1P-S2-3
NONINVASIVE ASSESSMEMT OF
PULMONARY HEMODYNAMICS
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.
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.