Characteristic impedance of the proximal aorta determined in the time and frequency domain: a comparison
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Pressure and flow were measured in the ascending aorta of eight anaesthetised dogs under control conditions, after volume expansion and after haemorrhage. For each case the characteristic impedance of the proximal aorta Zc was determined by means of two different methods. Zc was calculated in the time domain as the slope of the pressure-flow relationship in early ejection. For each case, six different values were also obtained in the frequency domain by averaging the impedance moduli in six different frequency ranges. Time- and frequency-domain values agreed well. Statistical analysis showed that both methods can be used to study changes in Zc. However, the time-domain method is easier to apply and does not require steady-state conditions.
KeywordsAortic impedance Characteristic impedance Time-domain method
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