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Biomedical subjects

S Kun

Publications and source records attributed to S Kun.

13 recordsLinked to original sources
PubMed2000

Effects of sample geometry and electrode configuration on measured electrical resistivity of skeletal muscle.

Over the past 40 years, researchers from a variety of scientific backgrounds have been using Rush's equations to analyze results of their electrophysiological studies. A lack of understanding of the constraints and the domain in which these equations are valid, often results in situations in which it is challenging to evaluate and compare results obtained by different investigators. In this paper, we reanalyzed the conditions for which Rush's equations were derived, and using mathematical modeling, computer simulation and in vitro measurements, we delineated areas of their appropriate application. Our studies showed that both sample geometry and test electrode configuration affect the measured tissue electrical resistivities: 1) The sample can be considered semi-infinite only if its dimensions are > 50 inter-electrode separation distances (IESD), and thickness > 2.5 IESD, 2) smaller sample sizes increase the transversally measured resistivity, 3) semi-infinite samples thinner than 2.5 IESD, and samples tested with needle electrodes demonstrate reduced anisotropy, and 4) when surface-spot electrodes are longitudinally aligned, as the IESD/tissue thickness ratio decreases, the measured resistivity increases. Our conclusion is that in most experimental situations, it is necessary to use modeling techniques to decouple the electrode configuration/sample geometry influence from the measured tissue resistivity.

Animals↗
PubMed1999

Real-time extraction of tissue impedance model parameters for electrical impedance spectrometer.

This paper presents a new algorithm for real-time extraction of tissue electrical impedance model parameters from in vivo electrical impedance spectroscopic measurements. This algorithm was developed as a part of a system for muscle tissue ischemia measurements using electrical impedance spectroscopy. An iterative least square fitting method, biased with a priori knowledge of the impedance model was developed. It simultaneously uses both the real and imaginary impedance spectra to calculate tissue parameters R0, R infinity, alpha and tau. The algorithm was tested with simulated data, and during real-time in vivo ischemia experiments. Experimental results were achieved with standard deviations of sigma R0 = 0.80%, sigma R infinity = 0.84%, sigma alpha = 0.72%, and sigma tau = 1.26%. On a Pentium II based PC, the algorithm converges to within 0.1% of the results in 17 ms. The results show that the algorithm possesses excellent parameter extraction capabilities, repeatability, speed and noise rejection.

Algorithms↗
PubMed1999

Selection of measurement frequencies for optimal extraction of tissue impedance model parameters.

The results are presented of a study performed to determine the measurement frequencies that provide optimal extraction of tissue impedance model parameters from in vivo measured electrical impedance spectra. Measurement frequency sets that are logarithmic and quasi-linear, and frequency sets that produce angularly equidistant points on the Nyquist loci are used to test the parametric fitting algorithm that calculates R0, R infinity, alpha and tau tissue parameters from complex impedance spectra. Simulated data, calculated in the presence of < or = 5% measurement noise, and in vivo experiments indicate that the quality of the fitted parameters depends upon the selection of measurement frequencies. The results show that, if measurements are performed with a system that has a realistic measurement bandwidth, then, for the best estimation of: R0, the measurement frequencies should include the decade from 100 Hz-1 kHz; R infinity, the algorithm should not include frequencies under 1 kHz; alpha and tau, the measurement frequencies should be equidistantly spaced on the Nyquist locus.

Algorithms↗
PubMed1999

Severe combined immunodeficiency: otolaryngological presentation and management.

In order to increase the awareness of otolaryngologists of severe combined immunodeficiency syndrome (SCIDS) so they may contribute to an earlier diagnosis of this disorder, we performed a retrospective chart review of a multicenter series from 2 children's hospital medical centers. Eighteen cases were identified, and 14 had an otolaryngological presentation. The average age of presentation was 3.3 months, and 72% were males. Most cases were inherited in an X-linked fashion. Five patients had thrush; 4 had recurrent otitis media. Other otolaryngological presentations included cough, mouth ulcers, pharyngitis, mastoiditis, and bilateral neck abscess. The most severe form of immunodeficiency, SCIDS is a rare condition that involves a disorder in both T and B cell functions. The manifestations involving the head and neck include recurrent upper respiratory tract infections, otitis media, thrush, oral ulcers, and abscesses. It is important that SCIDS be considered in any infant with recurrences of these common infections.

Abscess↗
PubMed1993

Conductance volumetric model of an eccentrically positioned catheter within a three-compartment ellipsoidal ventricle.

This paper presents a mathematical model of the electric field generated and resistance measured by a conductance catheter within a three-compartment ellipsoidal approximation of a cardiac ventricle. The model is based on a novel combination of analytical and numerical techniques. The numerical component of the model predicts displacement of the catheter along the central longitudinal ventricular axis, as well as eccentric positions off that axis. The analytical component of the model enables interactive definition of model parameters during simulation. This versatile combination enables performance of validation studies that include simulations of various catheter movements within a ventricle of changing geometry. The results of our simulation studies agree with the results of previous investigators studying ex-vivo systems.

Cardiac Catheterization↗
PubMed1992

Preoperative thyroid scanning in presumed thyroglossal duct cysts.

The purpose of this study was to determine if preoperative thyroid scans are essential in the workup of presumed thyroglossal duct cysts. Questionnaires were sent to pediatric otolaryngologists and pediatric general surgeons with a 65% response rate. Fifty-seven percent of the physicians have encountered ectopic thyroid. In 58% of these, this was the only functioning thyroid tissue. Twenty eight percent of pediatric surgeons vs 65% of pediatric otolaryngologists routinely order scans. Two of the physicians encountering ectopic thyroid volunteered that they had successful litigation directed against them for removing the sole functioning thyroid and creating permanent hypothyroidism. There is a likelihood of encountering ectopic thyroid during the course of one's practice. A case of ectopic thyroid is presented, and management strategies are discussed.

Humans↗
PubMed1987

Telephone assessment of parents' knowledge of home-care treatments and readmission outcomes for high-risk infants and toddlers.

Medical technology is enabling many high-risk infants and toddlers to be cared for at home. However, techniques for evaluation of home-care and discharge-planning outcomes have not been well documented. Using 60 subjects, we performed telephone assessment of home-care givers' knowledge base in basic knowledge of treatment, operation and maintenance of supplies and equipment, and vendor information, using standard questions, 48 hours following discharge from the hospital. Families giving apnea monitoring or Broviac catheter care as a single treatment scored 100% in all three areas. However, the scores for care givers providing gastrostomy care (54%, 100%, and 91%), tracheostomy care (80%, 70%, and 50%), or total parenteral nutrition (88%, 50%, and 100%) as single treatments were lower. Care givers providing multiple home-care treatments had the lowest scores (65%, 65%, and 76%). However, care givers of patients who were subsequently readmitted scored well (80%, 85%, and 85%), and none of the readmissions were due to a failure of home-care management. Telephone assessment 48 hours after discharge can be used to document home-care and discharge-planning outcomes for high-risk infants and toddlers.

Evaluation Studies as Topic↗
PubMed1985

Pediatric discharge planning: differing goals for two populations.

The role of the pediatric discharge planner is complex. Because of the constant changes in medical technology and reimbursement policies, it is important to remain knowledgeable about existing resources. In addition, the medical status and treatment plans of pediatric patients frequently change. The discharge planner must have the ability to be flexible in the organization and implementation of discharge plans to facilitate meeting the needs of the patients and their families. Discharge planning for the pediatric patient is not a simple process. Instead it is a collaborative effort between health care professionals and families whose primary goal is the optimum health of the child.

Child↗
PubMedDate not supplied

In-vitro and in-vivo comparative analysis of four tissue pH monitoring systems.

The purpose of this investigation was to identify the type of pH-reference electrode combination that is the most suitable and reliable in clinical applications involving long-term postoperative monitoring of microvascular reconstructive transplants and diagnosis of compartment syndrome. Four types of pH-sensing devices were chosen for the study: a standard glass pH electrode, a polymer-based pH electrode, an ISFET pH sensor, and a fiberoptic pH sensor. Various combinations of electrodes were tested in vitro for typically four days. The glass and polymer electrodes maintained stable pH readings, averaging drifts of 0.14 +/- 0.07 and 0.14 +/- 0.08 pH units per 96 hours, respectively. The fiberoptic sensors displayed an average drift of 0.20 +/- 0.15 pH units per 96 hours. ISFET sensors displayed nearly linear drifts, averaging 1.36 +/- 0.54 pH units per 96 hours. When placed in healthy animal tissue, glass and polymer electrode pH readings followed the arterial blood pH values, measured by a blood gas analyzer. In compromised tissue, both glass and polymer electrodes recorded falling pH levels correctly, indicating ischemic conditions. Generally, ISFET sensors in healthy tissue produced pH readings that did not correlate well with arterial blood pH values. Fiberoptic sensors monitored healthy-tissue pH correctly; however, mechanical disturbances of the fiberoptic sensor and occasional discontinuation of computer operation would shift the pH output significantly (at times by 0.2 pH units), resulting in subsequent inaccurate pH readings. The glass electrode was the only sensor evaluated clinically. It correctly indicated tissue viability in all clinical cases, involving both healthy and ischemic tissue. The authors conclude that the glass pH electrode has the best combination of characteristics for clinical tissue pH measurements.

Animals↗