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Biomedical subjects

David Rivera

Publications and source records attributed to David Rivera.

6 recordsLinked to original sources
PubMed2006

Five-beam interference pattern controlled through phases and wave vectors for diamondlike photonic crystals.

We demonstrate, for what is believed to be the first time, the design of diamondlike photonic crystals made by holographic lithography based on five-beam interference. All five beams are launched from the same half-space, and the exposure can easily be realized by a single diffractive optical element. The photonic structure can be constructed through the translation of the interference pattern controlled by the phase shift of laser beams. The proposed holographic lithography is capable of creating series photonic crystals with large photonic bandgaps by adjusting the phase and the wave vector of interfering beams.

Journal Article↗
PubMed2005

Impairment in orthostatic tolerance during heat exposure in individuals with Type I and Type II diabetes.

BACKGROUND: Diabetes is often associated with orthostatic hypotension and temperature intolerance. Studies have examined either one stress or the other and not both to see if the stresses are additive. MATERIAL/METHODS: Eight subjects with Type 1 and 12 subjects with Type 2 diabetes and 15 controls were tested for orthostatic intolerance during a vertical tilt in a thermally neutral environment (22 degrees C) and a warm room (42 degrees C). Blood pressure, cardiac output, stroke volume, heart rate, skin blood flow and skin and body temperature were recorded. RESULTS: All subjects experienced reductions in their cardiac output and blood pressure when tilted. In the warmer environment, significant impairments in the compensatory blood pressure response and redistribution of cardiac output were found in subjects with diabetes. When tilted to the vertical posture, subjects with diabetes experienced reductions of about 10 mmHg in systolic blood pressure in the cool environment, and a reduction of 21 mmHg when tilted in the warm environment. The fall in the systolic pressure in the subjects with diabetes was accompanied by corresponding reductions in stroke volume and cardiac output (from 5.06 L/min to 4.75 L/min) but no change in the heart rate. To compensate for a vertical tilt, skin blood flow was reduced by about half in the controls but there was only a small vasoconstriction in the subjects with diabetes. CONCLUSIONS: Individuals with Type 1 and Type 2 diabetes, while showing some loss in orthostatic tolerance in a cool environment, showed significant clinical impairment associated with heat exposure.

Blood Flow Velocity↗
PubMed2003

Elevated carotid artery intima-media thickness levels in individuals who subsequently develop type 2 diabetes.

OBJECTIVE: We examined whether B-mode ultrasound-detected carotid artery intima-media thickness (IMT) was elevated before the onset of clinical diabetes. METHODS AND RESULTS: The study population for these analyses included 1127 nondiabetic participants, 66 prediabetic participants, and 303 diabetic participants with a mean age of 49.8 years who participated in the Mexico City Diabetes Study, a prospective cohort study. Common carotid artery (CCA) and internal carotid artery (ICA) IMTs were measured bilaterally by B-mode ultrasound. Age- and sex-adjusted mean ICA and CCA IMTs were both significantly higher among prediabetic individuals [0.81 mm [95% confidence interval (CI), 0.75-0.88] and 0.72 mm [95% CI, 0.69-0.75], respectively] than in individuals who remained free of diabetes [0.71 mm (95% CI, 0.69-0.72) and 0.69 mm (95% CI, 0.68-0.69), respectively]. However, after adjustment for established cardiovascular risk factors, ICA IMT, but not CCA IMT, remained significantly higher among prediabetic individuals [0.81 mm (95% CI, 0.75-0.88) and 0.71 mm (95% CI, 0.68-0.74)] than in individuals who remained free of diabetes [0.71 mm (95% CI, 0.69-0.72) and 0.69 mm (95% CI, 0.68-0.70)]. CONCLUSIONS: The present study provides direct evidence at the vascular level that atherosclerosis levels are elevated before the clinical onset of diabetes.

Adult↗
PubMed2002

Pneumoperitoneum after rough sexual intercourse.

Our objective is to report on a case of nonsurgical pneumoperitoneum and review the mechanism/gynecologic causes of such. We present a case report and review of the literature based on a MEDLINE search using the keywords pneumoperitoneum and nonsurgical. Radiographic evidence of free intraperitoneal air suggests hollow viscus rupture and usually warrants urgent surgical management. Findings of diffuse rebound tenderness and guarding solidify the decision for urgent surgical exploration. We present a case of a patient who presented with all of the above findings that subsequently underwent a negative laparotomy. On the day after surgery she admitted to having had rough sexual intercourse 3 days before presentation. Nonsurgical pneumoperitoneum has a number of unusual causes. Intra-abdominal, thoracic, gynecologic, iatrogenic, and miscellaneous etiologies are encountered. It was determined that the pneumoperitoneum in this case was secondary to rough sexual intercourse. We concluded that pneumoperitoneum secondary to nonsurgical causes represents a diagnostic dilemma. In the patient with free intraperitoneal air on plain X-ray one should be suspicious of less common nonsurgical etiologies. The majority of patients will require laparotomy. Thorough sexual and gynecologic/obstetrical history is a valuable adjunct in identifying the patient who does not.

Adult↗
PubMedDate not supplied

Laparoscopic management of gallbladder-associated ectopic liver.

Ectopic liver is a rare entity discussed infrequently in the surgical literature. Liver ectopia develops due to rests of liver parenchyma retained at various intraperitoneal or intrathoracic locations during migration of the liver proper during embryologic development. It is usually found during exploration for other diagnoses, commonly diseases of the biliary tree. We report a case in which a 3.7-cm mass associated with the fundus of the gallbladder was visualized preoperatively by computed tomography and identified histologically as ectopic liver after diagnostic laparoscopy and cholecystectomy with en bloc resection of the associated mass.

Adult↗