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R Lao

Publications and source records attributed to R Lao.

7 recordsLinked to original sources

Spurious dynamics in somatosensory cortex.

Cortical networks are dynamical systems whose task is to process information. However, in addition to 'intended' dynamical behaviors, the sheer complexity of a cortical network's structure-regardless of its precise details-should generate additional 'unintended' dynamical behaviors. Dynamics observed in cortical network models and in the somatosensory cortex suggest that such spurious dynamical behaviors are likely to be pervasive but relatively simple, contributing to-rather than dominating-a network's response to stimuli. Spurious dynamics may be responsible for a variety of experimentally observed intriguing features of cortical dynamics. Because of their distributed origins and emergent nature, such dynamical features, while clearly identifiable, will resist attempts at identifying specific mechanisms to explain them. We describe some of the spurious dynamical phenomena associated with somatosensory cortical response to brushing stimulation, to illustrate how spurious dynamics can affect neurons' functional properties, cortical stimulus representation and, ultimately, perception.

Algorithms↗

Utility of thallium-201 scintigraphy in detecting right ventricular dysfunction in pulmonary embolism.

Acute right ventricular dysfunction has been established both as a diagnostic and prognostic indicator in pulmonary embolism. This report illustrates the utility of thallium-201 scintigraphy as an adjunctive noninvasive test in the diagnosis of pulmonary embolism by demonstrating increases in regional right ventricular perfusion and its subsequent resolution with treatment presumably as a result of decreased pressure work.

Acute Disease↗

Tissue harmonic imaging sonography: evaluation of image quality compared with conventional sonography.

OBJECTIVE: The purpose of this study was to determine if tissue harmonic imaging (THI) sonography produced higher quality images than did conventional sonography. SUBJECTS AND METHODS: A prospective study was performed on 89 patients to compare the image quality of THI sonography with that of conventional sonography. Each examination was performed using THI sonography (transmitted frequency, 2.0 MHz; received frequency, 4.0 MHz) and conventional sonography at 2.5 and 4.0 MHz. The pancreatic area was studied in 60 patients, and other anatomic areas were studied in 68 patients. The images were then graded for penetration, detail, and total image quality. Graders were unaware of the sonographic technique. RESULTS: Of the 60 pancreatic examinations, THI sonography was the best technique for penetration in 45, detail in 54, and total image quality in 50. For the pancreas, THI sonography was significantly better than 2.5-MHz conventional sonography for penetration (p = .0002), detail (p < .0001), and total image quality (p < .0001). THI sonography was significantly better than 4.0-MHz conventional sonography for penetration (p < .0001), detail (p < .0001), and total image quality (p < .0001). Of the 68 examinations of other anatomic areas, THI sonography was the best technique for penetration in 42, detail in 57, and total image quality in 58. For other anatomic areas, THI sonography was significantly better than 2.5-MHz conventional sonography for penetration (p = .05), detail (p < .0001), and total image quality (p < .0001). THI sonography was significantly better than 4.0-MHz conventional sonography for penetration (p < .0001), detail (p < .0001), and total image quality (p < .0001). CONCLUSION: The THI technique improved sonographic image quality.

Aged↗

Right ventricular dysfunction in obstructive sleep apnoea: reversal with nasal continuous positive airway pressure.

The incidence and pathogenesis of right ventricular dysfunction in obstructive sleep apnoea (OSA) remains controversial. Using nuclear ventriculography, the prevalence of right ventricular dysfunction (RVD) was therefore determined in obese patients with OSA, as well as their clinical characteristics, arterial blood gas values, spirometry and sleep parameters. The reversibility of RVD was evaluated after long-term use of nasal continuous positive airway pressure (nCPAP). We studied 112 obese patients with OSA by nuclear ventriculography, 35 with RVD (Group 1), 77 without RVD (Group 2), and 14 patients without OSA as controls (Group 3). Repeat nuclear ventriculography was performed in seven patients who used nCPAP nightly for 6-24 months. The mean right ventricular ejection fractions (RVEF) were 31%, 47% and 44% in Groups 1, 2 and 3, respectively. Group 1 also had a lower left ventricular ejection fraction (LVEF) of 55 vs 63% in Group 2. The OSA groups did not differ in mean spirometric or arterial blood gas values. Group 1 had a lower mean nocturnal arterial oxygen saturation (Sa,O2) of 82 vs 87% in Group 2, and a longer apnoea duration of 22.3 vs 19.2 s. All but two patients in Group 1 had either awake alveolar hypoventilation or an apnoea + hypopnoea index > 40 disordered breathing events.h-1. Repeat nuclear ventriculography after nCPAP revealed an increase in RVEF from 30 to 39%. In conclusion, right ventricular dysfunction is common in obstructive sleep apnoea, but it is reversible with nasal continuous positive airway pressure treatment and appears to be related to nocturnal oxygen desaturation.

Adult↗

Comparison of thallium-201 and gallium-67 citrate scintigraphy in the diagnosis of pulmonary disease.

Gallium is presently used in the diagnosis of inflammatory, granulomatous, and neoplastic lung disease despite its many logistical problems. In contrast, thallium-201 scintigraphy, which was initially developed for myocardial imaging, offers the principal advantage of immediate imaging and diagnosis although it had not been investigated previously for use in pulmonary disease. In this study, thallium and gallium were prospectively compared with each other for the diagnosis of a variety of lung diseases. The overall concordance rate was 75%. Thallium was found to be significantly more sensitive than gallium for the entire group studied (N = 51, p < 0.006). In a subset of patients in whom a firm diagnosis was established, thallium was also found to be more sensitive, 86% vs 64%. The greater sensitivity of thallium-201 and its several inherent advantages suggest that thallium-201 should replace gallium-67 citrate as the radioisotope of choice for nuclear imaging of the chest.

Adolescent↗

Stem cell factor amplifies newborn and sickle erythropoiesis in liquid cultures.

A two-phase liquid-culture system was used to substantially amplify and differentiate erythroblasts, starting with mononuclear cells from the blood of normal adults, newborn infants, and patients with sickle cell anemia. After the first 7 days (phase 1), in medium plus fetal bovine serum (FBS) alone, or in combination with stem cell factor (SCF) or conditioned medium (CM), the cell number was unchanged, and the cells all looked like lymphocytes. These cells were then diluted into medium with erythropoietin (Ep) alone, with Ep and either SCF or CM, or in methylcellulose with the same factors (phase 2). After 14 days in liquid phase 2 with SCF and Ep, the cell numbers increased an average of 30-fold in the sickle, 24-fold in the newborn, and 4-fold in the normal adult cultures; almost all the cells were erythroblasts and erythrocytes. SCF in phase 1 increased the number of late progenitors (CFU-E) assayed in methylcellulose, with the largest number in sickle, followed by newborn cultures and then adult cultures. We conclude that erythroid progenitor cells survive for at least 7 days without Ep (but with FBS). Progenitor cells are amplified, particularly with SCF. Later in culture, SCF with Ep increases the final number of differentiated erythroid cells. Both the early and the late effects of SCF are most effective in sickle, followed by newborn cultures and then adult cultures.

Adult↗

Bone scan evidence of renal osteodystrophy in undialyzed uremic patients.

Scintigraphy with the 99m-Tc complexes offers serveral distinct advantages to the nephrologist. The procedure is both easily performed and readily available, there have been no reports of toxicity, and the radiation exposure to the patient is lower than that of conventional radiography. We suggest that scintigraphic evidence of metabolic bone disease is present at the onset of terminal uremia with much higher frequency than is detectable by radiographs, and that unsuspected soft tissue calcification may also be detected on occasion. Therefore, 99m-Tc scans may be a valuable addition to the diagnostic regimen of the uremic, and should be thoroughly evaluated with more extensive studies, including quantitative analyses.

Adolescent↗