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Biomedical subjects

N Sanchez

Publications and source records attributed to N Sanchez.

32 records · Page 2Linked to original sources
PubMed1993

Chromatic aberration and ocular focus: Fincham revisited.

Longitudinal chromatic aberration of the eye (LCA) produces "color fringes" at edges that specify focus. Fincham [(1951) British Journal of Ophthalmology, 35, 381-393] concluded that these chromatic effects were important for accommodation, but most investigators disagree. We monitored accommodation in 25 subjects while they viewed a sinusoidally moving target (1.5-2.5 D at 0.2 Hz) in a Badal optometer. The target was monochromatic (590 nm with 10 nm bandwidth), or white (3000 K) with LCA normal, neutralized or reversed. Sensitivity to the effects of LCA is profound and widespread. Gain decreases substantially and phase-lag increases when LCA is eliminated, and reversing the aberration severely disrupts accommodation. The ordered arrangement of spectral foci produced by LCA seems to be a fundamental aspect of the stimulus for "reflex" accommodation.

Accommodation, Ocular↗
PubMed1992

von Willebrand factor antigen, tissue-type plasminogen activator antigen, and risk of death in human immunodeficiency virus 1-related clinical disease: independent prognostic relevance of tissue-type plasminogen activator.

Tissue-type plasminogen activator, von Willebrand factor, and plasminogen-activator inhibitor type 1 plasma levels were measured at first consultation in 85 consecutive patients infected with human immunodeficiency virus. Patients were assigned to three groups according to clinical status: mild disease group, intermediate group, and acquired immunodeficiency syndrome group. Significant differences were found in von Willebrand factor, tissue-type plasminogen activator, and plasminogen-activator inhibitor type 1 plasma levels among the three groups: severe clinical status was associated with higher von Willebrand factor, tissue-type plasminogen activator, and plasminogen-activator inhibitor type 1 plasma levels. Significant correlations were found among these three parameters, such known biologic prognostic indicators of human immunodeficiency virus infection as IgA, anti-p24 antibodies, p24 antigenemia, CD4+ lymphocytes, beta 2-microglobulin, and the clinical status. The prognostic relevance of plasma von Willebrand factor and tissue-type plasminogen activator levels at the time of entry into the study was then investigated in a cohort of 65 of the 85 patients who had follow-up during a median period of 22 months. The median survival time for all patients was 39 months after the first consultation. A plasma von Willebrand factor level greater than 200% of the control value had a positive predictive value of 86% for determining nonsurvivors; the median survival time for such patients was 9 months after the first consultation. A positive predictive value of 100% in recognizing nonsurvivors was found for tissue-type plasminogen factor plasma levels greater than 20 ng/ml; the median survival time for these patients was 2 months after the first consultation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

[Endothelial mediators regulating vascular tonus].

Vascular endothelium is the unavoidable interface between blood and tissues. Its role as regulator of vascular tone is discussed here. The endothelium possesses different receptors for vasoactive mediators. These receptors activate the endothelial cells which in turn may produce secondary mediators acting on smooth muscle cells by activating or inhibiting their contraction. Such mediators are the endothelins which have a vasoconstrictor effect, and prostacyclin or endothelium-derived relaxation factors (EDRF) which have a vasodilator effect. Thus, the vascular endothelium and the mediators it secretes play a crucial role in vascular tone physiology.

Endothelins↗
PubMed1990

Impact of smoking, physical training and weight reduction on FVII, PAI-1 and hemostatic markers in sedentary men.

The variations of FVII, PAI-1, TAT complexes, fibrinopeptide A, D-Dimers and beta thromboglobulin plasma levels were studied on 30 sedentary men, smokers and non-smokers, who were admitted to a 6 months' program of physical training and smoking cessation. After 3 months of intervention, sustained physical training was associated with the decrease of FVII and PAI-1 levels. Mild exercise performed during a second 3-month period could maintain normal FVII and PAI-1 activities but participants who stopped the training increased their FVII and PAI-1 plasma levels. FVII was not influenced by smoking habits. Smoking cessation seemed to slightly potentiate the decrease of PAI-1 levels associated with mild exercise. Overweight, FVII and PAI-1 levels were correlated and the weight reduction induced by training was related to the changes in the factors. In smokers, physical exercise was associated with a significant increase of hemostatic markers. This exercise-induced variation disappeared after 3 months of intervention in participants who stopped smoking and reappeared in those who smoked again after 6 months of intervention. This finding was not influenced by the physical training program.

Antithrombin III↗
PubMed1990

Impaired fibrinolytic capacity in patients with inflammatory bowel disease.

The venous occlusion test was applied to 17 patients with inflammatory bowel disease (IBD; 7 cases of Crohn's disease, 10 cases of ulcerative colitis). Results were compared to those obtained in 20 healthy matched control subjects. Patients with IBD had significantly decreased t-PA Ag release (p less than 0.001) and had no significant vWF Ag release. Residual PAI activity was evidenced after venous stasis in the IBD group but not in the control group. Hypofibrinolysis was more important in patients with an evolutive IBD than in patients with IBD in remission. Impaired systemic fibrinolytic capacity might contribute to an increased risk for thromboembolic complications and to the pathogenesis of inflammatory bowel disease.

Adult↗
PubMed1989

Isolation and characterization of a fibrinogen-clotting enzyme from venom of the snake, Lachesis muta muta (Peruvian bushmaster).

A fibrinogen-clotting enzyme from the venom of the Peruvian bushmaster snake was purified to homogeneity by gel filtration on Sephadex G-100 followed by DEAE-cellulose ion-exchange chromatography using a linear ionic strength gradient with NaCl. The specific activity of the enzyme was 866 NIH U/mg, representing a 55-fold purification, with a recovery of 45%. The amino acid composition was Asx30, Thr14, Ser15, Glx33, Pro23, Gly22, Ala15, Val22, Cys18, Met3, Ile18, Leu23, Tyr2, Phe13, His8, Lys11, Arg11. The total carbohydrate content was 13.4%, comprised of 3.4% hexose, 8.7% hexosamine and 1.3% sialic acid. The enzyme was active against the synthetic amide substrate alpha-N-benzoyl-DL-arginine-p-nitroanilide (BAPNA) and against the ester substrates alpha-N-benzoyl-L-arginine ethyl ester (BAEE) and tosyl-L-arginine methyl ester (TAME). Kinetic parameters for TAME esterolysis were: Vmax, 135 mumoles/min/mg and Km, 2.5 x 10(-4) M. The pH optimum was 8.0. Vmax for BAPNA amidolysis was 0.363 mumoles/min/mg and Km, 7.5 x 10(-5) M. Enzyme activity was reduced by diethylpyrocarbonate and by photo-oxidation, suggesting that the enzyme is a serine protease with a histidine residue involved in the active site. The enzyme released fibrinopeptide A rapidly from purified human fibrinogen and fibrinopeptide B more slowly. Factor XIII was not activated and the clotting activity was not inhibited by heparin. A dose of 50 micrograms/kg brought about defibrinogenation in anaesthetized rats but rabbits were unaffected. A dose of 80 micrograms/kg defibrinogenated conscious rats after 5 hr. There were no hypotensive or haemorrhagic effects.

Amino Acids↗
PubMed1989

Lack of specificity of Chlamydiazyme for detection of vaginal chlamydial infection in prepubertal girls.

A 1-year prospective study was undertaken of 65 prepubertal girls referred for evaluation of sexual abuse or vulvovaginitis to compare Chlamydiazyme, an enzyme immunoassay (EIA), with culture for the detection of Chlamydia trachomatis i in vaginal specimens. Five (8%) of 65 patients were initially EIA-positive. On repeat sampling without intervening antibiotic treatment, 4 girls who were initially positive became negative and 1 remained persistently positive. Chlamydial cultures were negative in all patients. The patient with the persistently positive EIA also had Group A streptococcal vaginitis. We were able to demonstrate that some strains of Group A Streptococcus can cause a positive reaction with the EIA. Cross-reactions with other bacterial species are also known to occur. We therefore conclude that Chlamydiazyme is not specific for the detection of chlamydial infection in the vagina of prepubertal girls and, for medicolegal reasons, should not be used for evaluation of sexual abuse.

Antigens, Bacterial↗
PubMed1979

Subcorneal pustular dermatosis: a variant of pustular psoriasis.

A patient with clinical lesions typical of subcorneal pustular dermatosis of Sneddon and Wilkinson also had stigmata of psoriasis, namely psoriatic plaques, pitting of nails, and psoriatic arthritis. Histologic studies of the pustular lesions were consonant with pustular psoriasis. Correlating the phenomena of previously reported cases of subcorneal pustular dermatosis with those of our patient, we conclude that subcorneal pustular dermatosis of Sneddon and Wilkinson is but another variant of psoriasis.

Aged↗
PubMed1973

Pharmacokinetics of digoxin: interpreting bioavailability.

Three subjects were first given a digoxin tablet in the fasting state and subsequently received the same formulation in the fed state, to simulate a spurious oral bioavailability difference. As expected, when measured by peak serum digoxin concentration as well as by area under the serum digoxin concentration-time curve the bioavailability of digoxin appeared to be higher in the fasting state than in the fed state. However, when measured by cumulative five-day urinary excretion of digoxin bioavailability was identical in both conditions.This simple experiment illustrates the fact that the estimation of bioavailability is subject to considerable methodological error, of which the clinician must be aware when evaluating reports on drug bioavailability in general and of digoxin in particular.

Administration, Oral↗