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Biomedical subjects

K H Chan

Publications and source records attributed to K H Chan.

At least 145 records · Page 8Linked to original sources
PubMed1995

In vivo observation with magnetic resonance imaging of middle ear effusion in response to experimental underpressures.

In this study, magnetic resonance imaging (MRI) was used to define, in vivo, the effect of acute middle ear (ME) underpressures on vascular permeability and the development of effusion. The MEs of four cynomolgus monkeys were unilaterally inflated with oxygen and carbon dioxide on different occasions and followed for a period of approximately 4 hours by tympanometry and MRI scanning. Carbon dioxide inflations caused the rapid development of ME underpressures of less than -600 mm H2O by 10 minutes. The MRI scans showed a progressive brightening of the ME and all associated air cells, indicative of the accumulation of effusion in three of the four experiments. An MRI contrast agent was administered to the vascular compartment during the course of the experiment and was rapidly transferred to the ME space, indicating vascular permeability to the agent. The contralateral, control side did not develop significant underpressures, effusion, or increased vascular permeability. Inflation with oxygen caused lesser underpressures and no accompanying changes in the MRI scans. These data support the hydrops ex vacuo theory and confirm the usefulness of MRI for in vivo documentation of the development of ME effusions and changes in vascular permeability of the mucosa in the experimental setting.

Animals↗
PubMed1995

Prospective double-blind placebo-controlled randomized trial on the use of ranitidine in preventing postoperative gastroduodenal complications in high-risk neurosurgical patients.

To determine the efficacy of ranitidine in preventing clinically acute overt gastroduodenal (GD) complications (bleeding and/or perforation) after neurosurgery, 101 patients with nontraumatic cerebral disease considered at high risk of developing postoperative GD complications were randomized in a standard double-blind manner to receive either ranitidine (50 mg every 6 hours) or placebo medication preoperatively. Postoperative serial GD endoscopy was used to document the occurrence of complications: an overt symptomatic complication was defined as bleeding requiring blood transfusion and/or surgery. Fifty-two patients received ranitidine and 49 received a placebo preoperatively; 30 developed overt GD bleeding; nine of these received ranitidine and 21 received a placebo. Ranitidine significantly reduced the incidence of bleeding (p < 0.05). Multivariate logistic regression analysis revealed three factors of independent significance in predicting overt GD bleeding: use of a placebo drug, a gastric pH of less than 4, and a high daily volume of gastric output. The authors conclude that ranitidine is useful in preventing postoperative GD complications in high-risk neurosurgical patients.

Adolescent↗
PubMed1995

Power spectral analysis of systemic arterial pressure signals during open heart surgery.

BACKGROUND: The close relationship between the balance of sympathetic and parasympathetic tones and the results of power spectral analysis (PSA) of systemic arterial pressure (SAP) has been suggested recently. The purpose of this study was to further describe the changes of balance between the two autonomic nervous components during open heart surgery for coronary arterial disease (CAD) or valvular heart disease (VHD) with the PSA technique of SAP. METHODS: By relaying the SAP signals to a personal computer utilizing a power spectral analysis algorithm, radial arterial pressure signals of 27 patients (11 with CAD for coronary artrial bypass graft, as CAD groups; 16 with VHD, as VHD group, including 8 for aortic valve replacement and 8 for mitral valve replacement) during open heart surgery were monitored in a continuous, on-line and real-time manner. On-line power spectral analysis was performed according to the five different stages of the operation. RESULTS: Power density tended to increase in the high frequency (HF) band during the ventilator-supported stages of the open heart procedures, i.e., the pre-cardiopulmonary bypass (CPB) and the off-CPB periods. The power density in other frequency bands during the whole course of general anesthesia otherwise decreased significantly, with the lowest values occurring during CPB. The power density in very low frequency (VLF) band was much higher than in other bands during CPB, and became the major component of total power density in this period. CONCLUSIONS: The balance between sympathetic and parasympathetic components of autonomic nervous system changes rapidly during open heart surgery and needs careful monitoring. By utilizing PSA of SAP, mathematical error might be an obstacle of using LF:HF ratio as an index of autonomic balance during the CPB period when the HF density approaches zero.

Aged↗
PubMed1995

Evaluation of stress response to surgery under general anesthesia combined with spinal analgesia.

BACKGROUND: Each type of anesthesia has varying influence on the amount of catecholamine secretion during surgery. Epidural or spinal anesthesia can markedly suppress the increase of many of the stress hormones. Our purpose of this study is to evaluate metabolism change during surgery under anesthesia and to see whether general anesthesia combined with intraspinal anesthetic and narcotic is a better way to suppress such stress response. METHODS: Seventeen patients in fit physical condition (ASA class I) with normal biochemical screening scheduled for radical gastrectomy were studied. All patients were premedicated with diazepam and glycopyrrolate and an indwelling catheter was inserted into a radial artery under local anesthesia for monitoring blood pressure and obtaining blood samples for glucose and hormonal assays. A CVP line was set up via the right internal jugular vein for the administration of fluid (free of sugar). In the study group, a 32-G intraspinal catheter was placed via lumbar interspaces. Spinal blockade up to T4 by titrating 0.25% marcaine. Then anesthesia in both groups was induced with thiopental 5 mg/kg, followed by succinylcholine 1.5 mg/kg for intubation. Anesthesia was maintained with isoflurane, N2O, O2 and pancuronium. Blood samples for measurement cortisol, catecholamine and sugar were taken after induction and 30 min after surgical incision. Thirty min after skin incision all patients were subjected to glucose tolerance test, accomplished by giving 50% dextrose at 0.33 g/kg in 3 min. Arterial blood samples were then obtained at 1, 3, 5, 7, 10, 20, 30, 45 and 60 min intervals for plasma glucose determination. RESULTS: No difference was evident in cortisol values, baseline, before and after surgical incision (p > 0.05) either intragroup or inter-group. Catecholamine and glucose were significantly higher in control group after surgical incision (p < 0.05, intra-gr and inter-gr). Following a glucose load the decay of plasma glucose was similar in both groups but glycemic level was higher in the control group. CONCLUSIONS: Better control of stress response by general anesthesia combined with subarachnoid block was disclosed in this study.

Aged↗
PubMed1994

Flattening of the contrast-detail curve for large lesions on liver CT images.

This study evaluated the relative roles of physical and perceptual factors in flattening the contrast-detail (CD) curve on liver CT scans. To estimate the role of physical factors, the theoretical CD curve for a calculated theoretical observer (i.e., a nonprewhitening matched filter) was predicted using the measured noise power spectrum and measured modulation transfer function of the CT system. Another theoretical CD curve was also produced from the output of the same calculated observer after taking the human visual response function (VRF) into account. Perceptual factors were evaluated by analyzing human observers' replicated ratings of the visibility of details super-imposed on liver CT scans. The CD curve for the calculated theoretical observer was below the CD curve actually measured for nine human observers and showed no flattening. With the VRF included, flattening of the theoretical CD curves was only produced by fixed image viewing distances of less than 30 cm, a reading style not employed by the human observers. Correlated ROC analysis of observers' replicated ratings indicated that while random, intraobserver variation was present, the magnitude of this so-called observer noise was insufficient to explain the flattening of CD curves. Use of narrow display windows did not eliminate this flattening effect. The main reason for human observers' inefficient detection of large, low contrast liver lesions appears to be a consistent misuse of the image information.

Humans↗
PubMed1994

Middle ear mucosal inflammation: an in vivo model.

The inflammatory process underlies the pathogenesis of otitis media (OM). Although knowledge concerning this common childhood disease continues to accumulate, most of the basic science research is based on in vitro or ex vivo methodologies. Magnetic resonance imaging (MRI), although lauded for its ability to image soft tissue, is often neglected as a research tool providing real-time in vivo information. This study attempts to assess experimental middle ear (ME) inflammation using MRI. The vasoactive effects of histamine and its interaction with antihistamines and a glucocorticoid were evaluated. Histamine was chosen because it is one of the naturally occurring inflammatory mediators. The antagonists were selected on the basis of their antihistaminic and vasoactive effects, respectively. Certainly there is substantial clinical interest in these agents because their efficacy for the treatment of OM is still being debated. The chinchilla model was chosen since it is one of the best characterized species in the study of OM. The three parts of the study are as follows: the effects of histamine on chinchilla ME mucosa; histamine challenge following pretreatment using hydroxyzine hydrochloride (H1 antagonist), ranitidine chloride (H2 antagonist), and the combination; and histamine challenge following pretreatment with dexamethasone. Sequential T1-weighted spin-echo (SE) MRI was used to detect extravasation of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) into the middle ear effusion (MEE). The results indicate that the vasoactive effects of histamine are dose-related and can be assessed across a wide spectrum of histamine dosages inclusive of the human MEE levels. The H1 antagonist alone, or in combination with the H2 antagonist, was able to prevent the increased vascular permeability induced by histamine. When used alone, the H2 antagonist did not abolish the effects of histamine. The vasoactive effects of histamine were also ameliorated by pretreatment with a glucocorticoid. These findings indicate the utility of MRI for assessing mucosal inflammation in a real-time manner rather than as an accumulation of events. This study also validates the efficacy of an H1 antagonist and a glucocorticoid in counteracting the vasoactive effects of histamine. This methodology may be suited for evaluating the effects of other classes of antiinflammatory mediators.

Animals↗
PubMed1994

Surgical management of substernal goiter.

Seventeen cases of large substernal goiter are reviewed. The commonest clinical features were frequent upper respiratory tract infections, dyspnea and a cervical mass. Five of the patients had previous thyroidectomy. The substernal goiter was located in the right chest in 11 cases, the left chest in five and bilaterally in one case. On computed tomograms it was pretracheal or prevascular in ten cases and retrovascular in seven. Tracheal deviation was present in 15 cases, causing tracheal compression or stenosis in 14. Thyroidectomy was performed on all 17 patients (8 subtotal, 9 total) through a low transverse collar incision. The recommended technique for substernal goiter extending from the neck to a level below the subcarinal region includes concomitant finger dissection and upward traction of the cervical thyroid through the subcapsular plane, with obliteration of the postresection substernal dead space by sutures. Follow-up radiography showed that all the deviated tracheas had resumed near normal position 2-3 months postoperatively and the average diameter of the compressed tracheas had increased significantly.

Adult↗
PubMed1994

The interaction of diazepam with vecuronium: a clinical study.

BACKGROUND: Diazepam, known to possess myorelaxation property, has been widely used clinically to control muscular rigidity and spasticity. The interactions of diazepam with neuromuscular blocking agents have been extensively studied, yet the results reported are somewhat controversial and inconclusive. METHODS: The interaction of diazepam with one of the neuromuscular blocking agents, vecuronium, was studied in 20 ASA I-II patients undergoing elective surgery. They were randomly assigned to two groups with ten in each group. Anesthesia was induced with fentanyl, thiopental and vecuronium and maintained with 1% halothane and 70% N2O in O2. The experimental group received diazepam (0.2 mg/kg) 3 minutes prior to vecuronium (0.1 mg/kg) during induction while the control group received vecuronium (0.1 mg/kg) straight without diazepam. Control records of the integrated electromyography showed the response to train-of-four supramaximal stimulation by a Datex Relaxograph during induction. In no time when the first twitch (T1) recovered to 25% of the control, it was topped up again with another intraoperative dose of vecuronium (0.025 mg/kg). From the derived data, the following parameters were calculated and analysed: (1) onset time T10 (the time from the end of injection of vecuronium during induction to depression of T1 to 10% of control twitch height); (2) duration time T25 (the time from administering vecuronium during induction to the time when T1 recovered to 25% of the original twitch height); (3) topup time T25-25 (the time from administering the top dose of vecuronium to the time when T1 returned to 25% of control twitch height again) and (4) recovery time T25-50 (the time of recovery of T1 from 25% to 50% of the control twitch height at the end of the operation). RESULTS: Significant differences between both groups were found in T10 (221.8 +/- 62.2 vs 135.4 +/- 23.3 sec, p < 0.01) and T25 (41.9 +/- 10.2 vs 50.6 +/- 9.4 min, p < 0.05). The results of T25-25 and T25-50 did not differ much (26.6 +/- 6.9 vs 29.3 +/- 4.4 min, p > 0.05 and 15.0 +/- 8.9 vs 16.9 +/- 8.7 min, p > 0.05 respectively). CONCLUSIONS: The administration of diazepam (0.2 mg/kg) three minutes prior to vecuronium (0.1 mg/kg) during induction may hasten the onset of vecuronium and prolong its duration of action.

Aged↗
PubMed1994

Sensorineural hearing loss in children. Classification and evaluation.

This article deals with sensorineural hearing loss (SNHL) from a classification perspective. Primarily, the clinical aspects of the most commonly seen disorders are covered. Whenever appropriate, information relating to temporal bone histopathology is emphasized. Evaluation of SNHL in this age of health care cost containment is also discussed.

Child↗
PubMed1994

A neural network classifier for cerebral perfusion imaging.

UNLABELLED: Artificial neural networks have been applied to a variety of pattern recognition tasks in medical imaging and have been shown to be a powerful classification tool. The potential usefulness to discriminate normal from abnormal cerebral perfusion patterns was investigated. METHODS: Cerebral perfusion imaging with 99mTc-labeled hexamethylpropyleneimine oxime was performed on 52 normal control subjects, 29 patients with clinically diagnosed Alzheimer's disease (AD) and 25 patients with chronic cocaine polydrug abuse. Each study was registered and scaled to a common anatomic coordinate system, yielding 120 standardized cortical regions. A back-propagation neural network classifier based on regional perfusion was used to classify normal and abnormal perfusion patterns. The neural network was trained to discriminate patients with AD from age-matched normal controls and cocaine polydrug abuse patients from normal controls. The performance of the neural network in these two tasks was evaluated quantitatively by receiver operating characteristic (ROC) analysis using cross-validation. RESULTS: For patients with AD, the area under the ROC curve was 0.93 +/- 0.04. When testing with the cocaine polydrug abuser data, the area under the ROC curve was 0.89 +/- 0.04. CONCLUSION: Neural networks provide a potentially useful tool in the decision-making task to discriminate patients with AD and cocaine abuse from normal controls.

Adult↗
PubMed1993

Epstein-Barr virus carriage by nasopharyngeal carcinoma in situ.

We studied the distribution of the EBV genome in tumour biopsies obtained from 42 patients with poorly differentiated or undifferentiated nasopharyngeal carcinoma (NPC) and 3 patients with well-differentiated NPC. Six carcinoma in situ (CIS) foci were seen in 5 tumour specimens. By in-situ hybridization, multiple copies of the EBV genome were detected in some of the tumour cells in 3 CIS lesions involving the full thickness of the mucosal epithelium, but without microinvasion, while the viral genome was present in the majority of the tumour cells contained in another 3 CIS lesions with microinvasion. In agreement with previous findings, poorly differentiated and undifferentiated carcinomas regularly carried the viral genome, the number of copies of which was similar to that seen in CIS, while some, but not all, of the tumour cells of the well-differentiated histological type carried the virus. The viral genome was otherwise rarely detected in other areas of the mucosal epithelium and, where present, the viral carriage was confined to a few epithelial cells, in which the viral genome contents were markedly lower than in tumour cells. These results suggest that EBV may first become associated with NPC at an early stage of the disease shortly after the tumour has been initiated.

Biopsy↗
PubMed1993

Otitis media in the Republic of Palau. A case-series study.

Race is a known epidemiologic determinant for the development of otitis media. This study assessed the severity of otitis media in a subpopulation (N = 73; mean age, 13.2 years) receiving care from the ear clinic in the Republic of Palau, a US Trust Territory, through a questionnaire and an otologic examination. The mean age of patients with otorrhea (2.5 years) was found to be significantly different from the mean age at which they began to swim (4 years). Otitis media-related sequelae were found to involve more than half of ears or subjects examined. No statistical difference was noted when various patient characteristics were compared with the severity of disease. Our clinical impression is that this subpopulation is severely affected by otitis media and its sequelae. Prospective studies are required to identify risk factors present in the population at large.

Adolescent↗
PubMed1993

Transcranial Doppler-sonography in severe head injury.

Ischaemic brain damage is present in over 90% of patients suffering from fatal head injury. Early detection and treatment of ischemia may improve outcome after head trauma. Monitoring of blood flow velocity of the middle cerebral artery by noninvasive transcranial doppler ultrasound provides an alternate means of identifying cerebral ischaemia.

Blood Flow Velocity↗
PubMed1993

Fatal gas embolism as a complication of Nd-YAG laser surgery during treatment of bilateral choanal stenosis.

A 40-day-old infant boy underwent Nd-YAG laser surgery because of congenital bilateral choanal stenosis. Cyanosis and cardiovascular collapse occurred during the operation. Resuscitation was initiated, but in vain; the patient died. The evolution of clinical events was consistent with a diagnosis of gas embolism. In the investigation of causes, the use of a sapphire tip with the Nd-YAG laser and the cooling of the tip with N2 gas were thought to have contributed to the fatal outcome. The authors warn of the potential risk of gas embolism with the Nd-YAG laser and a coaxial gas cooling system, and they emphasize the importance of monitoring for gas embolism in high-risk patients.

Choanal Atresia↗
PubMed1993

Comparative study of sultamicillin and amoxicillin-clavulanate: treatment of acute otitis media.

Sultamicillin is a mutual prodrug of ampicillin and sulbactam that is chemically linked by a diester bond. This investigational agent has beta-lactamase-inhibiting activity by virtue of sulbactam, a novel beta-lactamase inhibitor. A double blind randomized study was conducted to evaluate the safety, efficacy and tolerance of sultamicillin for treatment of acute otitis media compared with amoxicillin-clavulanate. A total of 144 subjects were included (96 randomly assigned to the sultamicillin and 48 to the amoxicillin-clavulanate groups). No safety concerns for sultamicillin were identified during the study. The clinical efficacy in effusion clearance between the two groups was found not to be statistically different at 10 days (P = 0.23) and 30 days (P = 0.72). Similar rates of side effects, primarily gastrointestinal, were reported in both study groups. Sultamicillin may be an alternative for the treatment of acute otitis media when persistence and recurrence of disease become an issue.

Acute Disease↗
PubMed1993

A comparison between vecuronium and atracurium in myasthenia gravis.

We evaluated the effect of vecuronium bromide and atracurium besylate on the train-of-four response in the management of muscle relaxation in 20 patients with myasthenia gravis (MG) who were undergoing thymectomy. We confirmed the safe use of these two non-depolarizing muscle relaxants in MG patients. Vecuronium (0.04 mg.kg-1) demonstrated a lesser clinical duration than did atracurium (0.2 mg.kg-1) (38 +/- 19 vs 50 +/- 21 min, mean +/- s.e.mean). The recovery time for vecuronium patients was shorter than that for atracurium patients (22 +/- 18 vs 38 +/- 18 min), but the time until onset of neuromuscular blockade was longer with vecuronium (246 +/- 105 vs 107 +/- 103 s). During spontaneous recovery from neuromuscular relaxation, at T1/C of 25% and 100%, the train-of-four fade with vecuronium was significantly greater than that with atracurium (0.04 +/- 0.02, 0.16 +/- 0.03 vs 0.17 +/- 0.01, 0.83 +/- 0.03), suggesting that vecuronium had a greater prejunctional effect than did atracurium.

Adult↗