Calculationof Left Ventricular Relaxation Time Constant (Tau) In Dogs With Continuous Wave Doppler Aortic Regurgitant Velocity Curve

Objective：To find a new method for evaluating the left ventricular relaxationtime constant with Continuous Wave Doppler.Methods: Eighteen Beagle dogs were included in the study. Firstly, a centralthoracotomy was performed, and the pericardium was incised. The heart wasstabilized in a pericardial cradle. Secondly, the aortic regurgitation was producedunder ultrasound guiding in the dogs. A manometer-tipped catheter (SPR-320，Millar) was introduced into the LV through cardiac apex. The arterial sheath inthe left carotid artery was introduced into the left coronary ostium underechocardiographic guidance. Then microspheres (51.7μm in diameter) wereinjected into the left coronary artery to induce acute ischemic LV dysfunction.After20minutes, dobutamine or esmolol was infused to alter LV function. Aorticregurgitation velocity spectrum was recorded by the continuous-wave Dopplerechocardiography in different hemodynamic status. At the same time, LV pressure,dP/dt, continuous ECG tracing and aortic pressure were displayed on themulti-channel physiological recorder (ML866Powerlab4,Adinstruments).Measurement was recorded of-dp/dtmax in the dp/dt tracings and the pressure atthe time of–dP/dtmax in the LV pressure tracings.Tau=-P/(dp/dtmax), Tau is thecatheter-derived time constant (Tau-catheter). Aortic regurgitation spectrum oforiginal audio data was post-processed with MATLAB mathematical software.The spectral lines refresh time of about300us was chosen to form a new Dopplerspectrum. Three points:(t1,1m/s)，(t2,2m/s) and (t3,3m/s) were selected in aorticregurgitation velocity spectrum and t1, t2and t3was put into the correspondingTau formula: Tau=(t2-t1)/ln((ADP-C-4)/(ADP-C-16))Tau=(t3-t1)/ln((ADP-C-4)/(ADP-C-36))Tau is the aortic regurgitant time constant(Tau-AR). correlation analysis test ofT-ARand Tau-catheter, difference test and Bland-Altman was done.Results:18dogs were successfully produced moderate aortic regurgitation Ofwhich right coronary valve perforation was found in6dogs and no coronary valveperforation in the other dogs. By repeated injection of microspheres, acuteischemic left ventricular diastolic dysfunction model was created. Two dogs diedof ventricular fibrillation during the procedure.The time constant derived from aortic regurgitation velocity spectra (Tau-AR)correlated well with catheter-derived time constant(Tau-catheter)(r=0.86,P=0.000<0.05). Tau-cathetewas(52.062±14.852)ms，Tau-ARwas(49.457±15.339)ms，the difference of Tau-ARand Tau-cathetewas notstatistically significant(P=0.0684>0.05). Tau-ARand Tau-cathetehave goodagreement.Conclusion: The dog aortic regurgitation model under ultrasound guidance is lesstraumatic. The method of inducing left ventricular diastolic dysfunction byrepeatedly injecting microspheres into the left coronary sinus is safe and reliable.Choosing three points:(t1,1m/s)，(t2,2m/s) and (t3,3m/s) in aortic regurgitantvelocity spectrum and putting into the corresponding formula, we can calculateTau, which had a good correlation with the catheter-derived Tau.