Thread by @strain_rate

🧵In our paper “Intraventricular Vector Flow Imaging with Blood Speckle Tracking in Adults: Feasibility, Normal Physiology and Mechanisms in Healthy Volunteers” pubmed.ncbi.nlm.nih.gov/34620522/ , findings were not only qualitative as described in previous threads, but also quantitative.

1/ Measures of kinetic energy (KE), vorticity (VO), energy loss (EL) and pressure gradients (PG) can be calculated. The figure from the paper shows the curves from all subjects in the study. What does these measures mean, and are they likely to add useful information?

2/ Starting with kinetic energy, this is the kinetic energy per volume, and can be integrated from the individual velocity vectors. As this was integrated over the 2D area only, the energy is given in J/m. The upper panel shows all subjects, the lower a curve from one subject.

3/ It's obvious that the peaks of KE is related to the in- and outflow phases where velocity peaks (and higher at the LV basis. This means that the pW velocities represent the resultant, and integrated KE represents mostly the same (squared).

4/ So chasing KE as a new measure, just because it's new, without establishing standards the method, and without any sound hypothesis that it gives added information seems unsound.😈 But what about Vorticity, which is a completely new measure?

5/ VO is the rotation of the blood in each point of the image, and is related to the complexity of the blood flow. It is calculated by the mean curl or momentum of the blood velocity field over the LV, and is given in Hz. However, still method dependent, with no gold standard.

6/ Which means
A: It can't be validated against other methods (like MR), B: Nor are values derived from different #echofirst methods comparable. However, qualitative information may be physiologically interesting, especially if they are consistent with other findings:

7/ VO peak seems to be somewhat more dispersed than KE, uncertain whether this difference in variability is methodological or biological. However, VO seems to peak close to, but slightly later than KE.

8/ This is consistent with qualitative findings that shows that the vortex is created by the interaction of inflow with the AV-plane motion subsequent to the inflow itself.

9/ Vorticity decreases in diastasis, but apparently less than KE, again consistent with the presence of a vortex through diastasis, where the septal flow closes the MV, and the lateral part conserves momentum for late filling.

10/ vorticity peaks again after peak KE of late filling, but this time extends into pre ejection, where the septal flow aligns the momentum with the ejection and closes the MV, while the lateral flow slowly fades, along with the whole vortex.

11/ vorticity decreasing during ejection where flow is mainly laminar, except at the very end where a slight apical momentum is imparted by the apical AV-plane motion.

12/ - and finally reaching minimum as the volume shift during iVR imparts a unidirectional flow gradient before early filling.

12/ VO is a new measure, and findings seems consistent with the qualitative evaluation of vortex formation, as well as colour flow and pw Doppler, so the physiology is credible.

13/ Caveats:
A:Actual peak values will differ with method.
B: There is no gold standard, ref. method will also be methodologically different, phantom validation might be possible though.

14/ I don't see the value of research stampeding along trying to run VO through the "sausage factory" of generating normal values or comparing patients with controls just because this is a new (and "sexy"?) method.

15/ so far, VO has confirmed what we see from flow patterns, and qualitative evaluation of the patterns and curve forms / timing, may give new information (like strain and strain rate) about physiology and pathophysiology, I'm specially optimistic about load.

16/ As you see, there are more measures available from the method, I'll probably return with a new thread about pressure gradients and maybe energy loss later.

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