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Biomedical subjects

P Tan

Publications and source records attributed to P Tan.

At least 73 records · Page 4Linked to original sources

Haemophagocytosis in bone marrow aspirate--a review of the clinical course of 10 cases.

The clinical course of 10 cases where marrow aspirate showed features of haemophagocytosis was reviewed. Eight of these had a fulminant clinical course characterized by high fever, constitutional symptoms, wasting, hepatosplenomegaly with liver dysfunction, sometimes lymphadenopathy, progressive pancytopenia and coagulopathy, like that described as 'malignant histiocytosis' in the past. The remaining 2 cases did not have this classical clinical syndrome. Among the former 8 cases, 4 of them had high-grade lymphoma, 3 of whom were confirmed to be peripheral T cell lymphoma. Three of the remaining 4 had suspicious lymphomatous infiltrate on marrow trephine. In every case an extensive search for viral etiology by serology was negative. The 2 cases which did not have fulminant clinical feature were found to have lymphoma of the diffuse large cell and Ki-1 anaplastic type, respectively. A review of the literature reveal that most cases with haemophagocytic syndrome have a fulminant clinical course and are peripheral T cell lymphoma, which generally has a poor prognosis. In our study, the 8 cases with the classical haemophagocytic syndrome had a median survival of 24 days and a long-term survival of 37.5% at 28 months. Prompt initiation of chemotherapy is a life-saving measure and the only chance of achieving a long-term survival in patients with haemophagocytic syndrome if the underlying lymphoma can be diagnosed early.

Adolescent↗

Limited role for intraoperative intact PTH measurement in parathyroid surgery.

Primary hyperparathyroidism may be cured surgically by complete excision of abnormal parathyroid tissue. Reoperation for persistent hypercalcaemia due to residual abnormal parathyroid tissue may be associated with a high complication rate. It is possible to assay intact parathormone (iPTH) intraoperatively and as iPTH has a relatively short half-life, its measurement intraoperatively may be used to predict successful parathyroidectomy. We have studied intraoperative iPTH levels in a consecutive series of 33 patients undergoing surgery for primary hyperparathyroidism. We found that iPTH levels fell significantly (P < 0.05) from a median pre-excision level of 122 pg/ml to a median level of 36 pg/ml 20 min after excision. However, in 3/31 successful parathyroidectomies, the intraoperative iPTH levels either remained unchanged or had risen. Reliance on intraoperative iPTH levels in these patients may have resulted in unnecessary re-exploration. We conclude that intraoperative iPTH measurement has limited usefulness as a predictor of successful parathyroidectomy for primary hyperparathyroidism.

Biomarkers↗

A qualitative approach to the evaluation of a cardiac education follow-up program.

The purpose of this study was to evaluate a Cardiac Education Follow-Up Program from the consumer's perspective. Nine cardiac patients between the ages of 51 and 70 participated. All had diagnoses of myocardial infarction and had taken the Program within the previous month. Patton's (1986) utilization-focused approach to evaluation provided the conceptual orientation and the Davis Patient Interview Guide (DPIG) was used for data collection. Results indicated that four aspects of the Program were of predominant interest/concern: information; support; the cardiologist's session; and the room in which the class was offered. Recommendations for program modification, using the results of the consumer's evaluation, are identified.

Aged↗

Effect of dynamic exercise on left atrial function in conscious dogs.

1. Dynamic changes in left atrial (LA) function during treadmill exercise were studied in ten conscious dogs instrumented to measure left ventricular (LV) pressure and diameter, LA pressure and diameter, and pulmonary venous blood flow (PVF, transit time flowmeter). 2. Systolic PVF volume (reservoir volume; a measure of LA reservoir function) increased from 38 +/- 4% of total PVF volume at baseline to 52 +/- 8% of total PVF volume during exercise, and diastolic PVF volume (conduit volume; a measure of LA conduit function) decreased from 62 +/- 5% at baseline to 48 +/- 8% during exercise (P < 0.005). 3. The increases in reservoir volume and the decrease in conduit volume were due not only to a greater decrease in diastolic interval than systolic interval but were also caused by a significantly greater increase (P < 0.05) in the mean systolic filling rate (93%) than in the mean diastolic filling rate (51%). 4. During exercise the pattern of LV filling derived from changes in LV diameter showed that a greater percentage of LV filling occurred during the second half of diastole at the time of atrial contraction (P < 0.05), suggesting that LA booster function was enhanced. 5. Changes in LA dimension revealed that during exercise more blood volume was reserved in the LA during systole and that this change was associated with an increase in the LA dimension at the beginning of LA contraction (r = 0.61, P < 0.05). 6. We conclude that LA reservoir and booster functions were augmented during exercise, whereas conduit function was not. Increased reservoir function may play an important role in accelerating LV filling by helping to maintain an enhanced atrioventricular pressure gradient during diastole and also by increasing LA booster function through an increase in LA preload.

Animals↗

Pharmacokinetic interactions between midazolam and propofol: an infusion study.

We have tested the hypothesis that the synergistic interaction which occurs when midazolam and propofol are combined for i.v. sedation is caused by an increase in the free plasma concentration of one of the drugs. Six patients undergoing general anaesthesia received an infusion of propofol with the addition of an infusion of midazolam commenced 30 min later. Another six patients received an infusion of midazolam with the addition of an infusion of propofol 30 min later. All infusions were administered via pharmacokinetic model-controlled syringe pumps programmed to maintain a constant plasma concentration. Venous blood samples were taken before and after introduction of the second infusion for later analysis. Free plasma concentration of midazolam increased from 2.0 (SD 1.5) ng ml-1 to 2.2 (1.9) ng ml-1 after introduction of the propofol infusion (P = 0.32). Free propofol plasma concentration was unchanged at 18.5 (5.3) ng ml-1 before and 18.7 (7.8) ng ml-1 after introduction of the midazolam infusion (P = 0.94). It was concluded that the observed synergism with this combination cannot be explained solely by alteration in free plasma concentration of either of these drugs when they are administered together.

Adolescent↗

A prospective evaluation of pharmacokinetic model controlled infusion of propofol in paediatric patients.

We have tested a published algorithm for pharmacokinetic model controlled infusion of propofol to supplement 67% nitrous oxide for general anaesthesia in Chinese children aged 4-10 yr. Initially we studied 10 children undergoing minor procedures with spontaneous ventilation; mean duration of surgery was 38 min and mean propofol infusion rate 497 micrograms kg-1 min-1. The precision of the model was 24.8% and bias -18.5%. The model was revised using an iterative linear least squares regression procedure and the revised model tested prospectively in another 20 children. The precision of the revised model was 21.5% (range in individuals 8.4-43.1%) and bias -0.1% (range -30 to 42%). Mean propofol infusion rate required to maintain anaesthesia was 474 micrograms kg-1 min-1 (range 125-737 micrograms kg-1 min-1). The mean blood concentration required for satisfactory anaesthesia was 6.6 micrograms ml-1 (range 3-11 micrograms ml-1) and the mean blood concentration at the time of waking, which occurred 40 min after switching off the infusion, 0.86 microgram ml-1 (range 0.40-1.45 micrograms ml-1). Our patient population required different pharmacokinetic variables from those in the previous study. Recovery was slow because of the high infusion rates required to maintain satisfactory anaesthesia and large difference between the blood concentration required for anaesthesia and that at which waking occurred.

Algorithms↗

A1 receptor mediated myocardial infarct size reduction by endogenous adenosine is exerted primarily during ischaemia.

OBJECTIVE: The aim was to test the hypothesis that A1 receptor mediated cardioprotection by endogenous adenosine is exerted during ischaemia rather than reperfusion. METHODS: Anaesthetised open chest rabbits were subjected to 30 min regional ischaemia and 120 min reperfusion, and randomised to one of six groups: group I--saline vehicle (VEH) (n = 12) to allow A1 and A2 adenosine receptor interactions during ischaemia and reperfusion; group II--both A1 and A2 receptors were antagonised during ischaemia and reperfusion with 8-p-sulphophenyltheophylline (SPT) (10 mg.kg-1) (SPTIR, n = 14); groups III and IV--the selective A1 adenosine receptor antagonist 8-(3-noradamantyl)-1,3-dipropylxanthine (KW-3902) was given during ischaemia-reperfusion in low dose (1 mg.kg-1, LA1-IR, n = 11) and higher dose (2 mg.kg-1, HA1-IR, n = 6); group V--KW-3902 (1 mg.kg-1) was given only during reperfusion (A1-R, n = 12); group VI--SPT was given only at reperfusion (SPTR, n = 11). RESULTS: In in vitro studies, (1) KW-3902 completely inhibited negative inotropic effects of the A1 agonist R(-)N6-(2-phenylisopropyl) adenosine (R-PIA) in catecholamine stimulated papillary muscles, and (2) had no effect on concentration dependent vasorelaxation to adenosine or R-PIA. In in vivo studies, transmural myocardial blood flow in the area at risk (determined using 15 microns radiolabelled microspheres) was reduced by 98% in all groups from 139(SEM 15.8) to 2.7(1.1) ml.min-1 x 100 g-1 (p < 0.001). At 120 min of reperfusion, blood flow in the area of necrosis was significantly less in groups LA1-IR [48.6(6.2)], HA1-IR [36.1(7.1)], SPTIR [35.9(6.4)], and SPTR [25.1(5.4)] compared to groups VEH [69.1(15.8)] and A1-R [77.2(11.8)]. The area at risk (Ar) was equivalent among groups. SPT treatment during ischaemia-reperfusion in the SPTIR group increased the area of necrosis (An, assessed by triphenyltetrazolium chloride) relative to Ar (An/Ar) to 51(1.9)% v 26.0(1.7)% in VEH group. KW-3902 in LA1-IR and HA1-IR during both ischaemia and reperfusion increased An/Ar to 35.2(2.5)% and 35.2(2.1)% of area at risk, respectively, both of which were significantly less than the SPTIR group. With A1 blockade at reperfusion (A1-R), An/Ar was equivalent to that in VEH [27.0(1.9)%], while an infarct size of 46.7(2.1)% was still observed in SPTR. CONCLUSIONS: While adenosine exerts its predominant modulation of infarct size during reperfusion, the cardioprotection mediated by A1 receptor mechanisms is modest and exerted principally during the ischaemic time period.

Adenosine↗

Midazolam and flumazenil pharmacokinetics and pharmacodynamics following simultaneous administration to human volunteers.

Resedation after antagonism of midazolam sedation with flumazenil may occur because some individuals have rapid elimination of flumazenil but slow elimination of midazolam. To determine whether there are parallel or divergent rates of elimination of the two drugs between individuals, the pharmacokinetic profiles of midazolam and flumazenil were studied simultaneously in 12 adult male volunteers. Free drug concentration data for the two drugs were incorporated into a receptor occupancy model and psychomotor testing was performed and correlated with receptor occupancy. Variation was found between individuals in the pharmacokinetics of the two drugs. There were significant correlations between Cltot (P < 0.01) but not in t1/2 alpha, t1/2 beta, Vc, or VDss. In individuals, midazolam elimination half-life ranged from less than half that of flumazenil to more than three times that of flumazenil. There was a relatively poor, although statistically significant linear correlation found between calculated receptor occupancy and critical flicker fusion frequency, r = 0.50, P < 0.01, and linear analogue scales of sedation r = 0.56, P < 0.005; and anxiolysis, r = 0.54, P < 0.005. There is divergence in the disposition and elimination of midazolam and flumazenil in some individuals. A benzodiazepine receptor occupancy model is useful for predicting the consequent differences in clinical effect when the drugs are given together.

Adult↗

Accelerated myocardial relaxation in conscious dogs during acute cardiac tamponade.

Eight chronically instrumented conscious dogs were used to test the hypothesis that left ventricular (LV) relaxation is accelerated during cardiac tamponade. The time constant of LV transmural pressure fall was measured before and during intrapericardial (IP) saline infusion (baseline) with and without beta-adrenergic blockade (propranolol 1 mg/kg iv). Heart rate was controlled by atrial pacing. Increasing IP pressure caused a progressive linear decrease in stroke volume before and during beta-blockade in each animal. The time constant of LV transmural pressure fall also decreased continuously with an increase in IP pressure from 26 +/- 7 ms during baseline to 18 +/- 5 ms during severe cardiac tamponade (P < 0.01) before beta-blockade. However, after beta-blockade, the time constant of LV transmural pressure fall was constant over a wide range of IP pressures despite a continuous decrease in LV end-diastolic volume. The time constant of LV transmural pressure fall was not altered by vena caval occlusions that caused the same decrease in LV preload observed during cardiac tamponade. We concluded that despite decreased pump function, LV relaxation was accelerated progressively during graded cardiac tamponade, and this change was dependent not on changes in loading conditions but on an intact beta-adrenergic influence.

Acute Disease↗

[Rumen bacteria degrading toxic mimosine and dihydroxypyridine compounds in China].

Four anaerobic strains were isolated from the rumen of the cattle which no specific toxic symptoms were seen when Leucaena was fed in Weizhou island Beihai city, Guangxi Province, China. All of these strains (BR-1, BR-2, BR-5 and BR-7) possess degradative activities to toxic mimosine, 3-hydroxy-4 (1H) -pyridone (3, 4-DHP) and 2, 3-dihydroxypyridine (2, 3DHP) from Leucaena, that were confirmed by analysis of HPLC. Pure and mixed cultures of these four strains in vitro degraded 44-59% of mimosine, 30-47% of 3, 4 DHP, and 58-60% of 2, 3 DHP respectively in 3 days. Strains of Both BR-1 and BR-2 were almost identical and were characterized as Lactobacillus, may be a new species. Strains of BR-5 and BR-7 were characterized as Streptococcus bovis and Clostridium sporogenes respectively. It has not yet been reported that these Gram positive facultatively and obligately anaerobic bacteria were able to degrade mimosine, 3, 4 DHP and 2, 3 DHP. These detoxic bacteria were existing in the rumen microflora of cattle in Weizhou island, protecting therefore their hosts animal from Leucaena toxicity.

Animals↗

Induction of alloantigen-specific hyporesponsiveness in human T lymphocytes by blocking interaction of CD28 with its natural ligand B7/BB1.

The specificity of T lymphocyte activation is determined by engagement of the T cell receptor (TCR) by peptide/major histocompatibility complexes expressed on the antigen-presenting cell (APC). Lacking costimulation by accessory molecules on the APC, T cell proliferation does not occur and unresponsiveness to subsequent antigenic stimulus is induced. The B7/BB1 receptor on APCs binds CD28 and CTLA-4 on T cells, and provides a costimulus for T cell proliferation. Here, we show that prolonged, specific T cell hyporesponsiveness to antigenic restimulation is achieved by blocking the interaction between CD28 and B7/BB1 in human mixed leukocyte culture (MLC). Secondary T cell proliferative responses to specific alloantigen were inhibited by addition to the primary culture of monovalent Fab fragments of anti-CD28 monoclonal antibody (mAb) 9.3, which block interaction of CD28 with B7/BB1 without activating T cells. Hypo-responsiveness was also induced in MLC by CTLA4Ig, a chimeric immunoglobulin fusion protein incorporating the extracellular domain of CTLA-4 with high binding avidity for B7/BB1. Cells previously primed could also be made hyporesponsive, if exposed to alloantigen in the presence of CTLA4Ig. Maximal hyporesponsiveness was achieved in MLC after 2 d of incubation with CTLA4Ig, and was maintained for at least 27 d after removal of CTLA4Ig. Accumulation of interleukin 2 (IL-2) and interferon gamma but not IL-4 mRNA was blocked by CTLA4Ig in T cells stimulated by alloantigen. Antigen-specific responses could be restored by addition of exogenous IL-2 at the time of the secondary stimulation. Addition to primary cultures of the intact bivalent anti-CD28 mAb 9.3, or B7/BB1+ transfected CHO cells or exogenous IL-2, abrogated induction of hyporesponsiveness by CTLA4Ig. These data indicate that interaction of CD28 with B7/BB1 during TCR engagement with antigen is required to maintain T cell competence and that blocking such interaction can result in a state of T cell hyporesponsiveness.

Animals↗

Heavy metals in some Chinese herbal plants.

The concentrations of nine heavy metals, cadmium, cobalt, copper, iron, manganese, nickel, lead, zinc, and mercury in 42 Chinese herbal medicinal plants were determined. Generally, all the samples studied had, relative to the other trace metals, higher concentrations of iron, manganese, and zinc. The concentration range of the metals determined was comparable to that in many of the East Asian vegetables and fruits. A few samples were found to contain relatively higher concentrations of the toxic metals such as cadmium, lead, and mercury. This was probably caused by contamination during air-drying and preservation.

Drugs, Chinese Herbal↗

Plasma catecholamines and neonatal condition after induction of anaesthesia with propofol or thiopentone at caesarean section.

Increased maternal sympathetic nervous system activity may decrease placental perfusion and cause adverse neonatal effects. We have studied the catecholamine response and neonatal outcome in Chinese patients with uncomplicated, singleton pregnancies undergoing Caesarean section. Anaesthesia was induced with thiopentone 4 mg kg-1 (n = 32) or propofol 2 mg kg-1 (n = 30) followed by suxamethonium. Laryngoscopy was performed after 1 min and tracheal intubation completed by 2 min. Anaesthesia was continued with atracurium, nitrous oxide and isoflurane. Maternal venous blood samples were taken at 0, 1, 2, 3, 4 min and at delivery for assay of catecholamines. The increase from baseline values in mean arterial pressure after tracheal intubation was greater in the thiopentone group (29 (SD 15) mm Hg) compared with the propofol group (18 (14) mm Hg) (P < 0.01). The concentrations of noradrenaline and adrenaline increased in both groups after tracheal intubation. Maximum noradrenaline concentrations were greater in the thiopentone group (413 (177) pg ml-1) compared with the propofol group (333 (108) pg ml-1) (P < 0.05), but there were no differences between groups in adrenaline concentrations. Neonatal Apgar scores, neurobehavioural testing and umbilical catecholamine, blood-gas tension and oxygen content analysis were similar between groups. Propofol attenuated the hypertensive and catecholamine response associated with laryngoscopy and tracheal intubation but there was no improvement in neonatal outcome.

Adult↗

Pharmacokinetic model-controlled infusion of midazolam. A prospective evaluation during general anaesthesia.

The accuracy of a computer-controlled infusion of midazolam, based on previously published pharmacokinetic parameters, was tested prospectively in 12 adult female patients undergoing general anaesthesia. Anaesthesia consisted of an initial bolus followed by an exponentially decreasing infusion of midazolam given according to body weight, fentanyl, nitrous oxide and vecuronium. Venous blood samples were taken at 15 min-intervals throughout the procedures and for 1-2 h postoperatively. The bias of the model was -5.1% (95% CI -11.3 to 1.2%) and precision 24.8% (95% CI 20.9 to 28.6%). Least squares regression analysis decreased the bias to -2.8% but did not alter precision. Retrospective fitting of an alternative set of published parameters for midazolam resulted in significant deterioration of the model. The precision was similar to that found in past studies of intravenous anaesthetic agents. Further improvement in the accuracy of midazolam infusion awaits improved understanding of the causes of pharmacokinetic variability.

Adult↗

Acadesine improves surgical myocardial protection with blood cardioplegia in ischemically injured canine hearts.

BACKGROUND: Adenosine is a cardioprotective autacoid that exerts receptor-mediated protection from ischemia/reperfusion injury. In ischemically injured hearts, avoidance of ischemia/reperfusion injury with hypothermic chemical cardioplegia may be incomplete, and consequently, postischemic left ventricular (LV) function may be severely depressed and chamber stiffness increased. This study tested the hypothesis that the adenosine-regulating agent acadesine improves myocardial protection with hypothermic blood cardioplegia (BCP), resulting in better postischemic LV function and diastolic characteristics in hearts injured by 45 minutes of normothermic global ischemia. METHODS AND RESULTS: Eighteen anesthetized (350 micrograms fentanyl citrate, 5 mg diazepam) dogs on total vented bypass were randomized to receive vehicle (n = 5), low-dose acadesine (LDA, 0.125 mg.kg-1.min-1, n = 6) or high-dose acadesine (HDA, 0.5 mg.kg-1.min-1, n = 7) continuously infused 30 minutes before global ischemia and discontinued 10 minutes after aortic cross-clamp removal. Hearts were protected with cold (4 degrees C) multidose (every 20 minutes) potassium BCP, which contained saline vehicle, 1 mg/L acadesine (LDA), or 4 mg/L acadesine (HDA) for a total of 1 hour of cardioplegic arrest. Postischemic LV function, assessed by the slope of the end-systolic pressure-volume (impedance catheter) relation, was depressed by 34 +/- 7% of baseline (5.6 +/- 1.0 versus 2.7 +/- 0.7 mm Hg/mL, P < .05) in vehicle. With LDA, there was variable improvement in postischemic function (5.1 +/- 1.3 versus 3.6 +/- 0.6 mm Hg/mL, P = .26 versus baseline). In contrast, there was complete postischemic functional recovery with HDA (5.9 +/- 0.6 versus 5.2 +/- 0.8 mm Hg/mL, P = .54). Postischemic chamber stiffness was preserved in both LDA and HDA. CONCLUSIONS: We conclude that the higher dose of acadesine improves myocardial protection when used as a pretreatment and BCP adjuvant, resulting in better postischemic LV systolic function and diastolic characteristics.

Aminoimidazole Carboxamide↗

[Swertiapunimarin from Swertia punicea Hemsl].

A new secoiridoid glycoside, swertiapunimarin (I), was isolated from the whole plant of Swertia punicea Hemsl. The structure was elucidated as 6'-O-beta-D-glucopyranosylsweroside on the basis of chemical and spectroscopic analysis. The other seven known compounds were identified as sweroside (II), swertiamarin (III), oleanolic acid (IV), daucosterol (V), beta-sitosterol (VI), 2,3-dihydroxy-1,4-benzodicarboxylic acid (VII) and methylswertianin (VIII).

Drugs, Chinese Herbal↗