Respuesta en frecuencia de la pared arterial: ¿inocente o culpable de las discrepancias entre filtrado sistémico y pulmonar?

Objective: To characterize the mechanical properties of the Aorta (AO) and the pulmonary (PA) arteries and the effect of the vascular smooth muscle activation (VSM). Method: Aortic and pulmonary pressures (Konigsberg) and diameters (sonomicrometry) were measured in 6 anaesthetized sheep. A ARTICULO DE INVESTIGACION ORIGINAL SOMIB REVISTA MEXICANA DE INGENIERIA BIOMEDICA Vol. XXIV, Num. 1 Marzo 2003 pp 45 54 Respuesta en frecuencia de la pared arterial: ? inocente o culpable de las discrepancias entre filtrado sistemico y pulmonar? Ricardo L. Armentano,*,** Daniel Bia,* Damian Craiem,** Lucas Gamero,** Jaime Levenson,*** Juan C. Grignola,* Fernando F. Gines* * Laboratorio de Fisiologia Cardiovascular. Departamento de Fisiologia. Facultad de Medicina. Universidad de la Republica. Montevideo, Uruguay. ** Consejo de Investigacion y Desarrollo. Universidad Favaloro. Buenos Aires, Argentina. *** Hopital Broussias, CMPCV, CNRS 2536. Paris, Francia. Correspondencia: Prof. Ricardo Armentano Departamento de Fisiologia, Facultad de Medicina, Universidad de la Republica. General Flores 2125, CP: 11800. Montevideo. Uruguay. Telefono: (5982) 9243414 Ext. 3313/3316. Fax: (5982) 9240395. E-mail: dbia@fmed.edu. uy Revista Mexicana de Ingenieria Biomedica • volumen XXIV • numero 1 • Marzo 2003 46 edigraphic.com INTRODUCCION Las grandes arterias, principalmente la aorta (AO) y la pulmonar (AP) tienen como funcion principal amortiguar las oscilaciones del flujo sanguineo a fin de nutrir con un regimen aproximadamente estacionario a los diversos tejidos de los organismos1,2. Los segmentos iniciales aortico y pulmonar, reciben en forma pulsatil la eyeccion sanguinea ventricular, por lo que su funcion amortiguadora es de vital trascendencia. Una elevada pulsatilidad ha mostrado ser altamente perjudicial para el organismo asi como para el sistema cardiovascular en si mismo1,2. Las propiedades mecanicas de las paredes de las grandes arterias, estan gobernadas principalmente por la viscosidad (η) y la elasticidad (E) parietal, debido a que la inercia (M) ha sido un factor generalmente despreciable en el analisis circulatorio1,3. La caracterizacion viscoelastica de la pared arterial en animales vivos con sistemas cardiovasculares intactos reviste gran importancia, sin embargo practicamente no existe informacion al respecto1,2. La no-linealidad en la relacion presion-diametro de la pared arterial es la principal complicacion en la evaluacion de los efectos viscosos si este analisis se realiza en el dominio de la frecuencia. Para meKelvin-Voigt model, with non-negligible mass was used to characterized the wall mechanical properties and identified by means of a linear auto-regressive model with exogenous input. Elasticity (E), viscosity (η) and inertial (M) indexes were calculated during control state and VSM activation (Phenylephrine, PHE 5 μg/kg/min). The frequency response of the arterial system was estimated by the natural frequency and buffering factor. The diastolic time constant was calculated as a global buffering function index (two-element Windkessel model). Results: Both arteries showed a low-pass filter response. The AO showed a higher E, η and M, however dissipation (η) /energy-storage (E) was similar in both arteries and in both experimental conditions. The dynamic range was similar for both arteries and with no change during PHE. The whole system buffering function was higher in the systemic circuit with respect to the pulmonary, and did not modify during activation. Conclusion: The enhanced attenuation revealed by the systemic circuit could be regarded to its longer effective length in respect with the pulmonary path. The sustained administration of PHE, by means of the local smooth muscle activation, exerts a beneficial effect for the circulation, preserving the wall dynamic range making more sensible the viscosity and less sensible the elasticity under pressure rises.