0
Correspondence |

Limitations Inherent to the Simplified Bernoulli Equation Explain the Inaccuracy of Doppler Echocardiographic Estimates of Pulmonary Artery Pressures in Patients With Pulmonary HypertensionBernoulli Equation and Pulmonary Hypertension FREE TO VIEW

Alessandro Giardini, MD, PhD
Author and Funding Information

From the Cardiorespiratory Unit, Great Ormond Street Hospital for Children.

Correspondence to: Alessandro Giardini, MD, PhD, Cardiorespiratory Unit, Great Ormond Street Hospital for Children, Great Ormond St, London, WC1N 3JH, England; e-mail: alessandro5574@iol.it


Financial/nonfinancial disclosures: The author has 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. doi:10.1378/chest.11-0344
Text Size: A A A
Published online

To the Editor:

I would like to congratulate Rich and colleagues,1 who, in their recent article in CHEST (May 2011), showed clinically relevant discrepancies between Doppler-estimated and invasively measured pulmonary artery systolic pressure (PASP) in >50% of measurements, discrepancies not resolved by simultaneous measurement of the two entities. Imprecise right atrial pressure estimation, suboptimal alignment between the Doppler beam and the regurgitant jet, and the presence of severe tricuspid valve regurgitation were suggested as the causes of the discrepancy. However, even when beam alignment and right atrial pressure estimation are correct, significant discrepancies between the two measurements should be expected because of limitations inherent to the simplified Bernoulli equation.2 Indeed, the simplified Bernoulli equation assumes negligible viscous and inertial forces and complete conversion of potential energy (the pressure in the right ventricle) into kinetic energy (that of the regurgitant jet).

However, as highlighted in a recent mock circuit experiment,2 many conditions commonly encountered in clinical practice can result in an imperfect transformation of potential to kinetic energy. For example, an eccentric regurgitant jet would interact with the nearby atrial wall, causing viscous losses that are evident as the Coanda effect and that are associated with a 24% underestimation by Doppler of invasive pulmonary artery pressure. Increased blood viscosity observed in patients with hypoxemia, and, in particular, in patients with intracardiac defects and Eisenmenger physiology, can also cause discrepancies between Doppler and invasive estimates of PASP. Indeed, increasing hematocrit causes occurrences of viscous losses that are not accounted for by the simplified Bernoulli equation, leading per se to a 43% underestimation of invasive PASP by Doppler.

All factors mentioned so far are associated with underestimation of PASP by Doppler. However, overestimation was as common as underestimation in the article by Rich et al,1 and some other factors have to intervene to explain this finding. Experimental evidence suggests that when blood viscosity is reduced, such as during anemia, or when absolute right atrial size (in centimeters) is small, such as in children or young women, inertial forces not accounted for by the simplified Bernoulli equation may cause pressure recovery in the receiving chamber, causing overestimation of PASP by Doppler.2

As mentioned by Rich et al,1 transthoracic echocardiography is an invaluable tool in the management of patients with pulmonary hypertension. Because conditions that limit the applicability of the simplified Bernoulli equation are ubiquitous in clinical practice, the education of clinicians in recognizing those conditions is of extreme importance.

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;1395:988-993. [CrossRef] [PubMed]
 
Giardini A, Tacy TA. Non-invasive estimation of pressure gradients in regurgitant jets: an overdue consideration. Eur J Echocardiogr. 2008;95:578-584. [CrossRef] [PubMed]
 

Figures

Tables

References

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;1395:988-993. [CrossRef] [PubMed]
 
Giardini A, Tacy TA. Non-invasive estimation of pressure gradients in regurgitant jets: an overdue consideration. Eur J Echocardiogr. 2008;95:578-584. [CrossRef] [PubMed]
 
NOTE:
Citing articles are presented as examples only. In non-demo SCM6 implementation, integration with CrossRef’s "Cited By" API will populate this tab (http://www.crossref.org/citedby.html).

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging & repositioning the boxes below.

  • CHEST Journal
    Print ISSN: 0012-3692
    Online ISSN: 1931-3543