Biomedical subjects

R Medrano

Publications and source records attributed to R Medrano.

6 recordsLinked to original sources

PubMed2001

Polymer characterization by size-exclusion chromatography with multiple detection.

Size-exclusion chromatography with coupled multiangle light scattering and differential refractometry detectors has been used to obtain molecular mass and radius of gyration distributions of polydisperse polymer samples. From these data the scaling law between dimensions and the absolute molecular mass is obtained with just one sample of each polymer. Three different kinds of polymers are presented: polystyrene which serves as reference polymer, polyphosphazenes which behave abnormally in solution and poly(ethylene oxide) which is soluble in water. Since the relationship between dimensions and molecular mass depends on the extent of interactions between chain segments and solvent molecules, the scaling law provides information about the solution properties of the polymer.

Chromatography, Gel↗

PubMed1997

Nitroglycerin-augmented 201T1 reinjection enhances detection of reversible myocardial hypoperfusion. A randomized, double-blind, parallel, placebo-controlled trial.

BACKGROUND: Recent observations suggest that administration of nitrates before 201Tl reinjection enhances the detection of reversible myocardial hypoperfusion. METHODS AND RESULTS: Ninety-six patients who underwent exercise-redistribution 201Tl single photon emission computed tomography (SPECT) and had persistent defects at 4-hour redistribution imaging were prospectively randomized into a double-blind protocol in which they received a reinjection of 201Tl (1.0 mCi) 5 minutes after either placebo or 0.8 mg sublingual nitroglycerin administration, followed by repeat SPECT imaging. Of the 69 patients who had coronary angiography, all except one had significant coronary stenoses. The overall extent of perfusion defect and the reversible component assessed by polar maps of the stress-redistribution images were similar in patients who received nitroglycerin or placebo. Among the 66 patients with persistent defects in the redistribution images, 58% of those receiving nitroglycerin showed improved reversibility after reinjection, compared with 33% of patients receiving placebo (P < .05). Among 68 patients with significant coronary stenoses, those who received nitroglycerin and had coronary collateral circulation were more likely to exhibit improved reversibility after reinjection than the remaining patients (50% versus 21%, P < .05). Moreover, the ratio of reversible to total defect in the vascular territories supplied by collaterals was > or = 0.50 after reinjection in 80% of patients who received nitroglycerin (n = 20) compared with 40% of the patients who received placebo (n = 15) (P < .05). CONCLUSIONS: Nitrate-augmented 201Tl reinjection significantly, albeit modestly, improves detection of defect reversibility, especially in patients with coronary collateral circulation.

Collateral Circulation↗

PubMed1996

Prognostic value of exercise 201Tl tomography in patients treated with thrombolytic therapy during acute myocardial infarction.

BACKGROUND: Although myocardial perfusion scintigraphy is of proven value in the risk stratification of patients with a recent myocardial infarction who receive conventional therapy, its value in patients undergoing thrombolytic therapy remains controversial. METHODS AND RESULTS: Seventy-one patients who received thrombolytic therapy for acute myocardial infarction had exercise 201Tl tomography and coronary angiography before hospital discharge. Eleven (15%) of 71 patients had ischemic ST-segment depression during exercise, whereas 27 patients (38%) had scintigraphic ischemia. Twenty-five (37%) of 68 patients had a cardiac event consisting of either death (n = 2), recurrent myocardial infarction (n = 5), congestive heart failure (n = 7), or unstable angina (n = 11) during a follow-up of 26 +/- 18 months. Univariate predictors of cardiac events were as follows: Killip class (P = .04); left ventricular ejection fraction (P < .0005); total (P = .002) and ischemic (P < .0005) perfusion defect size; percent thallium lung uptake (P = .001); presence of infarct-zone redistribution (P = .02); and multivessel coronary artery disease (P = .01). By multivariate analysis, the significant joint predictors of risk were ejection fraction (P < .0005) and ischemic perfusion defect size (P = .005). The combination of ejection fraction and thallium tomography added significant incremental prognostic information to the clinical data, whereas angiography did not further improve a model that included clinical, ejection fraction, and tomographic variables. CONCLUSIONS: Quantitative exercise 201Tl tomography provides important incremental, long-term prognostic information in patients receiving thrombolytic therapy for acute myocardial infarction.

Aged↗

PubMed1996

Assessment of myocardial viability with 99mTc sestamibi in patients undergoing cardiac transplantation. A scintigraphic/pathological study.

BACKGROUND: 99mTc sestamibi and 201 Tl are tracers that allow equivalent detection of myocardial infarction. However, because sestamibi does not undergo as much time-dependent redistribution as does 201Tl, it has been considered suboptimal for the detection of myocardial viability. METHODS AND RESULTS: Fifteen consecutive patients with ischemic cardiomyopathy who underwent orthotopic cardiac transplantation received an intravenous injection of 99mTc sestamibi at 1 to 6 hours before transplantation. Rotational tomography of the excised, intact, native hearts was performed to quantify the extent of myocardial hypoperfusion. The hearts were then sliced and reimaged on a gamma camera, followed by pathological quantification of the extent and severity of scarred and normal myocardium. Samples of normally and abnormally perfused myocardium underwent gamma well counting to determine tissue radioactivity and were examined under light microscopy for delineation of myocardial structure after trichrome staining. The mean extent of scintigraphic scar quantified through the use of rotational tomography was 45 +/- 14% of the left ventricle and correlated closely with pathological scar size (r = .89), despite a slight overestimation. Scintigraphic scar size determined with planar imaging of the individual myocardial slices also correlated closely with pathological scar size (r = .88). A good correlation existed between tissue 99mTc sestamibi activity determined through well counting and histological evidence of myocardial viability (r = .89). Most hypokinetic and 40% of akinetic/dyskinetic myocardial segments contained scintigraphically and histologically normal myocardium. CONCLUSIONS: 99mTc sestamibi scintigraphy can be used to accurately quantify the extent of myocardial scarring. Furthermore, the relative sestamibi activity in perfusion defects, measured several hours after administration, is a good indicator of myocardial viability determined with microscopy.

Adult↗

PubMedDate not supplied

[Arterial oxygen desaturation during transport of the post-surgery patient from operation site to recovery ward].

BACKGROUND: One of the most frequent complications in the immediate post-operation period is the fall in arterial oxygen saturation due to different factors, outstanding of which is the time that the patient remains disconnected from the oxygen supply during transport from the operation site to the recovery ward. The aim of the present paper is to measure the proportion of arterial desaturation in patients who arrive in the recovery room proceeding from the operation site without oxygen provision during transport. MATERIAL AND METHOD: The study was made with a sample of 208 cases corresponding to the patients who underwent operations in the period from March 20th to April 19th 2000. Saturation was measured by pulse oximeter at the moment of arrival in the recovery unit prior to the provision of oxygen. Patients were classified in four groups according to average saturation and they were grouped by ASA and the anaesthetic technique employed. The statistical treatment was carried out with Student's t and variance analysis. RESULTS: The sixty three per cent of patients showed a saturation of > or =95%; 26.4% slight desaturation; 6.3% moderate desaturation and 1% severe desaturation. The average of saturation of the ASA III patients showed significant differences with the ASA II and ASA I patients (p=0.004). Patients with general anaesthetic showed a desaturation with significant differences with respect to the other anaesthetic techniques employed (p<0.05). CONCLUSIONS: ASA III patients and those subjected to general anaesthetic require oxygen provision during transport from the operation site to the recovery ward.

English Abstract↗

PubMedDate not supplied

[Colorectal cancer].

OBJECTIVE: To describe the multistep carcinogenesis of the colon and rectum, and updated in the screening diagnosis and treatment of colorectal cancer. BACKGROUND: Colorectal cancer is one of the most frequent malignant neoplasia in developing countries. In Mexico, is the second malignant neoplasia of the gastrointestinal tract. MATERIAL AND METHODS: A literature search was performed to known the usefulness of screening, diagnosis and treatment procedures. Also, some of our actual proceedings are described. RESULTS: No impact in decreasing the mortality rate for colorectal cancer, has been observed with the contemporary screening programs in low risk population. The recommended treatment for colorectal cancer in early stages (Dukes A and B1) is the surgical resection alone. In those patients with colon metastasizing to the lymph nodes (Dukes C), a combination of surgery + chemotherapy is recommended. In patients with rectal cancer with full penetration until the perirectal fat or with lymph node metastasis (Dukes B2 and C) a combination of surgery, chemotherapy and radiotherapy is the elective treatment. Until today, is controversial if radiotherapy should be used pre- or postoperatively. CONCLUSION: The colorectal carcinogenesis included a multistep where are involved a tumor suppressor genes and oncogenes. Surgery is the accepted treatment for early colorectal cancer. A combination of surgery + chemotherapy +/- radiotherapy is the elective treatment for locally advanced colorectal cancer.

Adolescent↗