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Biomedical subjects

D Chu

Publications and source records attributed to D Chu.

At least 37 records · Page 2Linked to original sources
PubMed1998

Differences between sound scattering by weakly scattering spheres and finite-length cylinders with applications to sound scattering by zooplankton.

A modeling study was conducted to determine the conditions under which fluidlike zooplankton of the same volume but different shapes (spherical/cylindrical) have similar or dramatically different scattering properties. Models of sound scattering by weakly scattering spheres and cylinders of finite length used in this analysis were either taken from other papers or derived and herein adapted for direct comparison over a range of conditions. The models were examined in the very low- (ka << 1, kL << 1), moderately low- (ka << 1, kL > or = 1), and high-frequency regions (ka >> 1, kL >> 1), where k is the acoustic wave number, a is the radius (spherical or cylindrical) of the body, and L is the length of the cylinders (for an elongated body with L/a = 10, "moderately low" corresponds to the range 0.1 < or = ka < or = 0.5). Straight and bent cylinder models were evaluated for broadside incidence, end-on incidence, and averages over various distributions of angle of orientation. The results show that for very low frequencies and for certain distributions of orientation angles at high frequencies, the averaged scattering by cylinders will be similar, if not identical, to the scattering by spheres of the same volume. Other orientation distributions of the cylinders at high frequencies produce markedly different results. Furthermore, over a wide range of orientation distributions the scattering by spheres is dramatically different from that of the cylinders in the moderately low-frequency region and in the Rayleigh/geometric transition region: (1) the Rayleigh to geometric scattering turning point occurs at different points for the two cases when the bodies are constrained to have the same volume and (2) the functional dependence of the scattering levels upon the volume of the bodies in the moderately low-frequency region is quite often different between the spheres and cylinders because of the fact that the scattering by the cylinders is still directional in this region. The study demonstrates that there are indeed conditions under which different shaped zooplankton of the same volume will yield similar (ensemble average) scattering levels, but generally the shape and orientation distribution of the elongated bodies must be taken into account for accurate predictions.

Acoustics↗
PubMed1998

Sound scattering by several zooplankton groups. I. Experimental determination of dominant scattering mechanisms.

The acoustic scattering properties of live individual zooplankton from several gross anatomical groups have been investigated. The groups involve (1) euphausiids (Meganyctiphanes norvegica) whose bodies behave acoustically as a fluid material, (2) gastropods (Limacina retroversa) whose bodies include a hard elastic shell, and (3) siphonophores (Agalma okeni or elegans and Nanomia cara) whose bodies contain a gas inclusion (pneumatophore). The animals were collected from ocean waters off New England (Slope Water, Georges Bank, and the Gulf of Maine). The scattering properties were measured over parts or all of the frequency range 50 kHz to 1 MHz in a laboratory-style pulse-echo setup in a large tank at sea using live fresh specimens. Individual echoes as well as averages and ping-to-ping fluctuations of repeated echoes were studied. The material type of each group is shown to strongly affect both the overall echo level and pattern of the target strength versus frequency plots. In this first article of a two-part series, the dominant scattering mechanisms of the three animal types are determined principally by examining the structure of both the frequency spectra of individual broadband echoes and the compressed pulse (time series) output. Other information is also used involving the effect on overall levels due to (1) animal orientation and (2) tissue in animals having a gas inclusion (siphonophores). The results of this first paper show that (1) the euphausiids behave as weakly scattering fluid bodies and there are major contributions from at least two parts of the body to the echo (the number of contributions depends upon angle of orientation and shape), (2) the gastropods produce echoes from the front interface and possibly from a slow-traveling circumferential (Lamb) wave, and (3) the gas inclusion of the siphonophore dominates the echoes, but the tissue plays a role in the scattering and is especially important when analyzing echoes from individual animals on a ping-by-ping basis. The results of this paper serve as the basis for the development of acoustic scattering models in the companion paper [Stanton et al., J. Acoust. Soc. Am. 103, 236-253 (1998)].

Acoustics↗
PubMed1998

In vivo efficacy of ABT-255 against drug-sensitive and -resistant Mycobacterium tuberculosis strains.

Current therapy for pulmonary tuberculosis involves 6 months of treatment with isoniazid, pyrazinamide, rifampin, and ethambutol or streptomycin for reliable treatment efficacy. The long treatment period increases the probability of noncompliance, leading to the generation of multidrug-resistant isolates of Mycobacterium tuberculosis. A treatment option that significantly shortened the course of therapy, or a new class of antibacterial effective against drug-resistant M. tuberculosis would be of value. ABT-255 is a novel 2-pyridone antibacterial agent which demonstrates in vitro potency and in vivo efficacy against drug-susceptible and drug-resistant M. tuberculosis strains. By the Alamar blue reduction technique, the MIC of ABT-255 against susceptible strains of M. tuberculosis ranged from 0.016 to 0.031 microg/ml. The MIC of ABT-255 against rifampin- or ethambutol-resistant M. tuberculosis isolates was 0.031 microg/ml. In a murine model of pulmonary tuberculosis, 4 weeks of oral ABT-255 therapy produced a 2- to 5-log10 reduction in viable drug-susceptible M. tuberculosis counts from lung tissue. Against drug-resistant strains of M. tuberculosis, ABT-255 produced a 2- to 3-log10 reduction in viable bacterial counts from lung tissue. ABT-255 is a promising new antibacterial agent with activity against M. tuberculosis.

Animals↗
PubMed1998

[The role of recombinant interferon alpha-2b in the treatment of advanced malignancies].

OBJECTIVE: To identify the efficacy and toxicity of recombinant interferon alpha-2b in the treatment of advanced malignancis. METHODS: Interferon alpha-2b was administered intra-muscularly, the escalating dosage being 3 x 10(6) IU, twice in the first week, 6 x 10(6) IU twice in the second week and thereafter 9 x 10(6) IU twice weekly until the 8th week. RESULTS: Among 102 patients, 90 were eva luable. The overall response rate (RR) was 16.7%. The RR in patients with renal cell careinoma was 10.8% (4/37, with 2 complete and 2 partial responses), that in patients with malignant melanoma was 14.3% (4/28, 4 partial responses), it was 50% (4/8, 4 partial responses) in malignant lymphoma and 20% (3/15, 3 partial responses) in breast cancer. The median response duration was 40 months in the patients with complete response, while only 4.8 months in patients with partial response. The major adverse reactions were flu-like syndrome, while gastro-intestinal reactions and bone marrow suppression were mild. CONCLUSION: Recombinant interferon alpha-2b has antitumor activity in patients with advanced renal cell carcinoma, malignant melanoma and malignant lymphoma. It could be considered as a second line treatment regimen.

Adult↗
PubMed1997

Outcomes of stroke patients in Medicare fee for service and managed care.

CONTEXT: Increasing numbers of Medicare beneficiaries have been enrolling in health maintenance organizations (HMOs) because HMO participation reduces out-of-pocket expenses, and the federal government views HMOs as a way to contain Medicare costs. However, results comparing outcomes and quality of care in HMOs vs fee for service (FFS) have been mixed, and outcomes after stroke have not been adequately assessed. OBJECTIVE: To compare discharge destinations and survival rates following stroke in Medicare HMOs with similar FFS settings. DESIGN: An observational study for 2 groups evaluating stroke patients' discharge destinations and survival times from the date of hospital admission. SETTING: A total of 19 HMOs were selected from 12 states. The FFS sample was drawn from the same geographic areas. PATIENTS: The sample included 402 HMO patients from 71 hospitals and 408 FFS patients from 60 hospitals. PROCESS AND OUTCOME MEASURES: Data were abstracted from medical records on demographics, clinical characteristics of stroke, comorbid illnesses, and discharge destinations following hospitalization. Data on survival were obtained from Medicare files and included 25 to 37 months of follow-up (median, 30.4 months, HMO; 31.1 months, FFS) from the date of hospital admission. RESULTS: There were 109 patients who died during the hospitalization (49 HMO, 12.2%; 60 FFS, 14.7%), and a total of 410 patients had died by the end of follow-up (191 HMO, 47.5%; 219 FFS, 53.7%). Approximately one fourth of both groups had do-not-resuscitate orders (HMO, 25.4%; FFS, 27.9%; P=.68). After controlling for age, marital status, and characteristics of dependency at discharge, HMO patients were more likely than FFS patients to be sent to nursing homes (HMO, 41.8%; FFS, 27.9%; P=.001) and less likely to be discharged to rehabilitation hospitals or units (HMO, 16.2%; FFS, 23.4%; P=.03). At follow-up, no significant differences in relative risk of dying were found between HMO and FFS groups (relative risk, 0.96; 95% confidence interval, 0.73-1.26; P=.77). CONCLUSIONS: Patients in Medicare HMOs who experience strokes are more likely to be discharged to nursing homes and less likely to go to rehabilitation facilities following the acute event. However, they have similar survival patterns compared with comparable patients in FFS settings after adjusting for other factors.

Aged↗
PubMed1997

Isovolemic hemodilution with purified and polymerized bovine hemoglobin in a rabbit model of focal cerebral ischemia.

Isovolemic hemodilution with polymerized bovine hemoglobin (PoBH) was tested as a means of preventing infarction in a rabbit model of focal cerebral ischemia. The animals were divided into one control group and one hemodilution group. All animals underwent two hours of ischemia, caused by clipping the left internal carotid artery, the anterior cerebral artery, and the middle cerebral artery, followed by 4 hours of reperfusion. In the control group, the hematocrit was not manipulated (mean +/- SE: 33.8 +/- 1.3%), while in the hemodilution group, the Hct was reduced to 12.5 +/- 1.9% by exchange of blood with PoBH, before clipping the cerebral vessels. Staining with 2,3,5- triphenyltetrazolium chloride (TTC) was used to evaluate the infarct size. The infarct volume was 427 +/- 52 mm3 in the control animal, and 1026 +/- 311 mm3 (p < 0.01 when compared with the control group) in the animal hemodiluted with PoBH. PoBH hemodilution was found to be associated with vasoconstriction. This pathological vasoconstriction probably counteracted any beneficial effects from the lowered viscosity and explains our negative results. Vasoconstriction has to be overcome before hemodilution can have its beneficial effect in reducing the cerebral ischemia.

Animals↗
PubMed1997

Postoperative mitral valve abscess. A case report.

The authors report a case of a patient with postoperative perimitral bioprosthetic abscess and probable systemic embolization. The location of the abscess is not common and the use of porcine bioprostheses is supposedly associated with a low rate of embolic complications. Because of the high mortality and morbidity, it is stressed that patients with prosthetic valve endocarditis should be managed aggressively with surgery.

Abscess↗
PubMed1997

Transthoracic endoscopic sympathectomy for treatment of hyperhidrosis palmaris.

The objective of this study was to determine the effectiveness of modified transthoracic endoscopic sympathectomy (TES) being used in our institute for treatment of hyperhidrosis palmaris (HP). One hundred and eight cases of HP were treated using TES from June 1991 to June 1992. All underwent TES bilaterally. Palmar temperature was monitored during the operation as an indicator of a successful lesioning of the sympathetic trunk at the T2-level. The ages of the patients ranged from 10 to 61 years. Fifty-one percent of these patients had a positive family history. Seventy-three percent had onset during childhood. Eighty-nine percent had excessive plantar sweating in addition to hyperhidrosis palmaris. The increase in palmar temperature after lesioning the sympathetic trunk was inversely related to the preoperative temperature of the palms (r = 0.81, p < 0.005). Our treatment resulted in improvement of palmar sweating in all of the patients. Decrease of plantar sweating was also noted in 68% of the patients at follow up. No neurological deficits were found. Transient post-operative chest discomfort and compensatory hyperhidrosis (87%) were the most common complications. TES is an effective method for treating patients with HP, with a shorter operation time, fewer hospital days, and a better cosmetic result, as compared with the dorsal approach for thoracic sympathectomy.

Adolescent↗
PubMed1996

Mild hypothermia, hypertension, and mannitol are protective against infarction during experimental intracranial temporary vessel occlusion.

A rabbit model of focal temporary ischemia was used to test the protection provided by mild hypothermia, hypertension, mannitol and the combination of the three methods. Twenty-four New Zealand White rabbits were divided into five groups as follows: a control group, a hypertension group (mean arterial blood pressure increased by 42 mm Hg), a hypothermic group (rectal temperature decreased by 6 degrees C), a mannitol group (1 g/kg of body weight, administered intravenously), and the triple-therapy group. The intracranial internal carotid artery, the middle cerebral artery, and the anterior cerebral artery were clipped for 2 hours and then underwent 4 hours of reperfusion. Blood pressure, rectal and brain temperature, blood glucose level, hematocrit, and arterial blood gases were monitored during the experiment. For measuring the infarction size, the brain was divided into 4-mm slices and stained with 2,3,5-triphenyltetrazolium chloride. The severity of the neuronal damage was also evaluated by conventional histological examination with hematoxylin and eosin staining. The infarct volume was 193.2 +/- 34.8 (standard error of the mean) mm3 for the control group, 32.3 +/- 22.6 mm3 for the hypertension group (P < 0.0005 versus control), 40.9 +/- 17.6 mm3 for the hypothermia group (P < 0.0005), 58.0 +/- 41.0 mm3 for the mannitol group (P < 0.005), and 0.9 +/- 0.9 mm3 for the triple-therapy group (P < 0.0001). The infarct volume of the triple-therapy group was smaller than that of the hypertension, hypothermia, and mannitol groups but the difference was not statistically significant. The combination of hypertension, mild hypothermia, and mannitol to protect against temporary focal ischemia provides a set of manipulations that is readily available for neurovascular procedures.

Animals↗
PubMed1995

Technetium99m-sestamibi scanning before initial neck exploration in patients with primary hyperparathyroidism.

Technetium99m (Tc) sestamibi(mibi) has been proposed as an alternative to the standard radionuclide imaging technique of thallium 201 chloride-99mTc pertechnetate subtraction scan (TTS) in patients with primary hyperparathyroidism. In the present study, mibi was evaluated as an alternative to TTS in 37 patients who had either mibi-99mTc pertechnetate subtraction scans, mibi-iodine123 (I) subtraction scans or mibi single isotope washout scans. There were 30 females and 7 males with an average age of 57 years (range, 27-78 years). Parathyroid adenomas were found in 35 patients and hyperplasia in 2. Twenty-eight mibi scans were positive and 25 of these correctly localized the parathyroid abnormality for a sensitivity of 68% (25 of 37) and a positive predictive value of 89% (25 of 28). There were 3 false-positives (8%) and 9 false-negatives (25%). The scan was not helpful in either patient with parathyroid gland hyperplasia. Mibi-123I subtraction was the most accurate scan and was diagnostic clinically in all 7 patients studied. Mibi scans were significantly more likely to identify inferior rather than superior adenomas (P = 0.01). Twenty-seven of the 37 patients also had a TTS which was correct in only 37% of cases while the mibi scan was correct in 68% (P = 0.02). However, routine use of nuclear scanning with mibi was still not supported by these data. Further clinical evaluation of various techniques may improve accuracy. Since mibi was significantly more accurate than TTS, it should be considered preferentially when radionuclide imaging is used in patients with recurrent hyperparathyroidism.

Adenoma↗
PubMed1995

In vitro activity of A-86719.1, a novel 2-pyridone antimicrobial agent.

This study evaluated the in vitro activity of A-86719.1, a novel 2-pyridone antimicrobial agent. The drug inhibited all tested members of the family Enterobacteriaceae at < or = 0.5 microgram/ml and all tested Pseudomonas aeruginosa, Burkholderia (Pseudomonas) cepacia, and Xanthomonas maltophilia strains at < or = 2 micrograms/ml. All but two strains of gram-positive bacteria were inhibited by < or = 1 microgram of the new drug per ml, including isolates highly resistant to ciprofloxacin.

Anti-Bacterial Agents↗
PubMed1994

Transmission at the squid giant synapse was blocked by tetanus toxin by affecting synaptobrevin, a vesicle-bound protein.

1. The effect of whole tetanus toxin (TeTX) and of its light chain (TeTX L-chain) on transmitter release was determined by presynaptic pressure-injection in the squid giant synapse. 2. The results indicate that whole TeTX does not modify transmission while the L-chain blocks transmission within 20-30 min. This block does not involve changes in the sodium or potassium conductances responsible for spike generation or the voltage-dependent presynaptic calcium current responsible for transmitter release. 3. Western blotting of protein fractions from the squid optic lobe demonstrated the presence of a protein which reacted with specific antibodies against mammalian synaptobrevin, a vesicular protein. In addition, this protein was enzymatically cleaved by the L-chain component of the toxin in a similar fashion to its mammalian counterpart. 4. These results demonstrate that TeTX L-chain toxin acts directly on a squid synaptobrevin and prevents synaptic release probably by interfering with the docking-fusion synaptic vesicles at the active zone.

Animals↗
PubMed1991

Single photon emission computed tomography using 99mTc-HM-PAO in the routine evaluation of Alzheimer's disease.

Regional cerebral blood flow was studied in 7 patients with clinically suspected Alzheimer's disease and 10 normal controls by single photon computed emission tomography (SPECT) using HM-PAO. All patients with Alzheimer's disease and no controls had parietal lobe hypoperfusion which was usually bilateral. In patients with more severe dementia hypoperfusion extended into the frontal lobes. Parietal lobe hypoperfusion corresponds to parietal lobe degeneration which is the one of the first neocortical regions to show the typical degenerative changes of Alzheimer's disease. SPECT with HM-PAO is a non-invasive investigation available in most nuclear medicine departments and complements existing tests in the routine evaluation of patients presenting with dementia.

Aged↗