Methodological comparison of active- and passive-driven oscillations in blood pressure; implications for the assessment of cerebral pressure-flow relationships

Abstract

We examined the between-day reproducibility of active (squat-stand maneuvers)- and passive [oscillatory lower-body negative pressure (OLBNP) maneuvers]-driven oscillations in blood pressure. These relationships were examined in both younger (n = 10; 25 ± 3 yr) and older (n = 9; 66 ± 4 yr) adults. Each testing protocol incorporated rest (5 min), followed by driven maneuvers at 0.05 (5 min) and 0.10 (5 min) Hz to increase blood-pressure variability and improve assessment of the pressure-flow dynamics using linear transfer function analysis. Beat-to-beat blood pressure, middle cerebral artery velocity, and end-tidal partial pressure of CO2 were monitored. The pressure-flow relationship was quantified in the very low (0.02-0.07 Hz) and low (0.07-0.20 Hz) frequencies (LF; spontaneous data) and at 0.05 and 0.10 Hz (driven maneuvers point estimates). Although there were no between-age differences, very few spontaneous and OLBNP transfer function metrics met the criteria for acceptable reproducibility, as reflected in a between-day, within-subject coefficient of variation (CoV) of <20%. Combined CoV data consist of LF coherence (15.1 ± 12.2%), LF gain (15.1 ± 12.2%), and LF normalized gain (18.5 ± 10.9%); OLBNP data consist of 0.05 (12.1 ± 15.%) and 0.10 (4.7 ± 7.8%) Hz coherence. In contrast, the squat-stand maneuvers revealed that all metrics (coherence: 0.6 ± 0.5 and 0.3 ± 0.5%; gain: 17.4 ± 12.3 and 12.7 ± 11.0%; normalized gain: 16.7 ± 10.9 and 15.7 ± 11.0%; and phase: 11.6 ± 10.2 and 17.3 ± 10.8%) at 0.05 and 0.10 Hz, respectively, were considered biologically acceptable for reproducibility. These findings have important implications for the reliable assessment and interpretation of cerebral pressure-flow dynamics in humans.

Exaggerated systemic oxidative‐inflammatory‐nitrosative stress in chronic mountain sickness is associated with cognitive decline and depression

“…), participants then performed 5 min periods of repeated squat‐stand manoeuvres at randomly assigned frequencies of 0.05 Hz [10 s squat, 10 s standing) and 0.10 Hz (5 s squat, 5 s standing) with 5 min of standing rest between frequencies (Smirl et al . ). During these manoeuvres, we instructed participants to maintain normal breathing and to avoid Valsalva.…”

Implications of habitual endurance and resistance exercise for dynamic cerebral autoregulation

“…These large oscillations in MAP are extensively buffered by the cerebral vasculature when performed at frequencies within the high‐pass filter buffering range (< 0.20 Hz; Zhang, Zuckerman, Giller, & Levine, ). Repeated squat–stands optimizes the signal‐to‐noise ratio improving the reproducibility and interpretability of observations through a physiologically relevant MAP stimulus to the cerebral vessels (Smirl, Hoffman, Tzeng, Hansen, & Ainslie, ). Participants were reminded throughout to avoid the Valsalva manoeuvre, confirmed by the partial pressure of end‐tidal carbon dioxide () trace.…”

“…The point estimate of the driven frequency of 0.05 and 0.10 Hz was where the transfer function analysis coherence, gain and phase of the forced MAP oscillations were taken from. These point estimates were chosen as they are in the very low (0.02–0.07 Hz) and low (0.07–0.20 Hz) frequency ranges where dCA is thought to be most effective (Smirl et al., ). Only the TFA phase and gain values where coherence exceeded 0.50 were included in the analysis, to ensure the measures were robust for subsequent analysis (Zhang et al., ).…”

How many squat–stand manoeuvres to assess dynamic cerebral autoregulation?

“…Furthermore, they have been found to produce reproducible metrics of dCA (Barnes et al 2017a; Smirl et al 2015). However, they are physically demanding.…”