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Biomedical subjects

C Henriquez

Publications and source records attributed to C Henriquez.

12 recordsLinked to original sources
PubMed2006

Estimation of cardiac bidomain parameters from extracellular measurement: two dimensional study.

Cardiac tissue conductivity measurements can be used to assess the electrical substrate underlying normal and abnormal wavefront propagation. We describe a method of solving the inverse cardiac bidomain model to estimate average longitudinal and transverse intra and extra-cellular conductivities and fiber angle relative to an electrode array placed arbitrarily on the epi- or endocardial surface. A Newton-Raphson reconstruction method and two Tikhonov-type regularizations were able to stably identify conductivities and fiber angles in tissue models having anisotropies similar to those in real cardiac tissue. The reconstruction methods were tested with data from increasingly realistic two dimensional cardiac bidomain models and performed well both when measurement noise was added, and when simulated experimental and forward model matching was diminished. This approach may be a suitable basis for continuous monitoring of myocardial condition in-vivo via a catheter based electrode array.

Action Potentials↗
PubMed2000

A computer model of normal conduction in the human atria.

Although considerable progress has been made in understanding the process of wavefront propagation and arrhythmogenesis in human atria, technical concerns and issues of patient safety have limited experimental investigations. The present work describes a finite volume-based computer model of human atrial activation and current flow to complement these studies. Unlike previous representations, the model is three-dimensional, incorporating both the left and right atria and the major muscle bundles of the atria, including the crista terminalis, pectinate muscles, limbus of the fossa ovalis, and Bachmann's bundle. The bundles are represented as anisotropic structures with fiber directions aligned with the bundle axes. Conductivities are assigned to the model to give realistic local conduction velocities within the bundles and bulk tissue. Results from simulations demonstrate the role of the bundles in a normal sinus rhythm and also reveal the patterns of activation in the septum, where experimental mapping has been extremely challenging. To validate the model, the simulated normal activation sequence and conduction velocities at various locations are compared with experimental observations and data. The model is also used to investigate paced activation, and a mechanism of the relative lengthening of left versus right stimulation is presented. Owing to both the realistic geometry and the bundle structures, the model can be used for further analysis of the normal activation sequence and to examine abnormal conduction, including flutter. The full text of this article is available at http://www.circresaha.org.

Atrial Function↗
PubMed1980

Thyroid function in a uremic rat model. Evidence suggesting tissue hypothyroidism.

The main objective of this study was to determine whether the principal abnormality of thyroid function observed in patients with chronic renal failure, low serum triiodothyronine (T(3)) concentration, causes hypothyroidism at the tissue level. A partially nephrectomized (Nx) uremic rat model was developed and the following parameters of thyroid function were assessed: serum total thyroxine (TT(4)), total T(3) (TT(3)), and thyrotropin and liver T(3) content, and activity of two thyroid hormone-dependent enzymes, mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPD) and cytosol malate dehydrogenase (MDH). The results were compared to those of intact control (C), thyroidectomized (Tx), and nephrectomized-thyroidectomized (NxTx) littermates.Results expressed as mean+/-SEM showed that Nx rats had a fivefold increase in blood urea nitrogen, (112+/-20 mg/dl in Nx, and 22+/-1 mg/dl in C) and manifested all the changes of of thyroid function observed in uremic men, including a low serum TT(3) level (30+/-7 ng/dl in Nx and 50+/-6 ng/dl in C). In the liver, T(3) was significantly reduced (18+/-2 ng/total liver in Nx and 35+/-3 ng/total liver in C) as well as the activities of alphaGPD (8.8+/-1.0 and 16.1+/-1.5 DeltaOD/min per total liver in Nx and C, respectively) and MDH (6.3+/-1.6 and 12.6+/-2.2 U/total liver in Nx and C, respectively). The reduction in liver enzyme activities correlated significantly with the decrease in T(3) content. The changes in Tx rats were as expected, showing a profound reduction in serum hormone levels, liver T(3) content, and liver enzyme activities. Serum thyrotropin was markedly elevated to 2,390+/-212 ng/ml as compared to 703+/-61 in C and 441+/-87 ng/ml in Nx rats. The NxTx rats showed the combined effects of nephrectomy and thyroidectomy; blood urea nitrogen was elevated to 203, and serum levels of TT(4), TT(3), and thyrotropin were 0.4, <10, and 2,525, respectively. Total liver T(3) and alphaGPD and MDH were strikingly low; the corresponding values were 3.5, 2.4, and 2.5.l-triiodothyronine replacement (0.4 mug/100 g body wt/d) for 4 wk in the Nx rats resulted in significant increases in liver enzyme activities, alphaGPD and MDH rose by 70 and 60% over their respective basal values without alteration in the severity of azotemia. From these data, we conclude that the reduction of liver T(3) content in the uremic rats, accompanied by a decrease in alphaGPD and MDH activity, indicates the presence of hypothyroidism at the tissue level. Restoration of enzyme activities toward normal levels after T(3) administration provided further supporting evidence that the diminution in liver enzyme activity was causally related to tissue T(3) deficiency.

Animals↗
PubMed1980

Ovarian function in chronic renal failure: evidence suggesting hypothalamic anovulation.

The pathogenesis of ovarian dysfunction in uremia was evaluated in 24 patients by measurements of plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone, prolactin, estradiol, and progesterone basally and after clomiphene, ethinyl estradiol, and bromocriptine. In the 17 premenopausal women, levels of plasma estradiol, progesterone, and FSH were comparable to those found in normal women during the follicular phase of the ovarian cycle; plasma luteinizing hormone was slightly elevated. In most patients, there was an absence of cyclicity. After clomiphene, plasma levels of luteinizing hormone, FSH, and estradiol rose; after ethinyl estradiol, plasma luteinizing hormone levels failed to increase. In seven postmenopausal patients, plasma estradiol was undetectable and gonadotropin levels were markedly elevated. Although plasma prolactin was generally elevated, suppression of prolactin with bromocriptine resulted in resumption of ovulation in only one patient; the other 2 remained amenorrheic. In uremic women, the continued secretion of estrogen, the rise of plasma levels of luteinizing hormone, FSH, and estradiol after clomiphene, and the elevated gonadotropin levels during menopause suggest that the negative estradiol feedback, the tonic gonadotropin secretion, and the pituitary ovarian axis were normal. The positive estradiol feedback associated with cyclic release of luteinizing hormone, however, was impaired as indicated by the prevalence of acyclicity and the failure of luteinizing hormone levels, to rise after ethinyl estradiol.

Adolescent↗
PubMed1978

Endocrine abnormalities associated with chronic renal failure.

It is evident that chronic renal failure has far-reaching metabolic consequences because endocrine aberrations are common. Uremia may alter endocrine function through its effect on the hypothalamopituitary axis, the individual end organs, and the peripheral metabolism of various hormones. Deficiency of some hormones and excess of others coexist in patients with renal failure. Since the physiologic effects of many of these abnormalities are still not well defined, no treatment is necessary with the exception of true deficiency states such as testosterone deficiency. In the latter instance, exogenous hormonal supplementation is recommended.

Adrenal Cortex↗
PubMedDate not supplied

Surface coverage effects on defibrillation impedance for transvenous electrodes.

Transvenous defibrillation electrodes are constructed by wrapping conductive elements around an insulating base. However, these conductive elements do not cover the entire area of the base. The effects of varying the surface area coverage on the defibrillation impedance (DZ) are unknown. To understand the effects, four transvenous right ventricular test leads were specially fabricated. A ring design was used with 3 mm diameter cylinders equally spaced along a 5 cm length, ending 11 mm from the pacing tip. Three leads consisted of 4, 8, and 15 rings each of length approximately 2.4 mm so that the coverages were 20%, 40%, and 70%, respectively. The fourth lead used 8 rings of length approximately 1.2 mm each and had a coverage of 20%. DZ for each lead was obtained using three methods: (i) computer simulation; (ii) in vitro measurement in a tank; and (iii) in vivo measurement in nine dogs during defibrillation testing. The DZs from either of the first two methods correlated very well (r = 0.98) with the mean DZs from the third method, indicating that in vivo DZs can be predicted from computer and in vitro models. The study shows that: (i) at the same ring length, DZ decreases as coverage (number of rings) increases; (ii) at the same coverage, DZ decreases as ring length decreases; and (iii) in vivo, a statistically significant difference was observed in DZ between the leads with 20% coverage and the leads with higher coverages. No statistically significant difference was observed between leads with coverages > 40%.

Animals↗
PubMedDate not supplied

GH-IGF axis during catch up growth in small for gestational age (SGA) infants.

The hormonal profile in 47 small for gestational age (SGA) term newborns during their first year of life was studied. The newborns had a mean birth weight of 2290 +/- 230 g and a length of 45.5 +/- 2.0 cm, and they were followed up every month. Serum IGF-I, IGF-II, and urinary growth hormone (u-GH) concentrations were measured at 3 days of age and every 3 months during one year. Serum IGFBP-3 levels were measured at 3 and 6 months of age. Catch up growth (CUG) was defined as an increase in length z score greater than 1 SD between birth and 6 months of age. According to this definition, 27 infants (57.4%) experienced CUG. We compared the hormonal profile of the infants who demonstrated evidence of CUG [CUG(+)] with those who did not [CUG(-)]. Serum IGF-II levels were significantly higher in CUG(+) infants compared to CUG(-) infants at 3 months of age. We did not find any differences in serum IGF-I, IGFBP-3 and urinary GH between CUG(+) and CUG(-) infants at any time during the study.

Birth Weight↗
PubMedDate not supplied

[The risk of ligation of the external carotid in the treatment of cervico-facial angiodysplasia. A plea for this technique to be abandoned, and current radiosurgical solutions; based upon 13 cases of ligation amongst 200 angiomas explored (author's transl)].

After describing the different collateral sytems between the various cervicocephalic arteries, the authors indicate the consequences of ligation of the external carotid. This ligation proves to totally ineffective for distal vascular lesions and severely compromises the possibilities of later treatment.

Carotid Arteries↗