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Biomedical subjects

C Knapp

Publications and source records attributed to C Knapp.

At least 19 recordsLinked to original sources
PubMed2002

Numerical analysis of an anastomotic device.

The explicit dynamic finite element method was utilized to investigate the deformation behaviour of a woven wire mesh tubular device that is used in a side-to-side anastomotic procedure for achieving gastrointestinal anastomosis. The numerical model was initially verified by comparison to experimental results that were obtained using a specialized testing mechanism. Once validated, the finite element model (FEM) was parameterized to ascertain the influence of several device parameters on its deformation behaviour. The importance of these parameters, as related to its optimal design for use in minimally invasive surgery (MIS), was subsequently ascertained and discussed.

Anastomosis, Surgical↗
PubMed2000

Quality control limits for broth microdilution susceptibility tests of ten antifungal agents.

Broth microdilution susceptibility tests of Candida species have now been standardized by the National Committee for Clinical Laboratory Standards (NCCLS). An eight-laboratory collaborative study was carried out in order to document reproducibility of tests of Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258 by the NCCLS method. Replicate broth microdilution tests were used to define control limits for 24- and 48-h MICs of amphotericin B, flucytosine, fluconazole, voriconazole, ketoconazole, itraconazole, caspofungin (MK 0991), ravuconazole (BMS 207147), posaconazole (SCH 56592), and LY 303366.

Antifungal Agents↗
PubMed1998

Nonnasopharyngeal lymphoepithelioma of the head and neck.

BACKGROUND: Lymphoepithelioma (squamous cell carcinoma with associated lymphoid stroma) commonly occurs in the nasopharynx, rarely at other sites. As a result, the clinical course and optimal treatment of nonnasopharyngeal lymphoepithelioma of the head and neck have not been well described. This retrospective study was undertaken to analyze the clinical course of the disease in patients treated at a single institution and to formulate recommendations for treatment based on that experience as well as results reported in the literature. METHODS: Between 1950 and 1994, 34 patients with nonnasopharyngeal lymphoepithelioma of the head and neck were treated at the University of Texas M. D. Anderson Cancer Center. The patients' medical records were reviewed and their pathologic specimens evaluated. The primary tumor sites were: oropharynx (24 patients), salivary gland (4), laryngohypopharynx (4), and the maxillary sinus/nasal cavity (2). Assessed in accordance with the 1992 American Joint Committee Against Cancer TNM staging system, T classifications were TX-2, T1-7, T2-8, T3-10, and T4-7, and N classifications were N0-8, N1-5, N2-15, and N3-6. Treatment consisted of radiotherapy for 24 patients, excisional biopsy of the primary tumor followed by radiotherapy for 7 patients, and surgery for 3 patients. Of the patients treated with radiotherapy, neck dissections were performed on only two, both of whom had persistent lymph node masses after completing radiotherapy. The median dose delivered to the primary tumor was 65 gray (Gy) (range, 46-78 Gy). The median fraction size was 2.1 Gy (range, 1.6-3.2 Gy). RESULTS: The 5-year actuarial disease specific survival and overall survival rates were 59% and 39%, respectively. The 5-year actuarial local control rate for all patients was 94%. For the irradiated patients, the 5-year regional control rates were 77% overall and 83% within the radiation field. The 5-year actuarial rate of distant metastasis for all patients was 30%. For patients who presented with and without regional adenopathy, the 5-year rates of distant metastasis were 36% and 12%, respectively (P = 0.27). CONCLUSIONS: Nonnasopharygeal lymphoepithelioma is a radiosensitive disease. High rates of locoregional tumor control were achieved with radiotherapy at all head and neck sites. The main cause of treatment failure was distant metastasis, which occurred more frequently in patients with lymph node involvement. Radiotherapy is appropriate initial locoregional therapy for patients with this disease. Surgery should be reserved for patients who have persistent disease after completing radiotherapy. Systemic therapy is a reasonable approach for patients who present with regional adenopathy because they have a relatively high rate of distant metastasis.

Actuarial Analysis↗
PubMed1998

Use of amplitude-modulated breathing for assessment of cardiorespiratory frequency response within subrespiratory frequencies.

We present a new technique which uses amplitude-modulated breathing patterns to obtain estimates of frequency response between respiration and heart rate within subrespiratory frequencies. Frequency response between respiration and heart rate has been previously estimated using broadband respiration and metronomic breathing. However, the estimates obtained using these techniques show low coherence between respiration and heart rate within the subrespiratory frequencies (< 0.12-0.15 Hz). The advantages of amplitude-modulated breathing are: enhancement in the degree of perturbation within subrespiratory frequencies as indicated by relatively higher coherencies between respiration and heart rate (approximately equal to 0.7), and the subjects do not have to breathe at very low breathing frequencies or resort to breath holds. Use of a squared sine wave carrier modulated by sinusoidal functions enabled us to obtain energy distributions at subrespiratory frequencies without using demodulation. Results obtained at eight subrespiratory frequencies from ten subjects show that the new technique is easy to implement and produces relatively higher coherence between respiration and heart rate. The advantage of the new technique in terms of enhancing the level of perturbations within subrespiratory frequencies is particularly important, because it is in this frequency range that the interpretation of variability in heart rate in terms of autonomic origins is incompletely understood and is confounded by respiratory interactions.

Adult↗
PubMed1997

[Peripheral retinal cryocoagulation. Long-term outcome].

UNLABELLED: Peripheral retinal cryotherapy alone, without additional cyclocryotherapy, can for the short term lead to intraocular pressure reduction and regression of neovascularization. As there is little information concerning the long-term results of this treatment we reexamined all patients treated with peripheral retinal cryotherapy at the Department of Ophthalmology at Freiburg University between 1979 and 1990. PATIENTS AND METHODS: Neovascularization was secondary to proliferative diabetic retinopathy in 33 eyes (65%), secondary to retinal vascular occlusion in 13 eyes (25%), and secondary to a combination of both in 5 eyes (10%). Usually, 2 quadrants of each eye were treated with 9 applications per quadrant. RESULTS: Intraocular pressure was adequately reduced in 49% of the eyes and rubeosis iridis regressed in 57%. Visual acuity deteriorated in 53% of all cases. CONCLUSION: Intraocular pressure and rubeosis iridis can in the long term successfully be treated with peripheral retinal cryotherapy. Despite good intraocular pressure control and regression of rubeosis iridis visual acuity does not improve.

Adult↗
PubMed1997

Hemodynamic responses to the stroop and cold pressor tests after submaximal cycling exercise in normotensive males.

The effect of 30 min of cycling exercise at 60% VO2max on hemodynamic responses to the Stroop and cold pressor tests in 12 normotensive males was examined. Subjects were randomly assigned in a counterbalanced design to perform the stressors pre- and postexercise and served as their own controls. Cardiac output (CO), heart rate (HR), and stroke volume were measured continuously by impedance cardiography. Blood pressure was measured beat to beat using a photoplethysmographic volume transducer. Total peripheral resistance (TPR) was calculated. The systolic blood pressure response (elevation) to the Stroop test was significantly attenuated postexercise (4.2 +/- 1.4%, p < 0.05) as compared to preexercise and control (10.1 +/- 1.8%). Postexercise HR reactivity was also significantly attenuated to the Stroop test postexercise (0.3 +/- 1.7%) compared to preexercise and control (6.5 +/- 2.3%, p < 0.05). Hemodynamic variables among treatment groups, with the possible exception of HR, appeared to be unaffected during the cold pressor postexercise. Neither central (i.e., CO) nor peripheral (i.e., TPR) responses appeared to be solely responsible for the attenuated blood pressure response to the Stroop stressor.

Adult↗
PubMed1997

Alterations in pharmacodynamics of anxiolytics in abstinent alcoholic men: subjective responses, abuse liability, and electroencephalographic effects of alprazolam, diazepam, and buspirone.

Subjective responses, including those associated with abuse liability and changes in frontal electroencephalographic activity, were assessed in abstinent alcoholic men and control subjects after administration of alprazolam, diazepam, buspirone, and placebo. Plasma concentrations of alprazolam, diazepam, and desmethyldiazepam also were determined. Abuse liability scales were elevated for alcoholic participants above control levels after alprazolam and diazepam. Areas under the concentration-time curve differed only for desmethyldiazepam, which was lower for the alcoholic participants. Compared with control subjects, alcoholic participants had greater declines in the absolute power of the alpha band after diazepam challenge. Alcoholic participants, unlike control subjects, had areas under the effect-time curve for alpha and theta bands that were lower after administration of alprazolam or diazepam than they were after receiving placebo. These results suggest that alprazolam and diazepam are more likely to be abused by alcoholic men than by nonalcoholic men and that alcoholic men have enhanced sensitivity to the effects of benzodiazepines on alpha and theta activity.

Adult↗
PubMed1996

Photoinduced electron transfer from nucleotides to DNA intercalating viologens. A study by laser-flash photolysis and spectroelectrochemistry.

Fluorescent DNA-binding N,N'-dialkyl 6-(2-pyridinium)phenanthridinium dications (where dialkyl stands for -(CH2)2-or-(CH2)3-, abbreviated dq2pyp and dq3pyp, respectively) associate with GMP (guanosine-5'-monophosphate) in 0.1-mol l-1, pH 3.5-5.5, phosphate buffer solution to yield 1:1 and 1:2 non-emissive complexes, the formation constants of which range from 197-63 and 19-11 l mol-1, respectively. In addition to the strong static quenching, dynamic deactivation of their excited state occurs at diffusion-controlled rate ki = 5.2 x 10(9) l mol-1 s-1). Illumination of the GMP-containing solutions of the dyes with a 355 nm laser pulse produces a transient, with strong absorbance at 510 and 720 nm for dq2pyp, and 420 and 560 nm for dq3pyp. An identical transient is produced in the presence of ascorbic acid instead of the mononucleotide. By comparison to the electrochemically generated absorption spectra of the monoreduced dyes, the photogenerated transients have been assigned unequivocally to their corresponding radical-cations, formed by electron transfer to the anglet excited state. The back redox reaction between the oxidized quencher and dq2pyp+ proceeds at a rate of 1-2 x 10(9) l mol-1 s-1. The same transient has been observed also for the DNA intercalated viologens; this result, together with the little ability of these dyes to sensitize the formation of singlet dioxygen or to produce superoxide anion, demonstrate that their DNA photocleavaging activity is initiated by an efficient light-induced electron transfer from the nucleobases.

Animals↗
PubMed1996

An optimized index of human cardiovascular adaptation to simulated weightlessness.

Prolonged exposure to weightlessness is known to produce a variety of cardiovascular changes, some of which may influence the astronaut's performance during a mission. In order to find a reliable indicator of cardiovascular adaptation to weightlessness, we analyzed data from nine male subjects after a 24-hour period of normal activity and after a period of simulated weightlessness produced by two hours in a launch position followed by 20 hours of 6 degrees head-down tilt plus pharmacologically induced diuresis (furosemide). Heart rate, arterial pressure, thoracic fluid index, and radial flow were analyzed. Autoregressive spectral estimation and decomposition were used to obtain the spectral components of each variable from the subjects in the supine position during pre- and post-simulated weightlessness. We found a significant decrease in heart rate power and an increase in thoracic fluid index power in the high frequency region (0.2-0.45 Hz) and significant increases in radial flow and arterial pressure powers in the low frequency region (<0.2 Hz) in response to simulated weightlessness. However, due to the variability among subjects, any single variable appeared limited as a dependable index of cardiovascular adaptation to weightlessness. The backward elimination algorithm was then used to select the best discriminatory features from these spectral components. Fisher's linear discriminant and Bayes' quadratic discriminant were used to combine the selected features to obtain an optimal index of adaptation to simulated weightlessness. Results showed that both techniques provided improved discriminant performance over any single variable and thus have the potential for use as an index to track adaptation and prescribe countermeasures to the effects of weightlessness.

Adaptation, Physiological↗
PubMed1996

Detection of extended-spectrum-beta-lactamase-producing members of the family Enterobacteriaceae with Vitek ESBL test.

A three-phase analysis of the Vitek ESBL test and a double-disk (2 disk) test was performed to assess their ability to detect extended-spectrum beta-lactamases (ESBLs) in members of the family Enterobacteriaceae. In the first two phases involving detection of ESBLs in 157 stains processing well-characterized beta-lactamases, sensitivity and specificity were found to be 99.5 and 100%, respectively, for the Vitek ESBl test and 98.1 and 99.4%, respectively, for the 2-disk test. In the third phase, in which the ability of each test to detect ESBLs in 295 clinical isolates was assessed, there was only one false positive (Vitek ESBL test). Across all three phases, the Vitek ESBL test was found to be much easier to perform than the 2-disk test. The latter also involved subjective interpretation of results. There were a total of 176 Escherichia coli and 157 Klebsiella pneumoniae isolates and less than 40 isolates of each of 14 other species evaluated. In a supplemental study of Klebsiella oxytoca, an organism possessing a chromosomal beta-lactamase similar to an ESBL, the Vitek ESBL test was found to be capable of detecting hyperproduction of this enzyme in strains of this species as well. These data indicate that the Vitek ESBL test is reliable for the detection of ESBLs in E. coli and K. pneumoniae, the two species in which ESBLs are most common, and of hyperproduction of the K. oxytoca beta-lactamase, a situation which engenders a level of resistance to this species similar to that seen with ESBLs.

Cephalosporins↗
PubMed1996

Impact of chlorhexidine-silver sulfadiazine-impregnated central venous catheters on in vitro quantitation of catheter-associated bacteria.

To assess the impact of the antiseptic effects of silver sulfadiazine-chlorhexidine-impregnated central venous catheters on catheter culture systems, a series of in vitro experiments was performed. Segments of antiseptic and non-antiseptic-impregnated catheters were sonicated in thioglycolate broth and removed. After the addition of 10(3) CFU of Staphylococcus epidermidis per ml, aliquots of catheter-exposed broth were subcultured onto blood agar at 15-min intervals. Decreased mean colony counts were noted at 45 min for broth exposed to antiseptic-impregnated catheters compared with the colony counts for broth exposed to non-antiseptic-impregnated catheters (170 versus 540 CFU/ml). These effects, which were also demonstrated by the roll-plate method, were abrogated by the use of medium containing inhibitors of silver sulfadiazine and chlorhexidine. To assess the duration of the antiseptic effects, catheter segments were suspended for up to 14 days in phosphate-buffered saline, incubated with 10(6) CFU of S. epidermidis per ml, and cultured. Inhibition of bacterial growth by antiseptic-impregnated catheters disappeared after 14 days. These studies suggest that antiseptic compounds elute from catheters during broth- and solid medium-based culturing processes, making necessary the addition of inhibitors of these compounds in culture media. They further suggest that the antimicrobial effects of antiseptic-impregnated catheters wane within several days of placement.

Anti-Infective Agents, Local↗
PubMed1996

Liability to alprazolam abuse in daughters of alcoholics.

OBJECTIVE: The purpose of this study was to determine mood changes in women with a parental history of alcohol dependence (daughters of alcoholics) after challenge does of alprazolam and placebo in comparison with responses in women without a history of parental alcohol dependence. METHOD: Visual analog scales that assess liability to benzodiazepine abuse were administered to 12 adult daughters of alcoholics and 11 comparison subjects after alprazolam challenge. RESULTS: The daughters of alcoholics had greater pleasant mood responses after a single dose of alprazolam than did the comparison subjects despite having similar plasma alprazolam levels. CONCLUSIONS: The findings of this study suggest that the mood-enhancing effects of alprazolam are greater in daughters of alcoholics than in subjects without a history of parental alcohol dependence.

Adult↗
PubMed1995

Spectral patterns and frequency response characteristics of arterial pressure in heart paced dogs.

The role of heart rate in buffering and/or generating aortic pressure (AP) oscillations that occur at rest and in response to oscillatory blood volume shifts was studied. Six supine dogs with chronic AV blockade were used to examine: 1) resting HR and AP spectra when the ventricular rate was controlled by atrial depolarization (natural sinus rhythm); 2) resting AP and stroke volume (SV) spectra when the heart was AV sequentially paced at 60, 120, and 180 bpm before and after ganglionic blockade; and 3) the frequency response characteristics of AP and SV to whole-body sinusoidal acceleration (+/- 2gz, 0.008-0.23 Hz) at each heart rate before and after ganglionic blockade. During atrial regulation of HR, the spectra of both AP and HR had dominant peaks located at the breathing frequency (0.2-0.4 Hz) and relatively smaller peaks centered at approximately 0.05 Hz. During constant heart rate pacing, the spectra of AP had a dominant component at approximately 0.05 Hz. The power of this component was: 1) larger than during atrial regulation, 2) increased with increasing pacing rate, and 3) abolished by ganglionic blockade. There was no effect of pacing rate or ganglionic blockade on SV spectra. During oscillatory acceleration, AP regulation in the heart paced dogs was frequency dependent. Regions of good regulation occurred below 0.016 Hz and above 0.1 Hz, and poor regulation between 0.035 and 0.075 Hz centered at approximately 0.05 Hz. The oscillations in the poor regulation region were enhanced by increased pacing rate. After ganglionic blockade, the frequency response of AP was primarily hydraulic (low-pass). The frequency response of SV had a neural component. We conclude that: 1) resting AP fluctuations at respiratory frequencies resulted from respiration-linked HR variation; 2) the 0.05-Hz fluctuations in AP during rest and the poor regulation of AP at 0.05 Hz during acceleration resulted from a peripheral vascular response that lagged disturbances by approximately 10 s; 3) HR regulation was important in minimizing AP variation in the 0.05-Hz region both at rest and during oscillatory acceleration; and 4) inotropic control of SV was an important component of AP regulation during low-frequency acceleration.

Acceleration↗
PubMed1995

Multicenter clinical laboratory evaluation of a beta-lactamase disk assay employing a novel chromogenic cephalosporin, S1.

S1, a new chromogenic cephalosporin (International BioClinical, Inc., Portland, Oreg.), was used to detect beta-lactamase production among a variety of commonly encountered bacteria in a four-center collaborative study. Results of an S1 disk assay were compared with those obtained by a nitrocefin-based disk procedure (Cefinase; Becton-Dickinson Microbiology Systems, Cockeysville, Md.), with repetitive testing of five quality control organisms and with individual tests of recent clinical isolates of Neisseria gonorrhoeae (162 strains), Haemophilus influenzae (162 strains), Moraxella catarrhalis (155 strains), Staphylococcus aureus (161 strains), and Bacteroides fragilis (164 strains). The performances of the two beta-lactamase disk assays were comparable for the first three species cited above. However, the S1 assay appeared to be a more sensitive procedure than the Cefinase assay when applied to S. aureus and B. fragilis, with respect to both total numbers of positive results and length of time to a definitive positive endpoint.

Bacteria↗
PubMed1995

An animal model and computer-controlled surface pressure delivery system for the production of pressure ulcers.

Pressure ulcers continue to be a major health care problem. This paper describes an animal model and surface pressure delivery system for the production of experimentally derived pressure ulcers. A method for inducing dermal pressure lesions on the fuzzy rat was developed using a computer-controlled displacement column which produced a constant tissue interface pressure. The pressure column consists of a force transducer located between two 0.5-in (1.27-cm) diameter metal cylinders. The desired cutaneous pressure is maintained by a computer-controlled miniature stepper motor which displaces the column with the aid of interactive software. The force transducer signal is converted from analog to digital form, amplified, and recorded. Blood perfusion is monitored using a laser Doppler flowmeter (located in the tip of the column) during the application of pressure. The application of 145 mmHg pressure for 5 consecutive 6-hr sessions resulted in a greater than 90% incidence of pressure ulcers. The implications of our model and contributions of earlier animal models are discussed. This model provides a tightly controlled and measured environment making possible the scientific study of ulcer development and the evaluation of potential preventative or curative compounds.

Animals↗
PubMed1992

Revision of standards for adjusting the cation content of Mueller-Hinton broth for testing susceptibility of Pseudomonas aeruginosa to aminoglycosides.

A multilaboratory study was undertaken to reassess the amount of calcium and magnesium that should be added to Mueller-Hinton broth when testing Pseudomonas aeruginosa against amikacin, gentamicin, isepamicin, netilmicin, and tobramycin. To achieve parity with agar dilution tests, cation-adjusted broth should contain 20 to 25 mg of calcium and 10 to 12.5 mg of magnesium per liter rather than the 50- and 25-mg/liter supplements recommended previously. For quality control of tests with contemporary media, MIC control limits should be adjusted by lowering the current MIC limits by at least 1 doubling-dilution interval.

Aminoglycosides↗