Peripheral artery disease is associated with worse outcomes after TAVR

Introduction

Peripheral arterial disease (PAD) is common in patients undergoing transcatheter aortic valve replacement (TAVR) and presents unique challenges for TAVR arterial access. The impact of TAVR on limb ischemic events in PAD patients undergoing TAVR is unknown.

Purpose

Evaluate patients undergoing TAVR with and without PAD for outcomes involving limb ischemic and systemic cardiovascular events.

Methods

Patients undergoing TAVR were identified in the TriNetX database. The database provides access to electronic medical records (diagnoses and procedures) from approximately 86.5 million patients from 58 healthcare organizations. Patients were stratified by history of PAD. After propensity score matching, 30 day limb ischemic outcomes (peripheral revascularization, acute limb ischemia (ALI), lower extremity amputation), major adverse cardiac events (MACE), and mortality were compared between groups. 1 year outcomes for MACE and mortality were also compared. Event rates calculated using 1 year Kaplan-Meier estimator.

Results

We identified 22,405 patients undergoing TAVR. Of these patients 21.3% had diagnosed PAD. Patients with PAD had significantly increased 30 day peripheral revascularization (2.4% v. 1.2%; adjusted OR (aOR) 2.02, 95% CI 1.47–2.80) and ALI (2.27% v. 0.89%; aOR 2.59 95% CI 1.80–3.70) with a similar rate of amputation (Figure 1). 30 day MACE (13.2% vs. 11.4%; aOR 1.18 95% CI 1.04–1.33) and mortality (2.46% vs. 1.53%; aOR 1.63 1.21–2.19) were also significantly increased with continued significance at 1 year follow up (MACE: 25.8% v. 21.6%; aOR 1.26 95% CI1.15–1.39; Mortality: 9.4% vs. 7.3%; aOR 1.32 95% CI 1.14–1.52) (Figure 2).

Conclusions

In our study, TAVR in PAD patients was associated with increased limb ischemic events as well as increased MACE and mortality at 30 days and 1 year follow up.

Funding Acknowledgement

Type of funding sources: None.

Sex-related differences in long-term mortality after coronary artery bypass graft surgery: a systematic review and meta-analysis

Background

This meta-analysis assessed the sex-related differences in long-term mortality (>7 years) after Coronary Artery Bypass Graft (CABG) Surgery.

Purpose

Women has higher incidence of short-term cardiovascular mortality after CABG compared to men. However, data about long-term differences are controversial.

Methods

We searched the databases for studies reporting sex-specific mortality following CABG including Ovid MEDLINE, Ovid, Embase, Scopus, Web of Science, Google Scholar, and EBSCO CINAHL from inception up to December 31st, 2020. The search was not restricted to time or publication status. Outcomes included rates of long-term mortality (>7 year or longer).

Results

A total of 518 studies were resulted from literature search. A total of 14 studies and 204,223 patients; 158,663 men and 45,556 women, with a mean age of the men 60.2 years and 63.2 years for women, were included in our systematic review and meta-analysis. Our analysis suggested sex-related differences in long-term mortality (>7 years) following CABG (odds ratio (1), 1.15; 95% confidence interval (2), 1.017–1.30; P<.02).

Conclusions

Our results suggest that women had higher long-term mortality following CABG compared with men. It is the largest study to date of sex-specific differences in long-term mortality (>7 years).

Funding Acknowledgement

Type of funding sources: None. Meta-analysisDemographics

Impact of pacing-related differences on clinical and echocardiographic outcomes after TAVR with SAPIEN-3 valve

Background

Data regarding the impact of pacing on outcomes after transcatheter aortic valve replacement (TAVR) is evolving especially with regards to pre-existing PPM. We examined the impact of new and prior PPM on clinical and hemodynamic outcomes after SAPIEN-3 (S3) TAVR.

Methods

Consecutive patients who underwent transfemoral-TAVR using S3 valve between April 2015 and December 2018 at our Clinic were included.

Results

Among 1028 patients, 10.2% required new PPM within 30 days, while 14% had pre-existing PPM. The presence of either prior or new PPM had no impact on 3-year mortality (log-rank p=0.6), or 1-year major adverse cardiac and cerebrovascular event (MACCE) (log-rank p=0.65). New PPM was associated with lower left ventricular ejection fraction (LVEF) at both 30 days (54.4±11.3% vs. 58.4±10.1%; p=0.001), and 1 year (54.2±12% vs. 59.1±9.9%; p=0.009) compared to no PPM. Similarly, prior PPM was associated with worse LVEF at 30 days (53.6±12.3%; p<0.001) and 1 year (55.5±12.1%; p=0.006) compared to no PPM. Interestingly, new PPM was associated with lower 1-year mean gradient (11.4±3.8 vs. 12.6±5.6 mmHg; p=0.04), and peak gradient (21.3±6.5 vs. 24.1±10.4 mmHg; p=0.01) despite no baseline differences. Prior PPM was also associated with lower 1-year mean gradient (10.3±4.4 mmHg; p=0.001), and peak gradient (19.4±8 mmHg; p<0.001), and higher doppler velocity index (0.51±0.12 vs. 0.47±0.13; p=0.039). Moreover, 1-year LV end-systolic volume (LVESVi) was higher with new (23.2±16.1 vs. 20±10.8 ml/m2; p=0.038), and prior PPM (24.5±19.7; p=0.038) compared to no PPM. Prior PPM was associated with higher moderate-to-severe tricuspid regurgitation (35.3% vs. 17.7%; p<0.001). There were no differences with regards to the rest of the studied echocardiographic outcomes at 1 year.

Conclusion

In this S3 cohort, new and prior PPM did not affect 3-year mortality or 1-year MACCE, however they were associated with worse LVEF, higher LVESVi and lower mean and peak gradients on follow-up compared to no PPM.

Funding Acknowledgement

Type of funding sources: None. Figure 1. All-cause Survival

Magnetic Resonance Image-Guided Radiotherapy (MRIgRT): A 4.5-Year Clinical Experience

AIMS

Magnetic resonance image-guided radiotherapy (MRIgRT) has been clinically implemented since 2014. This technology offers improved soft-tissue visualisation, daily imaging, and intra-fraction real-time imaging without added radiation exposure, and the opportunity for adaptive radiotherapy (ART) to adjust for anatomical changes. Here we share the longest single-institution experience with MRIgRT, focusing on trends and changes in use over the past 4.5 years.

MATERIALS AND METHODS

We analysed clinical information, including patient demographics, treatment dates, disease sites, dose/fractionation, and clinical trial enrolment for all patients treated at our institution using MRIgRT on a commercially available, integrated 0.35 T MRI, tri-cobalt-60 device from 2014 to 2018. For each patient, factors including disease site, clinical rationale for MRIgRT use, use of ART, and proportion of fractions adapted were summated and compared between individual years of use (2014-2018) to identify shifts in institutional practice patterns.

RESULTS

Six hundred and forty-two patients were treated with 666 unique treatment courses using MRIgRT at our institution between 2014 and 2018. Breast cancer was the most common disease, with use of cine MRI gating being a particularly important indication, followed by abdominal sites, where the need for cine gating and use of ART drove MRIgRT use. One hundred and ninety patients were treated using ART in 1550 fractions, 67.6% (1050) of which were adapted. ART was primarily used in cancers of the abdomen. Over time, breast and gastrointestinal cancers became increasingly dominant for MRIgRT use, hypofractionated treatment courses became more popular, and gastrointestinal cancers became the principal focus of ART.

DISCUSSION

MRIgRT is widely applicable within the field of radiation oncology and new clinical uses continue to emerge. At our institution to date, applications such as ART for gastrointestinal cancers and accelerated partial breast irradiation (APBI) for breast cancer have become dominant indications, although this is likely to continue to evolve.

Donor cornea tissue in cases of drowning or water submersion: eye banks practice patterns and tissue outcomes

Surgical use of donor corneal tissue from victims of water submersion (drowning or submersion secondary to death) remains controversial due to limited evidence about the quality of these tissues. To assess the safety of donor corneal tissue from victims of water submersion, an investigation of eye banks' practice patterns and tissue outcomes was conducted. All 79 Eye Bank Association of America accredited eye banks were contacted for a phone interview of practices regarding tissue from victims of water submersion. A retrospective review of corneal tissues from 2014 to 2016 from a large eye bank network was performed to identify all donors submerged in water. Corneal epithelial integrity, endothelial cell density (ECD), rim cultures, and adverse events were analyzed for associations with water submersion characteristics. 49 eye banks (62% response) participated in the survey. 55% of these eye banks had specific, written protocol for tissue eligibility from donors submerged in water. With or without specific protocol, eye banks reported considering water type (84%) and length of time submerged (92%) to determine eligibility. 22% of eye banks reported medical director involvement when eligibility determination was unclear. 79 tissues from 40 donors who were submerged were identified in 2014-2016 eye bank data. No donor tissues had pre-processing corneal infiltrates, positive rim cultures, or adverse events post-keratoplasty. Corneal epithelial integrity and ECD were not associated with water type or length of time submerged. In conclusion, data from a large eye bank network showed no adverse events or outcomes, indicating these tissues may be safe.

Abstract PD8-03: ESR1 gene fusions drive endocrine therapy resistance and metastasis in breast cancer

Background. Dysregulation of the estrogen receptor gene (ESR1) is an established mechanism of inducing endocrine therapy resistance. We previously discovered a chromosomal translocation event generating an estrogen receptor gene fused in-frame to C-terminal sequences of YAP1 (ESR1-YAP1) that contributed to endocrine therapy resistance in estrogen receptor positive (ER+) breast cancer models. This study compares functional, transcriptional, and pharmacological properties of additional ESR1 gene fusion events of both early stage (ESR1-NOP2) late stage (ESR1-YAP1 and ESR1-PCDH11x) breast cancers to gain a better understanding of therapeutic resistance and metastasis. Understanding the role of ESR1 fusions in inducing metastasis is critical, since the primary cause of death in breast cancer patients is through metastasis to distant sites.

Methods. RNA-seq screens identified ESR1 fusions from early and late stage, endocrine therapy resistant breast tumor samples. Functional experiments were conducted using ER+ breast cancer cell lines, xenograft, and PDX models to test the ability of ESR1 fusions to induce therapeutic resistance and metastasis. ChIP-seq and RNA-seq were performed to examine transcriptional properties and differential gene expression induced by the fusions which directed subsequent pharmacological experiments with a CDK4/6 inhibitor.

Results. ESR1-YAP1 and ESR1-PCDH11x promoted estrogen-independent and fulvestrant-resistant growth in vitro and induced greater tumor growth and increased metastatic capacity to the lungs of xenografted mice. In contrast, the ESR1-NOP2 fusion was sensitive to low estrogen conditions in vitro, and did not promote tumor growth. RNA-seq profiling revealed E2F targets pathway as the most highly enriched pathway induced by the ESR1 fusions. IHC revealed higher levels of pRb in ESR1-YAP1 and ESR1-PCDH11x xenograft tumors and subsequent CDK4/6 inhibition completely blocked tumor growth in an ESR1-YAP1 PDX model. Integrating RNA-seq with ChIP-seq data, we discovered a set of EMT and metastasis genes bound by all ESR1 fusions and WT-ER, but whose expression was strongly and uniquely up-regulated only by the ESR1-YAP1 and ESR1-PCDH11x fusions. These studies also revealed gained sites bound only by the ESR1-YAP1 and ESR1-PCDH11x fusions, not bound by WT-ER nor ESR1-NOP2. Genes mapping to these sites have a role in metastatic biology and were highly up-regulated by the YAP1 and PCDH11x fusions, potentially mediated by long range transcriptional activation.

Conclusion. ESR1-YAP1 and ESR1-PCDH11x are driver fusions that occur in drug-resistant, advanced stage breast cancer and are a new class of recurrent somatic mutation that can cause acquired endocrine therapy resistance, yet can be treated with CDK4/6 inhibition. These driver fusions also confer increased metastatic ability through their ability to drive expression of genes that contribute to EMT and metastasis. In contrast, ESR1-NOP2 did not produce functional protein and appears to be a passenger event. These studies may provide pre-clinical rationale for targeting ESR1 translocated breast tumors, since the presence of an ESR1 driver fusion places a patient in a therapeutic category where none of the currently available endocrine therapies are likely to be effective.

Citation Format: Lei JT, Shao J, Zhang J, Iglesia M, Chan DW, Cao J, Anurag M, Singh P, Haricharan S, Kavuri SM, Matsunuma R, Schmidt C, Kosaka Y, Crowder R, Hoog J, Phommaly C, Goncalves R, Ramalho S, Rodrigues-Peres RM, Lai W-C, Hampton O, Rogers A, Tobias E, Parikh P, Davies S, Ma C, Suman V, Hunt K, Watson M, Hoadley KA, Thompson A, Perou CM, Creighton CJ, Maher C, Ellis MJ. ESR1 gene fusions drive endocrine therapy resistance and metastasis in breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD8-03.

Practical recommendation for rash and diarrhea management in Indian patients treated with tyrosine kinase inhibitors for the treatment of non-small cell lung cancer

Tyrosine kinase inhibitors (TKIs) are a pharmaceutical class of small molecules, orally available with manageable safety profile, approved worldwide for the treatment of several neoplasms, including lung, breast, kidney and pancreatic cancer as well as gastro-intestinal stromal tumours and chronic myeloid leukaemia. In recent years, management of lung cancer has been moving towards molecular-guided treatment, and the best example of this new approach is the use of the tyrosine kinase inhibitors (TKIs) in patients with mutations in the epidermal growth factor receptor (EGFR). The identification of molecular predictors of response can allow the selection of patients who will be the most likely to respond to these tyrosine kinase inhibitors (TKIs). Gastrointestinal (GI) adverse events (AEs) are frequently observed in patients receiving EGFR tyrosine kinase inhibitor therapy and are most impactful on the patient's quality of life. Dermatologic side effects are also relatively common among patients treated with EGFR inhibitors. Evidence has emerged in recent years to suggest that the incidence and severity of rash, positively correlated with response to treatment.These skin disorders are generally mild or moderate in severity and can be managed by appropriate interventions or by reducing or interrupting the dose. Appropriate and timely management make it possible to continue a patient's quality of life and maintain compliance; however if these adverse events (AEs) are not managed appropriately, and become more severe, treatment cessation may be warranted compromising clinical outcome. Strategies to improve the assessment and management of TKI related skin AEs are therefore essential to ensure compliance with TKI therapy, thereby enabling patients to achieve optimal benefits. This article provides a consensus on practical recommendation for the prevention and management of diarrhoea and rash in Non-Small Cell Lung Cancer (NSCLC) patients receiving TKIs.

Abstract PD2-03: Recurrent functionally diverse in-frame ESR1 gene fusions drive endocrine resistance in breast cancer

Background. We previously reported an alternative ESR1 somatic gain-of-function chromosomal translocation event in a patient presenting with aggressive, endocrine therapy resistant estrogen receptor (ER) positive disease, producing an in-frame fusion gene consisting of N-terminal ESR1 and the C-terminus of the Hippo pathway coactivator YAP1 (ESR1-YAP1). We recently identified another ESR1 fusion through RNA sequencing (RNA-seq) in advanced stage ER+ disease from a chest wall recurrence in a male patient that was refractory to multiple lines of treatment. Two examples of fusions discovered in primary breast cancer samples include ESR1 fused in-frame to C-terminal sequences from NOP2 (ESR1-NOP2), identified in a resistant cohort from a RNA-seq screen focused on 81 primary breast cancers from aromatase inhibitor clinical trials, and a second ESR1 fusion, fused in-frame to the entire coding sequence of POLH (ESR1-POLH), that was identified from RNA-seq analysis of 728 Cancer Genome Atlas breast samples. This current study extends our previous characterization of ESR1-YAP1 by comparing functional and pharmacological properties of these three additional ESR1 gene fusion events of both early stage and advanced breast cancers.

Methods. In vitro and in vivo experiments were conducted to test ESR1 fusions to induce therapeutic resistance, and metastasis. The transcriptional and binding properties of each fusion was also examined. Pharmacological inhibition with Palbociclib, a cyclin-dependent kinase 4/6 inhibitor, was utilized to assess drug sensitivity in ESR1 fusion containing breast cancer cells and in a patient derived xenograft (PDX) model expressing ESR1-YAP1 (WHIM18).

Results. The YAP1 and PCDH11x fusions conferred estrogen-independent and fulvestrant-resistant growth. Immunohistochemistry revealed significantly higher numbers of ER+ cells in lungs of mice xenografted with T47D cells expressing the YAP1 and PCDH11x fusions compared to YFP control, NOP2 and POLH fusions. Results from ChIP-seq and microarray studies suggest that these two fusions promote proliferation and metastasis through genomic action by binding estrogen response elements (ERE) and subsequent gene activation. We thereby define these fusions as “canonical” fusions compared to “non-canonical” NOP2 and POLH fusions, which demonstrated dramatically decreased genomic binding ability. The non-canonical fusions induced genes associated with basal-like breast cancer and promoted HER2, EGFR, and MAPK gene expression signatures in contrast to genes associated with cell cycle/proliferation induced by canonical fusions. The proliferative ability of canonical fusion-containing ER+ cells was inhibited by Palbociclib in a dose-dependent manner. In vivo WHIM18 tumors in mice fed with Palbociclib-containing chow demonstrated significantly reduced tumor volume, growth rate, and weight compared to tumors in mice on control chow.

Conclusions. In-frame ERE activating canonical fusions occur in end-stage drug resistant advanced breast cancer and can be added to ESR1 point mutations as a class of recurrent somatic mutation that may cause acquired resistance. Growth induced by these fusions can be antagonized by Palbociclib and is potentially clinically helpful.

Citation Format: Lei JT, Shao J, Zhang J, Iglesia M, Cao J, Chan DW, He X, Kosaka Y, Schmidt C, Matsunuma R, Haricharan S, Crowder R, Hoog J, Phommaly C, Goncalves R, Ramalho S, Lai W-C, Hampton O, Rogers A, Tobias E, Parikh P, Davies S, Ma C, Suman V, Hunt K, Watson M, Hoadley KA, Thompson A, Chen X, Perou CM, Creighton CJ, Maher C, Ellis MJ. Recurrent functionally diverse in-frame ESR1 gene fusions drive endocrine resistance in breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr PD2-03.

ID: 98: EFFECTIVENESS OF DAILY CHLORHEXIDINE BATHING FOR REDUCING GRAM NEGATIVE INFECTIONS: A META-ANALYSIS

Background

Multiple studies have demonstrated that daily chlorhexidine gluconate (CHG) bathing is associated with a significant reduction in infections caused by Gram positive pathogens. However, there is limited data on the effectiveness of daily CHG bathing on gram negative infections. The aim of this study was to determine if daily CHG bathing is effective in controlling and preventing gram negative infections in adult ICU patients.

Methods

We searched MEDLINE and 3 other databases for original studies comparing daily CHG bathing to soap and water bathing. All studies investigating the effectiveness of daily CHG bathing on gram negative infections were eligible. Two investigators extracted data independently on baseline characteristics, study design, form and concentration of CHG, incidence and outcomes related to gram negative infections. Data were combined by means of a random-effects model and pooled relative risk ratios (RRs) and 95% confidence intervals (CIs) were derived for overall gram negative infections and individual gram negative pathogens.

Results

Eleven studies (n=27,793 patients) met the inclusion criteria. Of these, 13,852 patients received daily CHG bathing, and 13,941 patients daily bathing with soap and water. Daily CHG bathing was not associated with a lower risk of gram negative infections (2.03% vs. 2.38%; RR 0.84; 95%CI: 0.64–1.09, P=.19). Subgroup analysis demonstrated that daily CHG bathing significantly reduced the risk of gram negative infections caused by Acinetobacter (RR, 0.33; 95% CI: 0.17–0.66, P<.00001) but was not effective for E. coli, Klebsiella, Enterobacter and Pseudomonas associated gram negative infections.

Conclusions

In a meta-analysis of 11 studies, the use of daily CHG was not associated with a lower risk of gram negative infections. However, daily CHG bathing appears to be effective for Acinetobacter associated gram negative infections. There is a need for larger and better designed trials with adequate power with gram negative infections as the primary endpoint to determine the effectiveness of daily CHG bathing.

Abstract ID: 98 Figure 1

Predicting 30-day Hospital Readmission with Publicly Available Administrative Database. A Conditional Logistic Regression Modeling Approach

INTRODUCTION

This article is part of the Focus Theme of Methods of Information in Medicine on "Big Data and Analytics in Healthcare".

BACKGROUND

Hospital readmissions raise healthcare costs and cause significant distress to providers and patients. It is, therefore, of great interest to healthcare organizations to predict what patients are at risk to be readmitted to their hospitals. However, current logistic regression based risk prediction models have limited prediction power when applied to hospital administrative data. Meanwhile, although decision trees and random forests have been applied, they tend to be too complex to understand among the hospital practitioners.

OBJECTIVES

Explore the use of conditional logistic regression to increase the prediction accuracy.

METHODS

We analyzed an HCUP statewide inpatient discharge record dataset, which includes patient demographics, clinical and care utilization data from California. We extracted records of heart failure Medicare beneficiaries who had inpatient experience during an 11-month period. We corrected the data imbalance issue with under-sampling. In our study, we first applied standard logistic regression and decision tree to obtain influential variables and derive practically meaning decision rules. We then stratified the original data set accordingly and applied logistic regression on each data stratum. We further explored the effect of interacting variables in the logistic regression modeling. We conducted cross validation to assess the overall prediction performance of conditional logistic regression (CLR) and compared it with standard classification models.

RESULTS

The developed CLR models outperformed several standard classification models (e.g., straightforward logistic regression, stepwise logistic regression, random forest, support vector machine). For example, the best CLR model improved the classification accuracy by nearly 20% over the straightforward logistic regression model. Furthermore, the developed CLR models tend to achieve better sensitivity of more than 10% over the standard classification models, which can be translated to correct labeling of additional 400 - 500 readmissions for heart failure patients in the state of California over a year. Lastly, several key predictor identified from the HCUP data include the disposition location from discharge, the number of chronic conditions, and the number of acute procedures.

CONCLUSIONS

It would be beneficial to apply simple decision rules obtained from the decision tree in an ad-hoc manner to guide the cohort stratification. It could be potentially beneficial to explore the effect of pairwise interactions between influential predictors when building the logistic regression models for different data strata. Judicious use of the ad-hoc CLR models developed offers insights into future development of prediction models for hospital readmissions, which can lead to better intuition in identifying high-risk patients and developing effective post-discharge care strategies. Lastly, this paper is expected to raise the awareness of collecting data on additional markers and developing necessary database infrastructure for larger-scale exploratory studies on readmission risk prediction.

Shear stress-associated acquired von Willebrand syndrome in patients with mitral regurgitation

BACKGROUND

Mitral valve regurgitation is associated with an acquired hemostatic defect.

OBJECTIVE

We sought to assess the prevalence and severity of acquired von Willebrand syndrome in patients with native valve mitral regurgitation (MR).

PATIENTS/METHODS

Fifty-three patients were prospectively observed with bleeding questionnaires and laboratory tests when undergoing an echocardiographic assessment of MR. In patients referred for mitral valve surgery, testing was repeated postoperatively.

RESULTS

Echocardiography identified 13 patients with mild MR, 14 with moderate MR, and 26 with severe MR. Among patients with mild, moderate or severe MR, loss of the highest molecular weight von Willebrand factor (VWF) multimers occurred in 8%, 64%, and 85%, respectively, median platelet function analyzer collagen ADP closure times (PFA-CADPs) were 84 s (interquartile range [IQR] 73-96 s), 156 s (IQR 104-181 s), and 190 s (IQR 157-279 s), respectively, and the ratios of VWF latex activity to antigen were 0.92 (IQR 0.83-0.97), 0.85 (IQR 0.76-0.89), and 0.79 (IQR 0.75-0.82), respectively (all P < 0.001). Nine patients reported clinically significant bleeding, and seven had intestinal angiodysplasia and transfusion-dependent gastrointestinal bleeding (Heyde syndrome), with the median number of transfusions required being 20 (IQR 10-33; range 4-50). In patients who underwent mitral valve repair (n = 13) or replacement (n = 7), all measures of VWF function reported above improved significantly.

CONCLUSION

The high-shear environment of moderate to severe MR is sufficient to produce prevalent perturbations in VWF activity. Acquired von Willebrand syndrome may occur in this setting, and appears to be reversible with mitral valve surgery.

Erklärung und Anwendung einer „schnellen" Modulations-Nachweistechnik für die magnetische Kernresonanzspektroskopie

Für den Nachweis von engen magnetischen Kernresonanzlinien eignet sich eine Modulations-Nach-weistechnik, bei der die Modulationsperiode kleiner als beide Relaxationszeiten ist. Die komplizierten Modulationseffekte, die wiederholt mathematisch beschrieben worden sind, werden auf einfache Weise an Hand eines makroskopischen Modells zur Analyse des Bewegungsablaufes der Kernmagnetisierung verständlich gemacht. Mit der Methode des rotierenden Koordinatensystems läßt sich der Verlauf der Absorptionssignale in Abhängigkeit von den Versuchsbedingungen verstehen. Die gewonnenen Ergebnisse werden in einigen graphischen Darstellungen wiedergegeben, welche die praktische Anwendung erleichtern. Es wird weiter gezeigt, daß neben anderen Vorteilen die Empfindlichkeit besser als bei den sonst in der Kernresonanzspektroskopie meist üblichen Nachweismethoden ist.