Ole Knudson

Intravascular ultrasonic characteristics and vasoreactivity of the pulmonary vasculature in children with pulmonary hypertension

We sought to describe the morphologic characteristics of pulmonary arteries by intravascular ultrasound (IVUS) in children with and without pulmonary hypertension to compare these anatomic findings with those of pulmonary wedge angiography, and to determine the relation between these structural findings and functional reactivity to pulmonary vasodilators. Direct evaluation of pulmonary vascular structure in children with pulmonary hypertension with current imaging techniques has been limited and little is known about the relation between structural and functional characteristics of the pulmonary vasculature. In 23 children undergoing cardiac catheterization (15 with pulmonary hypertension and 8 controls) we performed IVUS and pulmonary wedge angiography of the distal pulmonary arteries in the same lobe. IVUS was performed in 44 pulmonary arteries measuring 2.5 to 5.0 mm internal diameter with a 3.5Fr 30-MHz IVUS catheter. We assessed vasoreactivity to inhaled nitric oxide (NO) and oxygen in 13 of 15 children with pulmonary hypertension. Baseline pulmonary vascular resistance (PVR) was greater in the 15 children with pulmonary hypertension than in the 8 controls (9.5+/-1.9 vs 1.5+/-0.3 U x m2, p <0.05). NO lowered PVR in patients with pulmonary hypertension (p <0.05). IVUS studies in patients with pulmonary hypertension showed a thicker middle layer, wall thickness ratio, and diminished pulsatility than did those in controls (p <0.05). The inner layer was not visualized by IVUS in any control patient, but was seen in 9 of 15 patients with pulmonary hypertension. Pulmonary artery wedge angiography correlated with baseline mean pulmonary artery pressure and PVR as well as with IVUS findings of wall thickness ratio and inner layer thickness. The inner layer was not visualized by IVUS in any patient with grade 1 wedge angiograms or in 86% of patients with grade 2 wedge angiograms. All patients with grade 4 and 80% of patients with grade 3 wedge angiograms had a visible inner layer. Vasoreactivity to NO and oxygen did not correlate with structural assessment of the pulmonary vasculature by IVUS. Structural changes in the pulmonary arteries in children with pulmonary hypertension can be directly visualized by IVUS, but are not predictive of NO-induced pulmonary vasodilation. IVUS examination of pulmonary arteries may complement current techniques utilized in the evaluation of children with pulmonary hypertension.

THREE-DIMENSIONAL ULTRASOUND FLOW IMAGING PROVIDES MORE ACCURATE VISUALIZATION OF THE FLOW CONVERGENCE REGION THAN TWO-DIMENSIONAL COLOR FLOW MAPPING: IN-VITRO STUDIES. |[dagger]| 208

Two-dimensional (2D) color Doppler flow mapping (CDFM) of the flow convergence (FC) region provides important information on regurgitant volumes. However, the 2D view provided by CDFM may not reveal complete FC information especially for complex orifice geometries. We used a Toshiba ultrasound scanner (Nyquist limits (NL): 10 - 60 cm/sec) interfaced to a Tomtec 3D ultrasound reconstruction computer which provides multiple views of structure and flow, to visualize the FC region for pulsatile flow (20 - 90 cc/beat; 50 - 80 bpm) through a variety of orifice sizes (0.1 cm2 - 2.0 cm2) and shapes(circular, oval, Y-shaped). The FC region could be clearly visualized using 3D ultrasound Doppler flow imaging for all hemodynamic conditions at all NLs. Aliasing radii measured from the 3D flow images correlated well with actual flow volumes (y=0.05 x+0.21; r=0.98, NL= 38cm/sec) with best results obtained at intermediate (30 - 50 cm/sec) NLs. Increasing orifice size and decreasing flow rate both caused perceptible flattening of the 3D FC contour within the central convergence region where angle induced velocity errors are minimal. 3D ultrasound flow imaging of the proximal flow convergence region presents both qualitative and quantitative advantages over conventional 2D CDFM and should improve clinical application of this technique.

AUTOMATIC FLOW CALCULATION OF REGURGITANT JETS FROM VOLUME RENDERED THREE-DIMENSIONAL FLOW IMAGES: IN-VITRO STUDIES. 209

Three dimensional (3D) ultrasound flow imaging promises to provide true 3D depiction of regurgitant jets which can then be used to calculate regurgitant volume (RV). Methods: Steady (30 cc/sec - 100 cc/sec) and pulsatile(15 - 40 cc/beat) flows through orifices (0.2 - 1.8 cm2) were imaged using a Toshiba ultrasound scanner interfaced to a Tomtec 3D reconstruction system. 3D flow images were analyzed off-line by first calibrating the color Doppler velocity map to the 3D grey levels. Flow rate was computed by integration of all velocities over the cross-sectional slices of the distal 3D jet which allowed for true mean flows to be obtained with no velocity profile assumptions. Results: 3D calculated flow rates for steady flow correlated well with actual flows with overestimation (y = 3.64x - 0.42; r = 0.985; SEE = 0.51 L/min). 3D flow images of pulsatile flow could be also be used to automatically calculate instantaneous flow rates(Figure) Conclusions: 3D flow imaging of regurgitant jets promises to increase the accuracy of jet volume calculations. Automation of such flow calculations provides an effective and easy method to take advantage of the large amount of information provided by 3D flow imaging.

LONG TERM ECHOCARDIOGRAPHIC FOLLOW-UP OF INFANTS WITH SEVERE PERSISTENT PULMONARY HYPERTENSION OF THE NEWBORN. † 1677

LONG TERM ECHOCARDIOGRAPHIC FOLLOW-UP OF INFANTS WITH SEVERE PERSISTENT PULMONARY HYPERTENSION OF THE NEWBORN. † 1677

EFFECT OF MACHINE PARAMETERS ON THREE-DIMENSIONAL VOLUME MEASUREMENT OF JETS: IN VITRO STUDIES. 170

EFFECT OF MACHINE PARAMETERS ON THREE-DIMENSIONAL VOLUME MEASUREMENT OF JETS: IN VITRO STUDIES. 170