English to Russian Science Mathematics & Statistics clinical studies

The translation of "variable" is obviously "переменная (величина)", but what does the "echo" part mean here? The term is used in a discussion of a bar graph depicting the results of a clinical study. It seems that the speaker is Chinese, so perhaps this is a non-existent term, as I could not find it anywhere. It only seems to be used in the context of programming, but here it is used to describe a simple bar graph.

Examples:

"Both echo variables measure left atrial size"

"The linear model shows a significant diet by time interaction in both echo variables"