Search PubMed⌕ Search

Biomedical subjects

D N Jensen

Publications and source records attributed to D N Jensen.

12 recordsLinked to original sources
PubMed2001

Open-heart endocardial radiofrequency ablation: an alternative to incisions in Maze surgery.

BACKGROUND: Radiofrequency (RF) ablation produces transmural atrial lesions in vitro, and may provide advantages over incisions currently used in maze surgery. This study examines the feasibility, safety, and efficacy of open-heart endocardial RF ablation. METHODS: Eighteen sheep (42.8 +/- 4.4 kg, age < 2 years) underwent left thoracotomy with placement of pacing leads on a pulmonary vein and the left atrial dome. On cardiopulmonary bypass, lesions were made using incision and suture or a novel RF ablation device in three sites: PVC = circle excluding pulmonary veins, IAB = line across the interatrial bundle, SVC = line from the superior to the inferior vena cava. Pacing across the PVC lesion was attempted to assess the completeness of each lesion. Preselected animals (incision n = 4, RF n = 5) were recovered and pacing attempts were repeated at 1 month. After sacrifice, hearts were sectioned and measured for lesion size and completeness. RESULTS: RF ablation lesions took less time to create (total bypass time: RF 51.8 min vs incision 106 min, P < 0.001). No evidence of thromboembolism, atrial rupture, or coronary sinus thrombosis was seen. All PVC lesions were complete as demonstrated by the inability to pace across them. Stained sections demonstrated that acutely studied incision lesions were thinner than RF lesions; however, all lesions were transmural and similar in width at 1 month. CONCLUSIONS: RF ablation consistently created transmural lesions more quickly than the incision and suture method and without additional complications. Endocardial RF ablation appears to be a simple and effective alternative to surgical incisions during open-heart atrial Maze procedures.

Animals↗
PubMed2001

Correlation of impedance minute ventilation with measured minute ventilation in a rate responsive pacemaker.

Although rate responsive pacing based on impedance minute ventilation (IMV) is now standard, there is almost no data confirming the relationship between IMV from an implanted pacemaker and measured minute ventilation (VE) during exercise. Nineteen completely paced adults implanted with Medtronic Kappa 400 pacemakers underwent symptom-limited maximal metabolic treadmill testing using a modified Minnesota Pacemaker Response Protocol. Minute ventilation (VE, L/min) was simultaneously measured using the flowmeter of a respiratory metabolic gas analysis system and the transthoracic impedance minute ventilation circuitry of the pacemaker. Correlation coefficients (r) were used to find the best fit line to describe the relationship between the two measurements. Mean (+/- SD) r values for the first, second, and third order polynomial equations and for log and exponential equations were: 0.92 +/- 0.08, 0.94 +/- 0.04, 0.95 +/- 0.04, 0.91 +/- 0.06, and 0.91 +/- 0.07, respectively. None of the r values were statistically different from the first order equation. Transthoracic IMV as measured by the Medtronic Kappa 400 is closely correlated to measured minute ventilation and is represented well by a first order (linear) equation.

Adult↗
PubMed2000

Influence of posture, breathing pattern, and type of exercise on minute ventilation estimation by a pacemaker transthoracic impedance sensor.

Previous studies have shown a high correlation between transthoracic impedance minute ventilation (IMV) determined by a pacemaker sensor and actual minute ventilation (VE) measured by standard methods. We hypothesized that several factors (e.g., posture, breathing pattern, and exercise type) could potentially affect the calibration between IMV and VE. In patients with Medtronic Kappa 400 pacemakers, VE (L/min) was monitored using a standard cardiopulmonary metabolic gas analysis system with simultaneous recording of IMV (ohms/min) using DR-180 extended telemetry monitors. Effects of posture and of breathing pattern at rest (19 patients; age 60 +/- 13 years) were evaluated by monitoring each patient under three conditions: (a) slow breathing, supine, (b) slow breathing, sitting, and (c) shallow breathing, supine. Calibration at rest was defined as the ratio of IMV to VE. Effect of type of exercise on calibration compared treadmill versus graded bicycle ergometer exercise (18 patients; age 62 +/- 14 years). Calibration during exercise was defined as: (a) "Begin" (the IMV to VE ratio at VE = 10 L/min, the typical VE value at beginning of exercise), and (b) slope of the IMV/VE regression line. Calibration of IMV/VE was significantly smaller for sitting versus supine position (0.7130.177, P < 0.001) and for shallow versus slow breathing (0.7210.373, P < 0.001), and larger for treadmill versus bicycle exercise (Begin: 1.240.43, P = 0.018; Slope: 1.260.42, P = 0.013). In conclusion, posture, breathing pattern, and type of exercise affect the IMV estimation of the actual VE, possibly by altering the static or dynamic geometry (thus, the impedance) of the intrathoracic viscera.

Arrhythmias, Cardiac↗
PubMed2000

Tachycardia-related cardiomyopathy: a common cause of ventricular dysfunction in patients with atrial fibrillation referred for atrioventricular ablation.

OBJECTIVE: To determine the frequency of tachycardia-related cardiomyopathy in patients with atrial fibrillation and systolic dysfunction referred for atrioventricular node ablation. PATIENTS AND METHODS: This prospective multicenter cohort study was conducted at 16 tertiary care centers. The ejection fraction was measured before and 3 and 12 months after atrioventricular node ablation. Patients with reduced systolic function (ejection fraction < or = 45%) before atrioventricular ablation were included in this study. Patients whose ejection fraction increased by at least 15 percentage points and to higher than 45% were considered to have tachycardia-related cardiomyopathy. RESULTS: Of 63 patients with systolic dysfunction, 48 had at least 1 adequate follow-up echocardiographic study. Sixteen (25%) of the 63 had marked improvement in the ejection fraction (mean +/- SD change, 27 +/- 8 percentage points) to a value higher than 45% after ablation. CONCLUSIONS: Tachycardia-related cardiomyopathy is common in patients with atrial fibrillation and systolic dysfunction referred for atrioventricular node ablation. This diagnosis should be considered in all patients in whom systolic dysfunction occurs subsequent to or concomitant with onset of atrial fibrillation.

Atrial Fibrillation↗
PubMed1997

Tachycardia-induced cardiomyopathy: a review of animal models and clinical studies.

The increasing prevalence of congestive heart failure has focused importance on the search for potentially reversible etiologies of cardiomyopathy. The concept that incessant or chronic tachycardias can lead to ventricular dysfunction that is reversible is supported by both animal models of chronic rapid pacing as well as human studies documenting improvement in ventricular function with tachycardia rate or rhythm control. Sustained rapid pacing in experimental animal models can produce severe biventricular systolic dysfunction. Hemodynamic changes occur as soon as 24 h after rapid pacing, with continued deterioration in ventricular function for up to 3 to 5 weeks, resulting in end-stage heart failure. The recovery from pacing-induced cardiomyopathy demonstrates that the myopathic process associated with rapid heart rates is largely reversible. Within 48 h after termination of pacing, hemodynamic variables approach control levels, and left ventricular ejection fraction shows significant recovery with subsequent normalization after 1 to 2 weeks. In humans, descriptions of reversal of cardiomyopathy with rate or rhythm control of incessant or chronic tachycardias have been reported with atrial tachycardias, accessory pathway reciprocating tachycardias, atrioventricular (AV) node reentry and atrial fibrillation (AF) with rapid ventricular responses. Control of AF rapid ventricular responses has been demonstrated to improve ventricular dysfunction with cardioversion to sinus rhythm, pharmacologic ventricular rate control and AV junction ablation and permanent ventricular pacing. The investigation of potential tachycardia-induced cardiomyopathy in patients with heart failure requires further prospective confirmation in larger numbers of patients, with study of mechanisms, patient groups affected and optimal therapies.

Animals↗
PubMed1996

Expression of cell regulatory proteins in ovarian borderline tumors.

BACKGROUND: Tumors of borderline malignancy are still a controversial subgroup of ovarian neoplasms. The expression of several cell regulatory proteins was studied to characterize the molecular phenotype of these tumors, and to compare them with their benign and malignant counterparts. METHODS: Specimens from 22 patients with tumors of borderline malignancy (11 serous and 11 mucinous tumors), 12 patients with benign tumors, and 16 patients with invasive ovarian carcinomas were evaluated for expression of epidermal growth factor receptor (EGFR), HER-2/neu, PTP1B, and p53 by immunohistochemical techniques. RESULTS: One or both of the tyrosine kinase growth factor receptors EGFR and HER-2/neu was expressed by 42% of benign, 59% of borderline, and 81% of malignant ovarian tumors. EGFR was expressed in a significantly greater fraction of malignant lesions (69%) than borderline lesions (18%) (P< 0.004). EGFR expression was not observed among the 11 mucinous borderline tumors. HER-2/neu was expressed by 50% of borderline tumors and was not a marker for malignancy. The tyrosine phosphatase PTP1B was expressed by a similar fraction of benign (17%), borderline (27%), and malignant (19%) tumors. The number of cases studied precluded correlation of kinase and phosphatase activity. However, among 12 tumors with PTP1B expression, 9 also expressed EGFR or HER-2/neu. Overexpression of p53 was observed only in malignant serous tumors and was not found in malignant mucinous, borderline, or benign lesions. CONCLUSIONS: Either EGFR or HER-2/neu was detected in a majority of borderline cancers. PTP1B was present only in a minority of these cancers. Frankly malignant serous lesions differed from borderline and benign tumors with regard to expression of EGFR and overexpression of p53.

Carcinoma↗
PubMed1995

A combined abdominoperineal approach for the resection of a large giant cell tumor of the sacrum.

We describe the case of a 24-year-old woman with a giant cell tumor originating from the distal part of the sacrum, which was almost completely filling the pelvis and extending to the umbilicus. At laparotomy, the tumor was separated from all of the pelvic structures including the ureters. The sigmoid colon was transected and the tumor was dissected down to the pelvic floor. A separate perineal incision was made, the rectovaginal septum was entered, and the posterior vaginal wall was bisected to give better access. It was possible to mobilize the tumor completely after dividing the rectum 5 cm from the anus. All macroscopic tumor was removed in continuity with the sigmoid colon. The ovaries were transposed to the paracolic gutter to avoid artificial menopause following radiation therapy. A sigmoid colostomy was formed. Because histology could not provide definite evidence of complete removal of the tumor, radiation therapy to the sacrum was given. Forty-two months after her surgery, the woman remains free of disease. The abdominoperineal approach should be considered for patients with a large tumor which is fixed to the sacrum.

Abdomen↗
PubMed1995

Proposed criteria for the diagnosis of well-differentiated endometrial carcinoma. A diagnostic test for myoinvasion.

Existing criteria for separating clinically benign but architecturally complex or cytologically atypical endometrial proliferations (hyperplasia or metaplasia) from well-differentiated endometrial carcinoma are underspecified and poorly reproducible, in part due to the absence of a uniformly agreed on methodologically independent outcome against which to judge the efficacy of competing sets of criteria. Because myoinvasion is the first unambiguous indicator of clinically aggressive behavior for proliferations in this spectrum, we have employed the presence or absence of myoinvasion as a tool to develop clinically meaningful diagnostic criteria for the separation of complex atypical hyperplasia/metaplasia from well-differentiated carcinoma (CAHM/WDCA). We obtained the paired endometrial samplings and hysterectomy specimens of 520 patients; these were split into a training set of 306 cases and a test set of 214. The presence or absence of myoinvasion was assessed from an examination of the hysterectomy specimen. For the purposes of this study, myoinvasion was defined as the presence of irregular intramyometrial glands surrounded by a granulation tissue-like response. To determine the morphologic features that were most predictive of myoinvasion, a series of endometrial architectural, cytological, and stromal features was initially evaluated on the training set (149 myoinvasive and 157 nonmyoinvasive). Using a variety of exploratory data techniques including the classification algorithm CART, we developed a diagnostic rule for predicting myoinvasion that employed one architectural feature (glandular complexity captured by a pictorial architectural index) and two cytological features (nuclear pleomorphism and prominence of nucleoli). Extensive squamous differentiation, fibroblastic stroma, necrosis, stromal foam cells, and other cytologic features did not provide additional predictive value when cross-validated. The true misclassification rate of the CART-generated prediction rule was further assessed by applying the rule to the test set drawn largely from community hospitals. The sensitivity and specificity of this rule for detecting myoinvasion was 99.5 and 57%. The likelihood ratio was 2:1, (i.e., using prior odds of myoinvasion in the CAHM/WDCA spectrum of 1:10, the posterior odds on myoinvasion using the CART-generated rule would be 1:5). Comparison of the CART-generated myoinvasion prediction rule with the Kurman and Norris endometrial stromal invasion criteria for well differentiated endometrial carcinoma (25), using receiver operator characteristic curve (ROC) techniques, demonstrated a significant improvement in the ability to separate myoinvasive from non-myoinvasive endometrial proliferations with the CART-generated rule; the average area under the curve for the CART-generated rule was 0.78 (SE = 0.02) versus 0.67 (SE = 0.03) for the endometrial stromal invasion criteria.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenocarcinoma↗
PubMed1989

A monolithic patch-clamping amplifier with capacitive feedback.

Patch-clamping is an established method for directly measuring ionic transport through cellular membranes with sufficient resolution to observe open/close transitions of individual channel molecules. This paper describes an alternative technique for patch-clamping which uses a capacitor as the transimpedance element. This approach eliminates bandwidth and saturation limitations experienced with resistive patch-clamping amplifiers. A complete monolithic design featuring an on-chip operational amplifier, a capacitor array with gain-ranging from 30 pF down to 0.03 pF, and reset and gain ranging switches has been fabricated using 5 microns CMOS technology. It is shown that the voltage noise of the CMOS operational amplifier limits the overall noise performance, but that performance competitive with conventional instruments can be achieved over a 10 kHz bandwidth, at least for small input capacitances (less than or equal to 5 pF). Results are presented along with an analysis and comparison of noise performance using both resistive and capacitive elements.

Amplifiers, Electronic↗
PubMedDate not supplied

Neurologic manifestations of tri-O-cresyl phosphate delayed neurotoxicity in cats.

The neurotoxic effects of tri-o-cresyl phosphate (TOCP) were studied in the cat to define the elements of neurologic testing and to correlate dysfunction with the results of histopathologic studies. Neurologic examination of treated cats categorized clinical signs of TOCP-induced delayed neurotoxicity in the cat into four stages: leg weakness, mild ataxia, severe ataxia, and paresis. These deficits correlated well with histopathological lesions found in the central and peripheral systems. The improvement seen, is attributed to regeneration and/or collateral sprouting of remaining axons of peripheral nerves that would not be expected in tracts of the central nervous system.

Animals↗