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1.
Nature ; 630(8017): 619-624, 2024 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-38898294

RESUMEN

The basal plane of graphene can function as a selective barrier that is permeable to protons1,2 but impermeable to all ions3,4 and gases5,6, stimulating its use in applications such as membranes1,2,7,8, catalysis9,10 and isotope separation11,12. Protons can chemically adsorb on graphene and hydrogenate it13,14, inducing a conductor-insulator transition that has been explored intensively in graphene electronic devices13-17. However, both processes face energy barriers1,12,18 and various strategies have been proposed to accelerate proton transport, for example by introducing vacancies4,7,8, incorporating catalytic metals1,19 or chemically functionalizing the lattice18,20. But these techniques can compromise other properties, such as ion selectivity21,22 or mechanical stability23. Here we show that independent control of the electric field, E, at around 1 V nm-1, and charge-carrier density, n, at around 1 × 1014 cm-2, in double-gated graphene allows the decoupling of proton transport from lattice hydrogenation and can thereby accelerate proton transport such that it approaches the limiting electrolyte current for our devices. Proton transport and hydrogenation can be driven selectively with precision and robustness, enabling proton-based logic and memory graphene devices that have on-off ratios spanning orders of magnitude. Our results show that field effects can accelerate and decouple electrochemical processes in double-gated 2D crystals and demonstrate the possibility of mapping such processes as a function of E and n, which is a new technique for the study of 2D electrode-electrolyte interfaces.


Asunto(s)
Grafito , Protones , Grafito/química , Hidrogenación , Catálisis
2.
Nature ; 616(7958): 719-723, 2023 04.
Artículo en Inglés | MEDLINE | ID: mdl-37076621

RESUMEN

Intelligent transport of molecular species across different barriers is critical for various biological functions and is achieved through the unique properties of biological membranes1-4. Two essential features of intelligent transport are the ability to (1) adapt to different external and internal conditions and (2) memorize the previous state5. In biological systems, the most common form of such intelligence is expressed as hysteresis6. Despite numerous advances made over previous decades on smart membranes, it remains a challenge to create a synthetic membrane with stable hysteretic behaviour for molecular transport7-11. Here we demonstrate the memory effects and stimuli-regulated transport of molecules through an intelligent, phase-changing MoS2 membrane in response to external pH. We show that water and ion permeation through 1T' MoS2 membranes follows a pH-dependent hysteresis with a permeation rate that switches by a few orders of magnitude. We establish that this phenomenon is unique to the 1T' phase of MoS2, due to the presence of surface charge and exchangeable ions on the surface. We further demonstrate the potential application of this phenomenon in autonomous wound infection monitoring and pH-dependent nanofiltration. Our work deepens understanding of the mechanism of water transport at the nanoscale and opens an avenue for the development of intelligent membranes.

3.
Nat Mater ; 16(4): 461-466, 2017 04.
Artículo en Inglés | MEDLINE | ID: mdl-27842073

RESUMEN

The interaction of water with TiO2 is crucial to many of its practical applications, including photocatalytic water splitting. Following the first demonstration of this phenomenon 40 years ago there have been numerous studies of the rutile single-crystal TiO2(110) interface with water. This has provided an atomic-level understanding of the water-TiO2 interaction. However, nearly all of the previous studies of water/TiO2 interfaces involve water in the vapour phase. Here, we explore the interfacial structure between liquid water and a rutile TiO2(110) surface pre-characterized at the atomic level. Scanning tunnelling microscopy and surface X-ray diffraction are used to determine the structure, which is comprised of an ordered array of hydroxyl molecules with molecular water in the second layer. Static and dynamic density functional theory calculations suggest that a possible mechanism for formation of the hydroxyl overlayer involves the mixed adsorption of O2 and H2O on a partially defected surface. The quantitative structural properties derived here provide a basis with which to explore the atomistic properties and hence mechanisms involved in TiO2 photocatalysis.

4.
J Strength Cond Res ; 32(2): 356-363, 2018 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-29369953

RESUMEN

Marcos, MA, Koulla, PM, and Anthos, ZI. Preseason maximal aerobic power in professional soccer players among different divisions. J Strength Cond Res 32(2): 356-363, 2018-The purpose of this study was to examine and compare the anthropometric, maximal oxygen uptake (V[Combining Dot Above]O2max), and positional differences of first division (D1) professional football players from players of second (D2) and third (D3) divisions in Cyprus football leagues. Four hundred twenty-one professional male football players participated in this study. All subjects underwent anthropometric and body composition evaluation. In addition, they performed an incremental cardiopulmonary exercise testing (CPET) on a treadmill for V[Combining Dot Above]O2max evaluation. The results were analyzed using 1-way analysis of variance, between subjects design revealing significant effects among the divisions. Tukey's honest significant difference (HSD) tests demonstrated that players from D1 scored significantly higher on V[Combining Dot Above]O2max and lasted significantly longer on the treadmill than participants of D2 and D3 (p ≤ 0.05). Similar findings were demonstrated when D2 was contrasted against D3 players. Goalkeepers, defenders, and forwards demonstrated significantly higher anthropometric measurements, whereas wingers and midfielders demonstrated significantly higher V[Combining Dot Above]O2max (p ≤ 0.05) than goalkeepers and defenders. The findings of this study clearly demonstrated that cardiovascular fitness, as determined by CPET, is an important fitness parameter that differentiates professional football players who play at a more advanced level. This could be attributed to the different seasonal schedules that allow for longer transition time for lower division players and thus favoring greater detraining effects. Emphasis should be given by fitness professionals on transition period training to minimize the detraining effects especially in lower divisions.


Asunto(s)
Consumo de Oxígeno/fisiología , Fútbol/fisiología , Ejercicio de Calentamiento/fisiología , Adulto , Antropometría , Composición Corporal , Prueba de Esfuerzo , Frecuencia Cardíaca/fisiología , Humanos , Masculino , Reproducibilidad de los Resultados , Adulto Joven
5.
J Chem Phys ; 140(4): 041103, 2014 Jan 28.
Artículo en Inglés | MEDLINE | ID: mdl-25669494

RESUMEN

Ab initio simulations that account for nuclear quantum effects have been used to examine the order-disorder transition in squaric acid, a prototypical H-bonded antiferroelectric crystal. Our simulations reproduce the >100 K difference in transition temperature observed upon deuteration as well as the strong geometrical isotope effect observed on intermolecular separations within the crystal. We find that collective transfer of protons along the H-bonding chains - facilitated by quantum mechanical tunneling - is critical to the order-disorder transition and the geometrical isotope effect. This sheds light on the origin of isotope effects and the importance of tunneling in squaric acid which likely extends to other H-bonded ferroelectrics.

6.
Chem Sci ; 15(2): 516-527, 2024 Jan 03.
Artículo en Inglés | MEDLINE | ID: mdl-38179530

RESUMEN

It has long been known that the dielectric constant of confined water should be different from that in bulk. Recent experiments have shown that it is vanishingly small, however the origin of the phenomenon remains unclear. Here we used ab initio molecular dynamics simulations (AIMD) and AIMD-trained machine-learning potentials to understand water's structure and electronic properties underpinning this effect. For the graphene and hexagonal boron-nitride substrates considered, we find that it originates in the spontaneous anti-parallel alignment of the water dipoles in the first two water layers near the solid interface. The interfacial layers exhibit net ferroelectric ordering, resulting in an overall anti-ferroelectric arrangement of confined water. Together with constrained hydrogen-bonding orientations, this leads to much reduced out-of-plane polarization. Furthermore, we directly contrast AIMD and simple classical force-field simulations, revealing important differences. This work offers insight into a property of water that is critical in modulating surface forces, the electric-double-layer formation and molecular solvation, and shows a way to compute it.

7.
Nat Mater ; 10(10): 794-8, 2011 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-21892176

RESUMEN

Resolving the atomic structure of the surface of ice particles within clouds, over the temperature range encountered in the atmosphere and relevant to understanding heterogeneous catalysis on ice, remains an experimental challenge. By using first-principles calculations, we show that the surface of crystalline ice exhibits a remarkable variance in vacancy formation energies, akin to an amorphous material. We find vacancy formation energies as low as ~0.1-0.2 eV, which leads to a higher than expected vacancy concentration. Because a vacancy's reactivity correlates with its formation energy, ice particles may be more reactive than previously thought. We also show that vacancies significantly reduce the formation energy of neighbouring vacancies, thus facilitating pitting and contributing to pre-melting and quasi-liquid layer formation. These surface properties arise from proton disorder and the relaxation of geometric constraints, which suggests that other frustrated materials may possess unusual surface characteristics.

8.
Phys Chem Chem Phys ; 13(44): 19988-96, 2011 Nov 28.
Artículo en Inglés | MEDLINE | ID: mdl-22008902

RESUMEN

Using a combination of X-ray photoemission and near-edge X-ray absorption spectroscopy (NEXAFS) as well as density-functional theory (DFT), we have investigated the adsorption of acetone on ice in the temperature range from 218 to 245 K. The adsorption enthalpy determined from experiment (45 kJ mol(-1)) agrees well with the adsorption energy predicted by theory (41 to 44 kJ mol(-1)). Oxygen K-edge NEXAFS spectra indicate that the presence of acetone at the ice surface does not induce the formation of a pre-melted layer at temperatures up to 243 K. DFT calculations show that the energetically most favored adsorption geometry for acetone on ice is with the molecular plane almost parallel to the surface.

9.
S Afr Med J ; 110(3): 204-209, 2020 Feb 26.
Artículo en Inglés | MEDLINE | ID: mdl-32657697

RESUMEN

BACKGROUND: South Africa (SA) has very low and unchanging organ donation rates. A key point in the pathway of organ donation is obtaining informed consent from the family, which is necessary before organ donation can proceed. There is no published SA research on the consent rate and factors that influence this. OBJECTIVES: To describe the number of requests for consent and factors influencing this process in the SA context. METHODS: A prospective descriptive study was performed of all requests to families for organ donation in Western Cape Province, SA, by Groote Schuur Hospital (state sector), Red Cross War Memorial Children's Hospital (state sector) and Netcare (private sector) transplant co-ordinators from 1 May 2017 to 1 May 2018 to describe factors influencing consent rates. RESULTS: The 6 co-ordinators (3 state sector and 3 private sector) recorded data of 83 consecutive families approached in 16 hospitals over the 1-year period. Consent to organ donation was granted for 23 family requests (n=18 (state sector); n=5 (private sector)). The number of families approached was greater in the state sector (n=74) than in the private sector (n=9). The overall consent rate was 27.7% (24.3% (state sector); 55.5% (private sector)). The majority of referrals came from trauma and emergency units (n=55; 66.3%) and very few from intensive care units (n=25; 30.1%). Immediate fluid resuscitation was required in 56 (67.5%) potential donors. The majority of families (n=74; 89.2%) were receptive to the organ donation request, independent of their ultimate decision regarding donation. The main reason given for refusing to consent was that it was against their religion (n=21) or culture (n=18). CONCLUSIONS: This study showed that the number of families approached for consent to organ donation were low in the Western Cape (lower in the private sector), with a low consent rate (lower in the state sector). Donor management by clinical teams needs to be ongoing and active during the consent process. Consent discussions (and public awareness initiatives) need to be sensitive to and deal with religious and cultural reservations about organ donation.


Asunto(s)
Obtención de Tejidos y Órganos/estadística & datos numéricos , Cultura , Familia , Humanos , Consentimiento Informado , Estudios Prospectivos , Religión , Sudáfrica
10.
Nat Commun ; 11(1): 1097, 2020 02 27.
Artículo en Inglés | MEDLINE | ID: mdl-32107369

RESUMEN

Manipulating the surface energy, and thereby the wetting properties of solids, has promise for various physical, chemical, biological and industrial processes. Typically, this is achieved by either chemical modification or by controlling the hierarchical structures of surfaces. Here we report a phenomenon whereby the wetting properties of vermiculite laminates are controlled by the hydrated cations on the surface and in the interlamellar space. We find that vermiculite laminates can be tuned from superhydrophilic to hydrophobic simply by exchanging the cations; hydrophilicity decreases with increasing cation hydration free energy, except for lithium. The lithium-exchanged vermiculite laminate is found to provide a superhydrophilic surface due to its anomalous hydrated structure at the vermiculite surface. Building on these findings, we demonstrate the potential application of superhydrophilic lithium exchanged vermiculite as a thin coating layer on microfiltration membranes to resist fouling, and thus, we address a major challenge for oil-water separation technology.

11.
J Hum Hypertens ; 31(12): 795-800, 2017 12.
Artículo en Inglés | MEDLINE | ID: mdl-28972573

RESUMEN

This pilot study evaluated the efficacy of a Hypertension Prevention Program (HPP) administered through a mobile application platform with human coaching (app) on reduction in blood pressure and weight in 50 adults with prehypertension or hypertension. Participants were recruited into a 24-week mobile application intervention to administer the HPP between January 2016 and July 2016. Dietary elements of the programme were based on the Dietary Approaches to Stop Hypertension. The programme included in-app human coaching with bi-weekly phone calls, meal logging, blood pressure tracking and educational material. Main outcome variables included change in systolic and diastolic blood pressure, hypertension category, and weight loss. Data were analysed between October 2016 and December 2016. The HPP yielded overall improvements in weight (-3.04±4.04 kg, P=<0.001), diastolic blood pressure (-5.06±11.89 mm Hg, P=0.004), and hypertension category (-0.48±0.74 mm Hg, P=<0.001). Sustained engagement of 80% resulted in significant reductions in systolic blood pressure (-7.75±12.56, P=<0.001) and weight (-3.73±4.01 kg, P<0.001) for programme completers, contributing to hypertension category change (-0.58±0.64 mm Hg, P<0.001). Mobile delivery of a lifestyle intervention for hypertension prevention showed short-term potential to reduce risk of hypertension, supporting the need for longer studies to investigate the use of mHealth lifestyle modification to reduce the risk of hypertension, a public health priority.


Asunto(s)
Hipertensión/prevención & control , Aplicaciones Móviles/estadística & datos numéricos , Adulto , Presión Sanguínea , Femenino , Humanos , Masculino , Persona de Mediana Edad , Proyectos Piloto , Pérdida de Peso
12.
Circulation ; 101(15): 1819-25, 2000 Apr 18.
Artículo en Inglés | MEDLINE | ID: mdl-10769283

RESUMEN

BACKGROUND: The aim of this study was to assess the sigmoid line of elasticity in the human aorta. METHODS AND RESULTS: The pressure-diameter relation was measured in the descending aorta in 120 subjects. In an additional group of 6 subjects, transient vena caval occlusion produced 5 sets of pressure-diameter data. We found that the best fit curve of the pooled pressure-diameter data was a third-order polynomial. A polynomial equation was used to calculate the sigmoid line of elasticity in the entire population and after the administration of diltiazem (15 patients) or enalaprilat (10 patients). The sigmoid line of elasticity was significantly different with respect to age (P<0.001), history of hypertension (P<0.004), and hypercholesterolemia (P<0.02). The difference between the transition point and the peak systolic pressure was increased in normal subjects compared with patients (P<0.0001). The sigmoid line shifted leftward and upward with diltiazem, but it remained unchanged with enalaprilat. During an average of 3 years of follow-up, 19 of 88 patients developed stroke (n=4), unstable angina (n=8), acute myocardial infarction (n=4), or acute pulmonary edema (n=3). CONCLUSIONS: This approach provides a quantitative evaluation of the aortic line of elasticity, which can differentiate the intrinsic from the extrinsic aortic elastic properties. Furthermore, it is a powerful and independent risk factor for cardiovascular events.


Asunto(s)
Aorta/fisiología , Presión Sanguínea/fisiología , Enfermedad Coronaria/fisiopatología , Interpretación Estadística de Datos , Diltiazem/farmacología , Elasticidad , Enalaprilato/farmacología , Insuficiencia Cardíaca/fisiopatología , Humanos , Hipertensión/fisiopatología , Análisis de Regresión , Factores de Riesgo , Vasodilatadores/farmacología
13.
Transplantation ; 72(1): 141-7, 2001 Jul 15.
Artículo en Inglés | MEDLINE | ID: mdl-11468549

RESUMEN

BACKGROUND: Human cytomegalovirus (HCMV) reactivation and disease remain relatively common in lung transplant recipients (LTR) despite the use of ganciclovir prophylaxis protocols for all HCMV at-risk patients. The specific aims of this study were to (1) describe the HCMV DNA viral load in the peripheral blood leukocytes (PBL) of a cohort of LTR during the first 6 months after lung transplantation; (2) prospectively determine whether HCMV DNA viral load predicts episodes of HCMV pneumonitis in LTR; and (3) study the effect of ganciclovir on HCMV viral load. METHODS: Competitive polymerase chain reaction using an internal standard and fluorometric detection were used to quantitate HCMV DNA in the PBL of a cohort of 26 LTR monthly for the first 6 months after transplantation (145 samples). All patients were treated with standard triple immunosuppression, and ganciclovir prophylaxis was given to all at-risk LTR (donor or recipient HCMV seropositive) for at least 8 weeks after transplantation. RESULTS: Thirteen episodes of histopathologically proven HCMV pneumonitis in nine subjects occurred during follow-up with a wide intra- and intersubject variation in the HCMV DNA PBL levels. HCMV detection had a sensitivity of 92% and specificity of 76% for HCMV pneumonitis (negative likelihood ratio, 9.5), whereas greater than 10-fold increases in HCMV DNA load had a specificity of 93% and sensitivity of 67% (positive likelihood ratio, 11). HCMV DNA detection had an adjusted odds ratio for HCMV pneumonitis of 107 (95% confidence interval, 14-821; P<0.005). In those with detectable HCMV DNA in PBL (n=44), HCMV DNA levels were 4.4 (95% confidence interval, 1.2-16.8) times higher in those with HCMV pneumonitis than in those without HCMV pneumonitis. Although ganciclovir treatment was very effective in treating HCMV pneumonitis and suppressing HCMV DNA levels, thrice weekly ganciclovir prophylaxis only partially controlled HCMV DNA levels and did not eliminate HCMV pneumonitis risk as three patients developed HCMV pneumonitis while on this regimen. CONCLUSIONS: HCMV DNA detection, absolute levels, and relative change from baseline in the PBL of LTR correlate with HCMV pneumonitis episodes and may be a useful intermediate outcome measure of the efficacy of ganciclovir prophylaxis and treatment strategies.


Asunto(s)
Infecciones por Citomegalovirus , Citomegalovirus/genética , ADN Viral/análisis , Leucocitos/virología , Trasplante de Pulmón , Neumonía/virología , Adulto , Antivirales/uso terapéutico , Sangre/virología , Estudios de Cohortes , Citomegalovirus/efectos de los fármacos , Citomegalovirus/aislamiento & purificación , Infecciones por Citomegalovirus/sangre , Infecciones por Citomegalovirus/genética , Infecciones por Citomegalovirus/prevención & control , Infecciones por Citomegalovirus/virología , Femenino , Ganciclovir/uso terapéutico , Humanos , Masculino , Persona de Mediana Edad , Neumonía/genética , Neumonía/prevención & control , Periodo Posoperatorio , Carga Viral
14.
Am J Cardiol ; 70(18): 1407-11, 1992 Dec 01.
Artículo en Inglés | MEDLINE | ID: mdl-1442609

RESUMEN

Myocardial ischemia may decrease conduction velocity and produce QRS prolongation in the surface electrocardiogram. In cases with normal intraventricular conduction, areas of the myocardium contributing to the development of the S wave receive blood from all 3 major coronary arteries, whereas in left anterior hemiblock or right bundle branch block, most of the blood supply to the areas of the myocardium contributing to the development of the S wave is from the left anterior descending (LAD) coronary artery. To test the hypothesis that the S wave will be prolonged with exercise only in patients with LAD coronary artery stenosis and left anterior hemiblock or right bundle branch block, 88 patients with normal intraventricular conduction, 66 with left anterior hemiblock and 36 with right bundle branch block were studied. Sixty-four, 32 and 21 patients had LAD, right and left circumflex coronary artery stenoses, respectively. In patients with normal coronary arteries, S-wave duration decreased with exercise regardless of the status of ventricular conduction. In patients with coronary artery disease and normal intraventricular conduction, the S wave was prolonged slightly with exercise, but in those with left anterior hemiblock and right bundle branch block, it was prolonged significantly (12.5 +/- 6 and 10.4 ms, respectively) only in those with LAD, but not in those with circumflex or right coronary artery stenosis. S-wave prolongation in patients with LAD coronary artery stenosis and left anterior hemiblock or right bundle branch block most likely is related to exercise-induced ischemia in the areas of the myocardium contributing to the development of the S wave.


Asunto(s)
Bloqueo de Rama/fisiopatología , Enfermedad Coronaria/fisiopatología , Vasos Coronarios/patología , Electrocardiografía , Prueba de Esfuerzo , Bloqueo Cardíaco/fisiopatología , Presión Sanguínea , Bloqueo de Rama/complicaciones , Angiografía Coronaria , Enfermedad Coronaria/complicaciones , Enfermedad Coronaria/diagnóstico por imagen , Enfermedad Coronaria/patología , Femenino , Bloqueo Cardíaco/complicaciones , Frecuencia Cardíaca , Humanos , Masculino , Persona de Mediana Edad
15.
Bone Marrow Transplant ; 32(8): 795-800, 2003 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-14520424

RESUMEN

Cytomegalovirus viral load measurement is a powerful new tool for monitoring of CMV disease; however, the optimal strategy for use is unknown. Weekly plasma CMV viral loads and CMV-related outcomes were monitored in 46 consecutive allogeneic bone marrow transplantation (BMT) recipients receiving standardised antiviral prophylaxis. A total of 412 CMV viral loads were quantitated in the first 100 days post transplantation with 77 positive samples (19%) in 20 patients (43%). No patient with all negative CMV viral load results developed CMV disease. Two of three patients with highly positive CMV viral loads (first positive < or =30 days post transplant, maximum viral load > or =5000 copies/ml, and > or =50% of samples positive) developed CMV disease. A total of 17 patients with positive CMV viral loads, who did not meet the criteria for highly positive, did not develop CMV disease. CMV viral load detection was higher in recipients who were CMV sero-positive. In conclusion, CMV disease did not occur in the setting of a persistently negative CMV viral load. A positive CMV viral load result occurred commonly after allogeneic BMT, even in patients receiving antiviral prophylaxis.


Asunto(s)
Antivirales/administración & dosificación , Trasplante de Médula Ósea/efectos adversos , Infecciones por Citomegalovirus/diagnóstico , Infecciones por Citomegalovirus/prevención & control , Ganciclovir/administración & dosificación , Carga Viral , Enfermedad Aguda , Adolescente , Adulto , Enfermedad Crónica , Infecciones por Citomegalovirus/tratamiento farmacológico , Femenino , Estudios de Seguimiento , Enfermedad Injerto contra Huésped/diagnóstico , Enfermedad Injerto contra Huésped/mortalidad , Humanos , Masculino , Persona de Mediana Edad , Estudios Prospectivos
16.
Int J Cardiol ; 71(1): 49-56, 1999 Sep 30.
Artículo en Inglés | MEDLINE | ID: mdl-10522564

RESUMEN

This study was undertaken to investigate the ability of the exercise-induced ST depression in lead V5 and concomitant ST elevation in lead aVR for the identification of the significantly narrowed coronary artery in patients with single vessel disease. We studied 229 consecutive patients who developed the aforementioned exercise-induced electrocardiographic changes. All underwent Thallium-201 scintigraphy and coronary arteriography. Patients were divided into three groups. In group A, 58 patients with ST depression in V5 and ST elevation in aVR, in group B 149 patients with ST depression in V5 without ST elevation in aVR, and in group C 22 patients with ST elevation in aVR without ST depression in V5 induced with exercise, were included. In group A, 81% of the patients while in group B, 29% and in group C only 18% of the patients had left anterior descending artery disease. According to Thallium-201 scintigraphy, 80% of the group A, 27% of the group B and 12% of the group C patients developed myocardial ischemia in areas supplied by the left anterior descending artery. Thus, exercise-induced ST depression in V5 and concomitant ST elevation in aVR, may detect left anterior descending artery significant stenosis in patients with single vessel disease.


Asunto(s)
Enfermedad Coronaria/diagnóstico , Electrocardiografía , Radioisótopos de Talio , Adulto , Anciano , Cateterismo Cardíaco , Angiografía Coronaria , Enfermedad Coronaria/fisiopatología , Electrocardiografía/métodos , Electrofisiología , Prueba de Esfuerzo , Femenino , Humanos , Masculino , Persona de Mediana Edad , Tomografía Computarizada de Emisión de Fotón Único
17.
Clin Cardiol ; 21(8): 585-90, 1998 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-9702386

RESUMEN

BACKGROUND: Heart rate variability (HRV) analysis is problematic during maximal treadmill exercise testing (ET) due to rapidly changing heart rate. HYPOTHESIS: The aim of this study was to assess HRV spectral components during treadmill ET in patients with coronary artery disease (CAD) and in healthy controls, and to search for possible differences between the two groups. METHODS: Thirty patients with CAD and 30 age-matched healthy controls underwent symptom-limited ET and continuous electrocardiographic monitoring. For adequate assessment of HRV during maximal ET, we calculated the HRV measures [normalized units (NU)]--low-frequency (0.040-0.150 Hz) power (LF), high-frequency (0.150-0.400 Hz) power (HF), and the LF/HF ratio--from all the sequential stages of the ET with limited changes (20 beats/min) in heart rate (stress 80-100, 100-120, 120-140, 140-160, 160-180/recovery 180-160, 160-140, 140-120, 120-100, 100-80). RESULTS: Both LF and HF were found to decrease gradually during ET and to increase during the recovery period in both patients and controls (p < 0.001). LF values were higher during the recovery period than during the respective stages of exercise time in both patients and controls, and LF/HF ratio was higher during recovery in patients only. CONCLUSIONS: During maximal ET (1) vagal tone withdraws during the exercise time and increases during the recovery period; (2) the sympathetic activity predominates during the recovery period, especially in patients with CAD and exercise-induced myocardial ischemia. This finding raises the possibility of ischemia-induced cardiocardiac sympathetic excitatory reflexes.


Asunto(s)
Enfermedad Coronaria/diagnóstico , Isquemia Miocárdica/fisiopatología , Reflejo/fisiología , Nervio Vago/fisiopatología , Estudios de Casos y Controles , Enfermedad Coronaria/fisiopatología , Electrocardiografía , Electrocardiografía Ambulatoria , Prueba de Esfuerzo , Femenino , Frecuencia Cardíaca/fisiología , Humanos , Masculino , Persona de Mediana Edad
18.
Clin Cardiol ; 22(6): 403-8, 1999 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-10376179

RESUMEN

BACKGROUND: ST-segment changes and QRS prolongation are electrocardiographic (ECG) markers of myocardial ischemia. HYPOTHESIS: This study was undertaken to investigate the appearance of QRS duration changes with or without concomitant ST-segment changes during a typical anginal episode. METHODS: For this purpose, 126 patients underwent 12-lead surface ECG and signal-averaged electrocardiogram (SAECG) during typical anginal pain as well as at the time the patient was asymptomatic. In both periods, QRS duration and ST-segment changes were evaluated. All patients underwent cardiac catheterization. RESULTS: Of the 126 patients, 108 (86%) had coronary artery disease (CAD), whereas the remaining 18 (14%) patients had normal coronary arteriograms. During typical anginal pain, 75 of the 108 (70%) patients with CAD and 2 of the 18 (11%) patients with normal coronary arteriograms developed QRS prolongation, whereas 60 of the 108 (56%) patients with CAD and 2 of the 18 (11%) patients with normal coronary vessels developed ST-segment changes. Thus, the sensitivities of QRS prolongation measured by SAECG and of ST-segment changes on the surface ECG for the detection of myocardial ischemia were found to be 70 and 56%, respectively, (p < 0.01), whereas the specificities were both found to be 89% (p = NS). CONCLUSIONS: During typical anginal pain, QRS prolongation on the SAECG is more sensitive than are ST-segment changes on the ECG for the detection of myocardial ischemia.


Asunto(s)
Electrocardiografía , Isquemia Miocárdica/diagnóstico , Adulto , Anciano , Femenino , Humanos , Masculino , Persona de Mediana Edad , Síndromes de Preexcitación/diagnóstico , Sensibilidad y Especificidad
19.
Parasite ; 8(1): 11-20, 2001 Mar.
Artículo en Francés | MEDLINE | ID: mdl-11304945

RESUMEN

Three surveys on canine leishmaniasis were carried out in Cyprus (1993, 1998 and 1999) emphasise the presence of eleven species of phlebotomine sandflies: Phlebotomus (Phlebotomus) papatasi, P. (Paraphlebotomus) alexandri, P. (Pa.) jacusieli (first mention in Cyprus), P. (Pa.) sergenti, P. (Larroussius) galilaeus, P. (L.) tobbi, P. (Transphlebotomus) economidesi, P. (T.) mascittii, Sergentomyia (Sergentomyia) azizi (its specific statute is validated by the authors), S. (S.) fallax et S. (S.) minuta. P. (Adlerius) kyreniae was not caught during the surveys. The authors propose hypothesis of settlement of the island by phlebotomine sandflies according this species inventory. A first migration period took probably place during the Miocene time and a second one during the Pleistocene time.


Asunto(s)
Phlebotomus/clasificación , Animales , Chipre , Femenino , Geografía , Insectos Vectores/parasitología , Leishmania infantum/aislamiento & purificación , Masculino , Phlebotomus/anatomía & histología , Phlebotomus/parasitología , Especificidad de la Especie
20.
Parasite ; 7(2): 143-6, 2000 Jun.
Artículo en Francés | MEDLINE | ID: mdl-10887662

RESUMEN

During two surveys conducted in Cyprus (August 1998 and September 1999), 2,910 phlebotomine sandflies females were caught by CDC miniature light traps then dissected under binocular and examined on microscope. Eleven species were identified: Phlebotomus papatasi, P. sergenti, P. jacusieli, P. alexandri, P. tobbi, P. galilaeus, P. mascittii, P. economidesi, Sergentomyia fallax, S. minuta et S. azizi. The Larroussius species (P. galilaeus and P. tobbi) are the most abundant (more than 60% of our captures). Promastigotes were isolated from one specimen identified as P. tobbi. A Leishmania stock was successfully cultured and identified by isoenzyme characterisation as belonging to L. infantum zymodeme MON 1. The same zymodeme was isolated and identified from four dogs too. Because of the absence of usual vectors of L. infantum in the eastern part of the Mediterranean basin (P. neglectus and P. syriacus), and according to its distribution in Cyprus, P. tobbi constitute certainly a good local vector. It seems to be not very anthropophilic, that could explain the very few human cases.


Asunto(s)
Leishmania infantum/aislamiento & purificación , Phlebotomus/parasitología , Animales , Chipre/epidemiología , Enfermedades de los Perros/epidemiología , Enfermedades de los Perros/parasitología , Perros , Humanos , Leishmaniasis Visceral/epidemiología , Leishmaniasis Visceral/parasitología , Leishmaniasis Visceral/veterinaria , Phlebotomus/clasificación
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