Assessment of Three Alternating Pressure Sequences Applied to a Dynamic Cushion to Relieve Pressure on Seating Areas / Evaluación de tres secuencias de inflado alternantes aplicadas a un cojín dinámico para la liberación de presión en el área de sentado

Pressure ulcers are injuries to the skin and/or underlying tissues caused by prolonged high pressures on supporting body areas, they affect mainly people with poor mobility that have stayed in seating position for a long time. Reducing the amount and duration of pressure has been widely accepted for minimizing the risk of formation of pressure ulcers. Recently, dynamic cushions have been developed to relieve pressure on supporting areas; nevertheless, there is no sufficient information about the adequate characteristics of alternating sequences for pressure ulcers prevention. Therefore, the aim of this work is to explore three sequences of alternating movements designed for an air cell cushion by comparing pressure redistribution on supporting areas when applied on healthy volunteers. The purpose of these sequences is to redistribute the pressure over a larger contact area. To evaluate the effect of the alternating sequences, eight healthy volunteers were asked to sit on the air cell cushion, and to try the three alternating sequences for 12 minutes, 2 minutes on static mode and 10 minutes on alternating mode. A parameter for quantitative assessment of alternating sequences was proposed in this work by determining the coefficient of variation of interface pressure. Furthermore, the percentage of relative change of coefficient of variation was computed for evaluating performance of the alternating sequences comparing to the static mode. It was found that the three proposed strategies maintained values of interface pressure lower than previous work. Additionally, the relative change allowed to differentiate the effects of alternation of each sequence showing the second strategy as the most effective. The results are encouraging for further studies in subjects who require a wheelchair for mobility.

Las úlceras por presión son lesiones en la piel y tejidos subyacentes, causadas por presiones excesivas y prolongadas en las superficies de apoyo del cuerpo. Estas lesiones afectan principalmente a personas con poca movilidad física, como aquellas que permanecen sentados por largos periodos. Para disminuir el riesgo del padecimiento de estas lesiones, se ha recomendado como punto de partida reducir la magnitud y el tiempo de acción de las presiones en las zonas de apoyo. Se han desarrollado cojines dinámicos para sillas de ruedas, los cuales generan movimientos alternantes en las diferentes zonas de apoyo, producido por la inyección de aire, con el fin de disminuir las presiones en esas zonas. Sin embargo, no se han encontrado referencias de las características adecuadas de las secuencias de movimientos alternantes para prevenir la aparición de esas lesiones. El propósito de este trabajo es evaluar tres secuencias de movimientos alternantes diseñadas para un cojín de aire. La evaluación se realizó comparando la distribución de presiones en zonas de apoyo antes y durante la aplicación de estas secuencias alternantes en personas sanas. Las secuencias propuestas se aplican para el inflado y desinflado de celdas que forman el cojín y fueron diseñadas con el objetivo de distribuir las presiones en un área mayor de apoyo. La prueba se realizó en 8 sujetos sanos, con un tiempo de estudio de 12 minutos para cada secuencia diseñada; 2 minutos en modo estático y 10 minutos en modo alternante. Se propuso determinar el coeficiente de variación para evaluar de forma cuantitativa el efecto de las secuencias alternantes sobre la presión de interfaz. Además se calculó el porcentaje de variación relativa del coeficiente de variabilidad entre los modos basal (estático) y alternante como una herramienta para evaluar el desempeño de las secuencias propuestas en relación a la presión de interfaz. Se encontró que las tres estrategias mantuvieron presiones de interfaz por debajo de los valores reportados en trabajos previos. El porcentaje de variación relativa permitió diferenciar el efecto de la alternancia de cada una de las secuencias propuestas, mostrando la segunda estrategia como la más efectiva. Los resultados obtenidos son alentadores para continuar el estudio en sujetos que requieren una silla de ruedas para su movilidad.

Preoperative and postoperative study of left ventricular function, hemodynamics and plasma catecholamine concentrations during dynamic exercise in patients with chronic mitral regurgitation.

We studied 7 patients before and after mitral valve replacement (MVR) for chronic mitral regurgitation (MR) and 5 control subjects by echocardiography and right heart catheterization to assess left ventricular function, hemodynamics and plasma catecholamine concentrations during supine bicycle exercise. Left ventricular (LV) end-systolic dimension decreased and LV systolic function increased significantly during exercise in patients and control subjects. LV systolic function (fractional shortening and mean velocity of circumferential fiber shortening) was significantly lower in patients after MVR than before MVR (p < 0.05). Cardiac index at peak exercise was significantly higher in patients after MVR than before MVR (p < 0.05). Significantly greater augmentation in plasma norepinephrine (NE) levels were observed during exercise in patients both before and after MVR than in control subjects (p < 0.05). No significant differences in mean pulmonary artery pressure (PAP) and pulmonary capillary wedge pressure (PCWP) were observed between the patients before and after MVR. Thus, it is concluded that LV systolic and pump function (CI) during exercise were augmented by a compensatory activation of sympathetic nervous system in patients both before and after MVR for chronic MR.

Response of sympathetic nervous system activity to dynamic exercise in patients with chronic mitral regurgitation and after valve replacement.

To evaluate sympathetic activity during dynamic exercise, 8 patients with mitral regurgitation (MR), 17 patients after mitral valve replacement (MVR) and 5 control subjects were studied by echocardiography, right heart catheterization and by estimation of plasma catecholamines from the right atrium during supine bicycle exercise. No differences in left ventricular (LV) systolic function were noted at rest and during exercise between the patients with MR and control subjects, but it was significantly lower in patients with MVR (p < 0.05) than in control subjects. Plasma norepinephrine (NE) levels during exercise were significantly higher in patients with MR and MVR than in control subjects (p < 0.01 and p < 0.05, respectively). Significant rise in plasma epinephrine levels were noted only in patients with MVR (p < 0.05) during exercise. The relationship of systolic blood pressure/end-systolic dimension and plasma NE levels during exercise, showed lower LV inotropic reserve in patients than in control subjects. Cardiac index (CI) and plasma NE relationship further showed that rise in CI at peak exercise was achieved in patients by a compensatory greater increase in plasma NE. Thus in MR, myocardial dysfunction may be manifested during exercise by a compensatory sympathetic activation and that it continues after MVR.

Hemodynamic changes during dynamic exercise in patients after mitral valve replacement for chronic mitral regurgitation.

To evaluate hemodynamic changes during dynamic exercise, we investigated 13 patients after mitral valve replacement (MVR) for chronic mitral regurgitation (MR) and 5 control subjects by right heart catheterisation during supine bicycle exercise. According to the sizes of the St. Jude Medical (SJM) prosthesis during MVR, patients were divided into group A (n = 8) with SJM 31mm and group B (n = 5) with SJM 29mm. Significant rise in cardiac index (CI) was noted during exercise in both groups A and B (from 3.3 +/- 0.8 to 5.5 +/- 0.9 l/min/m2, p < 0.01 and from 3.0 +/- 0.6 to 5.6 +/- 0.6 l/min/m2, p < 0.01 respectively) and also in control subjects (from 3.4 +/- 0.7 to 6.2 +/- 0.6 l/min/m2, p < 0.01). Mean pulmonary artery and pulmonary capillary wedge pressure were significantly higher during exercise in patients of both groups A and B than control subjects (p < 0.05 and p < 0.01 respectively). Total pulmonary vascular resistance was significantly higher during exercise in both groups A and B than control subjects (p < 0.05 and p < 0.01 respectively). No difference in hemodynamics were noted between the patients of group A and B during exercise. It is concluded that response of CI to exercise in patients after MVR for chronic MR was adequate in comparison to control subjects irrespective of two different valve sizes.