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Biomedical subjects

H L Tan

Publications and source records attributed to H L Tan.

At least 19 recordsLinked to original sources
PubMed2007

Laparoscopic dismembered pyeloplasty in children younger than 2 years.

PURPOSE: Since the first laparoscopic pyeloplasty was described in a child in 1995, there have been several reports of pyeloplasty in older children. However, to date there have been few reports of laparoscopic pyeloplasty in infants and toddlers. The aim of this study was to evaluate the results of laparoscopic pyeloplasty in children younger than 2 years. MATERIALS AND METHODS: All laparoscopic Anderson-Hynes pyeloplasties performed in children younger than 2 years were retrospectively reviewed. The diagnosis of ureteropelvic junction obstruction was confirmed on renal sonography and diuretic renogram. Laparoscopic pyeloplasties were performed via a transperitoneal route as originally described, with key modifications. All children were investigated with postoperative diuretic renogram and renal ultrasonography. RESULTS: A total of 38 children with ureteropelvic junction obstruction underwent laparoscopic Anderson-Hynes pyeloplasty between January 2001 and December 2005. Of these patients 11 (7 males and 4 females) were younger than 2 years at surgery (median 1.4, range 2 to 22 months) and 1 had bilateral ureteropelvic junction obstruction, for a total of 12 primary repairs. However, 2 patients (17%) required redo laparoscopic pyeloplasty, for a total of 14 laparoscopic dismembered pyeloplasties in this age group. Operative time ranged from 70 to 140 minutes (mean 100) and median hospital stay was 2 days. Followup studies showed normal drainage in all patients except 1, who after redo pyeloplasty exhibited significantly improved but still prolonged drainage. CONCLUSIONS: This study suggests that laparoscopic pyeloplasty can now be performed in young children with good results.

Female↗
PubMed2006

The role of diagnostic laparoscopy in micropremmies with suspected necrotizing enterocolitis.

BACKGROUND: The timely diagnosis of perforations or dead gut can be extremely difficult in micropremmies with necrotizing enterocolitis. A negative laparotomy is just as detrimental as failure to recognize early perforation in this group of patients. We have been exploring the role of microlaparoscopy using a needlescope to determine if this modality is feasible and useful in the surgical management of these patients. We report our technique and initial experience with needlescopic diagnosis. METHODS: Four patients (weight >500 to <1000 g) with abdominal distension and clinical sepsis not responsive to aggressive medical treatment were included in this study. None had radiologic evidence of pneumatosis or perforation. There was no absolute surgical indication for laparotomy except for strong suspicion of a surgical cause. Needlescopic diagnosis was performed in all these patients. RESULTS: There was no evidence of perforation or bile in the abdominal cavity in one patient. This patient improved on medical management, avoiding a laparotomy. The rest had bile or fibrin in the abdominal fluid with a localized perforation, and in each case we performed a microlaparotomy directly over the site of perforation to create a stoma. CONCLUSIONS: Needlescopic diagnosis is feasible and appears to be safe, even in critically ill micropremmies less than 1000 g. The technique can provide useful information for surgical decision-making and allows for precise placement of a microlaparotomy incision over the site of perforation, thus minimizing the trauma from open surgery in this special group of patients. We are currently expanding its role in patients with overt perforations to determine if we can limit the extent of surgical exploration without compromising the adequacy of surgical management.

Abdominal Cavity↗
PubMed2006

Laparoscopic surgery in children is associated with an intraoperative hypermetabolic response.

BACKGROUND: Laparoscopic surgery is thought to be associated with a reduced metabolic response compared to open surgery. Oxygen consumption (VO2) and energy metabolism during laparoscopic surgery have not been characterized in children. METHODS: We measured respiratory gas exchange intraoperatively in children undergoing 19 open and 20 laparoscopic procedures. Premature infants and patients with metabolic, renal, and cardiac abnormalities were excluded. Anesthesia was standardized. Unheated carbon dioxide was used for insufflation. VO2 was measured by indirect calorimetry. Core temperature was measured using an esophageal temperature probe. RESULTS: We found a steady increase in VO2 during laparoscopy. The increase in VO2 was more marked in younger children and was associated with a significant rise in core temperature. Open surgery was not associated with significant changes in core temperature or VO2. CONCLUSIONS: Laparoscopy in children is associated with an intraoperative hypermetabolic response characterized by increased oxygen consumption and core temperature. These changes are more marked in younger children.

Adolescent↗
PubMed2006

Cellular basis of sex disparities in human cardiac electrophysiology.

AIM: Sex disparities in electrocardiogram variables and dysrhythmia susceptibility exist, notably in long QT syndrome (LQTS) and Brugada syndrome, but the underlying mechanisms in man are unknown. We studied the cellular basis of sex distinctions in human cardiac electrophysiology and dysrhythmia susceptibility using mathematical models of human ventricular myocytes. METHODS: We implemented sex differences in the Priebe-Beuckelmann and ten Tusscher-Noble-Noble-Panfilov human ventricular cell models by modifying densities of the L-type Ca(2+) current (I(Ca,L)), transient outward K(+) current (I(to)), and rapid delayed rectifier K(+) current (I(Kr)), according to experimental data from male and female hearts of various species. Sex disparities in transmural repolarization were studied in transmural strands of cells with ion current densities based on canine experimental data. RESULTS: Female cells have longer action potential duration (APD), steeper APD-heart rate relationship, larger transmural APD heterogeneity, and a greater susceptibility to pro-dysrhythmogenic early afterdepolarizations (EADs) than male cells. Conversely, male cells have more prominent phase-1 repolarization and are more susceptible to all-or-none repolarization. CONCLUSION: Sex differences in I(Ca,L), I(to) and I(Kr) densities may explain sex disparities in human cardiac electrophysiology. Female cells exhibit a limited 'repolarization reserve' as demonstrated by their larger susceptibility to EADs, which, combined with their larger transmural electrical heterogeneity, renders them more vulnerable to tachydysrhythmias in LQTS. Conversely, male cells have a limited 'depolarization reserve', as shown by their larger susceptibility to all-or-none repolarization, which facilitates tachydysrhythmias in Brugada syndrome. These general principles may also apply to dysrhythmia susceptibility in common disease.

Action Potentials↗
PubMed2005

Clinical evaluation of USCOM ultrasonic cardiac output monitor in cardiac surgical patients in intensive care unit.

BACKGROUND: The USCOM ultrasonic cardiac output monitor (USCOM Pty Ltd, Coffs Harbour, NSW, Australia) is a non-invasive device that determines cardiac output by continuous-wave Doppler ultrasound. The aim of this study was to evaluate the accuracy of the USCOM device compared with the thermodilution technique in intensive care patients who had just undergone cardiac surgery. METHODS: We conducted a prospective study in the 18-bed intensive care unit of a 600-bed tertiary referral hospital. Twenty-four mechanically ventilated patients were studied immediately following cardiac surgery. We evaluated the USCOM monitor by comparing its output with paired measurements obtained by the standard thermodilution technique using a pulmonary artery catheter. RESULTS: Forty paired measurements were obtained in 22 patients. We were unable to obtain an acceptable signal in the remaining two patients. Comparison of the two techniques showed a bias of 0.18 and limits of agreement of -1.43 to 1.78. The agreement may not be as good between techniques at higher cardiac output values. CONCLUSIONS: The USCOM monitor has a place in intensive care monitoring. It is accurate, rapid, safe, well-tolerated, non-invasive and cost-effective. The learning curve for skill acquisition is very short. However, during the learning phase the USCOM monitor measurements are rather 'operator dependent'. Its suitability for use in high and low cardiac output states requires further validation.

Adult↗
PubMed2005

Novel Brugada syndrome-causing mutation in ion-conducting pore of cardiac Na+ channel does not affect ion selectivity properties.

AIM: Brugada syndrome is an inherited cardiac disease with an increased risk of sudden cardiac death. Thus far Brugada syndrome has been linked only to mutations in SCN5A, the gene encoding the alpha-subunit of cardiac Na+ channel. In this study, a novel SCN5A gene mutation (D1714G) is reported, which has been found in a 57-year-old male patient. Since the mutation is located in a segment of the ion-conducting pore of the cardiac Na+ channel, which putatively determines ion selectivity, it may affect ion selectivity properties. METHODS: HEK-293 cells were transfected with wild-type (WT) or D1714G alpha-subunit and beta-subunit cDNA. Whole-cell configuration of the patch-clamp technique was used to study biophysical properties at room temperature (21 degrees C) and physiological temperature (36 degrees C). This study represents the first measurements of human Na+ channel kinetics at 36 degrees C. Ion selectivity, current density, and gating properties of WT and D1714G channel were studied. RESULTS: D1714G channel yielded nearly 80% reduction of Na+ current density at 21 and 36 degrees C. At both temperatures, no significant changes were observed in V(1/2) values and slope factors for voltage-dependent activation and inactivation. At 36 degrees C, but not at 21 degrees C, D1714G channel exhibited more slow inactivation compared with WT channel. Ion selectivity properties were not affected by the mutation at both temperatures, as assessed by either current or permeability ratio. CONCLUSION: This study shows no changes in ion selectivity properties of D1714G channel. However, the profoundly decreased current density associated with the D1714G mutation may explain the Brugada syndrome phenotype in our patient.

Animals↗
PubMed2005

Preferences of cardiologists and clinical geneticists for the future organization of genetic care in hypertrophic cardiomyopathy: a survey.

In view of the increasing demands for genetic counselling and DNA diagnostics in cardiogenetics, the roles of cardiologists and clinical geneticists in the delivery of care need to be redefined. We investigated the preferences of both groups of professionals with regard to the future allocation of six cardiogenetic responsibilities in counselling and testing, using hypertrophic cardiomyopathy (HCM) as a prevalent model disease. In this cross-sectional survey, the participants were Dutch cardiologists (n = 643) and clinical geneticists (n = 60), all members of professional societies. Response rates were 33 and 82%, respectively. In both groups, the majority preferred to perform most of the tasks described above in collaboration. Informing HCM patients about the genetics of HCM and requesting DNA testing in symptomatic patients was viewed by 43 and 35% of cardiologists, respectively, as their sole responsibility, however, and 39 and 59% of clinical geneticists did not object to these views. Both groups felt that the task of discussing the consequences of HCM for offspring and that of discussing the results of DNA diagnostics should be shared or performed by clinical geneticists. Both groups considered co-ordination of family screening the sole responsibility of clinical geneticists. Opinions on who should request DNA diagnostics in asymptomatic relatives were divided: 86% of clinical geneticists considered it their exclusive responsibility, 10% of cardiologists believed that this task could be performed individually by either group and 30% preferred to collaborate. Most professionals said that they would appreciate education programmes and clinical guidelines. Both cardiologists and clinical geneticists prefer to share rather than divide most cardiogenetic responsibilities in caring for HCM patients. Consequently, capacity problems in both groups are to be expected. To safeguard current professional standards in genetic counselling and testing, deployment of non-medical personnel might be essential.

Attitude of Health Personnel↗
PubMed2005

Accuracy of various iron parameters in the prediction of iron deficiency in an acute care hospital.

INTRODUCTION: Iron parameters like serum ferritin and iron saturation are routinely used in diagnosing iron deficiency. However, these tests are influenced by many factors. We aimed to review the accuracy of iron parameters among inpatients in an acute care hospital. MATERIALS AND METHODS: From October 1997 to April 2002, bone marrow aspirate samples from patients on whom concurrent iron studies had been done were analysed. Accuracy of the various iron parameters was analysed using receiver operating characteristic curves. RESULTS: Among 92 bone marrow aspirate samples, 58, 86 and 83 had a concurrent serum ferritin, serum iron and percentage iron saturation done respectively. Serum ferritin is the best marker for predicting the presence of iron deficiency. This is followed by percentage iron saturation and lastly by serum iron. At the most optimal, a serum ferritin of <60 ng/mL has a positive likelihood ratio of 24.35, sensitivity of 69.6%, specificity of 97.1% and positive predictive value of 94.1%. An iron saturation of <7% has a positive likelihood ratio of 21.62, sensitivity of 44.1%, specificity of 98.0% and positive predictive value of 93.8%. Seven out of 50 samples, which had concurrent measurements of iron saturation and serum ferritin, were discordant in indicating the presence of iron deficiency. In 6 cases, the iron saturation was the spurious result. CONCLUSION: A serum ferritin of <60 ng/mL or a percentage iron saturation of <7% is highly predictive of iron deficiency among inpatients in an acute care hospital.

Adolescent↗
PubMed2004

Lymphatic sparing, laparoscopic varicocelectomy: a new surgical technique.

Several surgical options are available for managing varicoceles. Although conventional surgery offers good surgical results, the most common long-term complication of surgery is the development of hydroceles, thought to be due to interruption in the lymphatic outflow from the subservient testis. The authors describe a new technique of in vivo methylene blue mapping of testicular lymphatic vessels at laparoscopy, allowing these vessels to be spared during laparoscopic varicocelectomy. This novel method of in vivo staining of lymphatic vessels should prevent damage to the lymphatic system and avoid the late development of hydroceles. A prospective multicenter trial is currently underway to evaluate the medium- and long-term results.

Coloring Agents↗
PubMed2004

Family and population strategies for screening and counselling of inherited cardiac arrhythmias.

Family screening in inherited cardiac arrhythmias has been performed in The Netherlands since 1996, when diagnostic DNA testing in long QT syndrome (LQTS) and hypertrophic cardiomyopathy (HCM) became technically possible. In multidisciplinary outpatient academic clinics, an adjusted protocol for genetic counselling, originally derived from predictive testing in Huntington's disease, is being used. 1110 individuals, including 842 relatives of index patients, were informed about their risks, and most were tested molecularly and/or clinically for carriership of the disease present in their family. Of 345 relatives who were referred for cardiologic follow-up, 189 are being treated, because of an increased risk of life-threatening arrhythmias. Evaluation of the psychological and social consequences of family screening for inherited arrhythmias can be performed by using the adapted criteria of Wilson and Jüngner, i.e., from a point of view of public health. Preliminary results of psychological research show that parents of children at risk for LQTS show high levels of distress. Many other aspects have to be evaluated yet, making final conclusions about the feasibility of family screening difficult, particularly in HCM. Clinical guidelines are urgently needed. Population screening by molecular testing, for instance in athletic preparticipation screening, will become possible in the future and has its own prerequisites for success.

Arrhythmias, Cardiac↗
PubMed2004

Ca2+-activated Cl- current reduces transmural electrical heterogeneity within the rabbit left ventricle.

OBJECTIVE: Various cationic membrane channels contribute to the heterogeneity of action potential configuration between the transmural layers of the left ventricle. The role of anionic membrane channels is less intensively studied. We investigated the role of the Ca2+-activated Cl- current, ICl(Ca), in transmural electrical heterogeneity. METHODS AND RESULTS: We determined the density of ICl(Ca) and its physiological role in subepicardial and subendocardial ventricular myocytes of rabbit using the patch-clamp technique. ICl(Ca) was measured as the 4,4'diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) sensitive current. The current-voltage relationships and the densities of ICl(Ca) were similar in subepicardial and subendocardial myocytes. However, the functional role of ICl(Ca) exhibited striking differences. In subendocardial myocytes, blockade of ICl(Ca) by DIDS increased action potential duration (APD) significantly at all measured stimulus frequencies (3.33-0.2 Hz). In subepicardial myocytes, ICl(Ca) blockade increased APD only at 3.33 Hz, but not at the lower stimulus frequencies. At 1 Hz, ICl(Ca) blockade in subepicardial myocytes only caused an APD increase when the transient outward K+ current, Ito1, was blocked. CONCLUSIONS: The densities and gating properties of ICl(Ca) are similar in subepicardial and subendocardial myocytes. ICl(Ca) contributes to APD shortening in subendocardial, but not in subepicardial myocytes except at 3.33 Hz. These differences in functional expression of ICl(Ca) reduce the electrical heterogeneity in rabbit left ventricle.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2003

The successful medical management of severe duodenal strictures secondary to eosinophilic gastroenteritis in an infant.

Eosinophilic gastroenteritis is an uncommon condition of unknown etiology that has only been relatively recently reported. Its clinical manifestations range from a mild disease to more severe forms resembling Crohn's disease. Enteric strictures are a rare but recognized complication of this condition. We report a case of eosinophilic gastroenteritis in an infant presenting with severe duodenal strictures that was successfully managed with oral prednisolone. We believe that this is the first reported case of duodenal strictures secondary to eosinophilic gastroenteritis.

Diagnosis, Differential↗
PubMed2003

Laparoscopic resection of type I choledochal cyst.

Type I choledochal cyst is a rare saccular or fusiform congenital dilatation of the extrahepatic biliary tract. It is usually treated by laparotomy at which the cyst is completely excised and a Roux-en-Y hepaticojejunostomy is performed to establish biliary enteric drainage. We report the laparoscopic excision and hepaticoduodenostomy of type I choledochal cyst in two girls aged 1 and 3 years. The entire procedure was performed laparoscopically using needlescopic instruments. A 7-mm telescope port was inserted at the umbilicus, a 3-mm port in the right upper quadrant, and a 6-mm port in left upper quadrant. An additional 3-mm fan-shaped liver retractor was passed through the abdominal wall without a trocar. The gallbladder and choledochal cyst was dissected and removed en bloc. The lower end of the common bile duct was closed with 5-0 polydioxanone. The duodenum was anastomosed to the common hepatic duct below the confluence of the right and left hepatic ducts. There were no intraoperative complications, and the children were asymptomatic with no episodes of cholangitis at 6 months follow-up. Pediatric surgeons trained in advanced laparoscopic techniques including intracorporeal suturing can perform laparoscopic repair of choledochal cyst safely.

Anastomosis, Surgical↗
PubMed2003

Reduction in visceral slide is a good sign of underlying postoperative viscero-parietal adhesions in children.

BACKGROUND/PURPOSE: Viscera stuck to the anterior abdominal wall from previous surgery risk injury during laparoscopic surgery. A prospective study was conducted to determine if these adhesions are detectable on ultrasound scan by showing a reduction in the normal visceral slide. METHODS: Patients undergoing laparoscopic procedure after a previous laparotomy underwent preoperative real-time ultrasound scan to observe if viscera slides freely under the abdominal wall. A reduction in slide was considered a positive sign of underlying adhesions. These findings were correlated with the operative findings. RESULTS: Anterior abdominal wall scans were performed on 17 children. Reduced visceral slide was seen in 10. Viscero-parietal adhesions were found in 9 of 10 patients. Visceral slide was reduced in a very localized area in 6 patients, and, in these, a loop of bowel (n = 3), liver and bowel (n = 2), or liver (n = 1) was adherent. In 4, reduced visceral slide was seen over a wide area. Extensive adhesions were found in 3 of 4. One renal transplant patient with peritonitis had a false-positive ultrasound scan. At laparotomy there were no adhesions. The peritonitis is thought to have prevented an adequate examination. Seven patients had normal visceral slide. Of these, 4 had no adhesions, but 3 children had flimsy omental adhesions. The sensitivity and specificity of visceral slide in predicting adhesions were 75% and 80%, respectively. CONCLUSIONS: Reduction in visceral slide is a good sign of underlying postoperative viscero-parietal adhesions. Ultrasonographic mapping of the abdominal wall may be useful in selecting an adhesion-free site for trocar insertion in children with previous operations requiring laparoscopic procedures.

Abdominal Wall↗
PubMed2003

Role of Ca2+-activated Cl- current during proarrhythmic early afterdepolarizations in sheep and human ventricular myocytes.

OBJECTIVES: The proarrhythmic early afterdepolarizations (EADs) during phase-2 of the cardiac action potential (phase-2 EADs) are associated with secondary Ca2+-release of the sarcoplasmic reticulum. This makes it probable that the Ca2+-activated Cl- current [ICl(Ca)] is present during phase-2 EADs. Activation of ICl(Ca) during phase-2 of the action potential will result in an outwardly directed, repolarizing current and may thus be expected to prevent excessive depolarization of phase-2 EADs. The present study was designed to test this hypothesis. METHODS AND RESULTS: The contribution of ICl(Ca) during phase-2 EADs was studied in enzymatically isolated sheep and human ventricular myocytes using the patch-clamp methodology. EADs were induced by a combination of a low stimulus frequency (0.5 Hz) and exposure to 1 microm noradrenaline. In sheep myocytes, the ICl(Ca) blocker 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS, 0.5 mm) abolished phase-1 repolarization of the action potential in all myocytes tested. This indicates that ICl(Ca) is present in all sheep myocytes. However, DIDS had no effect on phase-2 EAD characteristics. In human myocytes, DIDS neither affected phase-1 repolarization nor phase-2 EAD characteristics. CONCLUSION: In sheep ventricular myocytes, but not in human ventricular myocytes, ICl(Ca) contributes to phase-1 repolarization of the action potential. In both sheep and human myocytes, ICl(Ca) plays a limited role during phase-2 EADs.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed2002

Severe hyperphosphataemia and associated electrolyte and metabolic derangement following the administration of sodium phosphate for bowel preparation.

Sodium phosphate is widely used as an effective bowel preparation agent. It is used in smaller volumes, leading to improved patient tolerance. Although it is generally safe, cases of severe hyperphosphataemia following sodium phosphate administration have been reported in the literature. The common risk factors identified are advanced age, impaired renal function, impaired colonic motility and multiple doses. However, many doctors remain unaware of the dangers associated with this agent. We report six cases of severe electrolyte and metabolic derangement due to sodium phosphate bowel preparation: two patients had delayed awakening from general anaesthesia, and four patients suffered life-threatening consequences.

Age Factors↗