Energetically wasteful wave reflections due to impedance mismatching in hypertension and their reversal with vasodilator: Time and frequency domain evaluations

Abstract

BackgroundIncreased pulse wave reflections in hypertension arise due to impedance mismatching and the effective energy transmission to the vasculature is compromised. Their quantification in the time and the frequency domains are compared and the beneficial effect of vasodilator is evaluated in the study. MethodsA simple, fast time domain method for the resolution of aortic pressure and flow pulses into their forward and reflected components is presented, together with frequency domain reflection coefficient and impedance calculations. Both steady and pulsatile energy components are quantified during induced hypertension (HBP) and subsequent vasodilator (VSD, nitroprusside) treatment in experimental mongrel dogs. Corresponding power generation and usage are also analyzed. ResultsCharacteristic impedance and peripheral resistance were not statistically different between the methods (p > 0.05). Time domain reflection coefficient identified significant differences among control, HBP and VSD groups (p < 0.05) while the frequency domain method did not adequately differentiate the control and the HBP groups. Impedance calculations were similar between the two methods. Frequency domain calculations of total, mean and pulsatile power were, on average, 32.6 mW higher, 12.8 mW lower and 45.4 mW higher than their respective time domain calculations (p < 0.05). Hypertension increased energy consumption, on average, by 88.8 mJ (p < 0.05) and subsequent VSD decreased the energy consumption, on average, by 99.4 mJ (p < 0.05). ConclusionImpedance mismatching in hypertension which leads to increased wave reflections and significantly increased pulsatile work, could be effectively alleviated through vasodilator therapy. This can be quantified through the time-domain method, which is fast and equally accurate as the time-consuming frequency domain approach. The time domain method to quantify crucial parameters such as stroke work cannot be readily determined using the frequency domain methods.