Limits of corrected flow time to monitor hemodynamic status in children

Objective. Doppler corrected flow time (i.e., corrected left ventricular ej ection time) as a noninvasive tool for assessing hemodynamic changes has be en previously reported for adult patients. Its use in paediatrics seems to be worthwhile but no data concerning its accuracy are presently available i n this population. The purpose of this work was to study the relationships between corrected flow time (FT) and indices of systemic vascular resistanc e (SVR) and of myocardial contractility in healthy children. Methods. Twent y healthy children performed a graded maximal bicycle exercise in order to induce physiological hemodynamic alterations. Hemodynamic parameters were m easured with an echocardiography-Doppler at rest and within a few minutes o f post exercise. Cycle time (RR), mean aortic flow velocity, mean systolic velocity (MSV), FT, peak velocity (PV), and stroke distance were measured o n the Doppler aortic velocity waveform. Cardiac index (CI) and SVR were cal culated from the classical volumetric equation. Corrected FT was calculated by using Bazett's formula (FTb = FT/root) and a simplified formula FTc = F Tmeasured + [1.29 . (HR - 60)]. Results. Post exercise, SVR, RR, FT, decrea sed, while CI, PV and MSV increased and stroke distance remained unchanged. After multiple regression analysis no significant correlation between SVR and FTb and SVR or FTc was noted. A significant correlation appeared betwee n FTb and, respectively, PV (r = -0.83; p < 0.001), stroke distance (r = 0. 78; p < 0.001) and RR (r = -0.52; p = 0.0016). A significant correlation wa s also shown between FTc and, respectively, PV (r = -0.71; p < 0.001) and s troke distance (r = 0.63; p < 0.001) but not with RR. Conclusions. These re sults show that the use of Bazett's formula correct FT could lead to hemody namic misinterpretations, because it does not rule out all the heart rate e ffect. Moreover, in healthy children corrected FT appears as an inaccurate index to monitor physiological afterload alterations, because of the involv ment of other hemodynamic factors such as contractility in its variation.