Assessment of right ventricular afterload by pressure waveform analysis in acute pulmonary hypertension.

AIM: To characterize hydraulic right ventricle (RV) afterload by pulmonary arterial pressure waveform analysis in an acute pulmonary hypertension (PH) model. METHODS: Pulmonary artery (PA) flow and pressure were recorded in six anesthetized sheep. Acute isobaric PH was induced by phenylephrine (active) and PA mechanical constriction (passive). We estimated the amplitude of the forward and reflected pressure waves according to the inflection point. In most cases the inflection pressure was smooth, thus the inflection point was defined as the time at which the first derivative of pulmonary arterial pressure reached its first minimum. We calculated the input and characteristic (Z(C), time-domain Li method) impedances, the capacitance index (stroke volume/pulse pressure), the augmentation index (AI) (reflected pressure/pulse pressure), the fractional pulse pressure (pulse pressure/mean pressure) and the wasted energy generated by the RV due to wave reflection during ejection (E(W)). RESULTS: Pulse pressure, fractional pulse pressure, AI and Z(C) increased and capacitance index decreased during passive PH with respect to control (P < 0.05). In contrast, Z(C) and the capacitance index did not change and E(W) and the AI decreased during active PH. Pulse pressure correlated with E(W) and Z(C) and the AI was correlated with E(W) (r > 0.6, P < 0.05). CONCLUSION: PA pressure waveform analysis allows the quantification of the dynamic RV afterload. Prospective clinical studies will be necessary to validate this time-domain approach to evaluate the dynamic RV afterload in chronic PH.

[Regional differences in viscosity, elasticity and wall buffering function in systemic arteries: pulse wave analysis of the arterial pressure-diameter relationship]. / Diferencias regionales en viscosidad, elasticidad y amortiguamiento parietal de arterias sistémicas: análisis isopulsátil de la relación presión-diámetro arterial.

INTRODUCTION AND OBJECTIVES: Regional variations in the incidence of vascular diseases have been related to regional differences in arterial viscoelasticity. The aim of this study was to characterize the differences in the elastic and viscous modulus and in wall buffering function between central and peripheral systemic arteries, through a time-series analysis of the pressure-diameter relationship. MATERIAL AND METHOD: Pressure and diameter were measured in seven arterial segments (carotid, brachiocephalic trunk, ascending aorta, proximal, middle and distal descending thoracic aorta, and femoral artery) from six sheep. Each segment was mounted on an in vitro mock circulatory system and perfused with Tyrode solution, with a pulse frequency of 1.8 Hz and systemic pressure levels. We used the Kelvin-Voigt model to calculate the pressure-diameter elastic (Epd, mmHg/mm) and viscous (Vpd, mmHg.s/mm) modulus, and to quantify the local wall buffering function (Vpd/Epd). We also calculated the incremental Young's and pressure-strain elastic modulus and pulse wave velocity for each segment. RESULTS: The elastic and viscous modulus increased from proximal to distal segments. The wall buffering function did not differ significantly between arteries. The lower rigidity of the central arteries compared to the distal ones may indicate that the systolic arterial compliance function is concentrated in the central arterial segments. On the other hand, the greater viscosity in the distal segments may indicate that viscous energy loss is concentrated in these segments. CONCLUSIONS: Arterial elasticity and viscosity can be interpreted as properties that are dependent on the region of the vessel, whereas wall buffering function can be considered region-independent.

Diferencias regionales en viscosidad, elasticidad y amortiguamiento parietal de arterias sistémicas: análisis isopulsátil de la relación presión-diámetro arterial / Regional differences in viscosity, elasticity and wall buffering function in systemic arteries: pulse wave analysis of the arterial pressure-diameter relationship

Introducción y objetivos. Variaciones regionales en la incidencia de diversas afecciones vasculares se han relacionado con diferencias regionales en la viscoelasticidad arterial. El objetivo de este trabajo fue caracterizar las diferencias regionales en el módulo elástico, viscoso y en el amortiguamiento parietal de arterias sistémicas, centrales y periféricas, mediante el análisis de la relación instantánea presión-diámetro arterial en el dominio temporal. Material y método. Se midieron la presión y el diámetro en 7 segmentos arteriales extraídos de 6 ovejas: carótida, tronco braquiocefálico, aorta ascendente, aorta torácica descendente proximal, media y distal, y arteria femoral. Cada segmento fue montado en un sistema circulatorio in vitro y perfundido con solución Tyrode, con frecuencia de estimulación de 1,8 Hz y valores de presión sistémica. Utilizando un modelo Kelvin-Voigt, se obtuvieron el módulo presión-diámetro elástico (Epd, mmHg/mm)y viscoso (Vpd, mmHg×s/mm), y se cuantificó la función de amortiguamiento parietal (FAP) como Vpd/Epd. Adicionalmente, se calculó el módulo de Young incremental y elástico presión-deformación y la velocidad de onda del pulso de cada segmento. Resultados. Los módulos elásticos y viscoso aumentaron hacia los segmentos periféricos, mientras que la FAPn o mostró diferencias entre segmentos. La menor rigidez en las arterias centrales y la mayor viscosidad en las arterias periféricas podrían indicar que la función de reservorio arterial sistólico se concentra en las primeras y la disipación viscosa de energía en las segundas. Conclusiones. La respuesta elástica y viscosa arterial podrían considerarse dependientes de la región arterial, mientras que la constante de FAP sería un indicador independiente de la región arterial

Introduction and objectives. Regional variations in the incidence of vascular diseases have been related to regional differences in arterial viscoelasticity. The aim of this study was to characterize the differences in the elastic and viscous modulus and in wall buffering function between central and peripheral systemic arteries, through a time-series analysis of the pressure-diameter relationship. Material and method. Pressure and diameter were measured in seven arterial segments (carotid, brachiocephalic trunk, ascending aorta, proximal, middle and distal descending thoracic aorta, and femoral artery) from sixs heep. Each segment was mounted on an in vitro mock circulatory system and perfused with Tyrode solution, with a pulse frequency of 1.8 Hz and systemic pressure levels. We used the Kelvin-Voigt model to calculate the pressure-diameter elastic (Epd, mmHg/mm) and viscous (Vpd,mmHg•s/mm) modulus, and to quantify the local wall buffering function (Vpd/Epd). We also calculated the incremental Young’s and pressure-strain elastic modulus and pulse wave velocity for each segment. Results. The elastic and viscous modulus increased from proximal to distal segments. The wall buffering function did not differ significantly between arteries. The lower rigidity of the central arteries compared to the distal ones may indicate that the systolic arterial compliance function is concentrated in the central arterial segments. On the other hand, the greater viscosity in the distal segments may indicate that viscous energy loss is concentrated in these segments. Conclusions. Arterial elasticity and viscosity can be interpreted as properties that are dependent on the region of the vessel, whereas wall buffering function can be considered region-independent