Age-related changes in sympathetic activity: Biochemical measurements and target organ responses

The aim of this study was to evaluate using several parameters the effect of aging on sympathetic nervous system activity. We measured heart rate, skin conductance level and free and total plasma catecholamines in 60 normal subjects aged 20-80 years, divided into three age groups, in basal supine conditions and in response to standing and to hyperventilation. Basal heart rate was similar in all subjects and failed to correlate with age. Skin conductance level decreased with increasing age and correlated negatively and significantly with age. In response to standing and to hyperventilation, heart rate and skin conductance level increased in all groups but the values attained became lower in older subjects. Basal free and total norepinephrine (NE) and total epinephrine (E) correlated positively and significantly with age. In response to standing, free NE determined at the peak heart rate response, increased significantly only in young subjects. In response to hyperventilation free and total NE increased in all subjects. In conclusion, our study supports and extends previous findings that sympathetic nervous system activity is altered in aging. Moreover, these data also show that biochemical measurements of sympathetic nerve activity do not reflect the same alterations as those involving target organ responses

Diagnostic electrocardiography in epidemiological studies of Chagas' disease: multicenter evaluation of a standardized method

An electrocardiographic recording method with an associated reading guide, designed for epidemiological studies on Chagas' disease, was tested to assess its diagnostic reproducibility. Six cardiologists from five countries each read 100 electrocardiographic (ECG) tracings, including 30 from chronic chagasic patients, then reread them after an interval of 6 months. The readings were blind, with the tracings numbered randomly for the first reading and renumbered randomly for the second reading. The physicians, all experienced in interpreting ECGs from chagasic patients, followed printed instructions for reading the tracings. Reproducibility of the readings was evaluated using the kappa (k) index for concordance. The results showed a high degree of interobserver concordance with respect to the diagnosis of normal vs. abnormal tracings (k = 0.66; SE 0.02). While the interpretations of some categories of ECG abnormalities were highly reproducible, others, especially those having a low prevalence, showed lower levels of concordance. Intraobserver concordance was uniformly higher than interobserver concordance. The findings of this study justify the use by specialists of the recording of readings method proposed for epidemiological studies on Chagas' disease, but warrant caution in the interpretation of some categories of electrocardiographic alterations.<br>Con objeto de evaluar su reproducibilidad diagnóstica, se ensayó un método de registrar resultados electrocardiográficos con una guía para su lectura, diseñado para estudios epidemiológicos de la enfermedad de Chagas. Seis cardiólogos de cinco países interpretaron, cada uno independientemente, los trazos de 100 electrocardiogramas (ECG), incluidos 30 de pacientes chagásicos crónicos, que los mismos cardiólogos releyeron después de un intervalo de 6 meses. Las lecturas se hicieron a ciegas, con los trazos enumerados al azar para la primera interpretación y reenumerados de la misma forma para la segunda lectura. Todos los cardiólogos que participaron en el estudio tenían experiencia en la interpretación de ECG de pacientes chagásicos y siguieron instrucciones impresas para la lectura. La reproducibilidad de las interpretaciones se evaluó por medio del índice kappa (k) de concordancia. Los resultados indicaron un alto grado de concordancia entre observadores con respecto al diagnóstico de gráfico normal frente a anormal (k = 0,66: EE 0,02). En tanto que las interpretaciones de algunas categorías de anormalidades ECG fueron reproducibles en alto grado, otras, especialmente las de baja prevalencia, tuvieron grados menores de concordancia. La concordancia intraobservador fue en todos casos mayor que la interobservador. Los resultados de este estudio justifican el uso por especialistas del método de lectura propuesto para estudios epidemiológicos sobre la enfermedad de Chagas, pero se recomienda interpretar con precaución ciertas categorías de alteraciones electrocardiográficas