to determine their effects on plasma lipids and lipoproteins. After a four-week placebo period, 10 hypertensive patients were randomly assigned to prazosin treatment (Group I) and another 10 to propranolol treatment (Group II) for eight weeks. After a second four-week placebo period, treatment in each group was switched to the alternative drug for eight weeks. The mean blood pressure was reduced to normal levels (diastolic blood pressure less than or equal to 90 mm Hg) by both drugs--prazosin (1 to 8 mg per day) and propranolol (40 to 240 mg per day). The results of the study indicate that prazosin decreases serum cholesterol levels. In contrast, propranolol not only increases serum triglyceride levels and very-low-density lipoprotein cholesterol, but decreases total high-density lipoprotein cholesterol, high-density lipoprotein2 cholesterol, high-density lipoprotein2, and apoprotein A-I. The data suggest that propranolol may induce significant, potentially atherogenic changes in lipid metabolism, whereas prazosin may represent an advantageous alternative as an antihypertensive agent, especially in subjects with an already atherogenic lipoprotein profile.

Adult↗
PubMed1986

Diagnostic accuracy of ultrasound in acute cholecystitis.

This work attempts to assess the diagnostic accuracy of ultrasound for acute cholecystitis in 98 clinically suspected patients from the emergency unit in whom at least 3 of 6 relevant criteria are present. Gallbladder distention to 5 cm or more transversely or in the anterior-posterior axis (criterion 1) was present in 64 patients; thickening of the gallbladder wall of at least 5 mm (criterion 2) in 95; cholelithiasis (criterion 3) in 86; sonolucent halo in the gallbladder wall (criterion 4) in 40; sonolucent fluid band surrounding the gallbladder (criterion 5) in 27; and intraluminal echogenic mass with no posterior acoustic shadow (criterion 6) in 35. A diagnostic accuracy index, corrected for chance, was statistically and clinically more relevant with 3 as the minimum number of criteria for the ultrasonic diagnosis of acute cholecystitis.

Acute Disease↗
PubMed1986

Subcortical correlates of the somatic, auditory and visual vertex activities. II. Referential EEG responses.

A systematic analysis of polarity, amplitude and latency of the referential EEG responses correlated to surface somatic (SVA), auditory (AVA) and visual (VVA) vertex activities (VA) was done in various subcortical structures of a non-specific system of the same group of patients with electrodes implanted and reported in a previous work. These structures included the caudal and rostral mesencephalic reticular formations (cttc and rttc), the subthalamic region (Sth), the centro-median (Ce), parafascicular (Pf), ventrolateral (VL), dorsolateral (DL) and reticularis (Rt) thalamic nuclei; the orbito-frontal cortex (GO), the anterior commissure (Acm), the pallidum medialis and lateralis (Pm and Pl), the putamen (Pt) and the amygdala (Am). Subcortical SVA, AVA and VVA were formed by 4 consecutive components O, A, B and C correlated to components P1, N1, P2 and N2 of the surface VA. Components A and B of the subcortical SVA reversed polarity 4 times when recorded in structures arranged in a caudo-rostral order: between rttc-Ce and VL, between Rt and GO, between GO and Acm and between Acm and Am. Components A and B of subcortical AVA and VVA reversed polarity two times each: AVA between cttc and rttc and between GO and Acm; while VVA between GO and Acm and between Acm and Pm. Components A and B of SVA and VVA attained maximal amplitudes and minimal latencies at GO. From here, their amplitude decreased and latency increased with distance along other structures rostrally and caudally located. Components A and B of AVA attained maximal amplitudes and minimal latencies at cttc.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain↗