Shu-Bao Chen, MD

Shanghai Children's Medical Center, Shanghai Second Medical University, China


Assessment of pulmonary hemodynamic status is helpful in the evaluation of patients with congenital heart disease. Currently, pulmonary hemodynamic indexes are obtained invasively by cardiac catheterization. It is not suitable for critical patients, nor for follow up study. Doppler echocardiography has allowed the development of several noninvasive methods for estimation of pulmonary hemodynamic indexes. The exploration of simple, more accurate noninvasive method for pulmonary hemodynamic assessment has still been a challenge.

Assessment of pulmonary arterial pressure

Doppler echocardiographic methods for assessing pulmonary arterial pressure fall under 3 basic categories, namely, right ventricular isovolumic relaxation time, calculated pressure gradient derived from abnormally developed blood flow and pulmonary systolic flow indexes. The measurement of right ventricular isovolumic relaxation time and pulmonary systolic flow indexes could not give exact pressure value which is necessary for calculating pulmonary vascular resistance. These measurements may be affected by many factors, such as heart rate, ventricular function, right ventricular preload and afterload, the presence of bundle branch block, cardiac output, right atrial pressure and doppler sampling sites. Pulmonary arterial systolic pressure may also be noninvasively estimated in patients with interventricular communication, systemic to pulmonary artery communication, or tricuspid regurgitation. One study found estimation of pulmonary arterial pressure by measurement of peak tricuspid regurgitation velocity superior to other doppler techniques. But, it is difficult to have good results in the presence of very mild tricuspid regurgitation or eccentric regurgitant jet.

In 1989, Morera et al. described a method to estimate pulmonary arterial pressure as a fraction of systemic arterial pressure. Preejection period (PEP), ejection time(ET) and mean acceleration to peak velocity( peak velocity/ acceleration time =ACCm) were measured from the right and left ventricular outflow tracings. The expression: F=(PEP xACCm)/ET was calculated. The product of the ratios of F for right outflow to F for the left outflow (waveform contour ratio) and arm systolic pressure was used to estimate systolic pulmonary pressure. The waveform contour ratios exhibited a striking similarity to the ratios of systolic and mean pulmonary to aortic pressure (r=0.98, 0.96, respectively). It is a universally applicable and accurate method for estimation of pulmonary arterial pressure, and could also provide absolute pressure value. There are too many parameters in the F described by Morera, making the method more complex and time consuming. We have done further study to simplify this method in 30 patients with congenital heart disease undergoing cardiac catheterization. Various F's ( F= PEP×ACCm)/ ET, F1= PEP/AT, F2= PEP/ET, F3= PEP/AT×ET, F4= PEP×peak velocity/AT ) were used to noninvasively estimate pulmonary arterial pressure. Estimated systolic and mean pulmonary arterial pressure adopting F3 highly correlated woth those directly measured by cardiac catheterization ( r=0.96, 0.81, respectively). With pulmonary hypertension the change of peak velocity of pulmonary flow is not consistent. Peak flow velocity may also be affected by hemodynamic status and incident angle etc. Eliminating peak flow velocity from the F described by Morera could simplify this method and improve its accuracy.

Feasibility of pulmonary arterial pressure estimation from doppler ultrasound audio signals.

Pulmonary arterial pressure could be universally estimated with doppler echocardiography adopting pulmonary to aortic time interval ratios (waveform contour ratios). However, it is a more complex and time consuming technique. Currently, all time interval parameters of aortic and pulmonary flow for estimation of pulmonary arterial pressure are calculated from aortic and pulmonary flow velocity spectrum which are doppler video signals. Its transit-time broading effect may cause frequency shift errors and amplitute distortion. Compared with doppler video signal, doppler audio signal is less affected, could be used to generate flow tracing, for automatically measuring time interval parameters.

To clarify the presumption, comparative study of pulmonary arterial pressure, pulmonary blood flow and pulmonary vascular resistance measured respectively by doppler echocardiography (DE), doppler audiosignal processing system (DASPS) and cardiac catheterization was done in 41 patients with left to right shunt congenital heart disease excluding outflow tract obstruction. PEP, ET, PV, AT were manually measured from aortic and pulmonary flow spectrum and automatically measured by DASPS . Diameters of aortic and pulmonary valvular annulus, brachial artery systolic and mean pressure were entered, then systolic and mean pulmonary arterial pressure, pulmonary blood flow and pulmonary vascular resistance will be given on the screen. Pulmonary to aortic flow time interval ratios ( PASP= FPA/FAO×BASP, PAMP= FPA/FAO×BAMP, F= PEP/(AT×ET) was adopted for estimating pulmonary arterial pressure. The results of study showed that PASP, PAMP measured by DASPS highly correlated with those measured by cardiac catheterization(r=0.98, 0.95, respectively). Reproducibility of DASPS was much better than that of doppler echocardiography. It did take less time to estimate pulmonary arterial pressure by DASPS (5.1±1.7min) than by doppler echocardiography (21.5±5.3min). In conclusion, doppler audio signal processing system adopting pulmonary to aortic time interval ratio could be used as an accurate and universal method for estimation of pulmonary arterial pressure.