Photocurrent imaging of p-n junctions in ambipolar carbon nanotube transistors.

We use scanning photocurrent microscopy (SPCM) to investigate the properties of internal p-n junctions in ambipolar carbon nanotube (CNT) transistors. Our SPCM images show strong signals near metal contacts whose polarity and positions change depending on the gate bias. SPCM images analyzed in conjunction with the overall conductance also indicate the existence and gate-dependent evolution of internal p-n junctions near contacts in the n-type operation regime. To determine the p-n junction position and the depletion width with a nanometer scale resolution, a Gaussian fit was used. We also measure the electric potential profile of partially suspended CNT devices at different gate biases, which shows that induced local fields can be imaged using the SPCM technique. Our experiment clearly demonstrates that SPCM is a valuable tool for imaging and optimizing electrical and optoelectronic properties of CNT based devices.

Hospital readmission after pulmonary resection: prevalence, patterns, and predisposing characteristics.

BACKGROUND: Our objective was to define the prevalence, patterns, and predisposing characteristics for hospital readmission after pulmonary resection. METHODS: Five years of pulmonary resections, excluding lung biopsies, were analyzed from a prospective, computerized database. Readmission was defined as inpatient or emergency department admission within 90 days of operation. Search of 1,173,912 admissions to the Providence Health System in Oregon identified readmissions. Readmission analysis excluded operative deaths. RESULTS: A total of 374 patients underwent pulmonary resections, of whom 8 died (2.1%). Of 366 patients discharged, 69 (18.9%) were readmitted a total of 113 times: 42 had only one readmission, 16 had two readmissions, 7 had three readmissions, 2 had four readmissions, and 2 had five readmissions. Slightly more than half (51%) were readmitted as inpatients. Causes of the 113 readmissions included pulmonary (27%), postoperative infection (14%), cardiac (7%), and other (16%). Mean time to readmission was 32.5 +/- 24.6 days. Inpatient readmission mean length of stay was 4.9 +/- 3.4 days. Readmission to hospitals other than the hospital of the operation was as follows: first readmission, 15.9%; second readmission, 14.8%; third readmission, 36.3%; fourth readmission, 25%; fifth readmission, 0%. Analysis revealed only pneumonectomy as a risk for readmission. Twelve of 33 (36%) pneumonectomies were readmitted (p = 0.005). Of the 297 patients discharged after pulmonary resection and not requiring readmission, 12 (4%) died over the study interval, whereas 8 of 69 patients (11.6%) requiring readmission died. CONCLUSIONS: Readmission after pulmonary resection is frequent and multiple readmissions are common. Causes are predominately pulmonary diagnoses and infections related to the operation. Pneumonectomy is a risk for readmission. An important portion of readmissions occurs outside the hospital of operation. The population requiring readmission after successfully undergoing pulmonary resection is at increased risk of subsequent mortality.

Surgery for second lung cancers.

PURPOSE: To evaluate the outcomes of patients surgically treated for their second primary lung cancer. METHOD: In a computerized surgical registry of > 800 consecutive patients treated for primary pulmonary carcinoma since 1980, 37 patients presented with a second lung cancer. These patients were analyzed regarding their original treatment, preoperative evaluation, operative procedures, and long-term follow-up. RESULTS: Three fifths of the patients were female, and 57% were > or = 65 years old at the time of their second operation. One patient originally had two synchronous tumors; another patient had three metachronous neoplasms. The interval between surgeries ranged from 5 to 239 months. In 31 patients, treatment for their original tumor was surgical resection alone. Lobectomy was the most common operation for the original tumor, and 78% were stage I. When the second tumor was diagnosed, 25 patients (68%) were asymptomatic. Eight patients (22%) were current smokers, and 29 patients (78%) were former smokers. The most common operation for the second tumor was a lobectomy. Surgical mortality was 5.4%. Nineteen patients (51%) survived 2 years, and 9 patients (24%) survived > or = 5 years. Eleven patients (30%) were still alive at last follow-up, 3 to 198 months postoperatively, and only 13 patients (34%) had died of their cancer. CONCLUSION: Surgical treatment of second primary pulmonary neoplasms can be performed in selected patients with acceptable long-term survival.

Median sternotomy versus thoracotomy to resect primary lung cancer: analysis of 815 cases.

BACKGROUND: We sought to determine if median sternotomy (MS) is an equivalent incision to thoracotomy (TH) in the treatment of primary pulmonary carcinoma. METHODS: We followed 801 patients undergoing 815 operations for primary lung carcinoma in a computer registry; 447 had MS, 368 had TH. RESULTS: Both groups were similar in preoperative risk assessment. Complete staging lymph node dissections were performed in 42% of MS patients and 17% of TH patients. Operative mortality (3.8% for MS, 3.3% for TH) and postoperative complications were similar. MS patients had a shorter postoperative hospital stay (7.5 days vs. 8.2 days). One hundred thirty-nine underwent pneumonectomy. Operative mortality was 12.5% for MS and 10.4% for TS (p = NS). Five hundred eighty-one underwent lobectomy with an operative mortality of 2.1% for MS and 2.0% for TH. Mean length of stay for MS lobectomy was 7.5 days compared with 8.5 days for TH (p = 0.06). Follow-up was 89% through 1998, comprising 1,339 MS and 1,463 TH patient-years. Survival for stage I at 5 and 10 years, respectively, was 51% and 34% for MS vs 54% and 32% for TH (p = NS). Survival for other stages was also similar. CONCLUSIONS: Median sternotomy provides more complete staging, shorter postoperative hospitalization, and better patient acceptance with equivalent operative and long-term survival when compared with thoracotomy. Concerns regarding increased wound infections in MS patients appear unfounded.

The use of nucleotide analogs to evaluate the mechanism of the heterotropic response of Escherichia coli aspartate transcarbamoylase.

As an alternative method to study the heterotropic mechanism of Escherichia coli aspartate transcarbamoylase, a series of nucleotide analogs were used. These nucleotide analogs have the advantage over site-specific mutagenesis experiments in that interactions between the backbone of the protein and the nucleotide could be evaluated in terms of their importance for function. The ATP analogs purine 5'-triphosphate (PTP), 6-chloropurine 5'-triphosphate (Cl-PTP), 6-mercaptopurine 5'-triphosphate (SH-PTP), 6-methylpurine 5'-triphosphate (Me-PTP), and 1-methyladenosine 5'-triphosphate (Me-ATP) were partially synthesized from their corresponding nucleosides. Kinetic analysis was performed on the wild-type enzyme in the presence of these ATP analogs along with GTP, ITP, and XTP. PTP, Cl-PTP, and SH-PTP each activate the enzyme at subsaturating concentrations of L-aspartate and saturating concentrations of carbamoyl phosphate, but not to the same extent as does ATP. These experiments suggest that the interaction between N6-amino group of ATP and the backbone of the regulatory chain is important for orienting the nucleotide and inducing the displacements of the regulatory chain backbone necessary for initiation of the regulatory response. Me-PTP and Me-ATP also activate the enzyme, but in a more complex fashion, which suggests differential binding at the two sites within each regulatory dimer. The purine nucleotides GTP, ITP, and XTP each inhibit the enzyme but to a lesser extent than CTP. The influence of deoxy and dideoxynucleotides on the activity of the enzyme was also investigated. These experiments suggest that the 2' and 3' ribose hydroxyl groups are not of significant importance for binding and orientation of the nucleotide in the regulatory binding site. 2'-dCTP inhibits the enzyme to the same extent as CTP, indicating that the interactions of the enzyme to the O2-carbonyl of CTP are critical for CTP binding, inhibition, and the ability of the enzyme to discriminate between ATP and CTP. Examination of the electrostatic surface potential of the nucleotides and the regulatory chain suggest that the complimentary electrostatic interactions between the nucleotides and the regulatory chain are important for binding and orientation of the nucleotide necessary to induce the local conformational changes that propagate the heterotropic effect.

MIDCAB: impact of epicardial stabilization upon outcomes.

BACKGROUND: Minimally invasive direct coronary artery bypass (MIDCAB) has been criticized as compromising anastomotic patency. Epicardial mechanical stabilization devices purportedly facilitate left internal mammary artery (LIMA) anastomosis, thereby enhancing patency and outcome. METHODS: From June 1996 through January 1999, 39 patients underwent MIDCAB via a small left anterior thoracotomy for revascularization of the left anterior descending coronary artery (LAD) without cardiopulmonary bypass (CPB). Immediate postoperative coronary angiography was performed on 38 of the patients. RESULTS: Group 1 consisted of 11 patients who were operated upon without epicardial stabilization. Mean age was 64 years. Two had undergone previous coronary artery bypass (CAB). Predicted mortality was 4.3%. Angiographic anastomotic patency was 60%. Revisions on CPB in three cases increased LIMA patency to 90%. There was one intra-operative death. Average length of stay (LOS) was 5.4 days. Group 2 consisted of 28 patients operated on with mechanical epicardial stabilization. Predicted risk of mortality was 4.4%. Mean age was 66 years. Twelve had undergone previous CAB. Anastomotic patency at angiography was 97.4%. There were no intra-operative deaths and mean LOS was 3.0 days. CONCLUSIONS: We conclude that mechanical epicardial stabilization has transformed the MIDCAB operation into one that offers excellent early patency and clinical outcomes. This operation is of particular value for revascularization of the anterior coronary circulation in patients with previous CAB; clinical results are significantly better than predicted for standard redo-CAB.

Cost analysis of the Novacor Left Ventricular Assist System as an outpatient bridge to heart transplantation.

Three patients were bridged to heart transplantation with the wearable Novacor Left Ventricular Assist System (Baxter Healthcare Corp., Oakland, CA) (LVAS). Two have been transplanted and discharged. The third patient remains at home. Hospitalization costs, which include the unit room charge, admission profile to the unit, and daily supply charge, were determined for all patients and compared. The patients were transferred from the surgical intensive care unit to a telemetry unit once they were hemodynamically stable. The projected hospitalization costs, if the patients had remained in the hospital, were calculated to determine probable savings for the third party payer. The average period from admission to placement of the Novacor LVAS was 15 days (range, 7-21 days). The average hospitalization cost from admission to time of Novacor left ventricular assist device implant was $2,240/day, and the average hospitalization cost after implant to discharge was $1,570/day. Hospitalization cost savings were $2,632 for the first patient, $5,922 for the second patient, and $132,124 for the third patient, who has not been transplanted. Although the number of patients is small, the daily hospitalization cost was higher before the Novacor LVAS was implanted. This is related to the severity of the disease and the length of stay in a surgical intensive care unit. There also is a significant cost savings for the third party payer, especially if the patient has to wait a significant amount of time before heart transplantation. These are important considerations in this time of managed care.

Heart-lung transplantation in situs inversus.

Reconstruction was accomplished in a 2 heart-lung recipients with situs inversus resulting in a left-sided systemic venous atrium. We created a large common atrium that was closed on the left side, leaving an atrial cuff on the inferior right quadrant. To this we anastomosed the donor right atrium, which had been opened laterally between the cavae. This resulted in some clockwise rotation of the ventricles and anterior positioning of the apex. The right pulmonary veins passed superior to the atrial anastomosis and posterior to the donor right atrium. Cardiopulmonary function was excellent in both cases.

Surgical treatment of symptomatic biliary stones in patients with cystic fibrosis.

Patients with cystic fibrosis have a high incidence of cholelithiasis. However, few studies have addressed the operative therapy for cholelithiasis in this group of patients with poor pulmonary function. We reviewed six patients with cystic fibrosis who were treated for symptomatic biliary stones. Five patients underwent cholecystectomy for chronic cholecystitis. One patient with extremely poor pulmonary status presented with choledocholithiasis and cholangitis, which was successfully treated with endoscopic sphincterotomy followed by ursodeoxycholic acid therapy. Five of these six patients had significant relief of their symptoms. One patient never recovered completely from the operation and eventually died from continued pulmonary deterioration. We conclude that in patients with cystic fibrosis and symptomatic biliary stones, careful attention to pulmonary care can afford safe, elective cholecystectomy. More conservative treatment is indicated in patients with marginal pulmonary reserve.

Does the retrocecal position of the vermiform appendix alter the clinical course of acute appendicitis? A prospective analysis.

Ninety-four adult patients undergoing appendectomy for acute appendicitis were prospectively studied during a 2-year period. Patients were divided into retrocecal (group 1; n = 27 [29%]) and anterior (group 2; n = 67 [71%]) groups according to the position of the appendix. There was no statistical difference between the two groups in duration of symptoms, presenting signs and symptoms, and initial white blood cell count. Furthermore, retrocecal appendicitis was not associated with a higher rate of perforation or increased morbidity. We conclude that the retrocecal position of the appendix does not alter the presentation of appendicitis.