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

A new Doppler pulmonary artery catheter was used to measure instantaneous and continuous cardiac output in both an in vitro model and in 44 patients undergoing cardiac catheterization. Cardiac output was calculated with use of the Doppler catheter-determined instantaneous space-average velocity and the ultrasonically determined instantaneous vessel area. Doppler flow and thermodilution were compared with electromagnetic flow in the in vitro model and with Fick cardiac output in patients. Doppler catheter-determined flow was highly predictive of electro-magnetic flow in the pulsatile flow model (r = 0.99, slope [m] = 1.01 and SEE = 0.05) and appeared comparable to thermodilution measurements (r = 1.00, m = 1.03 and SEE = 0.02). In patients undergoing cardiac catheterization, Doppler catheter-determined cardiac output appeared to modestly underestimate Fick cardiac output (r = 0.82, m = 0.80 and SEE = 0.09; mean error +/- SEM = -0.26 +/- 0.14 liters/min). However, predictive accuracy was comparable to simultaneously obtained thermodilution measurements (r = 0.85, m = 1.07 and SEE = 0.10; mean error +/- SEM = 0.61 +/- 0.16 liters/min). This new Doppler catheter system utilizes multiple ultrasound transducers to provide angle-independent measurements of vessel diameter and instantaneous velocity within the main pulmonary artery, resulting in a more accurate assessment of Doppler-derived cardiac output. In addition, useful information concerning hemodynamic variables such as peak flow, acceleration, deceleration, stroke work and pulmonary impedance may be derived.