RESUMEN
Limb blood flow is widely used as an indicator of the human vascular properties. There are only few non-invasive methods for its measurement such as venous occlusion plethysmography. However, several authors have questioned its validity. The problems appear to be related to the process of venous occlusion. We developed two methods to measure forearm blood flow by plethysmography without venous occlusion in combination with Doppler velocimetry (without imaging). Method 1: the gradient of a tangent drawn on the latter part of the down stroke of the plethysmographic volume pulse is an approximation of venous blood flow in the absence of diastolic blood flow. At equilibrium, it equals the average arterial flow in a cardiac cycle. The Doppler velocity waveform recorded simultaneously allows improvement of this approximation when there is diastolic blood flow. Method 2: the volume pulse detected by a plethysmograph calibrated in absolute volume is used to calibrate the velocity waveform recorded simultaneously to produce an approximation of arterial volumetric flow waveform. Bland-Altman analysis shows both methods have good correlation and agreement with venous occlusion plethysmography at rest. Method 1: mean difference (blood flow measured by venous occlusion minus calculated flow) = 0.10 ml/pulse (+/-0.18), limits of agreement = -0.41 and 0.61 ml/pulse. Method 2: mean difference = -0.041 ml/pulse (+/-0.15), limits of agreement = -0.45 and 0.37 ml/pulse. During hyperaemia, venous occlusion plethysmography grossly underestimated relative to the new methods. The new methods are not dependent on venous occlusion and produce consistent results with or without hyperaemia.
Asunto(s)
Algoritmos , Velocidad del Flujo Sanguíneo/fisiología , Antebrazo/irrigación sanguínea , Antebrazo/diagnóstico por imagen , Interpretación de Imagen Asistida por Computador/métodos , Pletismografía/métodos , Ultrasonografía Doppler de Pulso/métodos , Adulto , Femenino , Antebrazo/fisiología , Humanos , Masculino , Persona de Mediana Edad , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
An air plethysmograph with a sensitive phototransducer was constructed so that plethysmographic volume-change pulsations could be displayed in detail without using venous occlusion. Software was developed to allow analysis of the pulses using a modification of the backward extrapolation technique. This allowed calculation of the forward arterial blood flow and noninvasive derivation of the resting arterial flow waveform. There is good reproducibility of the technique, with 8% variability between pairs of measurements at rest and 4% variability after hand exercise. Direct comparison made with blood flows measured by venous occlusion plethysmography showed good average agreement. The mean blood flow for venous occlusion (rest and exercise) was 0.76 +/- 0.07 mL/beat (mean +/- SEM), and the mean blood flow for backward extrapolation (rest and exercise) was 0.74 +/- 0.09 mL/beat (mean +/- SEM). This corresponds to 3.86 +/- 0.36 mL/min/100 mL and 3.76 +/- 0.46 mL/min/100 mL, respectively. Important assumptions when using this method are that venous return is constant and that forward arterial flow is over before the end of the cardiac cycle.
Asunto(s)
Arterias/fisiología , Óptica y Fotónica/instrumentación , Pletismografía/instrumentación , Transductores , Adulto , Velocidad del Flujo Sanguíneo/fisiología , Diseño de Equipo , Prueba de Esfuerzo , Femenino , Antebrazo/fisiología , Mano/fisiología , Humanos , Masculino , Persona de Mediana Edad , Pletismografía/métodosRESUMEN
Occlusion plethysmographic recordings were obtained on 26 subjects prior to and immediately following repeated venous occlusions. A simple method of approximating the curve shape by 2 straight lines is described. The results indicate that, following an initial occlusion, the height of subsequent curves is reduced and the angulation between the 2 lines approximating the curves changes in a way that indicates that the principal mechanism is venous shunting. The degree of shunting was quantified by taking the relative percentage change in shape of the 2 lines approximating the curve, i.e., the percentage shunt. Venous shunting is shown to be much more marked after hand exercise than at rest in normal subjects and in those with heart failure or hypertension.