Effects of Orthostatism and Hemodialysis on Mean Heart Period and Fractal Heart Rate Properties of Chronic Renal Failure Patients.

The aim of this work was to evaluate the short-term fractal index (α1 ) of heart rate variability (HRV) in chronic renal failure (CRF) patients by identifying the effects of orthostatism and hemodialysis (HD), and by evaluating the correlation between α1 and the mean RR interval from sinus beats (meanNN). HRV time series were derived from ECG data of 19 CRF patients and 20 age-matched healthy subjects obtained at supine and orthostatic positions (lasting 5 min each). Data from CRF patients were collected before and after HD. α1 was calculated from each time series and compared by analysis of variance. Pearson's correlations between meanNN and α1 were calculated using the data from both positions by considering three groups: healthy subjects, CRF before HD and CRF after HD. At supine position, α1 of CRF patients after HD (1.17 ± 0.30) was larger (P < 0.05) than in healthy subjects (0.89 ± 0.28) but not before HD (1.10 ± 0.34). α1 increased (P < 0.05) in response to orthostatism in healthy subjects (1.29 ± 0.26) and CRF patients after HD (1.34 ± 0.31), but not before HD (1.25 ± 0.37). Whereas α1 was correlated (P < 0.05) with the meanNN of healthy subjects (r = -0.562) and CRF patients after HD (r = -0.388), no significance in CRF patients before HD was identified (r = 0.003). Multiple regression analysis confirmed that α1 was mainly predicted by the orthostatic position (in all groups) and meanNN (healthy subjects and patients after HD), showing no association with the renal disease condition in itself. In conclusion, as in healthy subjects, α1 of CRF patients correlates with meanNN after HD (indicating a more irregular-like HRV behavior at slower heart rates). This suggests that CRF patients with stable blood pressure preserve a regulatory adaptability despite a shifted setting point of the heart period (i.e., higher heart rate) in comparison with healthy subjects.

Preserved autonomic heart rate modulation in chronic renal failure patients in response to hemodialysis and orthostatism.

BACKGROUND: The aim of this work was to measure the impact of active orthostatism and hemodialysis (HD) upon heart rate variability (HRV) in chronic renal failure (CRF) patients before and after HD. METHODS: Nineteen healthy subjects (age 27 ± 8 years old, 13 were female) and 19 unmedicated CRF patients with HD thrice per week (average HD vintage = 12 months, age 32 ± 9 years old, 11 were female) were included. Five-minute length HRV time series were obtained during supine position and orthostatism. Recordings from CRF patients were obtained before and after HD. Time domain and frequency domain HRV indexes were compared by analysis of variance. The correlation between each HRV index and change in sympathetic weighting induced by different maneuvers was tested by Kendall's Tau correlation. A p value <0.05 was considered statistically significant. RESULTS: HRV indexes which are associated with sympathetic activity increased in response to orthostatism in the healthy group, e.g., low-frequency to high-frequency (LF/HF) ratio, Ln (LF/HF) = -0.3 ± 0.9 versus 0.9 ± 0.9. CRF patients before HD had higher sympathetic weighting than healthy participants, even in supine position, Ln (LF/HF) = 0.6 ± 1.0, but such a difference was accentuated during orthostatism, Ln (LF/HF) = 1.5 ± 1.0, and after HD: Ln (LF/HF) = 0.8 ± 1.3 (supine position) and 2.5 ± 2.1 (orthostatism). All HRV indexes were associated with increments in sympathetic weighting between maneuvers (Kendall's correlations absolute values ≥ 0.24). CONCLUSION: Unmedicated young CRF patients treated with hemodynamically stable maintenance HD showed preserved capacity of autonomic response (with gradual sympathetic increases) induced by cardiovascular challenges such as orthostatism and HD.

Phase resetting, phase locking, and bistability in the periodically driven saline oscillator: experiment and model.

The saline oscillator consists of an inner vessel containing salt water partially immersed in an outer vessel of fresh water, with a small orifice in the center of the bottom of the inner vessel. There is a cyclic alternation between salt water flowing downwards out of the inner vessel into the outer vessel through the orifice and fresh water flowing upwards into the inner vessel from the outer vessel through that same orifice. We develop a very stable (i.e., stationary) version of this saline oscillator. We first investigate the response of the oscillator to periodic forcing with a train of stimuli (period=Tp) of large amplitude. Each stimulus is the quick injection of a fixed volume of fresh water into the outer vessel followed immediately by withdrawal of that very same volume. For Tp sufficiently close to the intrinsic period of the oscillator (T0) , there is 1:1 synchronization or phase locking between the stimulus train and the oscillator. As Tp is decreased below T0 , one finds the succession of phase-locking rhythms: 1:1, 2:2, 2:1, 2:2, and 1:1. As Tp is increased beyond T0 , one encounters successively 1:1, 1:2, 2:4, 2:3, 2:4, and 1:2 phase-locking rhythms. We next investigate the phase-resetting response, in which injection of a single stimulus transiently changes the period of the oscillation. By systematically changing the phase of the cycle at which the stimulus is delivered (the old phase), we construct the new-phase--old-phase curve (the phase transition curve), from which we then develop a one-dimensional finite-difference equation ("map") that predicts the response to periodic stimulation. These predicted phase-locking rhythms are close to the experimental findings. In addition, iteration of the map predicts the existence of bistability between two different 1:1 rhythms, which was then searched for and found experimentally. Bistability between 1:1 and 2:2 rhythms is also encountered. Finally, with one exception, numerical modeling with a phenomenologically derived Rayleigh oscillator reproduces all of the experimental behavior.

Reentrant waves in a ring of embryonic chick ventricular cells imaged with a Ca2+ sensitive dye.

According to the classic model initially formulated by Mines, reentrant cardiac arrhythmias may be associated with waves circulating in a ring geometry. This study was designed to study the dynamics of reentry in a ring geometry of cardiac tissue culture. Reentrant calcium waves in rings of cultured embryonic chick cardiac myocytes were imaged using a macroscope to monitor the fluorescence of intracellular Calcium Green-1 dye. The rings displayed a variety of stable rhythms including pacemaker activity and spontaneous reentry. Waves originating from a localized pacemaker could lead to reentry as a consequence of unidirectional block. In addition, more complex patterns were observed due to the interactions between reentrant and pacemaker rhythms. These rhythms included instances in which pacemakers accelerated the reentrant rhythm, and instances in which the excitation was blocked in the vicinity of pacemakers. During reentrant activity an appropriately timed electrical stimulus could induce resetting of activity or cause complete annihilation of the propagating waves. This experimental preparation reveals many spontaneously occuring complex rhythms. These complex rhythms are hypothesized to reflect interactions between spontaneous pacemakers, wave propagation, refractory period, and overdrive suppression. This preparation may serve as a useful model system to further investigate complex dynamics arising during reentrant rhythms in cardiac tissue.

Alternans and higher-order rhythms in an ionic model of a sheet of ischemic ventricular muscle.

Life-threatening arrhythmias such as ventricular tachycardia and fibrillation often occur during acute myocardial ischemia. During the first few minutes following coronary occlusion, there is a gradual rise in the extracellular concentration of potassium ions ([K(+)](0)) within ischemic tissue. This elevation of [K(+)](0) is one of the main causes of the electrophysiological changes produced by ischemia, and has been implicated in inducing arrhythmias. We investigate an ionic model of a 3 cmx3 cm sheet of normal ventricular myocardium containing an ischemic zone, simulated by elevating [K(+)](0) within a centrally-placed 1 cmx1 cm area of the sheet. As [K(+)](0) is gradually raised within the ischemic zone from the normal value of 5.4 mM, conduction first slows within the ischemic zone and then, at higher [K(+)](0), an arc of block develops within that area. The area distal to the arc of block is activated in a delayed fashion by a retrogradely moving wavefront originating from the distal edge of the ischemic zone. With a further increase in [K(+)](0), the point eventually comes where a very small increase in [K(+)](0) (0.01 mM) results in the abrupt transition from a global period-1 rhythm to a global period-2 rhythm in the sheet. In the peripheral part of the ischemic zone and in the normal area surrounding it, there is an alternation of action potential duration, producing a 2:2 response. Within the core of the ischemic zone, there is an alternation between an action potential and a maintained small-amplitude response ( approximately 30 mV in height). With a further increase of [K(+)](0), the maintained small-amplitude response turns into a decrementing subthreshold response, so that there is 2:1 block in the central part of the ischemic zone. A still further increase of [K(+)](0) leads to a transition in the sheet from a global period-2 to a period-4 rhythm, and then to period-6 and period-8 rhythms, and finally to a complete block of propagation within the ischemic core. When the size of the sheet is increased to 4 cmx4 cm (with a 2 cmx2 cm ischemic area), one observes essentially the same sequence of rhythms, except that the period-6 rhythm is not seen. Very similar sequences of rhythms are seen as [K(+)](0) is increased in the central region (1 or 2 cm long) of a thin strand of tissue (3 or 4 cm long) in which propagation is essentially one-dimensional and in which retrograde propagation does not occur. While reentrant rhythms resembling tachycardia and fibrillation were not encountered in the above simulations, well-known precursors to such rhythms (e.g., delayed activation, arcs of block, two-component upstrokes, retrograde activation, nascent spiral tips, alternans) were seen. We outline how additional modifications to the ischemic model might result in the emergence of reentrant rhythms following alternans. (c) 2000 American Institute of Physics.

[Arrhythmic activity of the papillary muscle induced by high frequency stimulation: n1 rhythms,transition forms and hysteresis]. / Actividad rítmica del músculo papilar inducida por estimulación de alta frecuencia: ritmos n:1, formas de transición e histéresis.

Cardiac tissues are able to work within a wide range of frequencies to respond to the changing requirements an organism may have. However, during these frequency variations and under certain pathologic conditions arrhythmias such as blocks, tachycardia, fibrillation, etc, may arise some with fatal consequences. For this reason several experimental procedures have been developed that have shown to be useful in studying whole heart properties, or as an alternative from portions of it when changes in its work rate are imposed. This study reports different phenomena occurring in the papillary muscle of the guinea pig heart when stimulated at very high frequency, of several tens of pps, while analyzing its responses during gradual increments starting at 1 (pulses per second). We found that in our conditions papillary muscles display N:1 rhythms with progressive higher N; further more we found that between one and the next rhythm diverse transition patterns appear, among them a new one that we have named "burst pattern". Finally we show that our system exhibits a generalized process of hysteresis by frequency, being this the first report for guinea pig cardiac tissue and the first one to show also the presence of several hysteresis loops in the same experiment. Due to the large volume of generated data we used a faster and easier way to analyze and display them, based on the fast Fourier transform (FFT). The method is briefly described.

Nonlinear dynamics of heart rate variability in response to orthostatism and hemodialysis in chronic renal failure patients: recurrence analysis approach.

We studied the response of heart rate variability to hemodialysis and orthostatism using traditional linear indexes and 9 recurrence quantification analysis indexes to reveal changes in the heart rate dynamics. Twenty healthy subjects and 19 chronic renal failure patients treated with hemodialysis thrice a week were included. Five-minute heart rate variability time series were obtained during supine position (clinostatism) and orthostatism from each participant; recordings in renal patients were repeated after hemodialysis. Linear indexes were consistent with sympathetic predominance in response to orthostatism in the control group. Renal patients before hemodialysis showed increased sympathetic predominance in clinostatism, with further increase in orthostatism and hemodialysis. In response to orthostatism, 4 recurrence indexes changed in the control group, while in renal patients any of them changed before hemodialysis and 1 changed after hemodialysis. In clinostatism, renal patients (both before and after hemodialysis) had higher laminarity, trapping time, and recurrence time than the control group. Recurrence indexes showed that the heart rate dynamics in renal patients are different from healthy subjects, suggesting loss of access to some regulatory conditions. These findings are consistent with reports of sympathetic stimulation induced by hemodialysis and active standing.

Actividad rítmica del músculo papilar inducida por estimulación de alta frecuencia: ritmos n:1, formas de transición e histéresis / Arrhytmic actiitty of the papilary muscle induced by high frecuency stimulatiion: rhythm n:1, transition forms and hysteresis

Los tejidos cardíacos son capaces de trabajar en un amplio intervalo de frecuencias con el fin de atender las distintas demandas que el organismo impone al sistema cardiovascular. Sin embargo, bajo un régimen de cambios de frecuencia y con ciertas condiciones patológicas, pueden desarrollarse arritmias, como bloqueos, taquicardias, fibrilaciones, etc. de posibles consecuencias fatales. Esto motiva la realización de diversos arreglos experimentales en los cuales se explora el comportamiento del corazón, o de regiones de éste. En este artículo reportamos diversos fenómenos que ocurren en el músculo papilar de cobayo cuando se le estimula eléctricamente, desde una frecuencia basal de un pulso por segundo (pps) hasta frecuencias muy altas, de varias decenas de pps, pero incrementando paulatinamente la frecuencia de estimulación. Describimos que en nuestras condiciones experimentales, el músculo despliega sucesivamente ritmos tipo n:1 (una respuesta cada n estímulos) con n creciente; encontramos también que entre uno y otro de estos ritmos aparecen diversas formas de transición, entre las cuales describimos una totalmente nueva en este sistema, que hemos denominado por "ráfagas"; finalmente mostramos que este sistema exhibe de manera generalizada histéresis en la frecuencia, siendo el primer reporte que se hace para esta especie y además el primer reporte en el que se muestran varias "asas" o regiones de histéresis por frecuencia dentro de una misma excursión experimental. Debido al gran volumen de datos generados, hemos introducido una forma de presentación y análisis concisa y eficiente, basada en los espectros de potencia de los datos obtenidos a través de la transformada rápida de Fourier. Este método también se describe brevemente en el artículo.

Cardiac tissues are able to work within a wide range of frequencies to respond to the changing requirements an organism may have. However, during these frequency variations and under certain pathologic conditions arrhythmias such as blocks, tachycardia, fibrillation, etc, may arise some with fatal consequences. For this reason several experimental procedures have been developed that have shown to be useful in studying whole heart properties, or as an alternative from portions of it when changes in its work rate are imposed. This study reports different phenomena occurring in the papillary muscle of the guinea pig heart when stimulated at very high frequency, of several tens of pps, while analyzing its responses during gradual increments starting at 1 (pulses per second). We found that in our conditions papillary muscles display N:1 rhythms with progressive higher N; further more we found that between one and the next rhythm diverse transition patterns appear, among them a new one that we have named "burst pattern". Finally we show that our system exhibits a generalized process of hysteresis by frequency, being this the first report for guinea pig cardiac tissue and the first one to show also the presence of several hysteresis loops in the same experiment. Due to the large volume of generated data we used a faster and easier way to analyze and display them, based on the fast Fourier transform (FFT). The method is briefly described. (Arch Cardiol Mex 2004; 74:11-24).

Cesación del hábito de fumar meediante ensayos de intervención en la comunidad / Smoking cessation by intervention trials in the community

Se realiza el primer ensayo de intervención para la cesación del consumo tabáquico evaluado y controlado en una comunidad correspondiente al médico de familia del municipio Guanabacoa. Resultó significativa la disminución de la prevalencia del hábito de fumar en el 18,1 por ciento en el grupo en ensayo de intervención evaluada a los 6 meses. En el grupo control la disminución de la prevalencia fue del 2,3 por ciento . El grupo más responsable a la intervención resultó ser el grupo de 12 a 15 años de edad. Se considera que la creación de los círculos de adolescentes donde se reforzaban las intervenciones contribuyó significativamente a la reducción del tabaquismo

Tiara: hacia la reflexión y solución de sus problemas / Tiara: forword the reflection and soluction of its problems

Nuestro propósito fue demostrar que el Modelo de Investigación Acción Participante puede beneficiar a la comunidad, no sólo por los resultados obtenidos sino por el proceso mismo. Este debe involucrar a la comunidad desde la formulación del problema hasta el análisis de los resultados, discusión de las soluciones y acciones a tomar. En este proceso, el investigador no es líder sino copartícipe de la investigación. El marco metodológico consistió en el planteamiento de los principales problemas que presentaba la comunidad. Entre ellos, el más preocupante era la posibilidad del agua de consumo. Se tomaron muestras de las principales fuentes de agua. Todas las muestras resultaron contaminadas con bacterias coliformes. La comunidad analizó las implicaciones de esos resutados y decidió organizarse en la búsqueda de dos objetivos principales: educar a la población acerca de higiene del agua y los alimentos y acudir a instancias superiores gubernamentales para la resolución de sus problemas. Conclusión: una comunidad conciente de sus necesidades y organizada para la consecuencia de sus objetivos, puede lograr en el tiempo un desarrollo integral como grupo humano. De manera que el modelo de Investigación Acción Paticipante se transforma en un instrumento facilitador de dicho desarrollo