We thank Drs Chemla and Herve for their interest in our report. The authors correctly state that they first derived the equation for estimation of mean pulmonary artery pressure from pulmonary systolic pressure in their 2004 publication. The results of our study serve as a confirmation of the conclusions of their earlier work, which have important implications for the broad population of patients with pulmonary hypertension.
We also note the comments of Schiller and Ristow, who astutely emphasized the potential for misclassification of pulmonary hypertension when relying solely on this noninvasive method. Although the rate of misclassification according to the derived equation was low in our study, it is important to consider the range of estimation (with a standard deviation of 2 mm Hg). This range poses limitations for the clinical application of noninvasively derived estimates in the individual patient. Moreover, this relative lack of precision can be problematic when considering multiple points of reference for noninvasive estimation, such as when calculating pulmonary resistance. Although variability can occur with invasive measurements, the ability to ascertain absolute, rather than relative, pressure is a unique advantage currently available only with cardiac catheterization. Thus, cardiac catheterization remains the gold standard for assessing pulmonary pressure, the left-sided contribution, and pulmonary resistance and is an essential component for patients in whom pulmonary hypertension–specific therapy is being contemplated.