Random squat-stand maneuvers: a novel approach for assessment of dynamic cerebral autoregulation?

BACKGROUND: Squat-stand maneuvers (SSM) have been used to assess dynamic cerebral autoregulation (dCA), but always at a fixed-frequency (FF). This study aimed to assess the use of random-frequency (RF) SSMs as a stimulus for measuring dCA, and to determine the reproducibility of FF and RFSSMs. METHOD: 29 healthy volunteers (19 male, mean age 23.0 [4.9] years) completed the study; 11 returned for a repeat visit (median 45 days). Heart rate, beat-to-beat blood pressure, middle cerebral artery (MCA) blood flow velocity, end-tidal CO2 and angle of the squat movement were measured. Subjects underwent four recordings: 5 minutes sitting; 5 minutes standing; FFSSMs (0.05Hz); RFSSMs. Subjects were asked to rate the degree of exertion experienced while performing these maneuvers. RESULTS: 29 subjects completed the protocol; 9 data sets were deemed unsuitable for further analysis. Mean ARI of 6.21 (1.04) while standing was significantly greater than during the SSMs (p<0.01); mean (SD) ARI during the FF and RFSSMs being 5.16 (1.43) and 5.37 (1.21), respectively. However, no significant difference was found between the ARI estimates from the two SSMs (p=0.856) or for each of the four recordings between the two visits (p=0.645). RFSSMs were found to be significantly less tiring than FFSSMs (p<0.01). CONCLUSION: RFSSMs are an effective and non-invasive method of assessing dCA. There is no difference in the ARI estimates in comparison with FFSSMs. While FFSSMs have been well tolerated previously, RFSSMs are preferred by healthy subjects and thus may be better tolerated by a patient population in a clinical setting.