To find a new method for evaluating the left ventricular relaxation time constant Tau with aortic regurgitation by continuous wave Doppler.

Twelve Beagle dogs were included in the study. The dog aortic regurgitation model was produced under ultrasound guiding by carotid artery puncture. Aortic pressure was measured by pressure catheter and left ventricular pressure was measured by Millar catheter which was introduced into the left ventricular through cardiac apex. Then microspheres were injected into the left coronary artery under the guidance of ultrasound to induce acute ischemic left ventricular dysfunction, when left ventricular end-diastolic pressure increased more than 5 mmHg (1 mmHg=0.133 kPa). Dobutamine or esmolol was infused to alter left ventricular function. Aortic regurgitation velocity spectrum was recorded by the continuous-wave Doppler echocardiography in different hemodynamic status. At the same time, left ventricular pressure, dp/dt, aortic pressure and continuous ECG tracing were displayed on the multi-channel physiological recorder. Measurement was recorded of –dp/dtmax in the dp/dt tracings and the pressure at the time of –dp/dtmax in the left ventricular pressure tracings. Tau =-P/(dp/dtmax), Tau was the catheter-derived time constant (Tau_catheter). Aortic regurgitation spectrum of original audio data was post-processed with MATLAB mathematical software. The spectral lines refresh time of about 300 μs was chosen to form a new Doppler spectrum. Three points: (t1,1 m/s), (t2, 2 m/s) and (t3, 3 m/s) were selected in aortic regurgitation velocity spectrum and t1, t2 and t3 was put into the corresponding Tau formula: Tau=(t2-t1)/ln[(ADP-C-4)/(ADP-C-16)], Tau=(t3-t1)/ln[(ADP-C-4)/(ADP-C-36)]. Tau was the aortic regurgitant time constant (Tau_ultrasound). The difference between Tau_catheter and Tau_ultrasound was compared by paired t test. The correlation between Tau_catheter and Tau_ultrasound was analyzed by Pearson correlation analysis.

Twelve dogs were successfully produced aortic regurgitation model. Two dogs died of ventricular fibrillation during the procedure of acute ischemic left ventricular diastolic dysfunction. The range of the Tau_catheter was between 27.12 ms and 86.88 ms with an average of (48.973±14.667) ms; the range of the Tau_ultrasound was between 28.13 ms and 90.18 ms with an average of (51.236±15.146) ms. The difference was not statistically significant (t=1.841, P>0.05). Pearson correlation analysis showed that Tau_catheter was positively correlated with Tau_ultrasound (r=0.89, P=0.000).

Choosing three points: (t1, 1 m/s), (t2, 2 m/s) and (t3, 3 m/s) in aortic regurgitant velocity spectrum and putting into the corresponding formula, we can calculate Tau, which had a good correlation with the catheter-derived Tau.