Biomedical subjects

K H Chan

Publications and source records attributed to K H Chan.

At least 163 records · Page 9Linked to original sources

PubMed1993

Rigid bronchoscopy balloon catheter dilation for bronchial stenosis in infants.

Stenosis of the tracheobronchial tree can be a life-threatening problem. Management options for symptomatic stenosis include serial dilation, cryotherapy, laser resection, and open surgical correction. Recently, balloon angioplasty catheters have been used to dilate stenotic airway segments. The experience in infants is limited and has for the most part utilized guide wires and fluoroscopy for balloon placement. We present two infants with symptomatic bronchial stenosis who underwent endoscopic angioplasty balloon catheter dilation. Operative technique involved catheter placement under direct vision with a rigid bronchoscope. Catheters (6F) with 8-mm-diameter balloons were used. Balloon expansion was controlled with a hand-held manometer. Both infants demonstrated significant lumen size improvement intraoperatively and marked clinical improvement postoperatively, substantiated by endoscopy and radiographs. One infant has required one repeat dilation and has subsequently been asymptomatic. The other infant has had no further respiratory problems. Our technique, using a rigid bronchoscope with direct visualization of catheter placement, obviates the need for guide wires and C-arm fluoroscopy as previously described. Endoscopic placement enables direct visualization of balloon position, and fine adjustments are possible if further dilation is necessary. Rigid bronchoscopic balloon catheter dilation can be a successful technique for bronchial stenosis and should be considered prior to attempting more invasive surgical correction.

Bronchial Diseases↗

PubMed1993

Multimodality monitoring as a guide to treatment of intracranial hypertension after severe brain injury.

Transcranial doppler measurements of blood flow velocity in the middle cerebral artery were made during treatment of raised intracranial pressure (ICP) in 22 patients with severe brain injury. Twenty patients also had continuous measurement of arterial and jugular bulb venous oxygen saturation (SJO2). The transcranial Doppler parameters studied included both mean flow velocity and pulsatility index (PI). Successful treatment was defined as a reduction of ICP to less than 20 mm Hg with improvement or preservation of cerebral perfusion pressure (CPP) above 60 mm Hg. Successful therapy was associated with a significant rise in SJO2 and reduction of cerebral arteriovenous oxygen content difference (AVDO2) and PI only when the pretreatment CPP was less than 60 mm Hg. An increase in CPP beyond 70 mm Hg did not further improve cerebral oxygen delivery and PI, suggesting that autoregulation became a factor above this CPP threshold. Treatment failure during administration of hypnotic drugs resulted in a reduction in arterial pressure, CPP, SJO2, and mean velocity and in an increase in PI and AVDO2, despite a decrease in ICP. CPP is the most important parameter to monitor during ICP therapy. It should be maintained above 70 mm Hg in patients with severe brain injury.

Adolescent↗

PubMed1993

An experimental study of cerebrovascular resistance, pressure transmission, and craniospinal compliance.

To successfully match the treatment to the cause for raised intracranial pressure (ICP) after a severe head injury, it is important to know the underlying mechanism at a given moment for the raised pressure. In particular, it is important to distinguish between active cerebral vasodilation, indicating functional autoregulation, and a passive vascular dilation as the cause for raised ICP. An experimental study was performed in feline models of diffusely raised ICP (n = 6), of active arterial vasodilation caused by arterial hypercarbia (n = 6), and of passive arterial dilation caused by pharmacologically induced arterial hypertension (n = 6) to determine if wave form analysis of ICP can distinguish active from passive arteriolar vasodilation. Pulsatile pressure transmission from the blood pressure pulse to the ICP pulse (cerebrovascular pressure transmission [CVPT]), cerebrovascular resistance, and craniospinal compliance were measured simultaneously at each level of raised ICP, arterial hypercarbia, and arterial hypertension. Arterial hypercarbia, caused by both 5 and 10% inspired CO2 increased low-frequency CVPT, which was followed by an increasingly negative phase shift between the blood pressure and ICP wave form (P < 0.05). Diffusely raised ICP caused by intraventricular infusion of mock cerebrospinal fluid caused increased low-frequency CVPT (P < 0.01) but resulted in no overall change in phase shift, although the sign of the phase shift remained negative. After arterial hypertension, caused by the infusion of angiotensin II, where there was loss of myogenic tone, an increased low-frequency CVPT was accompanied by a positive phase shift (P < 0.01). These data demonstrate it may be possible to distinguish active arteriolar vasodilation from a passive loss of autoregulatory vascular tone through simultaneous measurement of the low-frequency CVPT and phase shift. Analysis of the ICP wave form provides information relevant to the management of raised ICP.

Animals↗

PubMed1993

The reversal effect of low dose aminophylline on thiopental-induced sedation.

Fifty-two ASA (American Society of Anesthesiologists) class I-II female patients, from 22 to 66 years of age, undergoing D & C (dilatation and curettage) procedure, were randomly divided into 2 groups in a double-blind and placebo-controlled design to investigate whether aminophylline could reverse the sedative effect of thiopental. Patients of both groups were anesthetized with fentanyl (2 micrograms/kg, i.v.) and thiopental (4 mg/kg, i.v. and 1 mg/kg, i.v. repeated if necessary). Postoperatively, they were intravenously given aminophylline (2 mg/kg) or normal saline in an equal volume solution over 5 minutes. The results showed that patients in the aminophylline group were more sedated (p < 0.05) than in the saline group 5 minutes after reversal, but were less sedated (p < 0.05) at minute 20. No significant differences between groups were found at other times. The total time spent in the postanesthetic unit was shorter in the aminophylline group (92 +/- 27 min.) than in the normal saline group (109 +/- 30 min.) (p < 0.05). The serum theophylline levels in some cases in the aminophylline group ranged between 3.2 and 4.9 micrograms/ml (4.3 +/- 0.7 micrograms/ml, n = 10). No apparent side effects, including tachyarrhythmias, were noted. We conclude that low dose aminophylline (2 mg/kg, i.v.) can partially reverse thiopental-induced sedation with safety in the early phase of recovery and it can reduce the total time spent in the postanesthetic unit.

Adult↗

PubMed1993

Postoperative pain relief: lumbar and thoracic epidural morphine in thoracotomy.

Twenty-two patients undergoing thoracotomy were enrolled in a controlled, randomized trial to compare the effects of thoracic (group T) or lumbar (group L) epidural morphine in relieving postoperative pain. Epidural morphine was given as the patient first complained of pain in the recovery room. The effect of epidural morphine on pain relief was assessed by visual analogue scale and subjective grade. All patients were investigated 0, 10, 20, 30, 40, 50, 60, 75, 90, 105 and 120 minutes after a single bolus injection of epidural morphine. In assessment of pain relief by visual analogue scale, the difference between two groups was statistically significant (p < 0.05), evaluated 20, 30 and 40 minutes following treatment. There was no significant difference between two groups with regard to the effect of morphine as assessed by subjective grading. We concluded that thoracic epidural morphine took effect faster than lumbar epidural morphine. However, the effects of both kept similar since 50 minutes after morphine injection.

Adult↗

PubMed1992

Direct detection of Epstein-Barr virus in peripheral blood and comparison of Epstein-Barr virus genotypes present in direct specimens and lymphoblastoid cell lines established from nasopharyngeal carcinoma patients and healthy carriers in Hong Kong.

By means of a PCR assay, EBV was demonstrated directly in peripheral blood of previously infected individuals. The virus was detected in approximately 80% of specimens from EBV-seropositive individuals, but not in cord-blood lymphocytes by this method. When virus present in peripheral blood was compared to that observed directly in NPC biopsies or throat washings, it was distinct from that seen in biopsies in 4/15 cases (27%) and from that seen in throat washes in 1/22 cases (5%). The throat-wash virus differed from the biopsy virus in 3/20 cases (15%). The prototype F virus was found in 7/10 LCLs (70%) established from NPC patients' peripheral blood, but was only detected in 2/9 specimens (22%) directly analyzed by the PCR assay. This finding suggests selective isolation of prototype F EBV in spontaneous LCLs established from NPC patients.

Blotting, Southern↗

PubMed1992

Involvement of major histocompatibility complex class II antigen in Epstein-Barr virus-mediated B cell proliferation.

Five MHC class II monoclonal antibodies costimulated proliferation of cord blood leukocytes with Epstein-Barr virus. These agonistic antibodies were of different isotypes, but all of them were either specific for or cross-reacting with HLA-DR. The other MHC class II antibodies, including three that were specific for HLA-DQ and one that was specific for HLA-DP and also those that were specific for MHC class I or leukocyte common antigen, were not costimulatory. The agonistic effect of different MHC class II antibodies was additive, such that costimulation by different antibodies combined significantly exceeded that achieved by either of these antibodies alone. Spent culture media of B cell lines also costimulated B cell proliferation with the virus. Although MHC class II antibodies augmented the effects of suboptimal concentration of the conditioned media, their combined effects did not exceed the maximum costimulation achieved by either the antibodies or the spent culture media alone. These results raised the possibility that MHC class II antigen may contain distinct functional domains involved in the regulation of B cell progression.

Antibodies, Monoclonal↗

PubMed1992

Ligament tension pattern in the flexed knee in combined passive anterior translation and axial rotation.

Twenty-two fresh-frozen specimens were used to measure tensions generated in selected bands of the major ligaments of the flexed knee (40-90 degrees) when an axially prerotated tibia is subjected to passive anterior shear and when an anteriorly pretranslated tibia is subjected to passive axial torque. The tensions were measured using the buckle transducer attached to the anteromedial band of the anterior cruciate ligament [ACL (am)], the posterior fibers of the posterior cruciate ligament [PCL (pf)], the long fibers of the medial collateral ligament [MCL (lf)], and in the total lateral collateral ligament [LCL]. The knee specimens were subjected to the combined motions in a 6-df passive loading apparatus. The results indicated that the joint resistance to anterior translation increased markedly with internal prerotation and only marginally with external prerotation. This increase in joint resistance, however, was associated with a decrease in ACL function. It has been inferred that the posterior structures, capsular and meniscal, contribute significantly to joint resistance when the tibia is prerotated in either sense. For internal prerotation, the interference between the medial femoral condyle and the central tibial eminence was found to be an additional mechanism of resistance to anterior translation. Also, it has been found that although the ACL (am) tension increased with internal rotation in the normal case, it decreased with internal rotation in the presence of an anterior pretranslation. It is concluded that ACL response to combined joint motion cannot be ascertained by a simple summation of its responses to individual motions.

Adult↗

PubMed1992

Transcranial Doppler waveform differences in hyperemic and nonhyperemic patients after severe head injury.

Although increased cerebral blood flow velocity is readily measured by transcranial doppler ultrasonography (TCD), the causes of the velocity elevation may differ. After severe head injury, increased blood flow velocity can develop both in patients with global hyperemia (suggestive of vasodilation) and in those without hyperemia (suggestive of vasospasm). The present study attempts to determine whether TCD can differentiate these two mechanisms of velocity increase. Fourteen severely brain-injured patients who developed increased middle cerebral artery blood flow velocity (time-averaged mean velocity > 100 cm/s) were studied. Eight cases were nonhyperemic and six were hyperemic as defined by arterial-jugular venous oxygen content differences of more than 4 mL/dL and less than 4 mL/dL, respectively. The TCD waveform of all eight nonhyperemic cases showed a diastolic notch, which was absent in all six hyperemic patients (p = 0.00066). TCD waveform profile appears to provide a noninvasive means of differentiating at the bedside the two causes of increased flow velocity. If associated with raised intracranial pressure, these require different treatment.

Adolescent↗

PubMed1992

Masseter spasm and malignant hyperthermia: a retrospective review of a hospital-based pediatric otolaryngology practice.

It has been claimed that the combination of halothane and succinylcholine, commonly used for anesthetic induction during short pediatric otolaryngologic procedures, is associated with a 1% incidence of masseter spasm (MS) which may be an early sign of malignant hyperthermia (MH). An 18-month retrospective chart review of all patients undergoing general anesthesia at the Children's Hospital of Pittsburgh (n = 14, 112) was conducted to assess the incidence of MS and its management. In addition, a separate subgroup of patients identified as being at risk for MH was also evaluated. In the otolaryngology service, the incidence of developing MS was 2 of 206 (1%) in children who were anesthetized with halothane and received succinylcholine, patients were identified in the MH high-risk group, and none developed MH. The findings affirmed the risks of using this combination of anesthetic and neuromuscular blocking agents during induction and the need for establishing management guidelines.

Anesthesia, General↗

PubMed1992

Cerebral blood flow at constant cerebral perfusion pressure but changing arterial and intracranial pressure: relationship to autoregulation.

Therapeutic agents for reducing raised intracranial pressure (ICP) may do so at the expense of reduced mean arterial pressure (MAP). As a consequence, cerebral perfusion pressure (CPP) = (MAP - ICP) may not improve. It is unknown whether the level of MAP alters cerebral blood flow (CBF) when MAP and ICP change in parallel so that CPP remains constant. This study investigates CBF at a constant CPP but varying levels of MAP and ICP in 12 anaesthetized cats. CBF was studied at three levels of CPP: 60 (n = 4), 50 (n = 4), and 40 mm Hg (n = 4) under conditions of both intact and impaired autoregulation. At CPP levels of 50 and 60 mm Hg, when autoregulation was intact, CBF remained unchanged. With loss of autoregulation, there was a trend for CBF to increase as MAP and ICP were increased in parallel at a CPP of 50 and 60 mm Hg, although the relationship did not achieve statistical significance. Absolute CBF levels were, however, significantly different between the autoregulating and nonautoregulating groups (p <0.001). At a CPP of 40 mm Hg, CBF showed a linear correlation with blood pressure (BP) (r = 0.57, p <0.05). These results demonstrate that when autoregulation is impaired, there is a functional difference between autoregulating and nonautoregulating cerebral vessels despite similar MAP and CPP. These results also show that at a CPP of 40 mm Hg when autoregulation is impaired, CBF depends more on arterial driving pressure than on CPP.

Journal Article↗

PubMed1992

Intracranial blood flow velocity after head injury: relationship to severity of injury, time, neurological status and outcome.

Middle cerebral artery (MCA) blood flow velocity was measured daily by transcranial Doppler ultrasonography in 121 patients with severe (50), moderate (16) and minor (55) head injury during their hospital stay, and the results compared with findings in control subjects. Admission MCA velocity was significantly lower after severe 35.8 (31.9-39.7) cm/s, mean (95% confidence limits), moderate 45.5 (40.0-51.0) cm/s and minor 51.7 (47.9-55.5) cm/s head injury when compared with normal controls 60.1 (56.9-63.3) cm/s. Initial mean velocity in severe head injury was significantly lower than in moderate and minor injury. At discharge, MCA velocity in severe injury remained below normal 46.2 (43.2-49.0) cm/s, whereas, in moderate and minor injury flow velocity had returned to normal. Correlation (r = 0.46, p less than 0.01) was found between MCA velocity and Glasgow Coma Score (GCS) on admission but not on discharge. Persistently low flow velocity was found in all 10 patients who died within 72 hours (early deaths). An admission MCA velocity of less than 28 cm/s correctly predicted 80% of the early deaths. Patients who made a good recovery or had only moderate disability at six months showed a significant increase in velocity from admission 36.2 (31.5-41.2) cm/s to discharge 47.8 (43.7-51.9) cm/s in contrast to those who were severely disabled, in whom velocity generally remained low.

Adolescent↗

PubMed1992

Experimental otitis media evaluated by magnetic resonance imaging: an in vivo model.

The use of magnetic resonance imaging in otitis media research is being explored in our laboratory. In this study, we present a new method for studying changes in the middle ear cleft due to an episode of induced otitis media in the chinchilla model. It uses gadolinium-diethylenetriamine pentaacetic acid, a magnetic resonance imaging contrast agent, to examine the uptake and washout characteristics of middle ear mucosa during an inflammatory episode. Parameters such as the time to maximum intensity of the mucosa and the washout rate of the contrast agent from the mucosa were significantly correlated to the duration of the infection.

Animals↗

PubMed1992

Unusual gastrointestinal complications in neurosurgery.

Nine neurosurgical patients with unusual gastrointestinal complications are presented. Their diagnostic clinical features, as well as pitfalls in their diagnosis are highlighted. A high index of clinical suspicion of these unusual complications is important as patients' decreased level of consciousness and concomitant steroid therapy often complicates the clinical presentation. Progressive abdominal distension and absent or sluggish bowel sounds were the most consistent clinical features in comatose patients with peritonitis, whereas, high fever and markedly elevated white cell counts were often absent.

Adult↗

PubMed1992

The effect of changes in cerebral perfusion pressure upon middle cerebral artery blood flow velocity and jugular bulb venous oxygen saturation after severe brain injury.

Middle cerebral artery blood flow velocity and jugular bulb venous oxygen saturation (SJO2) were measured by transcranial Doppler (TCD) ultrasonography and continuous venous oximetry, respectively, in 41 severely brain-injured patients. The purpose of the study was to examine the relationships between TCD flow velocity, SJO2, and alterations in blood pressure (BP), intracranial pressure (ICP), and cerebral perfusion pressure (CPP). In these patients, CPP was reduced either by rising ICP or by falling BP. Both forms of reduction of CPP resulted in a greater fall in diastolic flow velocity than other flow parameters. As CPP decreased below a critical value of 70 mm Hg, a progressive increase in TCD pulsatility index (PI) was observed (r = -0.942, p less than 0.0001), accompanied by a fall in SJO2 (r = 0.78, p less than 0.0001). At pressures above 70 mm Hg, there was no correlation of either PI or SJO2 with CPP. The relationship between PI and CPP held true in patients with both focal and diffuse pathologies and was the same whether changes in CPP resulted from alterations in ICP or BP. The PI and SJO2 correlated better with CPP than with ICP or BP. Transcranial Doppler ultrasonography can identify states of reduced CPP. Decreases in SJO2 with falling CPP suggested progressive failure of cerebral blood flow to meet metabolic demands. Monitoring of TCD and SJO2 may be used to define the optimum CPP level for management of severely brain-injured patients.

Adolescent↗

PubMed1992

Suspected anaphylactoid shock to aminocaproic acid (plaslloid) during operation.

Epsilon-aminocaproic acid (plaslloid) is one of the most common hemostatics used perioperatively. Although some minor untoward effects in association with its use are not uncommon, the incidence of anaphylactoid shock is extremely rare, especially in a patient under general anesthesia. Recently we came across a severe anaphylactoid reaction, possibly as a result of administration of plaslloid in a patient who was undergoing elective surgery for cervical carcinoma. It was manifested by profound hypotension, tachycardia, hypoxemia, skin-wheel eruption and conjunctival and labial edema. She was successfully resuscitated with prompt volume expansion and epinephrine injection. Our experience in the management of this patient is, hereunder, reported and discussed.

Aminocaproic Acid↗

PubMed1992

Synoviocyte derived granulocyte macrophage colony stimulating factor mediates the survival of human lymphocytes.

Synoviocytes have been shown to be effector cells capable of synthesizing and secreting a variety of cytokines and growth factors. We demonstrate here that synoviocyte derived conditioned medium has immunoregulatory properties as it enhances human peripheral blood lymphocyte survival in a dose dependent manner in vitro. The effect elicited by synoviocyte derived conditioned medium from patients with rheumatoid arthritis (RA) was greater than that induced by synoviocyte derived conditioned medium from patients with osteoarthritis. Granulocyte-macrophage colony stimulating factor (GM-CSF) was found in synoviocyte derived conditioned medium with significantly higher levels present in synoviocyte derived conditioned medium from patients with RA. Recombinant human GM-CSF induced survival of human lymphocytes in vitro and a monoclonal antibody to human GM-CSF fully abrogated synoviocyte derived conditioned medium induced survival. Our results demonstrate that synoviocyte derived GM-CSF may be important in the retention of lymphocytes, which is a central pathological characteristic of the rheumatoid joint.

Arthritis, Rheumatoid↗

PubMed1992

[Mannitol reduces plasma hydrogen peroxide free radical in patients undergoing coronary artery bypass graft surgery].

During the procedure of coronary artery bypass graft surgery (CABG), the release of free oxygen radicals as a result of ischemia and reperfusion which plants the seeds of post-operative low cardiac output and arrhythmias has grave consequence on the reestablishment of cardiac function. A variety of chemical agents such as mannitol, allopurinol, catalase (Q-10) and superoxide dismutase (SOD) has proved to be considerably effective to improve the myocardial necrosis following ischemia and reperfusion. In this study we chose mannitol (0.2 gm/kg) as the free oxygen radicals scavenger and utilized mass spectrophotometric method to detect the variation of concentration of [H2O2], a by-product of free oxygen radical, in an attempt to evaluate the efficacy of mannitol in this regard in patients undergoing CABG. Patients were divided into experimental group (n = 19) and control group (n = 20). In the experimental group the concentration of [H2O2] changed from 61 +/- 24 microM/L pre-operatively to 77 +/- 18 microM/L post-operatively as against 75 +/- 31 microM/L and 99 +/- 31 microM/L respectively in the control group. In comparison, only the change in experimental group was statistically significant (p less than 0.05). We confirmed that mannitol functions considerably as a free oxygen radical scavenger since it reduces the production of [H2O2] in patients undergoing CABG.

Aged↗