My purpose is twofold, (i) to quantify the change from baseline HRV and (ii) to determine whether the sensation corresponds to the change in HRV.

To solve (i) I am treating the baseline HRV values as fixed covariates in a linear regression of the HRV values. This works well enough. But to solve (ii) I am uncertain how to move forward. First I thought I might use a hierarchical model, conditioning the binary response on the HRV values, but I don't want to imply that causation between the two dependent variables. I only want to quantify correlation. That made me wonder about multivariate generalized linear models, but I couldn't find much about binomial-normal multivariate models. I also wonder whether a simple solution, using some non-parametric test for correlation isn't the best idea. But would this ignore relevant information in the regression analysis used to solve (i)?

If anyone has any thoughts or helpful links, I would appreciate it!

Have a nice day!