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Biomedical subjects

H Liu

Publications and source records attributed to H Liu.

At least 739 records · Page 41Linked to original sources
PubMed1998

Effects of L-NAME on cerebral metabolic, vasopressin, oxytocin, and blood pressure responses in hemorrhaged rats.

NG-nitro-L-arginine methyl ester (L-NAME; 250 micrograms/5 microliters), an inhibitor of NO synthase, or the vehicle artificial cerebrospinal fluid (aCSF; 5 microliters) was administered intracerebroventricularly to conscious rats hemorrhaged (0.7 ml/min) to a 20% volume depletion. Hypotension was maximal 5 min after hemorrhage ended, with compensatory recovery to basal levels 20 min later, regardless of drug treatment. L-NAME, however, elevated (P < 0.05) blood pressure (vs. aCSF controls) 40-45 min after intracerebroventricular administration. In normovolemic rats, L-NAME produced a significant pressor response and increased plasma levels of vasopressin (VP) and oxytocin (OT). After hemorrhage, both hormone levels increased, but only OT was further enhanced by L-NAME. Thus centrally produced NO tonically inhibits OT and VP secretion under basal normovolemic conditions and selectively inhibits OT release during hypovolemia. Hemorrhage increased the rates of glucose utilization in the neural lobe, indicative of enhanced efferent neural functional activity. L-NAME further enhanced the metabolic activity in the entire hypothalamoneurohypophysial system of hemorrhaged animals. Several other brain structures involved in the regulation of blood pressure and the stress response were also metabolically affected by the hemorrhage and L-NAME.

Animals↗
PubMed1998

High-field strength interventional magnetic resonance imaging for pediatric neurosurgery.

BACKGROUND: Interventional magnetic resonance (MR) imaging allows neurosurgeons to interactively perform surgery using MR guidance. High-field (1.5-Tesla) strength imaging provides exceptional visualization of intracranial and spinal pathology. The full capabilities of this technology for pediatric neurosurgery have not been defined or determined. MATERIALS AND METHODS: From January 1997 through June 1998, 10 of 85 cases performed in the interventional MR unit were in the pediatric population (mean age 8.3, median 8, range 2-15 years). Procedures included 2 brain biopsies, 5 craniotomies for tumor, 2 thoracic laminectomies for syringomyelia, and placement of a reservoir into a cystic brainstem tumor. The biopsies and reservoir placement were performed using MR-compatible equipment. Craniotomies and spinal surgery were performed with conventional instrumentation outside the 5-Gauss magnetic footprint. Interactive and intraoperative imaging was performed to assess the goals of surgery. RESULTS: Both brain biopsies were diagnostic for cerebral infarct and anaplastic astrocytoma and the reservoir was optimally placed within the tumor cyst. Of the 5 tumor resections, all were considered radiographically complete. One biopsy patient and 1 tumor resection patient experienced transient neurological deficits after surgery. The patient with the thoracic syrinx required reoperation when the syringosubarachnoid shunt migrated into the syrinx 3 months after initial placement. No patient sustained a postoperative hemorrhage. Tumor histologies found at craniotomy were craniopharyngioma, ganglioglioma, and 3 low-grade gliomas. No evidence of tumor progression has been seen in any of these patients at a mean follow-up of 5.3 (range 4-8) months. The goals of the procedure were achieved in all 10 cases. There were no untoward events experienced related to MR-compatible instrumentation or intraoperative patient monitoring, despite the present inability to monitor core body temperature. CONCLUSIONS: 1.5-Tesla interventional MR is a safe and effective technology for assisting neurosurgeons to achieve the goals of pediatric neurosurgery. Preliminary results suggest that surgical resection of histologically benign tumors is enhanced in the interventional MR unit. The incidence of surgically related morbidity is low.

Adolescent↗
PubMed1998

Apoptosis in a neonatal rat model of cerebral hypoxia-ischemia.

BACKGROUND AND PURPOSE: The mechanisms of excitotoxic cell death in cerebral ischemia are poorly understood. In addition to necrosis, apoptotic cell death may occur. The purpose of this study was to determine whether an established model of cerebral hypoxia-ischemia in the neonatal rat demonstrates any features of apoptosis. METHODS: Seven-day-old neonatal rats underwent bilateral, permanent carotid ligation followed by 1 hour of hypoxia, and their brains were examined 1, 3, and 4 days after hypoxia-ischemia. The severity of ischemic damage was assessed in the dentate gyrus and frontotemporal cortex by light microscopy. Immunocytochemistry was performed to detect the cleavage of actin by caspases, a family of enzymes activated in apoptosis. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) reactivity was examined in the cortical infarction bed and dentate gyrus. Neonatal rat brain DNA was run on agarose gel electrophoresis to detect DNA fragmentation. Ethidium bromide-staining and electron microscopy were used to determine whether apoptotic bodies, 1 of the hallmarks of apoptosis, were present. RESULTS: The frontotemporal cortex displayed evidence of infarction, and in most rats the dentate gyrus showed selective, delayed neuronal death. Immunocytochemistry demonstrated caspase-related cleavage of actin. TUNEL and DNA electrophoresis provided evidence of DNA fragmentation. Ethidium bromide-staining and electron microscopy confirmed the presence of chromatin condensation and apoptotic bodies. CONCLUSIONS: Features of apoptosis are present in the described model of cerebral hypoxia-ischemia. Apoptosis may represent a mode of ischemic cell death that could be the target of novel treatments that could potentially expand the therapeutic window for stroke.

Animals↗
PubMed1998

A computational fluid dynamic study of hawkmoth hovering

A computational fluid dynamic (CFD) modelling approach is used to study the unsteady aerodynamics of the flapping wing of a hovering hawkmoth. We use the geometry of a Manduca sexta-based robotic wing to define the shape of a three-dimensional 'virtual' wing model and 'hover' this wing, mimicking accurately the three-dimensional movements of the wing of a hovering hawkmoth. Our CFD analysis has established an overall understanding of the viscous and unsteady flow around the flapping wing and of the time course of instantaneous force production, which reveals that hovering flight is dominated by the unsteady aerodynamics of both the instantaneous dynamics and also the past history of the wing. A coherent leading-edge vortex with axial flow was detected during translational motions of both the up- and downstrokes. The attached leading-edge vortex causes a negative pressure region and, hence, is responsible for enhancing lift production. The axial flow, which is derived from the spanwise pressure gradient, stabilises the vortex and gives it a characteristic spiral conical shape. The leading-edge vortex created during previous translational motion remains attached during the rotational motions of pronation and supination. This vortex, however, is substantially deformed due to coupling between the translational and rotational motions, develops into a complex structure, and is eventually shed before the subsequent translational motion. Estimation of the forces during one complete flapping cycle shows that lift is produced mainly during the downstroke and the latter half of the upstroke, with little force generated during pronation and supination. The stroke plane angle that satisfies the horizontal force balance of hovering is 23.6 degrees , which shows excellent agreement with observed angles of approximately 20-25 degrees . The time-averaged vertical force is 40 % greater than that needed to support the weight of the hawkmoth.

Journal Article↗
PubMed1998

The entry of underrepresented minority students into US medical schools: an evaluation of recent trends.

OBJECTIVES: Recent challenges to affirmative action suggest the need to reassess the status of the admission of underrepresented minority students to US medical schools. METHODS: The Association of American medical colleges provided US medical school enrollment data and characteristics. Five measures of underrepresented minority enrolled and an overall performance scale were constructed for each school. Multivariate regression identified significant overall performance predictors. Predicted and observed values were compared. RESULTS: Underrepresented minority enrollment increased by 43% after 1986, peaked at 2014 in 1994, did not increase in 1995, and decreased by 5% in 1996. Enrollment was associated with increasing federal research funding and with percentage of underrepresented minorities in the sources population P < .001). The 1996 decline was almost entirely limited to public medical schools. Those in California, Texas, Mississippi, and Louisiana accounted for 18% of 1995 enrollment but 44% of the 1996 decline. CONCLUSIONS: Recent gains in medical school enrollment of underrepresented minorities are being reversed, particularly at public institutions. Implications exist for the health of poor, minority, and underserved communities, which are most likely to be cared for by underrepresented minority physicians.

Adolescent↗
PubMed1998

Teaching medical ethics to orthopaedic surgery residents.

Orthopaedic surgery residents will be faced with a variety of ethical issues when they enter clinical practice. A previous survey suggested that they lack knowledge about how to approach several types of medical ethics dilemmas. We developed a medical ethics curriculum for orthopaedic surgery residents and presented it over a one-year period to the residents in one training program. The effect of the educational intervention on the residents' knowledge of medical ethics and their ability to handle hypothetical situations was measured by comparing their responses to a questionnaire, administered before and after the intervention, with those of residents in a training program in which the intervention was not provided. The twenty-five residents at the site of the educational intervention had a mean improvement of 0.10 in the overall score, from a mean score of 0.71 on the baseline survey to a mean score of 0.81 on the follow-up survey. This improvement was significantly greater than the mean improvement of 0.02 for the thirty residents at the control site, who had a mean score of 0.72 on the baseline survey and a mean score of 0.74 on the follow-up survey (p = 0.002). Six residents who participated in the medical ethics curriculum rated it as very useful; seventeen, as somewhat useful; one, as slightly useful; and one, as not at all useful. A medical ethics curriculum can increase orthopaedic residents' knowledge of medical ethics. Whether this curriculum also will lead to behavioral changes requires additional evaluation.

California↗
PubMed1998

Distribution of SPR-like immunoreactivity in the medullary visceral zone of the rat and changes following acute myocardial ischemia induced by intravenous injection of vasopressin.

Substance P receptor-like immunoreactive (SPR-LI) structures and changes following intravenous injection of vasopressin in the medullary visceral zone (MVZ) of the rat were studied by using immunohistochemical methods. In normal control rats the distribution of SPR-LI structure in MVZ generally matched with that of immunostaining against substance P (SP-LI) except in some areas. SPR-LI neurons and dendrites differed in size and shape in different areas of MVZ. Their dendrites could be classified into three types, i.e, wool-shaped, smooth and varicose. Some SPR-LI neurons were also positive for tyrosine hydroxylase-like immunoreactivity (TH-LI) . After administration of vasopressin SPR-LI structures became denser, especially at levels of pyramidal decussation (PYX) and area postrema (AP). The dendrites of motor dorsal nucleus of X (NMDX) in the dorsal part of MVZ appeared thin and straight in morphology instead of curl and thick outlooks. These results implicate that some SPR-LI neurons might be involved in the modulation of the cardiovascular stress induced by vasopressin.

Acute Disease↗
PubMed1998

Downstream technique study of human tumor necrosis factor alpha and its mutant.

The study of downstream techniques for recombinant human necrosis factor alpha (rhTNF alpha) and its mutant (Lys2)-rhTNF alpha led to the results of approximately 50 g wet recombinant E. coli per liter with high expression level (> 50%) harvested from autocontrolled fed-batch culture in 15 L fermentor (B. Braun). The rhTNF alpha and (Lys2)-rhTNF alpha expressed are totally soluble. Followed by the process of ultrasonication, ammonium sulfate precipitation, ion-exchange chromatography (DEAE-sepharose FF, CM-sepharose FF), and molecular sieve (Sephacryl S-200), a yield of approximately 1 g pure recombinant protein from 1 L broth is obtained. The purity is up to 98%. The specific activity of rhTNF alpha and (Lys2)-rhTNF alpha are approximately 1.5 x 10(8) IU/mg and approximately 6 x 10(8) IU/mg, respectively.

Escherichia coli↗
PubMed1998

Experimental study on intramuscular injection of eukaryotic expression vector pcDNA3- IL-6 on BXSB mice.

OBJECTIVE: To study the role of IL-6 in systemic lupus erythematosis (SLE). METHODS: We constructed eukaryotic expression vector pcDNA3- IL-6 encoding for IL-6 and injected it intramuscularly into BXSB mice. 22 of the 3.5-month-old male BXSB mice were divided into two groups. One group was injected with the pcDNA3-IL-6 100 micrograms per mouse twice at the interval of 20 days. Another group was injected with plasmid pcDNA3 at the same time as control. The ANA and proteinuria were monitored every 10 days, and the IL-6 activity in serum, IgG, C3 deposition and IL-6 expression in kidney detected at the 40th day. RESULTS: IL-6 encoding plasmid had harmful effects on murine SLE with increased ANA level, proteinuria, IgG, C3 deposition and IL-6 expression in kidney, but there was no difference of serum GPT levels between the two groups. CONCLUSION: Excessive production of IL-6 could play an important pathogenic role in SLE. Blocking or reducing IL-6 secretion might be a new therapy for SLE.

Animals↗
PubMed1998

Diagnosis and treatment of acute central cervical cord injury.

OBJECTIVE: To clarify the diagnosis and management of acute central cervical cord injury. METHODS: Eighty-nine patients with acute cervical central cord injury were retrospectively reviewed. Sixty-three patients were treated conservatively and 26 were treated surgically. There were two acute deaths. Eighty-seven patients were followed up for 3 months to 15 years. RESULTS: Their average neurological score (ASIA) was increased from 41.7 at admission to 83.1 at follow-up. CONCLUSIONS: Acute central cervical cord injury should be differentiated from complete spinal cord injury, cervical myelopathy, cruciate paralysis and C8 nerve root injury. When compression of nerve tissue or cervical instability is identified, operative intervention should be indicated. The prognosis is less optimistic in the patients with severe primary injury and at old age.

Adult↗
PubMed1998

[Histological evaluation of collagen-hydroxyapatite composite as osseous implants in the repair of mandibular defect].

To observe the collagen-hydroxylaptite composite in the repair of bone defect, ten minipigs were chosen to make a mandibular dafect measuring 2 cm in diameter and the composite was implanted, while the use of autogenous bone graft and the blank wese served as control. On the 4, 8, 12, 24 and 48 weeks after the operation, the animals were sacrificed and the samples were examined under light microscope. The result showed that: no infection or necrosis occurred. The composite coalesced with host bone and the outcome was similar to that of the autogenous bone graft. No foreign body giant cells or vacuum left from osteonecrosis was observed. It was suggested that the composite had the advantage of abundant supply, easy to handle and no harm. The biocompatibility was good and might be hopeful as a bone substitute.

Animals↗
PubMed1998

[A new method to repair artery injuries in extremities by phleboplasty of branched vein graft].

In order to develope a new method to overcome the difficulties in anastomosis of blood vessels with different diameter, phleboplasty was utilized at the join-point to expand the diameter of branched vein graft, with a funnel-shaped stoma formed consequently. After successfully experimented in fresh blood vessels in vitro, the method was practised clinically to repair injured arteries in extremities, with the outcome that phleboplasty of branched vein graft could enlarge the diameter by 1-1.25 times, and with satisfied effects in 3 clinic cases. So, the conclusion was that: phleboplasty of branched vein graft was a new effective and convinient method to repair injured arteries with different diameters.

Adult↗
PubMed1998

[One-stage operative treatment of atlanto-axial instability with stenosis of lower cervical level of spinal canal].

To cure patients suffering from atlanto-axial instability following old fracture of odontoid process concomitant with stenosis of lower end of cervical spinal canal, a new operative method was designed. It included atlanto-axial fusion by Gallie technique and resection of right half of the laminae of C3-C7 spine at one stage. A female of 63 years old was treated. She was admitted with neck pain and numbness of the upper and lower limbs. A history of neck injury was noted in enquiry. In physical examination showed the sensation of pain of the upper limbs was decreased and the muscle power of the upper and lower limbs ranged from III degree to IV degree. The X-ray film and MRI suggested that there was instability of the atlanto-axial joint with stenosis of 4th-6th cervical spinal canal. The operation was satisfactory. After operation, the patient was followed up for 11 months. The physical examination indicated that sensation of the upper limbs had recovered to normal and the muscle power of the upper limbs reached IV degree and that the lower limbs reached V degree and X-ray showed bony fusion of the atlanto-axial joint. The conclusions were: 1. The stability of atlanto-axial joint was reconstructed with expanding of the spinal canal at the same time. 2. The duration, risk and cost of the therapy were reduced, and maintenance of the stability of the cervical spine throughout whole period of treatment was recommended.

Atlanto-Axial Joint↗
PubMed1998

Genetic analysis of dental traits in 82 pairs of female-female twins.

OBJECTIVE: To study systematically the heritability of dental traits. METHODS: Eighty-two pairs of female-female twins from 6 to 12 years old were collected. Twin zygosity diagnosis was made by DNA fingerprinting. The study was composed of questionnaires, oral examinations, model measurements, and panoramic radiographs. The same analytic method was used for each of the dental traits and comparison of their heritability was made. RESULTS AND CONCLUSIONS: According to the significance of difference and the level of heritability, the dental traits were divided into four types: strong, median, weak, and weaker heritability. The number of third molars present, tooth size, arch size, and upper lateral incisor malformation were under strong genetic influence; hypodontia indicated a median heritability; a weak heritability was seen in tooth eruption and caries, and a weaker heritability was found in occlusal traits. The division made it easy to learn the genetic characteristics of dental traits systematically and supplemented the theory of dental genetics.

Anodontia↗
PubMed1998

[Changes of blood supply from portal system after transcatheter arterial chemoembolization in huge hepatocellular carcinoma].

OBJECTIVE: Blood supply changes of the portal venous system to the tumor mass before and after transcatheterarterial chemoembolization(TACE) in a series of 22 patients with huge hepatocellular carcinoma were monitored to study the necessity of intervention via portal vein. METHODS: Twenty-two selected patients with huge hepatocellular carcinoma were enrolled in the study. Elscint double helical CT was used to scan liver during the maximum concentration of contrast medium in portal venous system. CT Angiography and MIP(Maximum Intensity Projection) were used to image formation of the portal venous system. RESULTS: The technique of scan and image formation were excellent to evaluate the attribution of portal venous blood supply to HCC. The portal venous blood supply was mainly the tumor periphery distribution (P < 0.01). After treatment of TACE, the portal venous blood supply to tumor periphery increased significantly (P < 0.05), and some did appear signs of enriched blood supply around the tumor. Negative correlation between the degree of reduction in tumor and portal venous blood supply to the tumor periphery before TACE was evident. CONCLUSION: The attribution of portal venous blood supply to HCC was in the tumor periphery, and regression of tumor after TACE was affected by portal venous blood supply to the tumor, thus it is reasonable to suggest interventional therapy via portal vein.

Adult↗
PubMed1998

[Clinical analysis of PIH with abnormal liver function in 66 patients].

Sixty-six patients of severe pregnancy induced-hypertension(PIH) with abnormal liver function were studied. The results showed that the incidence of abnormal liver function in severe PIH was 20.62%, which was significantly higher than that in moderate PIH and closely related to the course of the disease. The incidence of abnormal liver function in patients who were sick longer than 1 month was much higher than those with short course (P < 0.05). The liver function abnormality in PIH mainly showed the elevation of SGPT activity, increase of serum bilirubin was rarely seen. Besides these, the incidences of the fetal distress and postpartum hemorrhage in patients with abnormal liver function were significantly higher as compared with those having normal liver function (P < 0.05).

Adult↗