What recording duration is required to provide physiologically valid and reliable dynamic cerebral autoregulation transfer functional analysis estimates?

Objective. Currently, a recording of 300 s is recommended to obtain accurate dynamic cerebral autoregulation estimates using transfer function analysis (TFA). Therefore, this investigation sought to explore the concurrent validity and the within- and between-day reliability of TFA estimates derived from shorter recording durations from squat-stand maneuvers. Approach. Retrospective analyses were performed on 70 young, recreationally active or endurance-trained participants (17 females; age: 26 +/- 5 years, [range: 20-39 years]; body mass index: 24 +/- 3 kg m(-2)). Participants performed 300 s of squat-stands at frequencies of 0.05 and 0.10 Hz, where shorter recordings of 60, 120, 180, and 240 s were extracted. Continuous transcranial Doppler ultrasound recordings were taken within the middle and posterior cerebral arteries. Coherence, phase, gain, and normalized gain metrics were derived. Bland-Altman plots with 95% limits of agreement (LOA), repeated measures ANOVA's, two-tailed paired t-tests, coefficient of variation, Cronbach's alpha, intraclass correlation coefficients, and linear regressions were conducted. Main results. When examining the concurrent validity across different recording durations, group differences were noted within coherence (F ((4155)) > 11.6, p < 0.001) but not phase (F ((4155)) < 0.27, p > 0.611), gain (F ((4155)) < 0.61, p > 0.440), or normalized gain (F ((4155)) < 0.85, p > 0.359) parameters. The Bland-Altman 95% LOA measuring the concurrent validity, trended to narrow as recording duration increased (60 s: < +/- 0.4, 120 s: < +/- 0.3, 180 s < +/- 0.3, 240 s: < +/- 0.1). The validity of the 180 and 240 s recordings further increased when physiological covariates were included within regression models. Significance. Future studies examining autoregulation should seek to have participants perform 300 s of squat-stand maneuvers. However, valid and reliable TFA estimates can be drawn from 240 s or 180 s recordings if physiological covariates are controlled.