Comparison of systolic period duration using aortic flow or pressure based methods in anesthetized patients

It has been shown that Systolic Period Duration (SPD) measured with trans-esophageal echocardiography (TEE) is significantly shorter compared to measurements made with radial arterial pressure waveform. This difference could be interpreted in terms of arterial pressure amplification, a mechanism by which arterial pressure waveform is transformed alongside the arterial tree. This amplification is closely related to cardiac afterload as it shares common determinants, like arterial stiffness, pulse wave velocity, or aortic reflection waves. In turn, afterload estimated partly using arterial pressure amplification is useful during general anesthesia (GA) to evaluate detrimental or beneficial effects of vasopressors given to combat hypotensions. Despite TEE measurements comport some impracticalities, trans-esophageal Doppler (TE Doppler) is routinely used for cardiac output monitoring. The goal of this paper was to compare SPD measured with TE Doppler and with arterial pressure at the same location. A secondary goal was to describe a novel dicrotic notch identification algorithm that uses the interspace between the pressure waveform and the straight line going from the systolic peak of one beat to the foot of the subsequent beat. Twenty three patients undergoing GA for neurointerventional procedures were included. Central pressure was obtained by fluid filled radiologic guidewire connected to a pressure transducer. Flow velocity waveform was obtained using TE Doppler probe inserted in the esophagus after induction of GA. Pressure and flow velocity measurements were recorded simultaneously when the tip of the pressure catheter was placed in front of the Doppler probe, in the descending Aorta. SPD measured from Flow velocity waveform was significantly shorter than from Pressure waveform (343 ± 46 ms vs 415 ± 54 ms; p < 0.001 ). Flow velocity and Pressure waveform methods are not interchangeable. To measure SPD consistently at different locations, a consistent algorithm should be used, such as automated identification of dicrotic notch.