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Biomedical subjects

K Gan

Publications and source records attributed to K Gan.

At least 19 recordsLinked to original sources
PubMed2004

Modelling the isotope enrichment of leaf water.

Farquhar and Gan have proposed a model for the spatial variation in the isotopic enrichment of H(2)(18)O across a leaf, which is specifically formulated for monocotyledoneous leaves. The model is based on the interaction between mass fluxes longitudinally within the xylem, and fluxes laterally through veinlets into the lamina mesophyll, where moisture leaves the leaf through transpiration. The lighter, more abundant, molecule H(2)(16)O escapes preferentially with the evaporating water, resulting in the enrichment of H(2)(18)O at these sites. Enriched water diffuses throughout the leaf, and it is this spatial distribution of enriched water which the model seeks to capture. In this paper we present a general formulation of the model in terms of mass flux, extending it to include variable transpiration rates across the leaf surface, as well as a tapering xylem. Solutions are developed for the general case and, since the solutions present in the form of Kummer functions, properties are established as well as methods for estimating the solutions under certain conditions relevant to the biology. The model output is compared with Gan's data collected from maize plants.

Models, Biological↗
PubMed2000

Evidence of progressive delay of motor development in children with sensorineural hearing loss and concurrent vestibular dysfunction.

Gross motor development, and the effect of age, sex and vestibular function on it, was examined in 39 24- to 83-mo.-old children with sensorineural hearing impairment. Repeated testing was completed on 18 children. Delayed gross motor development was evident regardless of age, but only children less than 5 years of age had developmental balance deficits on initial testing. Both gross motor and balance development scores were lower on repeated testing. Furthermore, vestibular function scores facilitated identification of those children with a deficit in balance development as well as those with a progressive delay in motor or balance development. Implications for practice are discussed.

Age Factors↗
PubMed1999

Minimally invasive direct coronary artery bypass grafting using the gastroepiploic artery for reoperation after the Cabrol procedure.

Obstruction of the right coronary ostial anastomosis is a rare late complication after composite graft replacement of the ascending aorta and the aortic valve with separate Dacron coronary grafts (Cabrol method). Occlusion at the right coronary ostial anastomosis in a 36-year-old woman with aortitis syndrome who underwent a composite graft with a Dacron coronary graft is described. She underwent a third successful operation for right coronary reconstruction by minimally invasive direct coronary artery bypass grafting technique using the right gastroepiploic artery. This approach is likely to be extremely useful in avoiding resternotomy and cardiopulmonary bypass in patients requiring coronary reoperation.

Adult↗
PubMed1999

Retrograde cerebral perfusion versus selective cerebral perfusion as evaluated by cerebral oxygen saturation during aortic arch reconstruction.

BACKGROUND: Time limits for neuroprotection by retrograde cerebral perfusion (RCP) and selective cerebral perfusion (SCP) in aortic arch aneurysm repair or dissection are undergoing definition. METHODS: Using near-infrared optical spectroscopy, changes in regional cerebrovascular oxygen saturation (rSO2) were compared between the two perfusion methods. RESULTS: Immediately before cardiopulmonary bypass, baseline rSO2 was 63.9%+/-6.9% for the RCP and 66.1%+/-5.3% for the SCP group (no significant difference). As patients were core-cooled to 20 degrees C, rSO2 increased to 73.1%+/-8.8% and 74.1%+/-7.9% in the RCP and SCP groups, respectively. With circulatory arrest, rSO2 suddenly decreased. After starting cerebral perfusion, rSO2 returned to prearrest values in the SCP group but continued decreasing steadily in the RCP group, to levels below baseline after about 25 minutes. At the end of perfusion, rSO2 was 57.4%+/-12.2% for the RCP group and 71.7%+/-6.9% for the SCP group, and the ratio of rSO2 to baseline value was 0.89 for RCP and 1.08 for SCP despite a shorter brain perfusion time for RCP (38.8+/-18.0 versus 103.3+/-43.3 minutes). Three of 5 patients whose ratios of rSO2 to baseline at the end of brain protection were 0.7 or less had neurologic deficits. CONCLUSIONS: Although SCP showed no clinically important time limitation, rSO2 continued to decrease with time during RCP. An rSO2 ratio less than 0.7 could represent a critical lower limit.

Aged↗
PubMed1998

Emergency percutaneous cardiopulmonary bypass support for acute myocardial infarction.

We assessed the efficacy of emergency percutaneous cardiopulmonary bypass support (PCPS) in the treatment of patients with acute myocardial infarction complicated by cardiogenic shock. Emergency PCPS was instituted in 21 consecutive patients beginning in 1991. After the stabilization of the hemodynamics, coronary reperfusion was performed by means of coronary artery bypass grafting or percutaneous transluminal coronary angioplasty. Of the seven patients with acute myocardial infarction involving either the left main or two-vessel territories, five survived more than 1 month, but only one patient remained alive and well after 20 months. The main cause of death for this group was low output syndrome. Four of 12 patients with acute left main trunkal occlusion in the catheter laboratory survived and showed a preserved cardiac function (mean followup 28.5 months). The main cause of death for this group was brain damage. Two patients with single-vessel territory acute myocardial infarction underwent PCPS to treat refractory ventricular fibrillation. Both patients were still alive and well at a 12-month followup. Percutaneous cardiopulmonary bypass support successfully stabilized the hemodynamics, allowing time to perform revascularization for all three groups of patients with life-threatening acute myocardial infarction. Recanalization was nevertheless unable to salvage the damaged myocardium in cases of prolonged ischemic time.

Aged↗
PubMed1998

Statistical evaluation of in vitro dissolution of different brands of ciprofloxacin hydrochloride tablets and capsules.

The in vitro dissolution of ciprofloxacin from commercially available tablets and capsules in China was studied using the USP apparatus I to compare the product performance from nine different manufacturers. Cumulative release greater than 75% was obtained from all of the products tested within 45 min. However, statistically significant differences were found between some of the products when in vitro data were analyzed using the Weibull function, similarity factor (f2), and multivariate analysis of variances.

Anti-Infective Agents↗
PubMed1998

[Results of surgical treatment for pT3 primary lung cancer].

We reviewed pT3 lung cancer for 86 cases (13.1%) out of 659 cases treated surgically for primary lung cancer between 1985 and march 1998. Five-year and ten-year survival rates for all pT3 cases were 48% and 40% respectively and those for pT3N0M0 cases were 67.2%. The operative mortality between 1990 and 1998 (2.4%) was better than that between 1985 and 1989 (6.7%). The extensive resection for pT3 lung cancer was evaluated to be appropriate. However, the prognosis of the patients who underwent combined resection of mediastinal pleura, pericardium or diaphragm was very poor. Five-year survival rate was significantly worse in patients with N2 disease (17.3%) than in patients with N0 disease (65.8%) (p < 0.05). Although the surgical indication for the patients with mediastinal pleura, pericardium or diaphragm disease and N2 disease is still controversial, there is not the extensive surgical indication.

Adolescent↗
PubMed1997

Roles of histidine-103 and tyrosine-235 in the function of the prolipoprotein diacylglyceryl transferase of Escherichia coli.

Phosphatidylglycerol:prolipoprotein diacylglyceryl transferase (Lgt) is the first enzyme in the posttranslational sequence of reactions resulting in the lipid modification of lipoproteins in bacteria. A previous comparison of the primary sequences of the Lgt enzymes from phylogenetically distant bacterial species revealed several highly conserved amino acid sequences throughout the molecule; the most extensive of these was the region 103HGGLIG108 in the Escherichia coli Lgt (H.-Y. Qi, K. Sankaran, K. Gan, and H. C. Wu, J. Bacteriol. 177:6820-6824, 1995). These studies also revealed that the kinetics of inactivation of E. coli Lgt with diethylpyrocarbonate were consistent with the modification of a single essential histidine or tyrosine residue. The current study was conducted in an attempt to identify this essential amino acid residue in order to further define structure-function relationships in Lgt. Accordingly, all of the histidine residues and seven of the tyrosine residues of E. coli Lgt were altered by site-directed mutagenesis, and the in vitro activities of the altered enzymes, as well the abilities of the respective mutant lgt alleles to complement the temperature-sensitive phenotype of E. coli SK634 defective in Lgt activity, were determined. The data obtained from these studies, in conjunction with additional chemical inactivation studies, support the conclusion that His-103 is essential for Lgt activity. These studies also indicated that Tyr-235 plays an important role in the function of this enzyme. Although other histidine and tyrosine residues were not found to be essential for Lgt activity, alterations of His-196 resulted in a significant reduction of in vitro activity.

Amino Acid Sequence↗
PubMed1997

Leriche syndrome. Surgical procedures and early and late results.

During the past thirteen years, 29 patients underwent surgical intervention for Leriche syndrome. Fifteen patients (aged forty-two to seventy-two years, average 60.7 years) underwent anatomical bypass, and 9 of them whose thrombus was confined to the infrarenal aorta received a routine graft insertion. In the other 6 whose thrombus extended to the level of the renal arteries, an open thrombectomy of the juxtarenal aorta was first performed through a transection of the infrarenal aorta under renal ischemia (4-14 minutes, average 7). Twelve elderly or high-risk patients (aged sixty-eight to eighty-four years, average 75.3 years) underwent an axillobifemoral bypass, and another 2 (fifty-eight and sixty years old, respectively) who had been operated on at an earlier time received an ascending aortobifemoral bypass. In cases of anatomical bypass, no graft has occluded and all patients but 1, who died of cerebral infarction, have an active life now. In cases of extraanatomical bypass, 5 of the 28 grafts occluded and only 6 patients have survived. The other 8 patients died of malignancy, atherosclerotic complications, or unknown causes. The 10-year survival rate was 92.9% and 29.5% in the anatomical bypass and extraanatomical bypass group, respectively. In Leriche syndrome, anatomical bypass is preferred to extraanatomical bypass if conditions permit. In the juxtarenal type, an open thrombectomy under renal ischemia is mandatory for anatomical bypass, and a transection of the infrarenal aorta facilitates this procedure. Because the patients with Leriche syndrome are elderly and harbor arteriosclerotic lesions, a careful follow-up is mandatory.

Adult↗
PubMed1996

Surgical treatment of infective endocarditis complicated by annular infection and cerebral infarction.

The surgical treatment of nine patients with infective endocarditis (IE) complicated by annular infection and five with IE complicated by cerebral infarction is described herein. In those with annular infection, after thorough débridement of the infected tissues, valve replacement was performed at the original position in five, at the supraannular position in three, and one underwent a translocation procedure. Aortic valve replacement was able to be performed at the original position in two patients by closing the defect at the aortic annulus with a patch after through débridement. The five patients who underwent original valve position replacement recovered well. Of the three who underwent supraannular position replacement, two died of septicemia after a redo operation, and one received pacemaker implantation. The patient undergoing the translocation procedure died of intestinal infarction. In the five patients who suffered cerebral infarction due to embolus of the vegetation, valve replacement was performed between 40 h and 5 months after its onset. Although one patient died of the rapid progression of brain damage, the other four are alive and well, including two who developed mycotic cerebral aneurysm in the infarcted areas. In conclusion, early surgery for IE is mandatory irrespective of active infection, due to the high mortality and morbidity associated with serious sequelae such as annular abscess or cerebral infarction.

Abscess↗
PubMed1996

Delayed primary repair of intrathoracic esophageal perforation: is it safe?

The management of intrathoracic esophageal perforation with delayed diagnosis is a subject of controversy. Because of the obvious advantages of primary repair as a simple single-stage operation, this technique was preferentially used to treat 18 of 22 consecutive patients with esophageal perforation. These patients were stratified into three groups according to the time interval between perforation and repair: group A, less than 6 hours, five patients (28%); group B, 6 to 24 hours, six patients (33%); and group C, more than 24 hours, seven patients (39%). Group A patients were older (p < 0.05) and group B had fewer iatrogenic perforations (B, 17%; A, 80%; C, 57%, p < 0.1). Additional tissue was used to buttress the repair site in all three groups (A, 3/5 patients, 60%; B, 4/6 patients, 67%; C, 6/7 patients, 86%; p = not significant). In seven patients (39%), a fundic wrap was used to reinforce the site of primary repair. The outcomes of the three groups were analyzed. Group A had the lowest proportion of postoperative leaks (A, 0/4 patients, 0%; B, 4/6 patients, 67%; C, 5/6 patients, 83%; p < 0.05) and postoperative morbidity (A, 2/5 patients, 40%; B, 6/6 patients, 100%; C, 6/7 patients, 86%; p < 0.1). However the increased incidence of leak and morbidity did not lead to an increase in mortality. One death occurred in each group, with an overall mortality of 17% (A, 1/5 patients, 20%; B, 1/6 patients, 17%; C, 1/7 patients, 14%; p = not significant). We conclude that in the era of advanced intensive care capabilities, primary repair of intrathoracic esophageal perforation can be safely accomplished in most patients regardless of the time interval between perforation and operation. Leakage at the suture site is common unless primary repair is carried out without delay. Postoperative leakage, however, is usually inconsequential and does not necessarily result in an adverse outcome.

Aged↗
PubMed1996

[Graft replacement of a thoracic aneurysm and coronary artery bypass grafting using retrograde cerebral perfusion through left thoracotomy--a case report].

A 67-year-old woman having descending thoracic aneurysm and 90% stenosis of the obtuse marginal artery underwent a concomitant operation of graft replacement of a thoracic aneurysm and coronary artery bypass grafting. The operation was performed through left posterolateral thoracotomy with total cardiopulmonary bypass using femoral artery, femoral vein and the pulmonary artery cannulation, deep hypothermia and retrograde cerebral perfusion (RGCP). RGCP was performed by high central venous pressure (17-18 mmHg) resulted from low flow perfusion of the lower body under clamping of the descending aorta. Distal coronary anastomosis was done during an initial 100ling period and proximal anastomosis was put on the replaced thoracic graft after coming off extracorporeal circulation (ECC). ECC time was 167 minutes, and RGCP time was 27 minutes. The patient did well after the operation. Postoperative coronary angiography showed the patent coronary bypass graft. We conclude that this method provides good exposure of the thoracic aorta and the coronary artery, and satisfactory brain protection.

Aged↗
PubMed1995

Structure-function relationship of bacterial prolipoprotein diacylglyceryl transferase: functionally significant conserved regions.

The structure-function relationship of bacterial prolipoprotein diacylgyceryl transferase (LGT) Has been investigated by a comparison of the primary structures of this enzyme in phylogenetically distant bacterial species, analysis of the sequences of mutant enzymes, and specific chemical modification of the Escherichia coli enzyme. A clone containing the gene for LGT, lgt, of the gram-positive species Staphylococcus aureus was isolated by complementation of the temperature-sensitive lgt mutant of E. coli (strain SK634) defective in LGT activity. In vivo and in vitro assays for prolipoprotein diacylglyceryl modification activity indicated that the complementing clone restored the prolipoprotein modification activity in the mutant strain. Sequence determination of the insert DNA revealed an open reading frame of 837 bp encoding a protein of 279 amino acids with a calculated molecular mass of 31.6 kDa. S. aureus LGT showed 24% identity and 47% similarity with E. coli, Salmonella typhimurium, and Haemophilus influenzae LGT.S. aureus LGT, while 12 amino acids shorter than the E. coli enzyme, had a hydropathic profile and a predicted pI (10.4) similar to those of the E. coli enzyme. Multiple sequence alignment among E. coli, S. typhimurium, H. influenzae, and S. aureus LGT proteins revealed regions of highly conserved amino acid sequences throughout the molecule. Three independent lgt mutant alleles from E. coli SK634, SK635, and SK636 and one lgt allele from S. typhimurium SE5221, all defective in LGT activity at the nonpermissive temperature, were cloned by PCR and sequenced. The mutant alleles were found to contain a single base alteration resulting in the substitution of a conserved amino acid. The longest set of identical amino acids without any gap was H-103-GGLIG-108 in LGT from these four microorganisms. In E. coli lgt mutant SK634, Gly-104 in this region was mutated to Ser, and the mutant organism was temperature sensitive in growth and exhibited low LGT activity in vitro. Diethylpyrocarbonate inactivated the E. coli LGT with a second-order rate constant of 18.6 M-1S-1, and the inactivation of LGT activity was reversed by hydroxylamine at pH 7. The inactivation kinetics were consistent with the modification of a single residue, His or Tyr, essential for LGT activity.

Amino Acid Sequence↗
PubMed1995

The umpA gene of Escherichia coli encodes phosphatidylglycerol:prolipoprotein diacylglyceryl transferase (lgt) and regulates thymidylate synthase levels through translational coupling.

Using a combination of biochemical, physical, and genetic techniques, we have shown that the umpA gene of Escherichia coli is allelic with the lgt (phosphatidylglycerol:prolipoprotein diacylglyceryl transferase) of Salmonella typhimurium. These genes are essential for the viability of the respective organism and exhibit 92.8% sequence identity at the amino acid level. In E. coli, lgt and thyA (thymidylate synthase) form an operon. Thymidylate synthase levels are regulated by transcription from the lgt promoter and by translational coupling.

Amino Acid Sequence↗
PubMed1995

Respiratory-related heart rate variability persists during central apnea in dogs: mechanisms and implications.

The aim of this study was to determine the mechanism(s) responsible for the persistence of respiratory sinus arrhythmia (RSA) during central apnea. In five awake dogs, heart rate (HR) was recorded during constant mechanical ventilation (MV) and during central apneas produced by cessation of MV. For each of 10 control ventilator cycles before MV was stopped, instantaneous HR was plotted against the time from the onset of lung inflation; the fundamental and first harmonic of a sine wave (at the ventilator frequency) was then fitted to the HR data. For the control cycles, the mean r2 from the curve fits was 0.57 +/- 0.07, showing that a significant component of the HR variability was linked to the ventilator cycle. After MV was stopped, RSA persisted and only by the third "phantom" ventilator cycle during apnea had the degree of fit consistently decreased compared with control dogs (P < 0.02). The persistence of ventilator-linked RSA at the onset of central apnea supports the concept of a "memory" in the respiratory system. Toward the end of central apnea, HR variability reappeared and had the periodicity and rhythmic profile of RSA on 81% of occasions. The presence of RSA-like activity toward the end of central apnea suggests that subthreshold rhythmic respiratory-related activity may be present even before the onset of detectable lung volume changes.

Animals↗
PubMed1995

Mitral valve repair using an annuloplasty ring made of artificial woven Dacron graft.

A woven Dacron ring made of artificial graft was successfully used in combination with a modified Kay's annuloplasty for mitral valve repair. In this procedure, after excision and repair of the redundant prolapsed leaflets, Kay's annuloplasty was performed at both commissures to reduce the posterior annulus and to coapt the leaflets. A woven Dacron ring was then seated and tied to the annulus to provide long-term stabilization and prevent its further dilatation. The mitral orifice of the patient was reduced from 33 mm to 21 mm in diameter, and neither mitral regurgitation nor stenosis was found in the postoperative evaluation.

Female↗
PubMed1995

[Mitral valve repair for the treatment of ischemic mitral regurgitation].

Twenty-six patients with moderate and severe ischemic mitral regurgitation due to papillary muscle dysfunction underwent mitral valve replacement (MVR) or mitral annuloplasty (MAP) using modified Kay method. Emergent operation was performed in 12 patients of whom 11 had severe congestive heart failure even under IABP, 5 had cardiogenic shock and 9 needed respiratory care with intubation preoperatively. Elective operation was performed in 14 patients of whom 6 had history of congestive heart failure and 1 had episodes of ventricular tachycardia. As intraoperative findings of mitral valve, mural annular dilatation in 84.6%, prolapse of anterior leaflet in 23.1%, papillary muscle scar in 15.4%, chordal elongation in 15.4% and chordal rupture in 3.8% were seen separately or in combination. In 22 patients MAP using modified Kay method and CABG were performed, but in 4 patients MVR was needed because of the prominent prolapse of the anterior leaflet. Fourteen patients who underwent MAP with CABG and one MVR with CABG survived. Hospital mortality was higher in emergent (58.5%) than elective operation (28.6%). In the 15 survivors, mitral regurgitation decreased below Sellers 2, pulmonary wedge pressure decreased significantly (p < 0.01) and NYHA functional class improved to I or II postoperatively. During the follow up period of 15-100 (mean 38.7 +/- 21.6) months, 2 MAP+CABG patients died suddenly, but the remaining 13 patients were in NYHA class I or II and no progression of MR was seen. These results indicated that MAP+CABG is recommendable in the treatment of ischemic mitral regurgitation due to papillary muscle dysfunction, in order to preserve cardiac function and to reduce valve related complications.

Adolescent↗