Does depth of squat‐stand maneuver affect estimates of dynamic cerebral autoregulation?

Abstract

Repeated squat‐stand maneuvers (SSM) are an effective way of measuring dynamic cerebral autoregulation (dCA), but the depth of SSM required to improve dCA estimations has never been studied. We compared beat‐to‐beat cerebral hemodynamic parameters between maximal depth SSM (SSMD) and a shallower alternative (SSMS) in two age groups (younger [20–34 years] vs. older [50–71 years]) at a frequency of 0.05 Hz. Cerebral blood flow velocity, continuous blood pressure (BP) and end‐tidal CO2 (EtCO2) were measured using transcranial Doppler ultrasound, the Finometer device, and capnography, respectively. Coherence (at 0.05 Hz) was significantly higher in both SSM recordings compared to spontaneous BP oscillations at baseline standing (BS). Median (IQR) autoregulation index (ARI) was reduced during SSMD (4.46 [4.03–5.22], p < .01) compared to SSMS (5.96 [5.40–6.69]) and BS (6.03 [5.20–6.49], p < .01) with similar relative differences also observed for phase (at 0.05 Hz). End‐tidal CO2 was increased in SSMD (38.3 ± 3.7 mmHg, p < .01) compared to both SSMS (36.6 ± 3.6 mmHg) and BS (35.5 ± 3.2 mmHg). The older group demonstrated significantly lower ARI and phase estimates during SSM and found SSMS more effortful than SSMD. In conclusion, both SSMD and SSMS are effective at estimating dCA, and dCA appears to be less efficient during maximal depth SSM compared to baseline rest or a shallower alternative.

Extremes of cerebral blood flow during hypercapnic squat‐stand maneuvers

“…Notably, during hypercapnia, CBFV climbed consecutively with each maneuver. This could be an exercise effect directly impairing dCA (Barnes, Ball, Haunton, Panerai, et al, 2017 ; Batterham et al, 2020 ), yet no such trend is noted in the poikilocapnic state in our single participant.…”

Vascular and haemodynamic issues of brain ageing

“…TFA is widely used across studies of autoregulation to allow the estimation of dCA parameters from spontaneous rather than induced BP fluctuations [ 127 ]. For research studies focusing on older participants, this is particularly advantageous as this can be better tolerated than the thigh-cuff and squat-stand manoeuvre [ 4 ]. In a longitudinal study of ten subjects who were followed for 10 years, ARI measured by TFA was found to decrease, suggesting dCA became less efficient with age [ 13 ].…”

“…Thus, many studies of older adults instead use the sit-to-stand manoeuvre, which also generates a transient response of CBF to changes in BP, if measurements are taken immediately after standing up [ 64 , 128 ]. Recently, an older group of individuals (aged 50–71 years) as compared to a younger group (20–34 years) demonstrated lower ARI during maximal depth squats as compared to shallower squats—thereby suggesting less efficient dCA in older individuals during maximal depth squats as compared to rest or the shallower approach [ 4 ]. Similarly, reductions in NIRS-measured frontal cortex oxygenation were seen in 27 healthy older adults during sit-to-stand [ 65 , 66 ], and high-frequency dCA was impaired in older adults during sit-to-stand [ 74 ].…”

“…The various methods of assessing CA described above have provided mixed evidence of haemodynamic changes during ageing as assessed using non-respiratory paradigms. The majority of studies using sit-to-stand manoeuvres and resting TFA do not show any demonstrable effects of ageing on dCA, but there are some exceptions, specifically, the thigh-cuff manoeuvre [ 89 ] and the squat-stand measurement [ 4 ]. These conflicting findings may be due to methodological differences (resting vs induced and squat-stand vs sit-stand), and differences in the age ranges and population characteristics studied.…”

Cerebral critical closing pressure and resistance-area product: the influence of dynamic cerebral autoregulation, age and sex

“…The influence of larger oscillations in MAP to improve the reliability of CA metrics, 28,50 and facilitate the identification of the effects of ageing, is also illustrated by the findings of Batterham et al, who recently reported reduced ARI values in older subjects performing the squat-stand manoeuvre. 44 In both their younger and older groups, the sex ratio was 50%, but the influence of sex on the effect of age was not examined. Similarly, Smirl et al 42 compared groups of older and younger subjects undergoing mild exercise combined with oscillatory lower body negative pressure, which induced relatively large changes in MAP at fixed frequencies of 0.05 and 0.10 Hz.…”