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Jonathan D. Rich, MD; Sanjiv J. Shah, MD
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From the Department of Medicine, Section of Cardiology, University of Chicago Medical Center, Pritzker School of Medicine; and the Department of Medicine, Division of Cardiology, Northwestern University Feinberg School of Medicine.

Correspondence to: Jonathan D. Rich, MD, University of Chicago, 5841 S Maryland Ave, MC 6080, Chicago, IL 60637; e-mail: jonathan.rich@uchospitals.edu


Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2011 American College of Chest Physicians


Chest. 2011;140(1):270-271. doi:10.1378/chest.11-0594
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To the Editor:

We thank Dr Giardini for his interest in our study.1 Dr Giardini suggests that explanations exist beyond those cited in our article to explain the discrepancies in Doppler estimates of pulmonary artery systolic pressure (PASP). He cites limitations inherent to the modified Bernoulli equation, including the assumptions of (1) negligible viscous forces (which may not be the case under hypoxic, anemic, or polycythemic conditions), (2) the complete conversion of potential to kinetic energy (which may not occur in the presence of eccentric regurgitant jets), and (3) inertial forces (which may occur in small receiving chambers, resulting in the pressure recovery phenomenon).

We agree with Dr Giardini that alternative explanations, including some of those he cites, may exist to further explain Doppler-cardiac catheterization PASP discrepancies in patients with pulmonary hypertension. We were particularly interested in the possibility that viscous factors may have accounted for some of the inaccuracies we observed in our study. We, thus, created a multivariate model from our simultaneous Doppler-cardiac catheterization data to evaluate whether oxygen saturation and/or hemoglobin levels were associated with differences in Doppler-cardiac catheterization estimates of PASP. Neither oxygen saturation nor hemoglobin level were associated with differences in Doppler-cardiac catheterization estimates of PASP (β coefficient, − 1.72 ± 1.95 and − 2.24 ± 3.83, respectively; P = not significant). Insufficient sample size (N = 21) is a possible explanation for these negative results. Regarding the impact of inertial forces, most patients with severe pulmonary hypertension tend to have right atrial enlargement, which may minimize the impact of inertial forces and pressure recovery. Other explanations for the discrepancies may also exist beyond those cited in our study or by Dr Giardini, including the impact of changes in intrathoracic pressure occurring with respiration, which are not routinely accounted for during the standard noninvasive Doppler examination but are easily accounted for by measuring PASP at end-expiration during invasive cardiac catheterization.

Thus, although we do not completely agree with the statement by Dr Giardini that limitations inherent to the modified Bernoulli equation explain the inaccuracy, we do agree that it is the summation of many potential errors (including those associated with the modified Bernoulli equation) that may result in clinically relevant errors in Doppler estimates of PASP in patients with pulmonary hypertension. Larger studies, which could provide additional, clinically relevant insight into the effects of oxygen saturation and hemoglobin level on the discrepancies between Doppler and invasive measurements of PASP in patients with pulmonary hypertension, should be encouraged.

Rich JD, Shah SJ, Swamy RS, Kamp A, Rich S. Inaccuracy of Doppler echocardiographic estimates of pulmonary artery pressures in patients with pulmonary hypertension implications for clinical practice. Chest. 2011;5:139:988-993
 

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Rich JD, Shah SJ, Swamy RS, Kamp A, Rich S. Inaccuracy of Doppler echocardiographic estimates of pulmonary artery pressures in patients with pulmonary hypertension implications for clinical practice. Chest. 2011;5:139:988-993
 
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