Limits of Corrected Flow Time to Monitor Hemodynamic Status in Children

Abstract

Objective.Doppler corrected flow time (i.e., corrected leftventricular ejection time) as a noninvasive tool for assessing hemodynamicchanges has been previously reported for adult patients. Its use inpaediatrics seems to be worthwhile but no data concerning its accuracy arepresently available in this population. The purpose of this work was to studythe relationships between corrected flow time (FT) and indices of systemicvascular resistance (SVR) and of myocardial contractility in healthy children.Methods.Twenty healthy children performed a graded maximal bicycleexercise in order to induce physiological hemodynamic alterations. Hemodynamicparameters were measured with an echocardiography-Doppler at rest and withina few minutes of post exercise. Cycle time (RR), mean aortic flow velocity,mean systolic velocity (MSV), FT, peak velocity (PV), and stroke distance weremeasured on the Doppler aortic velocity waveform. Cardiac index (CI) and SVRwere calculated from the classical volumetric equation. Corrected FT wascalculated by using Bazett's formula (FT_b =FT/√) and a simplified formula FT_c =FT_measured + [1.29 ċ (HR −60)]. Results.Post exercise, SVR, RR, FT, decreased, while CI,PV and MSV increased and stroke distance remained unchanged. After multipleregression analysis no significant correlation between SVR and FT_band SVR or FT_c was noted. A significant correlation appearedbetween FT_b 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 significantcorrelation was also shown between FT_c and, respectively, PV(r = −0.71; p < 0.001) and stroke distance(r = 0.63; p < 0.001) but not with RR. Conclusions.These results show that the use of Bazett's formula correct FT couldlead to hemodynamic misinterpretations, because it does not rule out all theheart rate effect. Moreover, in healthy children corrected FT appears as aninaccurate index to monitor physiological afterload alterations, because ofthe involvment of other hemodynamic factors such as contractility in itsvariation.