Original article
Noninvasive Doppler Tissue Measurement of Pulmonary Artery Compliance in Children with Pulmonary Hypertension

https://doi.org/10.1016/j.echo.2005.11.012Get rights and content

Background

We have shown previously that input impedance of the pulmonary vasculature provides a comprehensive characterization of right ventricular afterload by including compliance. However, impedance-based compliance assessment requires invasive measurements. Here, we develop and validate a noninvasive method to measure pulmonary artery (PA) compliance using ultrasound color M-mode (CMM) Doppler tissue imaging (DTI).

Methods

Dynamic compliance (Cdyn) of the PA was obtained from CMM DTI and continuous wave Doppler measurement of the tricuspid regurgitant velocity. Cdyn was calculated as: [(Ds − Dd)/(Dd × Ps)] × 104; where Ds = systolic diameter, Dd = diastolic diameter, and Ps = systolic pressure. The method was validated both in vitro and in 13 patients in the catheterization laboratory, and then tested on 27 pediatric patients with pulmonary hypertension, with comparison with 10 age-matched control subjects. Cdyn was also measured in an additional 13 patients undergoing reactivity studies.

Results

Instantaneous diameter measured using CMM DTI agreed well with intravascular ultrasound measurements in the in vitro models. Clinically, Cdyn calculated by CMM DTI agreed with Cdyn calculated using invasive techniques (23.4 ± 16.8 vs 29.1 ± 20.6%/100 mm Hg; P = not significant). Patients with pulmonary hypertension had significantly lower peak wall velocity values and lower Cdyn values than control subjects (P < .01). Cdyn values followed an exponentially decaying relationship with PA pressure, indicating the nonlinear stress–strain behavior of these arteries. Reactivity in Cdyn agreed with reactivity measured using impedance techniques.

Conclusion

The Cdyn method provides a noninvasive means of assessing PA compliance and should be useful as an additional measure of vascular reactivity subsequent to pulmonary vascular resistance in patients with pulmonary hypertension.

Section snippets

In Vitro Validation

The method uses color M-mode (CMM) Doppler tissue imaging (DTI) to obtain instantaneous diameter of the PA, and couples this with noninvasively obtained peak systolic PA pressure by measurement of the tricuspid regurgitant (TR) jet velocity by continuous wave Doppler, to measure compliance. The CMM DTI method is a newly developed technique to measure instantaneous diameter. We first evaluated the use of CMM DTI in measuring diameter using a previously described in vitro model of an elastic PA.1

In Vitro Validation

Figure 1, A, shows instantaneous diameter measured using IVUS and using CMM DTI for one of the elastic mock arteries used in vitro, and Figure 1, B, shows an agreement analysis for all data points. As can be seen, good agreement between the two methods was found. In fact, CMM DTI provides a more temporally resolved trace of diameter because it has better temporal resolution than IVUS.

Clinical Studies

Demographic data for the control and hypertensive subjects are provided in Table 1, Table 2. Excellent CMM DTI

Discussion

The prognosis and management of pediatric PH primarily depend on assessment of vasoreactivity.4, 8 Conventionally, vasoreactivity has been measured by PVR, and recent work has shown the use of PVR with clinical challenge to predict outcomes in children with idiopathic PH.9 Although PVR provides valuable information, there are several important limitations to its exclusive use. First, PVR requires the use of invasive methods. We have recently introduced a novel noninvasive method of estimating

References (19)

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    Citation Excerpt :

    Pulmonary vascular capacitance (accounting for medium and large vessels), as assessed by echocardiography (stroke volume divided by pulmonary pulse pressure: [LVOT diameter2 × π/4 × subaortic VTI]/[4 × ([peak TR]2–[end-diastolic PR]2)]), is an independent predictor of outcomes in a cohort of adults with PAH [61]. Estimation of PA compliance, to determine the pulsatile nature of the PA flow, can be obtained using colour M-mode tissue Doppler imaging on the right PA (to measure diameters) and peak TR gradient (compliance [dyne] = [PA systolic–diastolic diameter]/[diastolic diameter × systolic pressure] × 104) and correlates well with invasive measurement of compliance [62] in children, normal compliance being >40% change/100 mmHg. Given its safety and technical progress, it is likely that the role of echocardiography in the management of PAH will increase in the future.

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Supported in part by grants from the National Institutes of Health (HL 067393, HL 072738).

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