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Biomedical subjects

T C Chan

Publications and source records attributed to T C Chan.

At least 37 records · Page 2Linked to original sources
PubMed2000

Longitudinal colour doppler study of superficial lymph nodes in non-Hodgkin's lymphoma patients on chemotherapy.

AIMS/METHODS: A longitudinal study of 22 malignant lymph nodes by colour Doppler (CD) and/or colour power (CP) ultrasonography was undertaken in 12 non-Hodgkin's lymphoma patients to delineate changes in vascularity, and correlate this response with clinical outcome. RESULTS: Reduced vascularity in response to chemotherapy was shown to be a positive prognostic sign. CONCLUSIONS: More persistent nodal vascularity may signify a less favourable prognosis.

Adult↗
PubMed2000

Spirometry in normal subjects in sitting, prone, and supine positions.

OBJECTIVE: Determine whether pulmonary function testing is affected by patient positioning. METHODS: In a descriptive study with measurements made in a sequential but randomized order at a university-based pulmonary function laboratory, 20 healthy men, ages 18-50 years, were evaluated with spirometric assessment of forced vital capacity (FVC), forced expiratory volume in the first second (FEV1), and maximum voluntary ventilation (MVV) in the sitting, supine, and prone positions. Subjects were excluded for body mass index (BMI) > 30 kg/m2 or abnormal baseline spirometry. RESULTS: Comparing sitting to supine and prone positions, there was a statistically significant decline in the spirometry values (reported as percent of predicted normal +/- standard error of the mean). FVC was 102% +/- 4% while sitting, 95% +/- 4% while supine, and 94% +/- 4% while prone. FEV1 was 104% +/- 3% while sitting, 96% +/- 3% while supine, and 94% +/- 3% while prone. MVV was 115% +/- 4% while sitting, 102% +/- 4% while supine, and 97% +/- 3% prone. CONCLUSION: In healthy men with BMI < 30 kg/m2, changing from the sitting to supine or prone position results in statistically significant change in respiratory pattern. However, all spirometry values in each position were normal by American Thoracic Society definitions.

Adolescent↗
PubMed1998

Intracisternal osteogenic protein-1 enhances functional recovery following focal stroke.

Osteogenic protein-1 (OP-1, BMP-7) is a member of the transforming growth factor-beta (TGF-beta) superfamily that selectively induces dendritic outgrowth from cultured neurons. We injected human recombinant OP-1 (1 or 10 micrograms) or vehicle into the cisterna magna of mature male Sprague-Dawley rats 1 and 4 days after focal cerebral infarction induced by middle cerebral artery (MCA) occlusion. OP-1 treatment was associated with a marked enhancement of recovery of sensorimotor function of the impaired forelimb and hindlimb (contralateral to infarcts) as assessed by limb placing tests. This effect appeared to be dose dependent. There was no difference in infarct volume between OP-1 and vehicle-treated rats. The mechanisms of enhanced recovery by intracisternal OP-1 may include promotion of dendritic sprouting in the intact uninjured brain.

Analysis of Variance↗
PubMed1998

Postpartum coronary artery dissection.

A 34-year-old woman presented to the emergency department 12 weeks postpartum with chest pain. An ECG indicated an acute myocardial infarction. The patient underwent cardiac catheterization with findings suggestive of coronary artery dissection later confirmed on intravascular ultrasonography. She underwent emergency coronary artery bypass grafting and has subsequently done well.

Adult↗
PubMed1998

Outcome study of prehospital patients signed out against medical advice by field paramedics.

STUDY OBJECTIVE: To describe the incidence and demographic data of prehospital patients who contact paramedics by way of the 911 system, refuse transport against medical advice (AMA), then call 911 and are subsequently reevaluated by paramedics in the following 48 hours. METHODS: We conducted a retrospective observational review of records using the San Diego County Quality Assurance Network database for prehospital providers. All paramedic 911 responses that made base hospital contact over a 3-month period were reviewed to identify patients who signed out AMA. The main outcome measure was to identify patients who signed out AMA and then called 911 again within 48 hours. The demographics, complaints, treatments, and dispositions of these patients are described. RESULTS: Of 6,512 total 911 responses reviewed, 443 (7%) involved patients who signed out AMA. Of these patients, 156 cases (35.2%) were listed as trauma and 287 (64.8%) were medical, with cardiac chest pain, seizure, and respiratory distress/shortness of breath the most frequently noted medical subcategories. Fifty-one (11.5%) such patients received treatment; 34 received dextrose, 12 naloxone, 4 albuterol, and 1 a splint. Patient names were available in 5,515, of the total 6,512 responses and 431 of the 443 AMA cases, permitting computer searching of reevaluations by paramedics. Of the 431 AMA patients for whom a name was available, 10 (2%) called 911 again within 48 hours. All 10 callbacks were made for a related chief compliant, and all 10 of these patients were transported (4 admitted to hospital, 1 died en route, 1 transferred to another facility, 4 discharged from the ED). Of these 10 patients, 7 (70%) were older than 65 years, compared with 17% of all AMA patients older than 65 years. CONCLUSION: On the basis of our findings, patients over the age of 65 years have a propensity to recontact paramedics and should be aggressively encouraged to seek emergency medical treatment. Future prospective studies should be mounted to examine at patient outcome and to assess why patients sign out AMA after making contact with paramedics.

Adolescent↗
PubMed1998

Reexamination of custody restraint position and positional asphyxia.

The use of the hogtie restraint (also known as hobble or prone maximal restraint) by law enforcement and prehospital personnel has come under scrutiny because of reports of sudden deaths in persons placed in this restraint position. Some contend that this body position restricts chest and abdominal movement to the point that individuals are at risk for hypoventilatory respiratory compromise and "positional" asphyxiation. We review case reports of custody deaths in subjects placed in the hogtie position, as well as related medical literature regarding positional asphyxia. We also review the current research findings from human physiology studies that have investigated the effects of the hogtie position on respiratory and pulmonary function. We conclude that the hogtie restraint position by itself does not cause respiratory compromise to the point of asphyxiation and that other factors are responsible for the sudden deaths of individuals placed in this position.

Asphyxia↗
PubMed1998

Recombinant human osteogenic protein-1 (OP-1) stimulates periodontal wound healing in class III furcation defects.

Osteogenic protein-1 (OP-1) is a member of the transforming growth factor beta superfamily and is a potent modulator of osteogenesis and bone cell differentiation. This preclinical study in dogs sought to assess the effects of OP-1 on periodontal wound healing in surgically created critical size Class III furcation defects. Eighteen male beagle dogs were subjected to the creation of bilateral mandibular 5 mm osseous defects. A split-mouth design was utilized which randomly assigned opposing quadrants to control therapy (surgery alone or collagen vehicle) or 1 of 3 ascending concentrations of OP-1 in a collagen vehicle (0.75 mg OP-1/g collagen, 2.5 mg/g, or 7.5 mg/g). Thus, 9 quadrants per test group received OP-1, 9 quadrants per control group received surgery alone, and 9 quadrants received collagen vehicle alone. Test articles were delivered by a surgeon masked to the treatment, and fluorogenic bone labels were injected at specified intervals post-treatment. Eight weeks after defect creation and OP-1 delivery, tissue blocks of the mandibulae were taken for masked histomorphometric analysis to assess parameters of periodontal regeneration (e.g., bone height, bone area, new attachment formation, and percent of defect filled with new bone). Histomorphometry revealed limited evidence of osteogenesis, cementogenesis, and new attachment formation in either vehicle or surgery-alone sites. In contrast, sites treated with all 3 concentrations of OP-1 showed pronounced stimulation of osteogenesis, regenerative cementum, and new attachment formation. Lesions treated with 7.5 mg/g of OP-1 in collagen regenerated 3.9+/-1.7 mm and 6.1+/-3.4 mm2 (mean +/-S.D.) of linear bone height and bone area, respectively. Furthermore, these differences were statistically different from both control therapies for all wound healing parameters (P < 0.0001). No significant increase in tooth root ankylosis was found among the treatment groups when compared to the surgery-alone group. We conclude that OP-1 offers promise as an attractive candidate for treating severe periodontal lesions.

Alveolar Process↗
PubMed1998

The reproducibility of cephalometric landmarks: an experimental study on skulls.

Few previous cephalometric studies have used dry skulls in order to eliminate the effects of the facial soft tissues. The aim of this study were to quantify the intra-examiner reproducibility of the commonly used cephalometric landmarks, angles and distances, using dry skulls and to compare these errors with previous error data obtained from normal cephalograms of living patients. Thirty skulls were mounted in a purpose-designed holder and repeat cephalograms of each skull were recorded and digitised. All measurements were made relative to an X-Y coordinate reference grid. Scattergrams were produced to show the characteristic distribution of the intra-examiner reproducibility errors for the landmarks, and the reproducibility of the angles and distances were tabulated. This data was compared with a related study that included the soft tissue profile. The standard deviations of the skeletal and dental angles and distances were greater in the presence of the soft tissues. These differences were up to four times larger for measurements including the location of Nasion (e.g. SNA, SNB and SNPg), which was the landmark location most affected by the presence of soft tissues, and for the distance: Incisal tip of Lower Incisor to Pogonion. Anterior Nasal Spine, in the horizontal plane, was also greatly affected by the presence of the soft tissues. By using dry skulls, the errors observed in this study may serve as standards for the rational interpretation of clinical cephalometric values.

Adult↗
PubMed1997

Restraint position and positional asphyxia.

STUDY OBJECTIVE: To determine whether the "hobble" or "hog-tie" restraint position results in clinically relevant respiratory dysfunction. METHODS: This was an experimental, crossover, controlled trial at a university-based pulmonary function laboratory involving 15 healthy men ages 18 through 40 years. Subjects were excluded for a positive urine toxicology screen, body mass index (BMI) greater than 30 kg/m2, or abnormal screening pulmonary function testing (PFT). Forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), and maximal voluntary ventilation (MVV) were obtained with subjects in the sitting, supine, prone, and restraint positions. After a 4-minute exercise period, subjects rested in the sitting position while pulse, oxygen saturation, and arterial blood gases were monitored. The subjects repeated the exercise, then were placed in the restraint position with similar monitoring. RESULTS: There was a small, statistically significant decline in the mean FVC (from 5.31 +/- 1.01 L [101% +/- 10.5% of predicted] to 4.60 +/- .84 L [88% +/- 8.8% of predicted]), mean FEV1 (from 4.31 +/- .53 L [103% +/- 8.4%] to 3.70 +/- .45 L [89% +/- 7.7%]), and mean MVV (from 165.5 +/- 24.5 L/minute [111% +/- 17.3%] to 131.1 +/- 20.7 L/minute [88% +/- 16.6%]), comparing sitting with restraint position (all, P < .001). There was no evidence of hypoxia (mean oxygen tension [PO2] less than 95 mm Hg or co-oximetry less than 96%) in either position. The mean carbon dioxide tension (PCO2) for both groups was not different after 15 minutes of rest in the sitting versus the restraint position. There was no significant difference in heart rate recovery or oxygen saturation as measured by co-oximetry and pulse oximetry. CONCLUSION: In our study population of healthy subjects, the restraint position resulted in a restrictive pulmonary function pattern but did not result in clinically relevant changes in oxygenation or ventilation.

Adolescent↗
PubMed1997

Drug-induced hyperthermia.

Drug-related causes of hyperthermia can often be overlooked in the setting of elevated body temperature. This article reviews the pathophysiology, presentation, and treatment of several drug-induced hyperthermia syndromes: malignant hyperthermia, neuroleptic malignant syndrome, sympathomimetic poisoning, and anticholinergic toxicity. Although the general approach is similar, specific management strategies may be required for each syndrome.

Cholinergic Antagonists↗
PubMed1996

The situational effects on haptic perception of rod length.

Three experiments were conducted to investigate situational effects (manipulation, range, and prior experience) on the haptic perception of rod length. Each rod was held between its two ends with one hand. In Experiment 1, 32 participants judged length of rods using different manipulations. Perceived lengths were found to be dependent on manner of manipulation and not necessarily equal to actual lengths. Different parameters were detected in different manipulations. In Experiment 2, 8 participants judged rod lengths by wielding rods of two ranges: long and short. Perceived length was found to be affected by the range of rods evaluated successively in a single set. In Experiment 3, 9 participants judged rod lengths after an experience of handling dense or light rods. Perceived length was found to be affected by prior experience. Results are discussed in terms of how rod lengths can be perceived accurately by haptic modality without involving direct perception.

Adult↗
PubMed1996

Survey of illegal immigrants seen in an emergency department.

There is growing controversy regarding illegal immigrants and their use of social services, including health care, in this country. We surveyed undocumented persons presenting at our emergency department to investigate the reasons why they sought care in the United States. Overall, 227 visits (8.6%) were made in the emergency department by illegal immigrants, mostly Hispanics. Of 104 patients surveyed, all sought care in this country because they were here at the time, and 86 (83%) intended to remain permanently. Of the 104 persons, 83 (80%) cited lack of funding as a reason for seeking emergency department care. Undocumented Hispanics had a higher uninsured rate (64%) than both Hispanics (32%) and non-Hispanics (30%). Of the 104 patients, 38 (36%) had difficulty obtaining care elsewhere because of their status, 53 (51%) knew of no other sources of care, and 46 (44%) said that even if available, only the emergency department was acceptable. Many undocumented persons seek care in the United States because they reside here permanently, often using this emergency department as their source of care. These findings may be important in light of recent efforts to restrict services for this group.

Adolescent↗
PubMed1995

Ultrastructure and cytochemical staining characteristics of canine natural killer cells.

BACKGROUND: The purpose of this work was to describe the ultrastructure and cytochemical staining characteristics of canine peripheral blood lymphocytes with natural killer (NK) cell activity, with comparison made to non-NK lymphocytes. METHODS: Canine lymphocyte populations evaluated for ultrastructure, cytochemical staining, and NK function (by 51chromium release assay) included: peripheral blood lymphocytes; lymphocytes from band 1 (NK-enriched), band 2, and the pellet of a 45/50% percoll gradient; lymphocytes from the supernatant fluid (non-conjugated lymphocytes) and pellet (lymphocytes conjugated to tumor cell targets) of a 17% percoll gradient; and null (CD4-CD8-) and CD4-CD8+ lymphocytes. RESULTS: NK activity was concentrated in band 1 lymphocytes of the 45/50% percoll gradient with further enhancement of activity occurring in sorted null cells. Canine NK cells were 5.5 to 6.5 microns in diameter with a reniform (kidney bean shape) nucleus, and electron-dense cytoplasmic granules. NK cells (percoll band 1 cells and null cells) had larger cell and nuclear area, and less round nuclei when compared to non-NK lymphocytes. The overall cytochemical staining (chloracetate esterase, peroxidase, sudan black B, naphthyl acetate esterase, naphthyl butyrate esterase periodic acid-Schiff stain, and acid phosphatase with and without tartrate) pattern was similar in all the lymphocyte populations evaluated. CONCLUSIONS: This work confirms the usefulness of a 45/50% percoll gradient in obtaining a NK-enriched fraction of canine lymphocytes, and shows further enhancement of NK activity in sorted CD4- CD8- cells. The ultrastructure of canine NK cells is similar to that reported for human NK cells, but is different from that of other canine peripheral blood lymphocytes. Standard cytochemical staining does not discriminate canine NK cells from other lymphocytes.

Animals↗
PubMed1995

Spontaneous metastasis of PC-3 cells in athymic mice after implantation in orthotopic or ectopic microenvironments.

The ability of subcutaneous, prostatic, and nonprostatic intraabdominal organ microenvironments to influence local tumor growth and metastasis of PC-3 human prostate carcinoma cells in athymic mice was determined. Tumorigenesis and metastasis of PC-3 were evaluated 60 days after subcutaneous and intraprostatic (orthotopic) implantation of 5 x 10(5) PC-3 cells in 6-week-old, male athymic mice. Intraprostatic implantation of PC-3 cells resulted in paraaortic lymph node metastases in 10 of 10 (100%) mice with prostatic tumors, whereas metastases were present in only 2 of 9 (22%) mice after subcutaneous implantation. Next, we determined whether the urinary bladder (nonprostatic, urogenital microenvironment) or stomach (nonurogenital, intraabdominal microenvironment) would facilitate the metastasis of PC-3 cells in athymic mice. Tumorigenesis and metastasis were 100% after subserosal implantation of PC-3 cells within the wall of the urinary bladder (n = 6 mice). Subserosal implantation of PC-3 cells into the stomach wall (n = 7 mice) also resulted in tumor formation and metastasis to regional lymph nodes in 100% of mice. In all experiments, regional lymph nodes were the most frequent site of metastasis, regardless of implantation site. We conclude that tumor microenvironment factors responsible for the metastasis of PC-3 cells in athymic mice may not be organ-specific, since nonprostatic visceral microenvironments are sufficient for predictable metastasis. Use of these models may further our understanding of how tumor microenvironment modulates expression of the metastatic phenotype by human prostate carcinoma cells.

Animals↗