Instantaneous and continuous cardiac output obtained with a Doppler pulmonary artery catheter

Stanford University School of Medicine, California.

A newly developed, flow-directed, Doppler pulmonary artery catheter, capable of measuring instantaneous and continuous cardiac output, was evaluated in both an in vitro pump model and an animal model. Quantitative flow was calculated with use of the instantaneous, space-average velocity (obtained from the velocity profile) and the instantaneous area (obtained from the vessel diameter) and compared with electromagnetic flow. Additionally, simultaneous thermodilution flow measurements were obtained. Doppler catheter-determined flow was highly predictive of electromagnetic flow in both continuous and pulsatile pump models (r2 = 0.98, slope or m = 1.04, SEE = 0.44; and r2 = 0.97, m = 1.04 and SEE = 0.33, respectively). Thermodilution was less predictive and appeared to underestimate electromagnetic flow in both the continuous and the pulsatile model (r2 = 0.99, m = 0.91, SEE = 0.20 and r2 = 0.95, m = 0.84 and SEE = 0.34, respectively). In the animal model, Doppler catheter-determined cardiac output appeared to modestly underestimate electromagnetic flow (r2 = 0.80, m = 0.87, SEE = 0.61). However, Doppler determinations of flow remained more accurate than did simultaneous thermodilution measurements (r2 = 0.73, m = 0.79, SEE = 0.72). Accurate, continuous and instantaneous cardiac output measurements appear possible with use of a flow-directed, Doppler pulmonary artery catheter. This catheter system also provides instantaneous diameter measurements and mapping of instantaneous velocity profiles within the main pulmonary artery and may lead to more accurate Doppler-derived assessment of cardiac output in humans.

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