Modeling methodology for vascular input impedance determination and interpretation

Abstract

The significance of pulse wave reflections in the pulmonary vascular system is elaborated using a new method to determine the broadband frequency response of input impedance up to frequencies of 100 Hz. A simple data model, based on the signal construct of a wavelet, is used to generalize and reconcile the common approaches to vascular frequency response estimation so that an accurate response can be calculated from physiological waveforms. Input impedance interpretation is accomplished using a structural and functional modeling methodology. To identify internal structural system properties, the methodology of inverse scattering is used to relate observed pulse wave echoes in the frequency response to a longitudinal distribution of reflection sites of anatomic significance. To identify functional interactions with pulmonary vascular wave mechanics, a time series analysis methodology is proposed to describe vascular interactions using a generalized principle of superposition. The methods of determination and interpretation are applied to a sample pressure-flow data set from the pulmonary circulation of a lamb experiencing vascular-ventilatory interaction. The example suggests that the frequency response is consistent with a discrete longitudinal distribution of reflection sites that may be affected by the ventilator.