RESUMEN
BACKGROUND: Sialic acid-protein interactions are involved in regulating central nervous system immunity; therefore, derangements in sialylation could be involved in neurodegeneration. OBJECTIVES: We evaluate the differences in serum transferrin sialylation in prodromal and early-stage Parkinson's disease (PD), its relation to substantia nigra degeneration, and the risk of phenoconversion to manifest disease. METHODS: Sixty treatment-naive PD patients; 72 polysomnography-confirmed isolated rapid eye movement sleep behavior disorder (iRBD) patients, that is, patients with prodromal synucleinopathy; and 46 healthy volunteers aged ≥45 years and drinking ≤60 standard drinks per month were included. The proportion of serum low-sialylated, carbohydrate-deficient transferrin (CDT) isoforms was assessed using high-performance liquid chromatography, and the values were adjusted for alcohol intake (CDTadj ). Dopamine transporter single-photon emission computed tomography (DaT-SPECT) imaging was performed. In iRBD, phenoconversion risk of DaT-SPECT and CDTadj was evaluated using Cox regression adjusted for age and sex. RESULTS: Median CDTadj was lower in PD (1.1 [interquartile range: 1.0-1.3]%) compared to controls (1.2 [1.1-1.6]%) (P = 0.001). In iRBD, median CDTadj was lower in subjects with abnormal (1.1 [0.9-1.3]%) than normal (1.3 [1.2-1.6]%) DaT-SPECT (P = 0.005). After a median 44-month follow-up, 20% of iRBD patients progressed to a manifest disease. Although iRBD converters and nonconverters did not significantly differ in CDTadj levels (P = 0.189), low CDTadj increased the risk of phenoconversion with hazard ratio 3.2 (P = 0.045) but did not refine the phenoconversion risk associated with abnormal DaT-SPECT yielding hazard ratio 15.8 (P < 0.001). CONCLUSIONS: Decreased serum CDTadj is associated with substantia nigra degeneration in synucleinopathies. iRBD patients with low CDTadj are more likely to phenoconvert to manifest disease. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson Movement Disorder Society.
Asunto(s)
Enfermedad de Parkinson , Trastorno de la Conducta del Sueño REM , Sinucleinopatías , Humanos , Enfermedad de Parkinson/complicaciones , Enfermedad de Parkinson/diagnóstico por imagen , Trastorno de la Conducta del Sueño REM/complicaciones , Trastorno de la Conducta del Sueño REM/diagnóstico por imagen , Tomografía Computarizada de Emisión de Fotón Único/métodos , TransferrinaRESUMEN
OBJECTIVES: To recognize the radiographic patterns of coronavirus disease 2019 (COVID-19) in Malaysia. MATERIALS AND METHODS: Chest radiographs of patients confirmed with COVID-19 in Hospital Tawau, Sabah, Malaysia were retrospectively analyzed by two radiologists. The radiographic pattern, distribution among subgroups and evolution of the disease over time were determined. RESULTS: Among the 82 patients studied, 65 (79.3%) were males. Mean age of our cohorts was 37 ± 15 years. Baseline chest radiographs were abnormal in 37 patients (45.1%). Over half (52.9%) of the symptomatic patients had abnormal baseline radiograph. Among the children, patients with comorbidities, and patients 60 years of age and above, the abnormal radiographs were 14.3%, 71.4% and 69.3% respectively. Ground glass opacities were the commonest abnormal radiographic feature (35.4%), were peripherally located (35.4%) with predilection for the lower zones (29.3%). Most radiographic abnormalities were multifocal (20.7%) and frequently located in the left lung (19.5%). Radiographic recovery was observed in 15 of 18 patients (83%). Computed tomography (CT) scan demonstrated greater extent of the disease than observed in radiographs of the same patient. CONCLUSIONS: COVID-19 pneumonia presented with a specific radiographic pattern in our cohort of patients, comprising of ground glass opacities in peripheral and basilar distribution, affecting a single lung field and was observed in both symptomatic and asymptomatic patients. Chest radiograph is a useful adjunct screening tool, and in combination with clinical and epidemiological assessment may facilitate in early diagnosis of COVID-19 pneumonia.
Asunto(s)
COVID-19/complicaciones , COVID-19/diagnóstico por imagen , Pulmón/diagnóstico por imagen , Adolescente , Adulto , Anciano , Prueba de COVID-19 , Niño , Preescolar , Femenino , Humanos , Malasia , Masculino , Persona de Mediana Edad , Radiografía Torácica , Estudios Retrospectivos , Tomografía Computarizada por Rayos X , Adulto JovenRESUMEN
We conducted this study to determine if placement of infraclavicular catheters guided by ultrasound is quicker than placement guided by nerve stimulation. Infraclavicular brachial plexus catheters were inserted in 210 randomly allocated patients who were scheduled for elective hand or elbow surgery. Needle and catheter placement was guided by ultrasound (n = 105) or by nerve stimulation (n = 105). The primary outcome was time to sensory block success. Success rate was similar between the two techniques (83.2% vs 81.4%, p = 0.738). However, placement of ultrasound-guided catheters took less time (7.2 [2.5] vs 9.6 [3.6] min, p < 0 .001). Pain and satisfaction scores, and incidence of nerve deficit, were also similar with both techniques.
Asunto(s)
Anestésicos Locales/administración & dosificación , Bloqueo del Plexo Braquial/métodos , Estimulación Eléctrica , Dolor/prevención & control , Ultrasonografía Intervencional , Codo/cirugía , Femenino , Mano/cirugía , Humanos , Periodo Intraoperatorio , Masculino , Persona de Mediana Edad , Dolor Postoperatorio/tratamiento farmacológico , Satisfacción del Paciente/estadística & datos numéricos , Estudios Prospectivos , Método Simple Ciego , Resultado del TratamientoRESUMEN
In community and family practice, infections are a common OPD presentation. In the management of common bacterial infections seen in community especially RTI, UTI, SSTI; cefuroxime a second generation cephalosporin with a broad spectrum of activity can be used for empirical treatment. To know current place of cefuroxime in the management of infections, physicians, surgeons, microbiologist, chest physician, gynecologist and pediatrician came together to discuss and debate their experience with cefuroxime and its place in today's world. Cefuroxime is a drug which balances efficacy with safety. Several international bodies and guidelines including the US FDA and The British Thoracic Society, the World Society of Emergency Surgery (WSES) have recommended cefuroxime for the management of community acquired pneumonia and skin and soft tissue infection respectively. Cefuroxime has been recommended in the 2015 list of the US FDA list of drugs which can be used safely during pregnancy. Cefuroxime can become a useful empiric choice antibiotic for the Indian physicians treating urinary tract infections, respiratory tract infections and skin and soft tissue infections in their outpatient departments.
Asunto(s)
Antibacterianos/uso terapéutico , Cefuroxima/uso terapéutico , Infecciones del Sistema Respiratorio/tratamiento farmacológico , Enfermedades Cutáneas Bacterianas/tratamiento farmacológico , Infecciones de los Tejidos Blandos/tratamiento farmacológico , Infecciones Urinarias/tratamiento farmacológico , Infecciones Comunitarias Adquiridas/tratamiento farmacológico , HumanosRESUMEN
BACKGROUND: Clear visibility of the needle and catheter tip is desirable to perform safe and successful ultrasound-guided peripheral nerve blocks. This can be challenging with deeper blocks in obese patients. This study compared the visibility of echogenic and non-echogenic block needles and catheters in proximal sciatic blocks when performed with a low-frequency curved probe. METHODS: Seventy-eight patients undergoing total knee joint arthroplasty were randomized to receive an ultrasound-guided continuous sciatic nerve block using either a non-echogenic needle and stimulating catheter or an echogenic needle and echogenic non-stimulating catheter. Block needles in both groups were placed using both neurostimulation and ultrasound guidance, after which the catheter was positioned using either neurostimulation alone (Stimulating group) or imaging alone (Echogenic group). Three anaesthetists blinded to group allocation graded video clips recorded during the blocks for nerve, needle and catheter visibility. Performance characteristics and block parameters were also compared. RESULTS: No significant differences between the two groups were observed with regard to needle or catheter visibility (P=0.516). The Stimulating group required more needle redirections (P=0.009), had a longer procedure time [Echogenic median 274 s vs Stimulating 344 s (P=0.016)], and resulted in greater patient discomfort (P=0.012). There were no significant differences between the two groups in terms of block onset or completion time. CONCLUSIONS: Use of echogenic needles and catheters reduced procedure time and patient discomfort compared with a stimulating catheter system. There were no differences in the visibility scores of the two systems. CLINICAL TRIAL REGISTRATION: CTR Protocol ID: R-11-495, Clinical Trials.Gov ID: NCT 01492660.
Asunto(s)
Bloqueo Nervioso/métodos , Nervio Ciático/diagnóstico por imagen , Ultrasonografía Intervencional/métodos , Adulto , Anciano , Anciano de 80 o más Años , Anestésicos Locales/administración & dosificación , Artroplastia de Reemplazo de Rodilla , Cateterismo Periférico/métodos , Método Doble Ciego , Estimulación Eléctrica/instrumentación , Estimulación Eléctrica/métodos , Femenino , Humanos , Estimación de Kaplan-Meier , Masculino , Persona de Mediana Edad , Agujas , Bloqueo Nervioso/instrumentación , Dimensión del Dolor/métodos , Dolor Postoperatorio/prevención & control , Ultrasonografía Intervencional/instrumentaciónRESUMEN
BACKGROUND: Bilateral dual transversus abdominis plane (BD-TAP) injections were devised to cover the T7-8 and L1 dermatomes, which are usually spared with classical and mid-axillary TAP injections. The purpose of this study was to delineate the vertical and lateral extent of injectate spread following a lateral to medial approach for TAP injections in embalmed cadavers. METHODS: Ultrasound-guided subcostal and lateral TAP injections were performed on nine embalmed cadavers using 30 ml of 0.5% methylcellulose (20 ml for subcostal and 10 ml for lateral injections) with a 12-cm Tuohy needle in the first six cadavers (nine hemi-abdomens). Vertical extent and the medial to lateral extent of the dye spread were recorded after dissections of the abdominal wall. In a pilot of three cadavers not receiving TAP injections, anatomical impediments to proximal injectate spread were explored separately. RESULTS: The vertical spread of injectate was T7-L1 (n = 2/9), T8-L1 (n = 5/9) and T9-L1 (n = 2/9). None of the TAP injections extended beyond the mid-axillary line. No anatomical impediments for the flow of injectate to the T7 or T8 intercostal nerves were found at the level of the interdigitations of the transversus abdominis muscle and diaphragm. CONCLUSION: A lateral to medial approach for TAP injection resulted in spread of the injectate ranging from T7/8-L1 dermatomes in the majority of the hemi-abdomens. Subcostal and lateral TAP injections do not cover the lateral cutaneous branches of the segmental nerves.
Asunto(s)
Músculos Abdominales/diagnóstico por imagen , Colorantes/farmacocinética , Ultrasonografía Intervencional , Anciano , Anciano de 80 o más Años , Cadáver , Disección , Femenino , Humanos , MasculinoRESUMEN
The objective of this study is to develop and validate the Binaural Fusion Test (BFT) in the Tamil language for children with learning disability. As many children with learning disability exhibit an auditory processing deficit there is a need for language specific assessment tool for these children. The BFT in Tamil comprises 100 words organized into four lists, with each list containing 25 words. A total of 84 children with normal auditory processing and 45 children diagnosed with learning difficulties were administrated the BFT in Tamil. Test-retest reliability was evaluated in a sample of 30 children who exhibited normal auditory processing. The results of BFT in children with normal auditory processing demonstrated satisfactory reliability by the Cronbach Alpha test. A statistically significant difference was seen in the mean scores of BFT in Tamil when comparing the groups. The present study offers novel normative data for the binaural fusion test in Tamil, which has not been previously documented in the existing literature. For children, the BFT in Tamil, which is a part of the CAPD test battery, can be used to find binaural interaction deficiencies.
RESUMEN
Due to the workload and lack of a critical mass of trained operational researchers within their ranks, health systems and programmes may not be able to dedicate sufficient time to conducting operational research (OR). Hence, they may need the technical support of operational researchers from research/academic organisations. Additionally, there is a knowledge gap regarding implementing differentiated tuberculosis (TB) care in programme settings. In this 'how we did it' paper, we share our experience of implementing a differentiated TB care model along with an inbuilt OR component in Tamil Nadu, a southern state in India. This was a health system initiative through a collaboration of the State TB cell with the Indian Council of Medical Research institutes and the World Health Organisation country office in India. The learnings are in the form of eleven tips: four broad principles (OR on priority areas and make it a health system initiative, implement simple and holistic ideas, embed OR within routine programme settings, aim for long-term engagement), four related to strategic planning (big team of investigators, joint leadership, decentralised decision-making, working in advance) and three about implementation planning (conducting pilots, smart use of e-tools and operational research publications at frequent intervals). These may act as a guide for other Indian states, high TB burden countries that want to implement differentiated care, and for operational researchers in providing technical assistance for strengthening implementation and conducting OR in health systems and programmes (TB or other health programmes). Following these tips may increase the chances of i) an enriching engagement, ii) policy/practice change, and iii) sustainable implementation.
Asunto(s)
Investigación Biomédica , Tuberculosis , Humanos , India , Tuberculosis/prevención & control , Programas de Gobierno , OrganizacionesRESUMEN
To reduce TB deaths in resource-limited settings, a differentiated care strategy can be used to triage patients with high risk of severe illness (i.e., those with very severe undernutrition, respiratory insufficiency, or inability to stand without support) at diagnosis and refer them for comprehensive assessment and inpatient care. Globally, there are few examples of implementing this type of strategy in routine program settings. Beginning in April 2022, the Indian state of Tamil Nadu implemented a differentiated care strategy called Tamil Nadu-Kasanoi Erappila Thittam (TN-KET) for all adults aged 15 years and older with drug-susceptible TB notified by public facilities. Before evaluating the impact on TB deaths, we sought to understand the retention and delays in the care cascade as well as predictors of losses. During April-June 2022, 14,961 TB patients were notified and 11,599 (78%) were triaged. Of those triaged, 1,509 (13%) were at high risk of severe illness; of these, 1,128 (75%) were comprehensively assessed at a nodal inpatient care facility. Of 993 confirmed as severely ill, 909 (92%) were admitted, with 8% unfavorable admission outcomes (4% deaths). Median admission duration was 4 days. From diagnosis, the median delay in triaging and admission of severely ill patients was 1 day each. Likelihood of triaging decreased for people with extrapulmonary TB, those diagnosed in high-notification districts or teaching hospitals, and those transferred out of district. Predictors of not being comprehensively assessed included: aged 25-34 years, able to stand without support, and diagnosis at a primary or secondary-level facility. Inability to stand without support was a predictor of unfavorable admission outcomes. To conclude, the first quarter of implementation suggests that TN-KET was feasible to implement but could be improved by addressing predictors of losses in the care cascade and increasing admission duration.
Asunto(s)
Desnutrición , Adulto , Humanos , India/epidemiologíaRESUMEN
The aim of the study was to find the association of various risk factors with permanent hearing impairment in infants. A case-control study was designed on 420 infants with permanent hearing impairment and normal hearing. The case control ratio was 1:1. Alternate sampling method was used for selecting the control group. Review of medical records and parent interview was done to collect the information of risk factors. Family history(adj. OR 7.5; 95% CI 3, 14; P = 0.000), Consanguinity (adj. OR: 4; 95% CI 2,4; P = 0.000), intra uterine infection (adj. OR 18, 95% CI: 2.3-126.5, P = 0.000), post natal infection (adj. OR 3, 95% CI: 1.3-5, P = 0.004), low Apgar score (adj.OR: 4.6, 95% CI: 1.3-15), craniofacial anomaly (OR-4.6, 95% CI: 1.4-9.5, P = 0.005) and low birth weight (adj. OR: 2.3, 95% CI: 1.2-3.8) were significantly associated with hearing impairment. Among the risk factors, intra uterine infection was having highest significant association with permanent hearing impairment. This is followed by family history, low Apgar score, craniofacial anomaly, consanguinity, post natal infection and low birth weight.
RESUMEN
High-quality monoclinic planar waveguide crystals of Tm-doped KY(WO4)2 codoped with Gd3+ and Lu3+ were grown by liquid-phase epitaxy. For the first time, planar waveguide lasing was demonstrated in a monolithic cavity in the 2 µm spectral range. The laser was operated in the Q-switched mode using a Cr2+:ZnSe crystal as saturable absorber and in the continuous-wave regimes. The Q-switched planar waveguide laser delivered pulse energies up to 120 nJ at a repetition rate of 7 kHz.
Asunto(s)
Rayos Láser , Óxidos/química , Refractometría/instrumentación , Tulio/química , Tungsteno/química , Diseño Asistido por Computadora , Diseño de Equipo , Análisis de Falla de EquipoRESUMEN
INTRODUCTION: Mortality following traumatic femoral neck fractures in the elderly (age >60 years) is influenced by many factors. Addressing some of them may reduce the mortality rate thus improving patient survival and quality of life. MATERIALS AND METHODS: This study was a retrospective research using data collected from Hospital Sultanah Bahiyah, Kedah between the years 2008-2018. We measured outcomes such as age, gender, hospital stay, default rate, ambulation post-surgery, American Society of Anaesthesiologists score (ASA) and surgical timing in correlation with mortality rate and 10-year survival of elderly patients treated with Total Hip Arthroplasty for femoral neck fractures in this centre. RESULTS: A total of 291 traumatic femoral neck fractures aged above 60 years post total hip arthroplasty performed were included. There was higher number of female (n =233) compared to male (n=53) Estimated 10 years survival from Kaplan Meier was 42.88% (95% CI: 33.15, 52.54). One year mortality rate in our study was found to be 18.9%. The average time to event was 7.1 years (95% CI:33.15, 52.24) with a mean age group of 75. DISCUSSION: Total hip arthroplasty patients not ambulating after surgery had a 4.2 times higher hazard ratio compared to ambulators. Those with pre-existing systemic disease (ASA III and IV) were found to have the highest hazard ratio, almost five times that of healthy patients, after adjusting for confounding factors. Delay of more than seven days to surgery was found to be a significant factor in 10-year survival with a hazard ratio of 3.8, compared to surgery performed earlier. CONCLUSION: Delay of more than 7 days to surgery in 10 years survival was significant with high hazard ratio. It is a predictor factor for survival in 10 years. A larger sample size with a prospective design is required to confirm our findings regarding "unacceptable surgical timing" for femoral neck fractures in patients above 60 years of age.
RESUMEN
SETTING: Tuberculosis (TB) control programmes in Bangladesh, India and Malawi. OBJECTIVE: To compare the interval from symptom onset to diagnosis of TB for men and women, and to assess socio-cultural and gender-related features of illness explaining diagnostic delay. DESIGN: Semi-structured Explanatory Model Interview Catalogue (EMIC) interviews were administered to 100 or more patients at each site, assessing categories of distress, perceived causes and help seeking. Based on time from initial symptoms to diagnosis of TB, patients were classified with problem delay (>90 days), timely diagnosis (< or =30 days) or moderate delay. EMIC interview data were analysed to explain problem delay. RESULTS: The median interval from symptom onset to diagnosis was longest in India and shortest in Malawi. With adjustment for confounding, female sex (Bangladesh), and status of married woman (India) and housewife (Malawi) were associated with problem delay. Prominent non-specific symptoms--chest pain (Bangladesh) and breathlessness (Malawi)--were also significant. Cough in India, widely associated with TB, was associated with timely diagnosis. Sanitation as a perceived cause linked to poor urban conditions was associated with delayed diagnosis in India. Specific prior help seeking with circuitous referral patterns was identified. CONCLUSION: The study identified gender- and illness-related features of diagnostic delay. Further research distinguishing patient and provider delay is needed.
Asunto(s)
Tuberculosis/diagnóstico , Tuberculosis/epidemiología , Bangladesh , Atención a la Salud , Femenino , Humanos , India , Malaui , Masculino , Factores Sexuales , Factores Socioeconómicos , Factores de TiempoRESUMEN
PURPOSE: We describe our experience of combining the use of ultrasound (US) guidance with contrast enhancement and peripheral nerve stimulation for the insertion of infraclavicular brachial plexus catheters. METHODS: Thirty patients scheduled to have upper limb surgery under regional block were studied. Under US guidance and peripheral nerve stimulation assistance, continuous peripheral nerve block needle and stimulating catheter were placed in the infraclavicular area. Needle and catheter tip location was confirmed with agitated 5% dextrose and seen under colour Doppler with US before injecting local anaesthetic (LA). Patients were evaluated in terms of onset times and efficacy of block. Post-operatively, on block recession a catheter was stimulated and visualization of spread of LA during injection through the catheter was done. Secondary block (subsequent to re-injection of LA) was assessed. Patients were followed-up for a week. RESULTS: Mean time to onset of block was 19.7 (+/- 4.9) min. There were no incomplete blocks and all components of the plexus were blocked completely. Post-operatively, in 95.7% of patients, the spread of hand-agitated LA via the catheter could be seen by color Doppler with ultrasonography. All patients had excellent post-operative analgesia and high degree of satisfaction. There were no complications. CONCLUSION: Contrast enhancement with US guidance during infraclavicular brachial plexus block enables direct visualization of needle and catheter tip location. Our early experience suggests that this leads to successful initial and subsequent post-operative block. Further controlled studies are needed to compare this technique with more prevalent and conventional techniques of catheter insertion.
Asunto(s)
Arteria Axilar/diagnóstico por imagen , Plexo Braquial/diagnóstico por imagen , Cateterismo/métodos , Bloqueo Nervioso/métodos , Ultrasonografía Intervencional/métodos , Extremidad Superior/cirugía , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Medios de Contraste , Estimulación Eléctrica , Femenino , Glucosa/administración & dosificación , Humanos , Inyecciones , Masculino , Persona de Mediana Edad , Estudios ProspectivosRESUMEN
BACKGROUND: Secondary catheter failure has been reported in up to 40% of patients with continuous peripheral nerve blocks resulting in failure to provide pain relief after the initial block wears off. Introduction of stimulating catheters as well as ultrasound for regional anaesthesia has facilitated correct placement of catheter tip, closer to the plexus. This randomized study was conducted to compare the efficacy of continuous infraclavicular brachial plexus blocks using non-stimulating catheter, stimulating catheter and ultrasound-guided catheter placement with nerve stimulation assistance. METHODS: Patients undergoing elective hand surgery were randomly allocated to receive continuous infraclavicular brachial plexus block using non-stimulating catheter [group traditional nerve stimulation (TR)], stimulating catheter [group stimulating catheter (ST)] or ultrasound-guided catheter placement with nerve stimulation assistance [group ultrasound guidance with nerve stimulation assistance (US)]. Motor and sensory blocks were assessed every 5 min and primary block success was determined at 30 min. After resolution of the primary block, threshold stimulating current and resulting response, spread of drug on re-injection as seen ultrasonographically and the capacity to re-establish block was documented. Complications and need for supplement was noted. RESULTS: The primary block success was significantly higher in the US group [96% US, 58% ST, 59% TR (P=0.0005)]. Secondary catheter failure was significantly lower in the US group [9% US, 17% ST, 86% TR (P<0.0001)]. Axillary nerve was blocked more predictably in the US group (100% US, 79% ST, 50% TR (P=0.0003). CONCLUSION: In this study, ultrasound guidance with nerve stimulation assistance significantly improved primary success and reduced secondary catheter failure in continuous infraclavicular brachial plexus blocks.
Asunto(s)
Plexo Braquial/efectos de los fármacos , Plexo Braquial/diagnóstico por imagen , Cateterismo/métodos , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Femenino , Estudios de Seguimiento , Humanos , Masculino , Persona de Mediana Edad , Estudios Prospectivos , UltrasonografíaRESUMEN
Nanocrystalline SnO2 samples of different grain sizes, prepared by inert gas condensation technique (IGCT) and chemical precipitation method and conforming to the tetragonal phase, have been studied by variable speed (3-10 kHz) 119Sn MAS NMR at 11.74 Tesla field. 119Sn solid-state NMR results show that the IGCT prepared samples have good crystallinity and phase purity compared to the samples prepared by the chemical method. The determination of 119Sn chemical shielding parameters (delta iso, delta delta and eta) from slow MAS spectra shows that the 119Sn isotropic chemical shift (delta iso) is strongly influenced at smaller grain sizes, attributable to the change in the O2- local symmetry for the surface 119Sn ions at smaller grain sizes. The observed line widths in MAS spectra are significantly larger than the life-time broadening due to spin-lattice (T1) and spin-spin (T2) relaxation. The 119Sn MAS NMR spectra are thus inhomogeneously broadened by a distribution of isotropic chemical shifts, the line broadening increasing with decrease in grain size.
RESUMEN
We here report on the influence of heteronuclear dipolar decoupling on the (27)Al 3QMAS, 5QMAS, and the double-quantum filter-satellite-transition magic-angle spinning (DQF-STMAS) spectra of a strongly dipolar-coupled system, gibbsite. The requirements for heteronuclear dipolar decoupling increase with the order of coherence evolving in the indirect dimension of a two-dimensional (2D) experiment. The isotropic line width of the high-resolution 2D spectra, in samples like gibbsite, is composed of four parts: the distribution of isotropic shifts (delta(ISO), delta(QIS)), the homogeneous broadening related to the proton-proton flip-flop terms, the (27)Al-(27)Al homonulcear dipolar couplings, and the (1)H-(27)Al heteronuclear dipolar couplings. It is shown that, even in the case of gibbsite, where a strong proton-proton bath exists, the main resolution limiting factor in these experiments resides in the (1)H-(27)Al dipolar interaction.