Validity and reliability of deriving the autoregulatory plateau through projection pursuit regression from driven methods.

To compare the construct validity and between‐day reliability of projection pursuit regression (PPR) from oscillatory lower body negative pressure (OLBNP) and squat‐stand maneuvers (SSMs). Nineteen participants completed 5 min of OLBNP and SSMs at driven frequencies of 0.05 and 0.10 Hz across two visits. Autoregulatory plateaus were derived at both point‐estimates and across the cardiac cycle. Between‐day reliability was assessed with intraclass correlation coefficients (ICCs), Bland–Altman plots with 95% limits of agreement (LOA), coefficient of variation (CoV), and smallest real differences. Construct validity between OLBNP‐SSMs were quantified with Bland–Altman plots and Cohen's d. The expected autoregulatory curve with positive rising and negative falling slopes were present in only ~23% of the data. The between‐day reliability for the ICCs were poor‐to‐good with the CoV estimates ranging from ~50% to 70%. The 95% LOA were very wide with an average spread of ~450% for OLBNP and ~350% for SSMs. Plateaus were larger from SSMs compared to OLBNPs (moderate‐to‐large effect sizes). The cerebral pressure‐flow relationship is a complex regulatory process, and the "black‐box" nature of this system can make it challenging to quantify. The current data reveals PPR analysis does not always elicit a clear‐cut central plateau with distinctive rising/falling slopes. [ABSTRACT FROM AUTHOR]