Published Online
on October 18, 2004

A more recent version of this article appeared on October 26, 2004

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Submitted on May 22, 2004
Revised on August 2, 2004
Accepted on August 18, 2004

Extraction of Pulmonary Vascular Compliance, Pulmonary Vascular Resistance, and Right Ventricular Work From Single-Pressure and Doppler Flow Measurements in Children With Pulmonary Hypertension: a New Method for Evaluating Reactivity. In Vitro and Clinical Studies

Craig E. Weinberg PhD, Jean R. Hertzberg PhD, D. Dunbar Ivy MD, K. Scott Kirby RDCS, K. Chen Chan MD, Lilliam Valdes-Cruz MD, and Robin Shandas PhD^*

From the Department of Mechanical Engineering (C.E.W., J.R.H., R.S.), University of Colorado, Boulder, and the Children’s Hospital/University of Colorado Health Sciences Center (D.D.I., K.S.K., K.C.C., L.V.-C., R.S.), Denver, Colo.

^* To whom correspondence should be addressed. E-mail: shandas.robin{at}tchden.org.

Background--Current evaluation of pulmonary hypertension (PH) in children involves measurement of pulmonary vascular resistance (PVR); however, PVR neglects important pulsatile components. Pulmonary artery (PA) input impedance and ventricular power (VP) include mean and pulsatile effects and have shown promise as alternative measures of vascular function. Here we report the utility of pulsed-wave (PW) Doppler-measured instantaneous flow and pressure measurements for estimation of input impedance and VP and use this method to develop a novel parameter: reactivity in compliance.

Methods and Results--An in vitro model of the general pulmonary vasculature was used to obtain impedance and VP, measured by PW Doppler and a reference flow meter. The method was then tested in a preliminary clinical study in subjects with normal PA hemodynamics (n=4) and patients with PH undergoing reactivity evaluation (8 patients; 23 data points). In vitro results showed good agreement between the impedance spectra computed from both flow-measurement methods. Excellent correlation was seen in vitro between actual resistance and the zero-frequency (Z_o) impedance value (r²=0.984). Excellent agreement was also found between Z_o and PVR in the clinical measurements (y=1.075x+0.73; r=0.993). Furthermore, total VP and VP/cardiac output increased significantly with hypertension (128.73 to 365.91 mW and 2.42 to 6.69 mW · mL^-1 · s^-1, respectively). The first-harmonic value of impedance (Z₁) was used as a measure of compliance reactivity; older patients exhibited markedly less compliance reactivity than did younger patients.

Conclusions--Input impedance and VP calculated from Doppler measurements and a single-catheter pressure measurement provide comprehensive characterization of PH and reactivity.

Key words: hypertension, pulmonary • pulmonary heart disease • pediatrics • echocardiography • hemodynamics

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